Abstract

This proposal extends HTMLMediaElement [HTML51] providing APIs to control playback of encrypted content.

The API supports use cases ranging from simple clear key decryption to high value video (given an appropriate user agent implementation). License/key exchange is controlled by the application, facilitating the development of robust playback applications supporting a range of content decryption and protection technologies.

This specification does not define a content protection or Digital Rights Management system. Rather, it defines a common API that may be used to discover, select and interact with such systems as well as with simpler content encryption systems. Implementation of Digital Rights Management is not required for compliance with this specification: only the Clear Key system is required to be implemented as a common baseline.

The common API supports a simple set of content encryption capabilities, leaving application functions such as authentication and authorization to page authors. This is achieved by requiring content protection system-specific messaging to be mediated by the page rather than assuming out-of-band communication between the encryption system and a license or other server.

Status of This Document

Status Update (December 2019): The link to the Latest Editor's Draft was updated in place in anticipation of the initial link becoming broken.

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.

This document was published by the HTML Media Extensions Working Group as a Recommendation. Comments regarding this document are welcome. Please send them to the github repository. An archive of the mailing list is also available.

Please see the Working Group's implementation report used during the Candidate Recommendation exit phase.

The section on CDM constraints was added since the previous publication.

This document has been reviewed by W3C Members, by software developers, and by other W3C groups and interested parties, and is endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited from another document. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This document is governed by the 1 March 2017 W3C Process Document.

1. Introduction

This section is non-normative.

This specification enables script to select content protection mechanisms, control license/key exchange, and execute custom license management algorithms. It supports a wide range of use cases without requiring client-side modifications in each user agent for each use case. This enables content providers to develop a single application solution for all devices.

Supported content is encrypted per container-specific "common encryption" specifications, enabling use across key systems. Supported content has an unencrypted container, enabling metadata to be provided to the application and maintaining compatibility with other HTMLMediaElement features.

Implementers should pay attention to the mitigations for the security and privacy threats and concerns described in this specification. In particular, the specification requirements for security and privacy cannot be met without knowledge of the security and privacy properties of the Key System and its implementation(s). 8. Implementation Requirements contains security and privacy provisions related to the integration and use of underlying Key System implementations. 10. Security focuses on external threats, such as input data or network attacks. 11. Privacy focuses on the handling of user-specific information and providing users with adequate control over their own privacy.

Note

While this specification is independent of the source of the media data, authors should be aware that many implementations only support decrypting media data provided via Media Source Extensions [MEDIA-SOURCE].

A generic stack implemented using the API is shown below. This diagram shows an example flow; other combinations of API calls and events are possible.

A generic stack implemented using the proposed APIs

2. Definitions

Content Decryption Module (CDM)

Content Decryption Module (CDM) is the client component that provides the functionality, including decryption, for one or more Key Systems.

Note

Implementations may or may not separate the implementations of CDMs or treat them as separate from the user agent. This is transparent to the API and application.

Key System

A Key System is a generic term for a decryption mechanism and/or content protection provider. Key System strings provide unique identification of a Key System. They are used by the user agent to select a CDM and identify the source of a key-related event. User agents MUST support the Common Key Systems. User agents MAY also provide additional CDMs with corresponding Key System strings.

A Key System string is always a reverse domain name. Key System strings are compared using case-sensitive matching. It is RECOMMENDED that CDMs use simple lower-case ASCII key system strings.

Note

For example, "com.example.somesystem".

Note

Within a given system ("somesystem" in the example), subsystems may be defined as determined by the key system provider. For example, "com.example.somesystem.1" and "com.example.somesystem.1_5". Key System providers should keep in mind that these will be used for comparison and discovery, so they should be easy to compare and the structure should remain reasonably simple.

Key Session

A Key Session, or simply Session, provides a context for message exchange with the CDM as a result of which key(s) are made available to the CDM. Sessions are embodied as MediaKeySession objects. Each Key session is associated with a single instance of Initialization Data provided in the generateRequest() call.

Each Key Session is associated with a single MediaKeys object, and only media element(s) associated with that MediaKeys object may access key(s) associated with the session. Other MediaKeys objects, CDM instances, and media elements MUST NOT access the key session or use its key(s). Key sessions and the keys they contain are no longer usable for decryption once the session has been closed, including when the MediaKeySession object is destroyed.

All license(s) and key(s) associated with a Key Session which have not been explicitly stored MUST be destroyed when the Key Session is closed.

Key IDs MUST be unique within a session.

Session ID

A Session ID is a unique string identifier generated by the CDM that can be used by the application to identify MediaKeySession objects.

A new Session ID is generated each time the user agent and CDM successfully create a new session.

Each Session ID SHALL be unique within the browsing context in which it was created. For session types for which the Is persistent session type? algorithm returns true, Session IDs MUST be unique within the origin over time, including across browsing sessions.

Note

The underlying content protection protocol does not necessarily need to support Session IDs.

Key

Unless otherwise stated, key refers to a decryption key that can be used to decrypt blocks within media data. Each such key is uniquely identified by a key ID. A key is associated with the session used to provide it to the CDM. (The same key may be present in multiple sessions.) Such keys MUST only be provided to the CDM via an update() call. (They may later be loaded by load() as part of the stored session data.)

Note

Authors SHOULD encrypt each set of stream(s) that requires enforcement of a meaningfully different policy with a distinct key (and key ID). For example, if policies may differ between two video resolutions, stream(s) containing one resolution should not be encrypted with the key used to encrypt stream(s) containing the other resolution. When encrypted, audio streams SHOULD NOT use the same key as any video stream. This is the only way to ensure enforcement and compatibility across clients.

Usable For Decryption

A key is considered usable for decryption if the CDM is certain the key is currently usable to decrypt one or more blocks of media data.

Note

For example, a key is not usable for decryption if its license has expired. Even if its license has not expired, a key is not usable for decryption if other conditions (e.g., output protection) for its use are not currently satisfied.

Key ID

A key is associated with a key ID that is a sequence of octets and which uniquely identifies the key. The container specifies the ID of the key that can decrypt a block or set of blocks within the media data. Initialization Data MAY contain key ID(s) to identify the keys that are needed to decrypt the media data. However, there is no requirement that Initialization Data contain any or all key IDs used in the media data or media resource. Licenses provided to the CDM associate each key with a key ID so the CDM can select the appropriate key when decrypting an encrypted block of media data.

Known Key

A key is considered to be known to a session if the CDM's implementation of the session contains any information - specifically the key ID - about it, regardless of whether the actual key is usable or its value is known. Known keys are exposed via the keyStatuses attribute.

Keys are considered known even after they become unusable, such as due to expiration or if they are removed but a record of license destruction is available. Keys only become unknown when they are explicitly removed from a session and any license release message is acknowledged.

Note

For example, a key could become unknown if an update() call provides a new license that does not include the key and includes instructions to replace the license(s) that previously contained the key.

License

A license is key system-specific state information that includes one or more key(s) - each associated with a key ID - and potentially other information about key usage.

Initialization Data
Note

Key Systems usually require a block of initialization data containing information about the stream to be decrypted before they can construct a license request message. This block could be a simple key or content ID or a more complex structure containing such information. It SHOULD always allow unique identification of the key(s) needed to decrypt the content. This initialization information MAY be obtained in some application-specific way or provided with the media data.

Initialization Data is a generic term for container-specific data that is used by a CDM to generate a license request.

The format of the initialization data depends upon the type of container, and containers MAY support more than one format of initialization data. The Initialization Data Type is a string that indicates the format of the accompanying Initialization Data. Initialization Data Type strings are always matched case-sensitively. It is RECOMMENDED that Initialization Data Type strings are lower-case ASCII strings.

The Encrypted Media Extensions Stream Format and Initialization Data Format Registry [EME-INITDATA-REGISTRY] provides the mapping from Initialization Data Type string to the specification for each format.

When the user agent encounters Initialization Data in the media data, it provides that Initialization Data to the application in the initData attribute of the encrypted event. The user agent MUST NOT store the Initialization Data or use its content at the time it is encountered. The application provides Initialization Data to the CDM via generateRequest(). The user agent MUST NOT provide Initialization Data to the CDM by other means.

Initialization Data MUST be a fixed value for a given set of stream(s) or media data. It MUST only contain information related to the keys required to play a given set of stream(s) or media data. It MUST NOT contain application data, client-specific data, user-specific data, or executable code.

Initialization Data SHOULD NOT contain Key System-specific data or values. Implementations MUST support the common formats defined in [EME-INITDATA-REGISTRY] for each Initialization Data Type they support.

Note

Use of proprietary formats/contents is discouraged, and supporting or using only proprietary formats is strongly discouraged. Proprietary formats should only be used with pre-existing content or on pre-existing client devices that do not support the common formats.

Associable Values

Two or more identifiers or other values are said to be associable if they are identical or it is possible - with a reasonable amount of time and effort - to correlate or associate them. Otherwise, the values are non-associable.

Note

For example, values created in the following ways are associable:

  • Using a trivially-reversible hash function.

  • Sharing a prefix or other subset

  • Replacing random value N with N+10

  • XORing the origin with a fixed value (because it is trivially reversible)

In contrast, two values that are completely unrelated or cryptographically distinct, such as via a cryptographically strong non-reversible hash function, are non-associable.

Two or more identifiers or other values are said to be associable by an entity if it is possible - with a reasonable amount of time and effort - for the referenced entity or set of entities to correlate or associate them without participation of additional entity(ies). Otherwise, the values are non-associable by an entity.

Two or more identifiers or other values are said to be non-associable by the application if they are non-associable by an entity where the entity is set that includes the application, all other applications, and other entities such as servers that they use or with which they communicate. Otherwise, the values would be considered associable by the application, which is forbidden.

Distinctive Value

A Distinctive Value is a value, piece of data, implication of the possession of a piece of data, or an observable behavior or timing that is not shared across a large population of users or client devices. A Distinctive Value may be in memory or persisted.

Note

Examples of Distinctive Values include but are not limited to:

Note

While a Distinctive Value is typically unique to a user or client device, a value does not need to be strictly unique to be distinctive. For example, a value shared among a small number of users could still be distinctive.

Permanent Identifiers

A Permanent Identifier is a value, piece of data, implication of the possession of a piece of data, or an observable behavior or timing that is indelible in some way or otherwise non-trivial for the user to remove, reset, or change. This, includes but is not limited to:

  • A hardware or hardware-based identifier

  • A value provisioned in the hardware device in the factory

  • A value associated with or derived from the operating system installation instance

  • A value associated with or derived from the user agent installation instance

  • A value associated with or derived from the CDM or other software component

  • A value in a configuration file or similar semi-permanent data, even if generated on the client

  • Client or other user account values

A Distinctive Permanent Identifier is a Permanent Identifier that is distinctive.

When exposed outside the client, Distinctive Permanent Identifiers and values derived from or otherwise related to them MUST be encrypted. Distinctive Permanent Identifiers MUST NOT ever be exposed to the application, even in encrypted form.

Note

While a Distinctive Permanent Identifier is typically unique to a user or client device, a Distinctive Permanent Identifier does not need to be strictly unique to be distinctive. For example, a Distinctive Permanent Identifier shared among a small number of users could still be distinctive.

Note

A Distinctive Permanent Identifier is not a Distinctive Identifier because it is not derived or generated (within the scope of this specification).

Note

distinctiveIdentifier controls whether Distinctive Permanent Identifiers may be used. Specifically, Distinctive Permanent Identifiers may only be used when the value of the distinctiveIdentifier member of the MediaKeySystemAccess used to create the MediaKeys object is "required".

Distinctive Identifier
Note

A Distinctive Identifier is a value, including in opaque or encrypted form, for which it is possible for any entity external to the client to correlate or associate values beyond what a user may expect on the web platform (e.g., cookies and other site data). For example, values that are associable by an entity other than the application across a) origins, b) browsing profiles, or c) browsing sessions even after the user has attempted to protect his or her privacy by clearing browsing data or values for which it is not easy for a user to break such association. In particular, a value is a Distinctive Identifier if it is possible for a central server, such as an individualization server, to associate values across origins, such as because the individualization requests contained a common value, or because values provided in individualization requests are associable by such server even after attempts to clear browsing data. Possible causes of this include use of Distinctive Permanent Identifier(s) in the individualization process.

Distinctive Identifiers exposed to the application, even in encrypted form, MUST adhere to the identifier requirements, including being encrypted, unique per origin and profile, and clearable.

While the instantiation or use of a Distinctive Identifier is triggered by the application's use of the APIs defined in this specification, the identifier need not be provided to the application to trigger conditions related to Distinctive Identifiers. (The Distinctive Permanent Identifier(s) MUST NOT ever be provided to the application, even in opaque or encrypted form.)

Note

distinctiveIdentifier controls whether Distinctive Identifiers may be used. Specifically, Distinctive Identifiers may only be used when the value of the distinctiveIdentifier member of the MediaKeySystemAccess used to create the MediaKeys object is "required".

A Distinctive Identifier is a value, piece of data, implication of the possession of a piece of data, or an observable behavior or timing for which all of the following criteria hold:

  • It is distinctive.

    Note

    While a Distinctive Identifier is typically unique to a user or client device, an identifier does not need to be strictly unique to be distinctive. For example, an identifier shared among a small number of users could still be distinctive.

  • It, information about it, or values derived from or otherwise related to it are exposed, even in encrypted form, outside the client. This includes but is not limited to providing it to the application and/or license, individualization, or other server.

  • It has one or more the following properties:

    Note

    Other properties of concern that are normatively prohibited for values exposed to the application include:

    Examples of such normatively prohibited values include but is not limited to:

    • A single hardware-based value used for all origins.

    • A single random based value used for all origins.

    • A single value obtained from an individualization process that is used for all origins.

    • Values that include all or part of any of the above values.

    • A single value that is used for multiple but not all origins.

    • A single value that is used for all origins on a domain. (Identifiers must be per-origin.)

    • A pre-provisioned origin-specific value.

    • Values generated by trivially-reversible means, which are thus associable by the application, regardless of whether generated on the client or involving an a individualization process. For example, XORing or otherwise integrating (part of) the origin with a fixed value.

Note

While Distinctive Identifier are usually associable by the entity that generated them they MUST be non-associable by applications. In other words, such correlation or association is only possible by the entity, such as an individualization server, that originally generated the Distinctive Identifier values. Entities with access to the Distinctive Permanent Identifier(s) MUST NOT expose this capability to applications, as this would make resulting Distinctive Identifiers associable by the application, and SHOULD take care to avoid exposing such correlation to other entities or third parties.

Note

Examples of Distinctive Identifiers include but are not limited to:

  • A series of bytes that is included in key requests, different from the series of bytes included by other client devices, and based on or was acquired directly or indirectly using a Distinctive Permanent Identifier.

  • A public key included in key requests that is different from the public keys included in the requests by other client devices and is based on or was acquired directly or indirectly using a Distinctive Permanent Identifier.

  • Demonstration of possession of a private key (e.g., by signing some data) that other client devices do not have and is based on or was acquired directly or indirectly using a Distinctive Permanent Identifier.

  • An identifier for such a key.

  • Such a value used to derive another value that is exposed even though the first value is not directly exposed.

  • A value derived from another Distinctive Identifier.

  • A random value that was reported to a (e.g., individualization) server along with a Distinctive Permanent Identifier or provided by such a server after providing a Distinctive Permanent Identifier.

  • A value derived from a unique value provisioned in the hardware device in the factory.

  • A value derived from a unique hardware value (e.g., MAC address or serial number) or software value (e.g., operating system installation instance or operating system user account name) in the hardware device in the factory.

  • A value derived from a unique value embedded in the CDM binary or other file used by the CDM.

Examples of things that are not Distinctive Identifiers:

  • A public key shared among all copies of a given CDM version if the installed base is large.

  • A nonce or ephemeral key that is unique but used in only one session.

  • A value that is not exposed, even in derived or similar ways, outside the client, including via individualization or similar.

  • Device-unique keys used in attestations between, for example, the video pipeline and the CDM when the CDM does not let these attestations further flow to the application and instead makes a new attestation on its own using a key that does not constitute a Distinctive Identifier.

  • A value that is fully cleared/clearable along with browsing data, such as cookies, after which it will be replaced by a value that is non-associable (not just non-associable by applications), even by a central server such as an individualization server, AND one or more of the following:

    • No Distinctive Permanent Identifier or Distinctive Identifier was involved in the generation of the value.

    • It is a random value generated without inputs from the system.

    • It is a value provided by a server without the use of or knowledge of another Distinctive Identifier.

Use of Distinctive Identifiers and Distinctive Permanent Identifiers

An implementation, configuration, instance, or object uses Distinctive Identifier(s) if, at any time during its lifetime or the lifetime of related such entities, it exposes, even in encrypted form, one or more Distinctive Identifier(s), information about them, or values derived from or otherwise related to them outside the client. This includes but is not limited to providing such a value to the application and/or license, individualization, or other server.

An implementation, configuration, instance, or object uses Distinctive Permanent Identifier(s) if, at any time during its lifetime or the lifetime of related such entities, it exposes, even in encrypted form, one or more Distinctive Permanent Identifier(s), information about them, or values derived from or otherwise related to them outside the client. This includes but is not limited to providing such a value to an individualization server. Such values MUST NOT be provided to the application.

An implementation, configuration, instance, or object uses Distinctive Identifier(s) or Distinctive Permanent Identifier(s) if it uses Distinctive Identifier(s) and/or uses Distinctive Permanent Identifier(s).

Note

distinctiveIdentifier controls whether Distinctive Identifiers and Distinctive Permanent Identifiers may be used. Specifically, such identifiers may only be used when the value of the distinctiveIdentifier member of the MediaKeySystemAccess used to create the MediaKeys object is "required".

Cross Origin Limitations

During playback, embedded media data is exposed to script in the embedding origin. In order for the API to provide Initialization Data in the encrypted event, media data MUST be CORS-same-origin with the embedding page. If media data is cross-origin with the embedding document, authors SHOULD use the crossorigin attribute on the HTMLMediaElement and CORS headers on the media data response to make it CORS-same-origin.

Mixed Content Limitations

During playback, embedded media data is exposed to script in the embedding origin. In order for the API to provide Initialization Data in the encrypted event, media data MUST NOT be Mixed Content [MIXED-CONTENT].

Time

Time MUST be equivalent to that represented in ECMAScript Time Values and Time Range [ECMA-262].

Time will equal NaN if no such time exists or if the time is indeterminate. It should never have the value Infinity.

Note

Time generally represents an instant in time with millisecond accuracy; however, that alone is not a sufficient definition. The defined Time Values and Time Range reference adds other important requirements.

Expiration Time

The time after which key(s) will no longer be usable for decryption.

Browsing Profile

A User Agent on a given machine may support execution in a variety of different contexts or modes or temporary states that are expected to behave independently with respect to application-visible state and data. In particular, all stored data is expected to be independent. In this specification we refer to such independent contexts or modes as "Browsing Profiles".

Note

Examples of such independent contexts include if the user agent is running in different operating system user accounts or if the user agent provides the capability to define multiple independent profiles for a single account.

Valid Media MIME Type

A valid media MIME type is a media MIME type that is also a valid MIME type [HTML51]. When a MIME type includes parameters, such as `"codecs"` [RFC6381], such parameters MUST also be valid per the relevant specification.

When used with the features defined in this specification, MIME type strings SHOULD explicitly specify codecs and codec constraints (e.g., per [RFC6381]) unless these are normatively implied by the container.

3. Obtaining Access to Key Systems

This section defines the mechanism for obtaining access to a key system. The inclusion of capabilities in the request also enables feature detection.

The steps of an algorithm are always aborted when rejecting a promise.

3.2 MediaKeySystemConfiguration dictionary

enum MediaKeysRequirement {
    "required",
    "optional",
    "not-allowed"
};

The MediaKeysRequirement enumeration is defined as follows:

Enumeration description
required
When used in a call to requestMediaKeySystemAccess()
The returned object MUST support this feature.
When returned by a MediaKeySystemAccess object
CDM instances created by the object MAY use this feature.
optional
When used in a call to requestMediaKeySystemAccess()
The returned object MAY support and use this feature.
When returned by a MediaKeySystemAccess object
This value cannot and MUST NOT be present in such an object.
not-allowed
When used in a call to requestMediaKeySystemAccess()
The returned object MUST function without using this feature and MUST NOT use it at any time.
When returned by a MediaKeySystemAccess object
CDM instances created by the object MUST NOT use this feature.
 
dictionary MediaKeySystemConfiguration {
    DOMString                               label = "";
    sequence<DOMString>                     initDataTypes = [];
    sequence<MediaKeySystemMediaCapability> audioCapabilities = [];
    sequence<MediaKeySystemMediaCapability> videoCapabilities = [];
    MediaKeysRequirement                    distinctiveIdentifier = "optional";
    MediaKeysRequirement                    persistentState = "optional";
    sequence<DOMString>                     sessionTypes;
};

The dictionary MediaKeySystemConfiguration contains the following members:

label of type DOMString, defaulting to ""
An optional label that will be preserved in the MediaKeySystemConfiguration returned from the getConfiguration() method of MediaKeySystemAccess.
initDataTypes of type sequence<DOMString>, defaulting to []
A list of supported Initialization Data Type names. The Initialization Data Type capability of this object is considered supported if the list is empty or contains one or more values that are supported with all other members (as determined by the algorithm). Values in the sequence MUST not be the empty string.
audioCapabilities of type sequence<MediaKeySystemMediaCapability>, defaulting to []
A list of supported audio type and capability pairs. The audio capability of this object is considered supported if the list is empty or contains one or more values that are supported with all other members (as determined by the algorithm). When there is a conflict between values, the earlier value will be selected. An empty list indicates that no audio capabilities are supported. In this case, the videoCapabilities element must not be empty.
videoCapabilities of type sequence<MediaKeySystemMediaCapability>, defaulting to []
A list of supported video type and capability pairs. The video capability of this object is considered supported if the list is empty or contains one or more values that are supported with all other members (as determined by the algorithm). When there is a conflict between values, the earlier value will be selected. An empty list indicates that no video capabilities are supported. In this case, the audioCapabilities element must not be empty.
distinctiveIdentifier of type MediaKeysRequirement, defaulting to "optional"
Whether use of a Distinctive Identifier(s) is required.

When this member is "not-allowed", the implementation MUST NOT use Distinctive Identifier(s) or Distinctive Permanent Identifier(s) for any operations associated with any object created from this configuration.

persistentState of type MediaKeysRequirement, defaulting to "optional"
Whether the ability to persist state is required. This includes session data and any other type of state.

The CDM MUST NOT persist any state related to the application or origin of this object's Document when this member is "not-allowed".

Note

For the purposes of this member, persistent state does not include persistent unique identifiers (Distinctive Identifiers) controlled by the Key System implementation. distinctiveIdentifier independently reflects this requirement.

Only "temporary" sessions may be created when persistent state is not supported.

Note

For "temporary" sessions, the need and ability to store state is Key System implementation-specific and may vary by feature used.

Note

Applications intending to create non-"temporary" sessions, should set this member to "required" when calling requestMediaKeySystemAccess().

sessionTypes of type sequence<DOMString>
A list of MediaKeySessionTypes that must be supported. All values must be supported.

If this member is not present [WebIDL] when the dictionary is passed to requestMediaKeySystemAccess(), the dictionary will be treated as if this member is set to [ "temporary" ].

Implementations SHOULD NOT add members to this dictionary. Should member(s) be added, they MUST be of type MediaKeysRequirement, and it is RECOMMENDED that they have default values of "optional" to support the widest range of application and client combinations.

Note

Dictionary members not recognized by a user agent implementation are ignored per [WebIDL] and will not be considered in the requestMediaKeySystemAccess() algorithm. Should an application use non-standard dictionary member(s), it MUST NOT rely on user agent implementations rejecting a configuration that includes such dictionary members.

This dictionary MUST NOT be used to pass state or data to the CDM.

3.3 MediaKeySystemMediaCapability dictionary

dictionary MediaKeySystemMediaCapability {
    DOMString contentType = "";
    DOMString robustness = "";
};

Dictionary MediaKeySystemMediaCapability Members

contentType of type DOMString, defaulting to ""

The type of the media resource. Its value must be a valid media MIME type. The empty string is invalid.

robustness of type DOMString, defaulting to ""

The robustness level associated with the content type. The empty string indicates that any ability to decrypt and decode the content type is acceptable.

Note

Implementations MUST configure the CDM to support at least the robustness levels specified in the configuration of the MediaKeySystemAccess object used to create the MediaKeys object. Exact configuration of the CDM is implementation-specific, and implementations MAY configure the CDM to use the highest robustness level in the configuration even if a higher robustness level is available. If only the empty string is specified, implementations MAY be configured to use the lowest robustness level the implementation supports.

Applications SHOULD specify the robustness level(s) they require to avoid unexpected client incompatibilities.

In order for the capability represented by this object to be considered supported, contentType MUST NOT be the empty string and its entire value, including all codecs, MUST be supported with robustness.

Note

If any of a set of codecs is acceptable, use a separate instances of this dictionary for each codec.

4. MediaKeySystemAccess Interface

The MediaKeySystemAccess object provides access to a Key System.

[SecureContext]
interface MediaKeySystemAccess {
    readonly attribute DOMString keySystem;
    MediaKeySystemConfiguration getConfiguration();
    Promise<MediaKeys>          createMediaKeys();
};

Attributes

keySystem of type DOMString, readonly
Identifies the Key System being used.

Methods

getConfiguration

Returns the supported combination of configuration options selected by the requestMediaKeySystemAccess() algorithm.

The returned object is a non-strict subset (plus any implied defaults) of the first satisfiable MediaKeySystemConfiguration configuration passed to the requestMediaKeySystemAccess() call that returned the promise that was resolved with this object. It does not contain values capabilities not specified in that single configuration (other than implied defaults) and thus may not reflect all capabilities of the Key System implementation. All values in the configuration may be used in any combination. Members of type MediaKeysRequirement reflect whether the capability is required for any combination. They will not have the value "optional".

No parameters.
Return type: MediaKeySystemConfiguration

When this method is invoked, the user agent must run the following steps:

  1. Return this object's configuration value.

    Note

    This results in a new object being created and initialized from configuration each time this method is called.

createMediaKeys

Creates a new MediaKeys object for keySystem.

No parameters.
Return type: Promise<MediaKeys>

When this method is invoked, the user agent must run the following steps:

  1. Let promise be a new promise.

  2. Run the following steps in parallel:

    1. Let configuration be the value of this object's configuration value.

    2. Let use distinctive identifier be true if the value of configuration's distinctiveIdentifier member is "required" and false otherwise.

    3. Let persistent state allowed be true if the value of configuration's persistentState member is "required" and false otherwise.

    4. Load and initialize the Key System implementation represented by this object's cdm implementation value if necessary.

    5. Let instance be a new instance of the Key System implementation represented by this object's cdm implementation value.

    6. Initialize instance to enable, disable and/or select Key System features using configuration.

    7. If use distinctive identifier is false, prevent instance from using Distinctive Identifier(s) and Distinctive Permanent Identifier(s).

    8. If persistent state allowed is false, prevent instance from persisting any state related to the application or origin of this object's Document.

    9. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name.

    10. Let media keys be a new MediaKeys object, and initialize it as follows:

      1. Let the use distinctive identifier value be use distinctive identifier.

      2. Let the persistent state allowed value be persistent state allowed.

      3. Let the supported session types value be be the value of configuration's sessionTypes member.

      4. Let the cdm implementation value be this object's cdm implementation value.

      5. Let the cdm instance value be instance.

    11. Resolve promise with media keys.

  3. Return promise.

5. MediaKeys Interface

The MediaKeys object represents a set of keys that an associated HTMLMediaElement can use for decryption of media data during playback. It also represents a CDM instance.

A MediaKeys object may be destroyed by the user agent when it is no longer accessible

Note

For example, when there are no script references and no attached media element.

For methods that return a promise, all errors are reported asynchronously by rejecting the returned Promise. This includes [WebIDL] type mapping errors.

The steps of an algorithm are always aborted when rejecting a promise.

enum MediaKeySessionType {
    "temporary",
    "persistent-license"
};

The MediaKeySessionType enumeration is defined as follows:

Enumeration description
temporary

A session for which the license, key(s) and record of or data related to the session are not persisted.

The application need not worry about managing such storage. Support for this session type is REQUIRED.

persistent-license

A session for which the license (and potentially other data related to the session) will be persisted. A record of license destruction SHALL be persisted when the license and key(s) it contains are destroyed. The record of license destruction is a Key System-specific attestation that the license and key(s) it contains are no longer usable by the client. Support for this session type is OPTIONAL.

Sessions of this type can only be created if the configuration associated with the MediaKeySystemAccess object that created this object has a persistentState value of "required". The session MUST be loadable via its Session ID once update() is called successfully. A message of type "license-release" containing the record of license destruction will be generated when remove() is called until the record is acknowledged by a response passed to update().

The application is responsible for ensuring that data persisted for such sessions is removed when the application no longer needs it. See Session Storage and Persistence. 

[SecureContext]
interface MediaKeys {
    MediaKeySession  createSession(optional MediaKeySessionType sessionType = "temporary");
    Promise<boolean> setServerCertificate(BufferSource serverCertificate);
};

Methods

createSession

Returns a new MediaKeySession object.

Parameter Type Nullable Optional Description
sessionType MediaKeySessionType = "temporary" ✘ ✔ The type of session to create. The session type affects the behavior of the returned object.
Return type: MediaKeySession

When this method is invoked, the user agent must run the following steps:

  1. If this object's supported session types value does not contain sessionType, throw [WebIDL] a NotSupportedError.

    Note

    sessionType values for which the Is persistent session type? algorithm returns true will fail if this object's persistent state allowed value is false.

  2. If the implementation does not support MediaKeySession operations in the current state, throw [WebIDL] an InvalidStateError.

    Note

    Some implementations are unable to execute MediaKeySession algorithms until this MediaKeys object is associated with a media element using setMediaKeys(). This step enables applications to detect this uncommon behavior before attempting to perform such operations.

  3. Let session be a new MediaKeySession object, and initialize it as follows:

    1. Let the sessionId attribute be the empty string.

    2. Let the expiration attribute be NaN.

    3. Let the closed attribute be a new promise.

    4. Let key status be a new empty MediaKeyStatusMap object, and initialize it as follows:

      1. Let the size attribute be 0.

    5. Let the session type value be sessionType.

    6. Let the uninitialized value be true.

    7. Let the callable value be false.

    8. Let the closing or closed value be false.

    9. Let the use distinctive identifier value be this object's use distinctive identifier value.

    10. Let the cdm implementation value be this object's cdm implementation.

    11. Let the cdm instance value be this object's cdm instance.

  4. Return session.

setServerCertificate

Provides a server certificate to be used to encrypt messages to the license server.

Key Systems that use such certificates MUST also support requesting the certificate from the server via the Queue a "message" Event algorithm.

Note

This method allows an application to proactively provide a server certificate to implementations that support it to avoid the additional round trip should the CDM request it. It is intended as an optimization, and applications are not required to use it.

Parameter Type Nullable Optional Description
serverCertificate BufferSource ✘ ✘ The server certificate. The contents are Key System-specific. It MUST NOT contain executable code.
Return type: Promise<boolean>

When this method is invoked, the user agent must run the following steps:

  1. If the Key System implementation represented by this object's cdm implementation value does not support server certificates, return a promise resolved with false.

  2. If serverCertificate is an empty array, return a promise rejected with a new a newly created TypeError.

  3. Let certificate be a copy of the contents of the serverCertificate parameter.

  4. Let promise be a new promise.

  5. Run the following steps in parallel:

    1. Let sanitized certificate be a validated and/or sanitized version of certificate.

      Note

      The user agent should thoroughly validate the certificate before passing it to the CDM. This may include verifying values are within reasonable limits, stripping irrelevant data or fields, pre-parsing it, sanitizing it, and/or generating a fully sanitized version. The user agent should check that the length and values of fields are reasonable. Unknown fields should be rejected or removed.

    2. Use this object's cdm instance to process sanitized certificate.

    3. If the preceding step failed, resolve promise with a new DOMException whose name is the appropriate error name.

    4. Resolve promise with true.

  6. Return promise.

5.1 Algorithms

5.1.1 Is persistent session type?

The Is persistent session type? algorithm is run to determine whether the specified session type supports persistence of any kind. Requests to run this algorithm include a MediaKeySessionType value.

The following steps are run:

  1. Let the session type be the specified MediaKeySessionType value.

  2. Follow the steps for the value of session type from the following list:

    "temporary"
    Return false.
    "persistent-license"
    Return true.

5.1.2 CDM Unavailable

The CDM unavailable algorithm is run to close all MediaKeySession objects associated with a MediaKeys object, media keys when the CDM instance becomes unavailable.

The following step is run:

  1. For each MediaKeySession created by the media keys that is not closed, queue a task to run the Session Closed algorithm on the session.

5.2 Storage and Persistence

This section describes general requirements related to storage and persistence.

If a MediaKeys object's persistent state allowed value is false then the object's cdm instance SHALL NOT persist state or access previously persisted state as a result of operations on this object or any sessions that it creates.

If a MediaKeys object's persistent state allowed value is true then the object's cdm instance MAY persist state or access previously persisted state as a result of operations on this object or any sessions that it creates.

Persisted data MUST always be stored such that only the origin of this object's Document can access it. In addition, the data MUST only be accessible by the current browsing profile; other browsing profiles, user agents, and applications MUST NOT be able to access the stored data. See Information Stored on User Devices.

See 10. Security and 11. Privacy for additional considerations when supporting persistent storage.

6. MediaKeySession Interface

The MediaKeySession object represents a key session.

A MediaKeySession object is closed if and only if the object's closed attribute has been resolved.

The User Agent SHALL execute the Monitor for CDM Changes algorithm continuously for each MediaKeySession object that is not closed. The Monitor for CDM Changes algorithm MUST be run in parallel to the main event loop but not in parallel to other procedures defined in this specification that are also defined to be run in parallel.

A MediaKeySession object SHALL NOT be destroyed and SHALL continue to receive events if it is not closed and the MediaKeys object that created it remains accessible. Otherwise, a MediaKeySession object that is no longer accessible SHALL NOT receive further events and MAY be destroyed.

Note

The above rule implies that the CDM instance must not be destroyed until all MediaKeys objects and all MediaKeySession objects associated with the CDM instance are destroyed.

If a MediaKeySession object is not closed when it becomes inaccessible to the page, the CDM SHALL close the key session associated with the object.

Note

Closing the key session results in the destruction of any license(s) and key(s) that have not been explicitly stored.

Note

Exactly when the key session is closed is an implementation detail, and applications SHOULD NOT rely on specific timing. Applications that want to ensure a session is closed before taking some other action SHOULD call close() and wait for the returned promise to be resolved.

For methods that return a promise, all errors are reported asynchronously by rejecting the returned Promise. This includes [WebIDL] type mapping errors.

The following steps of an algorithm are always aborted when rejecting a promise.

[SecureContext]
interface MediaKeySession : EventTarget {
    readonly attribute DOMString           sessionId;
    readonly attribute unrestricted double expiration;
    readonly attribute Promise<void>       closed;
    readonly attribute MediaKeyStatusMap   keyStatuses;
             attribute EventHandler        onkeystatuseschange;
             attribute EventHandler        onmessage;
    Promise<void>    generateRequest(DOMString initDataType,
                                     BufferSource initData);
    Promise<boolean> load(DOMString sessionId);
    Promise<void>    update(BufferSource response);
    Promise<void>    close();
    Promise<void>    remove();
};

Attributes

sessionId of type DOMString, readonly

The Session ID for this object and the associated key(s) or license(s).

expiration of type unrestricted double, readonly

The expiration time for all key(s) in the session, or NaN if no such time exists or if the license explicitly never expires, as determined by the CDM.

Note

This value MAY change during the session lifetime, such as when an action triggers the start of a window.

closed of type Promise<void>, readonly

Signals when the object becomes closed as a result of the Session Closed algorithm being run. This promise can only be fulfilled and is never rejected.

keyStatuses of type MediaKeyStatusMap, readonly

A reference to a read-only map of key IDs known to the session to the current status of the associated key. Each entry MUST have a unique key ID.

Note

The map entries and their values may be updated whenever the event loop spins. The map MUST NOT ever be inconsistent or partially updated, but it may change between accesses if the event loop spins in between the accesses. Key IDs may be added as the result of a load() or update() call. Key IDs may be removed as the result of a update() call that removes knowledge of existing keys (or replaces the existing set of keys with a new set). Key IDs MUST NOT be removed because they became unusable, such as due to expiration. Instead, such keys MUST be given an appropriate status, such as "expired".

Note

Some older platforms may contain Key System implementations that do not expose key IDs, making it impossible to provide a compliant user agent implementation. To maximize interoperability, user agent implementations exposing such CDMs SHOULD implement this member as follows: Whenever a non-empty list is appropriate, such as when the key session represented by this object may contain key(s), populate the map with a single pair containing the one-byte key ID 0 and the MediaKeyStatus most appropriate for the aggregated status of this object.

onkeystatuseschange of type EventHandler

Event handler for the keystatuseschange event.

onmessage of type EventHandler

Event handler for the message event.

Methods

generateRequest

Generates a license request based on the initData. A message of type "license-request" or "individualization-request" will always be queued if the algorithm succeeds and the promise is resolved.

Parameter Type Nullable Optional Description
initDataType DOMString ✘ ✘ The Initialization Data Type of the initData.
initData BufferSource ✘ ✘ Initialization Data
Return type: Promise<void>

When this method is invoked, the user agent must run the following steps:

  1. If this object's closing or closed value is true, return a promise rejected with an InvalidStateError.

  2. If this object's uninitialized value is false, return a promise rejected with an InvalidStateError.

  3. Let this object's uninitialized value be false.

  4. If initDataType is the empty string, return a promise rejected with a newly created TypeError.

  5. If initData is an empty array, return a promise rejected with a newly created TypeError.

  6. If the Key System implementation represented by this object's cdm implementation value does not support initDataType as an Initialization Data Type, return a promise rejected with a NotSupportedError. String comparison is case-sensitive.

  7. Let init data be a copy of the contents of the initData parameter.

  8. Let session type be this object's session type.

  9. Let promise be a new promise.

  10. Run the following steps in parallel:

    1. If the init data is not valid for initDataType, reject promise with a newly created TypeError.

    2. Let sanitized init data be a validated and sanitized version of init data.

      The user agent MUST thoroughly validate the Initialization Data before passing it to the CDM. This includes verifying that the length and values of fields are reasonable, verifying that values are within reasonable limits, and stripping irrelevant, unsupported, or unknown data or fields. It is RECOMMENDED that user agents pre-parse, sanitize, and/or generate a fully sanitized version of the Initialization Data. If the Initialization Data format specified by initDataType supports multiple entries, the user agent SHOULD remove entries that are not needed by the CDM. The user agent MUST NOT re-order entries within the Initialization Data.

    3. If the preceding step failed, reject promise with a newly created TypeError.

    4. If sanitized init data is empty, reject promise with a NotSupportedError.

    5. Let session id be the empty string.

    6. Let message be null.

    7. Let message type be null.

    8. Let cdm be the CDM instance represented by this object's cdm instance value.

    9. Use the cdm to execute the following steps:

      1. If the sanitized init data is not supported by the cdm, reject promise with a NotSupportedError.

      2. Follow the steps for the value of session type from the following list:

        "temporary"

        Let requested license type be a temporary non-persistable license.

        Note

        The returned license must not be persistable or require persisting information related to it.

        "persistent-license"

        Let requested license type be a persistable license.

      3. Let session id be a unique Session ID string.

        If the result of running the Is persistent session type? algorithm on session type is true, the ID MUST be unique within the origin of this object's Document over time, including across Documents and browsing sessions.

      4. If a license request for the requested license type can be generated based on the sanitized init data:

        1. Let message be a license request for the requested license type generated based on the sanitized init data interpreted per initDataType.

          The cdm MUST NOT use any stream-specific data, including media data, not provided via the sanitized init data.

          The cdm SHOULD NOT store session data, including the session ID, at this point. See Session Storage and Persistence.

        2. Let message type be "license-request".

        Otherwise:

        1. Let message be the request that needs to be processed before a license request request for the requested license type can be generated based on the sanitized init data.

          In a subsequent call to update() the CDM MUST generate a license request for the requested license type based on the sanitized init data, which is interpreted per initDataType.

        2. Let message type reflect the type of message, either "license-request" or "individualization-request".

    10. Queue a task to run the following steps:

      1. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name.

      2. Set the sessionId attribute to session id.

      3. Set this object's callable value to true.

      4. Run the Queue a "message" Event algorithm on the session, providing message type and message.

      5. Resolve promise.

        Note

        Since promise handlers are queued as microtasks, these will be executed ahead of any events queued by the preceding steps.

  11. Return promise.

load

Loads the data stored for the specified session into this object.

Parameter Type Nullable Optional Description
sessionId DOMString ✘ ✘ The Session ID of the session to load.
Return type: Promise<boolean>

When this method is invoked, the user agent must run the following steps:

  1. If this object's closing or closed value is true, return a promise rejected with an InvalidStateError.

  2. If this object's uninitialized value is false, return a promise rejected with an InvalidStateError.

  3. Let this object's uninitialized value be false.

  4. If sessionId is the empty string, return a promise rejected with a newly created TypeError.

  5. If the result of running the Is persistent session type? algorithm on this object's session type is false, return a promise rejected with a newly created TypeError.

  6. Let origin be the origin of this object's Document.

  7. Let promise be a new promise.

  8. Run the following steps in parallel:

    1. Let sanitized session ID be a validated and/or sanitized version of sessionId.

      Note

      The user agent should thoroughly validate the sessionId value before passing it to the CDM. At a minimum, this should include checking that the length and value are reasonable (e.g., not longer than tens of characters and alphanumeric).

    2. If the preceding step failed, or if sanitized session ID is empty, reject promise with a newly created TypeError.

    3. If there is a MediaKeySession object that is not closed in this object's Document whose sessionId attribute is sanitized session ID, reject promise with a QuotaExceededError.

      Note

      In other words, do not create a session if a non-closed session, regardless of type, already exists for this sanitized session ID in this browsing context.

    4. Let expiration time be NaN.

    5. Let message be null.

    6. Let message type be null.

    7. Let cdm be the CDM instance represented by this object's cdm instance value.

    8. Use the cdm to execute the following steps:

      1. If there is no data stored for the sanitized session ID in the origin, resolve promise with false and abort these steps.

      2. If the stored session's session type is not the same as the current MediaKeySession session type, reject promise with a newly created TypeError.

      3. Let session data be the data stored for the sanitized session ID in the origin. This MUST NOT include data from other origin(s) or that is not associated with an origin.

      4. If there is a MediaKeySession object that is not closed in any Document and that represents the session data, reject promise with a QuotaExceededError.

        Note

        In other words, do not create a session if a non-closed persistent session already exists for this sanitized session ID in any browsing context.

      5. Load the session data.

      6. If the session data indicates an expiration time for the session, let expiration time be that expiration time.

      7. If a message needs to be sent, execute the following steps:

        1. Let message be a message generated based on the session data.

        2. Let message type be the appropriate MediaKeyMessageType for the message.

    9. Queue a task to run the following steps:

      1. If any of the preceding steps failed, reject promise with a the appropriate error name.

      2. Set the sessionId attribute to sanitized session ID.

      3. Set this object's callable value to true.

      4. If the loaded session contains information about any keys (there are known keys), run the Update Key Statuses algorithm on the session, providing each key's key ID along with the appropriate MediaKeyStatus.

        Should additional processing be necessary to determine with certainty the status of a key, use "status-pending". Once the additional processing for one or more keys has completed, run the Update Key Statuses algorithm again with the actual status(es).

      5. Run the Update Expiration algorithm on the session, providing expiration time.

      6. If message is not null, run the Queue a "message" Event algorithm on the session, providing message type and message.

      7. Resolve promise with true.

        Note

        Since promise handlers are queued as microtasks, these will be executed ahead of any events queued by the preceding steps.

  9. Return promise.

update

Provides messages, including licenses, to the CDM.

Parameter Type Nullable Optional Description
response BufferSource ✘ ✘ A message to be provided to the CDM. The contents are Key System-specific. It MUST NOT contain executable code.
Return type: Promise<void>

When this method is invoked, the user agent must run the following steps:

  1. If this object's closing or closed value is true, return a promise rejected with an InvalidStateError.

  2. If this object's callable value is false, return a promise rejected with an InvalidStateError.

  3. If response is an empty array, return a promise rejected with a newly created TypeError.

  4. Let response copy be a copy of the contents of the response parameter.

  5. Let promise be a new promise.

  6. Run the following steps in parallel:

    1. Let sanitized response be a validated and/or sanitized version of response copy.

      Note

      The user agent should thoroughly validate the response before passing it to the CDM. This may include verifying values are within reasonable limits, stripping irrelevant data or fields, pre-parsing it, sanitizing it, and/or generating a fully sanitized version. The user agent should check that the length and values of fields are reasonable. Unknown fields should be rejected or removed.

    2. If the preceding step failed, or if sanitized response is empty, reject promise with a newly created TypeError.

    3. Let message be null.

    4. Let message type be null.

    5. Let session closed be false.

    6. Let cdm be the CDM instance represented by this object's cdm instance value.

    7. Use the cdm to execute the following steps:

      1. If the format of sanitized response is invalid in any way, reject promise with a newly created TypeError.

      2. Process sanitized response, following the stipulation for the first matching condition from the following list:

        If sanitized response contains a license or key(s)
        Note

        This includes an initial license, an updated license, and a license renewal message.

        Process sanitized response, following the stipulation for the first matching condition from the following list:

        If sessionType is "temporary" and sanitized response does not specify that session data, including any license, key(s), or similar session data it contains, should be stored
        Process sanitized response, not storing any session data.
        If sessionType is "persistent-license" and sanitized response contains a persistable license
        Process sanitized response, storing the license/key(s) and related session data contained in sanitized response. Such data MUST be stored such that only the origin of this object's Document can access it.
        Otherwise

        Reject promise with a newly created TypeError.

        See also Session Storage and Persistence.

        State information, including keys, for each session MUST be stored in such a way that closing one session does not affect the observable state in other session(s), even if they contain overlapping key IDs.

        Note

        When sanitized response contains key(s) and/or related data, cdm will likely store (in memory) the key and related data indexed by key ID.

        Note

        The replacement algorithm within a session is Key System-dependent.

        Note

        It is RECOMMENDED that CDM implementations support a standard and reasonably high minimum number of keys per MediaKeySession object, including a standard replacement algorithm, and a standard and reasonably high minimum number of MediaKeySession objects. This enables a reasonable number of key rotation algorithms to be implemented across user agents and may reduce the likelihood of playback interruptions in use cases that involve various streams in the same element (e.g., adaptive streams, various audio and video tracks) using different keys.

        If sanitized response contains a record of license destruction acknowledgement and sessionType is "persistent-license"

        Run the following steps:

        1. Close the key session and clear all stored session data associated with this object, including the sessionId and record of license destruction.

          Note

          A subsequent call to load() with the value of this object's sessionId would fail because there is no data stored for that session ID.

        2. Set session closed to true.

        Otherwise
        Process sanitized response, not storing any session data.
        Note

        For example, sanitized response may contain information that will be used to generate another message event. In this case, there is no need to verify the contents against the sessionType.

      3. If a message needs to be sent, execute the following steps:

        1. Let message be that message.

        2. Let message type be the appropriate MediaKeyMessageType for the message.

    8. Queue a task to run the following steps:

      1. If session closed is true:

        Run the Session Closed algorithm on this object.

        Otherwise:

        Run the following steps:

        1. If the set of keys known to the CDM for this object changed or the status of any key(s) changed, run the Update Key Statuses algorithm on the session, providing each known key's key ID along with the appropriate MediaKeyStatus.

          Should additional processing be necessary to determine with certainty the status of a key, use "status-pending". Once the additional processing for one or more keys has completed, run the Update Key Statuses algorithm again with the actual status(es).

        2. If the expiration time for the session changed, run the Update Expiration algorithm on the session, providing the new expiration time.

        3. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name.

        4. If message is not null, run the Queue a "message" Event algorithm on the session, providing message type and message.

      2. Resolve promise.

        Note

        Since promise handlers are queued as microtasks, these will be executed ahead of any events queued by the preceding steps.

  7. Return promise.

close

Indicates that the application no longer needs the session and the CDM should release any resources associated with the session and close it. Persisted data should not be released or cleared.

Note

The returned promise is resolved when the request has been processed, and the closed attribute promise is resolved when the session is closed.

No parameters.
Return type: Promise<void>

When this method is invoked, the user agent must run the following steps:

  1. If this object's closing or closed value is true, return a resolved promise.

  2. If this object's callable value is false, return a promise rejected with an InvalidStateError.

  3. Let promise be a new promise.

  4. Set this object's closing or closed value to true.

  5. Run the following steps in parallel:

    1. Let cdm be the CDM instance represented by this object's cdm instance value.

    2. Use cdm to close the key session associated with this object.

      Note

      Closing the key session results in the destruction of any license(s) and key(s) that have not been explicitly stored.

    3. Queue a task to run the following steps:

      1. Run the Session Closed algorithm on this object.

      2. Resolve promise.

        Note

        Since promise handlers are queued as microtasks, these will be executed ahead of any events queued by the preceding steps.

  6. Return promise.

remove

Removes all license(s) and key(s) associated with the session. For persistent session types, other session data will be cleared as defined for each session type once a release message acknowledgment is processed by update().

No parameters.
Return type: Promise<void>

When this method is invoked, the user agent must run the following steps:

  1. If this object's closing or closed value is true, return a promise rejected with an InvalidStateError.

  2. If this object's callable value is false, return a promise rejected with an InvalidStateError.

  3. Let promise be a new promise.

  4. Run the following steps in parallel:

    1. Let cdm be the CDM instance represented by this object's cdm instance value.

    2. Let message be null.

    3. Let message type be null.

    4. Use the cdm to execute the following steps:

      1. If any license(s) and/or key(s) are associated with the session:

        1. Destroy the license(s) and/or key(s) associated with the session.

          Note

          This implies destruction of the license(s) and/or keys(s) whether they are in memory, persistent store or both.

        2. Follow the steps for the value of this object's session type from the following list:

          "temporary"

          Continue with the following steps.

          "persistent-license"

          1. Let record of license destruction be a record of license destruction for the license represented by this object.

          2. Store the record of license destruction.

          3. Let message be a message containing or reflecting the record of license destruction.

    5. Queue a task to run the following steps:

      1. Run the Update Key Statuses algorithm on the session, providing all key ID(s) in the session along with the "released" MediaKeyStatus value for each.

      2. Run the Update Expiration algorithm on the session, providing NaN.

      3. If any of the preceding steps failed, reject promise with a new DOMException whose name is the appropriate error name.

      4. Let message type be "license-release".

      5. If message is not null, run the Queue a "message" Event algorithm on the session, providing message type and message.

      6. Resolve promise.

        Note

        Since promise handlers are queued as microtasks, these will be executed ahead of any events queued by the preceding steps.

  5. Return promise.

6.1 MediaKeyStatusMap Interface

The MediaKeyStatusMap object is a read-only map of key IDs to the current status of the associated key.

A key's status is independent of whether the key is currently being used and of media data.

Note

For example, if a key has output requirements that cannot currently be met, the key's status should be "output-downscaled" or "output-restricted", as appropriate, regardless of whether that key has been or is currently needed to decrypt media data.

[SecureContext]
interface MediaKeyStatusMap {
    iterable<BufferSource, MediaKeyStatus>;
    readonly attribute unsigned long size;
    boolean has(BufferSource keyId);
    any     get(BufferSource keyId);
};

Attributes

size of type unsigned long, readonly

The number of known keys.

Methods

has

Returns true if the status of the key identified by keyId is known.

Parameter Type Nullable Optional Description
keyId BufferSource ✘ ✘ The key ID of the key.
Return type: boolean
get

Returns the MediaKeyStatus of the key identified by keyId or undefined if the status of the key identified by keyId is not known.

Parameter Type Nullable Optional Description
keyId BufferSource ✘ ✘ The key ID of the key.
Return type: any

This interface has entries, keys, values, forEach and @@iterator methods brought by iterable (see WebIDL, 3.2.7 Iterable declarations).

The value pairs to iterate over are a snapshot of the set of pairs formed from the key ID and associated MediaKeyStatus value for all known keys, sorted by key ID. Key IDs are compared as follows: For key IDs A of length m and B of length n, assigned such that m <= n, let A < B if and only if the m octets of A are less in lexicographical order than the first m octets of B or those octets are equal and m < n. 

enum MediaKeyStatus {
    "usable",
    "expired",
    "released",
    "output-restricted",
    "output-downscaled",
    "status-pending",
    "internal-error"
};

The MediaKeyStatus enumeration is defined as follows:

Enumeration description
usable The CDM is certain the key is currently usable for decryption.
Keys that may not currently be usable for decryption MUST NOT have this status.
expired The key is no longer usable for decryption because its expiration time has passed.
The time represented by the expiration attribute MUST be earlier than the current time. All other keys in the session MUST have this status.
released The key itself is no longer available to the CDM, but information about the key, such as a record of license destruction, is available.
output-restricted There are output restrictions associated with the key that cannot currently be met. Media data decrypted with this key may be blocked from presentation, if necessary according to the output restrictions. The application should avoid using streams that will trigger the output restrictions associated with the key.
output-downscaled There are output restrictions associated with the key that cannot currently be met. Media data decrypted with this key may be presented at a lower quality (e.g., resolution), if necessary according to the output restrictions. The application should avoid using streams that will trigger the output restrictions associated with the key.
Support for downscaling is OPTIONAL. Applications SHOULD NOT rely on downscaling to ensure uninterrupted playback when output requirements cannot be met.
status-pending The status of the key is not yet known and is being determined. The status will be updated with the actual status when it has been determined.
internal-error The key is not currently usable for decryption because of an error in the CDM unrelated to the other values. This value is not actionable by the application.

6.2 MediaKeyMessageEvent

The MediaKeyMessageEvent object is used for the message event.

Events are constructed as defined in Constructing events [DOM].

enum MediaKeyMessageType {
    "license-request",
    "license-renewal",
    "license-release",
    "individualization-request"
};

The MediaKeyMessageType is defined as follows:

Enumeration description
license-request The message contains a request for a new license.
license-renewal The message contains a request to renew an existing license.
license-release The message contains a record of license destruction.
individualization-request The message contains a request for App-Assisted Individualization (or re-individualization).
As with all other messages, any identifiers in the message MUST be distinctive per origin and profile and MUST NOT be Distinctive Permanent Identifier(s). 
[SecureContext,
 Constructor(DOMString type, MediaKeyMessageEventInit eventInitDict)]
interface MediaKeyMessageEvent : Event {
    readonly attribute MediaKeyMessageType messageType;
    readonly attribute ArrayBuffer         message;
};

Constructors

MediaKeyMessageEvent
Parameter Type Nullable Optional Description
type DOMString ✘ ✘
eventInitDict MediaKeyMessageEventInit ✘ ✔

Attributes

messageType of type MediaKeyMessageType, readonly
The type of the message.

Implementations MUST NOT require applications to handle message types. Implementations MUST support applications that do not differentiate messages and MUST NOT require that applications handle message types. Specifically, Key Systems MUST support passing all types of messages to a single URL.

Note

This attribute allows an application to differentiate messages without parsing the message. It is intended to enable optional application and/or server optimizations, but applications are not required to use it.

message of type ArrayBuffer, readonly
The message from the CDM. Messages are Key System-specific.

6.2.1 MediaKeyMessageEventInit

dictionary MediaKeyMessageEventInit : EventInit {
    required MediaKeyMessageType messageType;
    required ArrayBuffer         message;
};
Dictionary MediaKeyMessageEventInit Members
messageType of type MediaKeyMessageType
The type of the message.
message of type ArrayBuffer
The message.

6.3 Event Summary

This section is non-normative.

Event name Interface Dispatched when...
keystatuseschange Event There has been a change in the keys in the session or their status.
message MediaKeyMessageEvent The CDM has generated a message for the session.

6.4 Algorithms

6.4.1 Queue a "message" Event

The Queue a "message" Event algorithm queues a message event to a MediaKeySession object. Requests to run this algorithm include a target MediaKeySession object, a message type, and a message.

message MUST NOT contain Distinctive Permanent Identifier(s), even in an encrypted form. message MUST NOT contain Distinctive Identifier(s), even in an encrypted form, if the MediaKeySession object's use distinctive identifier value is false.

The following steps are run:

  1. Let the session be the specified MediaKeySession object.

  2. Queue a task to create an event named message that does not bubble and is not cancellable using the MediaKeyMessageEvent interface with its type attribute set to message and its isTrusted attribute initialized to true, and dispatch it at the session.

    The event interface MediaKeyMessageEvent has:

6.4.2 Update Key Statuses

The Update Key Statuses algorithm updates the set of known keys for a MediaKeySession or the status of one or more of the keys. Requests to run this algorithm include a target MediaKeySession object and a sequence of key ID and associated MediaKeyStatus pairs.

Note

The algorithm is always run in a task.

The following steps are run:

  1. Let the session be the associated MediaKeySession object.

  2. Let the input statuses be the sequence of pairs key ID and associated MediaKeyStatus pairs.

  3. Let the statuses be session's keyStatuses attribute.

  4. Run the following steps to replace the contents of statuses:

    1. Empty statuses.

    2. For each pair in input statuses.

      1. Let pair be the pair.

      2. Insert an entry for pair's key ID into statuses with the value of pair's MediaKeyStatus value.

    Note

    The effect of this steps is that the contents of session's keyStatuses attribute are replaced without invalidating existing references to the attribute. This replacement is atomic from a script perspective. That is, script MUST NOT ever see a partially populated sequence.

  5. Queue a task to fire a simple event named keystatuseschange at the session.

  6. Queue a task to run the Attempt to Resume Playback If Necessary algorithm on each of the media element(s) whose mediaKeys attribute is the MediaKeys object that created the session.

6.4.3 Update Expiration

The Update Expiration algorithm updates the expiration time of a MediaKeySession. Requests to run this algorithm include a target MediaKeySession object and the new expiration time, which may be NaN.

Note

The algorithm is always run in a task.

The following steps are run:

  1. Let the session be the associated MediaKeySession object.

  2. Let expiration time be NaN.

  3. If the new expiration time is not NaN, let expiration time be that expiration time.

  4. Set the session's expiration attribute to expiration time expressed as time.

6.4.4 Session Closed

The Session Closed algorithm updates the MediaKeySession state after a key session has been closed by the CDM.

Note

The algorithm is always run in a task.

When a session is closed, the license(s) and key(s) associated with it are no longer available to decrypt media data. All MediaKeySession methods will fail and no further events will be queued for this object after this algorithm is run.

Note

The CDM may close a session at any point, such as when the session is no longer needed or when system resources are lost. In that case, the Monitor for CDM Changes algorithm detects the change and runs this algorithm.

Keys in other sessions MUST be unaffected, even if they have overlapping key IDs.

After this algorithm has run, event handlers for the events queued by this algorithm will be executed, but no further events can be queued. As a result, no messages can be sent by the CDM as a result of closing the session.

The following steps are run:

  1. Let session be the associated MediaKeySession object.

  2. Let promise be the session's closed attribute.

  3. If promise is resolved, abort these steps.

  4. Set the session's closing or closed value to true.

  5. Run the Update Key Statuses algorithm on the session, providing an empty sequence.

  6. Run the Update Expiration algorithm on the session, providing NaN.

  7. Resolve promise.

6.4.5 Monitor for CDM State Changes

The Monitor for CDM State Changes algorithm executes steps required when various aspects of CDM state change.

Note

This algorithm only applies to CDM state changes that are not covered by other algorithms. For example, update() may result in messages, key status changes and/or expiration changes, but those are all handled within that algorithm.

Note

The algorithm is always run in parallel to the main event loop.

The following steps are run:

  1. Let session be the MediaKeySession object.

  2. Let cdm be the CDM instance represented by session's cdm instance value.

  3. If cdm has an outgoing message that has not yet been sent, queue a task to execute the following steps:

    1. Let message type and message be the message type and message, respectively.

    2. Run the Queue a "message" Event algorithm, passing session, message type and message.

  4. If cdm has changed the set of keys known to session or the status of one or more of the keys, queue a task to execute the following steps:

    1. Let statuses be a list of key ID and MediaKeyStatus value pairs containing one pair for each key known to session.

    2. Run the Update Key Statuses algorithm, passing session and statuses.

  5. If cdm has changed the expiration time of session, queue a task to execute the following steps:

    1. Let expiration time be the new expiration time of session.

    2. Run the Update Expiration algorithm, passing session and expiration time.

  6. If cdm has closed session, queue a task to run the Session Closed algorithm on session.

  7. If cdm had become unavailable, queue a task to run the Session Closed algorithm on session.

6.5 Exceptions

The methods report errors by rejecting the returned promise with a simple exception [WebIDL] or a DOMException. The following simple exceptions and DOMException names from [WebIDL] are used in the algorithms. Causes specified specified in the algorithms are listed alongside each name, though these names MAY be used for other reasons as well.

Name Possible Causes (non-exhaustive)
TypeError The parameter is empty.
Invalid initialization data.
Invalid response format.
A persistent license was provided for a "temporary" session.
NotSupportedError The existing MediaKeys object cannot be removed.
The key system is not supported.
The initialization data type is not supported by the key system.
The session type is not supported by the key system.
The initialization data is not supported by the key system.
The operation is not supported by the key system.
InvalidStateError The existing MediaKeys object cannot be removed at this time.
The session has already been used.
The session is not yet initialized.
The session is closed.
QuotaExceededError The MediaKeys object cannot be used with additional HTMLMediaElements.
A non-closed session already exists for this sessionId.

6.6 Session Storage and Persistence

This section provides an overview of session storage and persistence that complements the algorithms.

The following requirements apply in addition to those in Storage and Persistence.

If the result of running the Is persistent session type? algorithm on this object's session type is false, the user agent and CDM MUST NOT persist a record of or data related to the session at any point. This includes license(s), key(s), record(s) of license destruction, and the Session ID.

The remainder of this section applies to session types for which the Is persistent session type? algorithm returns true.

The CDM SHOULD NOT store session data, including the Session ID, until update() is called the first time. Specifically, the CDM SHOULD NOT store session data during the generateRequest() algorithm. This ensures that the application is aware of the session and knows it needs to eventually remove it.

All data associated with a session MUST be cleared when the session is cleared, such as in update() when processing a record of license destruction acknowledgement. See Persistent Data.

The CDM MUST ensure that data for a given session is only present in one MediaKeySession object that is not closed in any Document. In other words, load() MUST fail when there is already a MediaKeySession representing the session specified by the sessionId parameter, either because the object that created it via generateRequest() is still active or it has been loaded into another object via load(). A session MAY only be loaded again if all objects that have ever represented it are closed.

An application that creates a session using a type for which the Is persistent session type? algorithm returns true SHOULD later remove the stored data by first initiating the removal process using remove() and then ensuring that the removal process, which may involve message exchange(s), successfully completes. The CDM MAY also remove sessions as appropriate, but applications SHOULD NOT rely on this.

See 10. Security and 11. Privacy for additional considerations when supporting persistent storage.

7. HTMLMediaElement Extensions

This section specifies additions to and modifications of the HTMLMediaElement [HTML51] when the Encrypted Media Extensions are supported.

The following internal values are added to the HTMLMediaElement:

The following modifications are made to the behaviour of the HTMLMediaElement:

For methods that return a promise, all errors are reported asynchronously by rejecting the returned Promise. This includes [WebIDL] type mapping errors.

The steps of an algorithm are always aborted when rejecting a promise.

partial interface HTMLMediaElement {
    [SecureContext]
    readonly attribute MediaKeys?   mediaKeys;
             attribute EventHandler onencrypted;
             attribute EventHandler onwaitingforkey;
    [SecureContext] Promise<void> setMediaKeys(MediaKeys? mediaKeys);
};

Attributes

mediaKeys of type MediaKeys, readonly , nullable

The MediaKeys being used when decrypting encrypted media data for this media element.

onencrypted of type EventHandler

Event handler for the encrypted event. It MUST be supported by all HTMLMediaElements as both a content attribute and an IDL attribute.

onwaitingforkey of type EventHandler

Event handler for the waitingforkey event. It MUST be supported by all HTMLMediaElements as both a content attribute and an IDL attribute.

Methods

setMediaKeys

Provides the MediaKeys to use when decrypting media data during playback.

Note

Support for clearing or replacing the associated MediaKeys object during playback is a quality of implementation issue. In many cases it will result in a bad user experience or rejected promise.

Parameter Type Nullable Optional Description
mediaKeys MediaKeys ✔ ✘ A MediaKeys object.
Return type: Promise<void>

When this method is invoked, the user agent must run the following steps:

  1. If this object's attaching media keys value is true, return a promise rejected with an InvalidStateError.

  2. If mediaKeys and the mediaKeys attribute are the same object, return a resolved promise.

  3. Let this object's attaching media keys value be true.

  4. Let promise be a new promise.

  5. Run the following steps in parallel:

    1. If all the following conditions hold:

      • mediaKeys is not null,

      • the CDM instance represented by mediaKeys is already in use by another media element

      • the user agent is unable to use it with this element

      then let this object's attaching media keys value be false and reject promise with a QuotaExceededError.

    2. If the mediaKeys attribute is not null, run the following steps:

      1. If the user agent or CDM do not support removing the association, let this object's attaching media keys value be false and reject promise with a NotSupportedError.

      2. If the association cannot currently be removed, let this object's attaching media keys value be false and reject promise with an InvalidStateError.

        Note

        For example, some implementations may not allow removal during playback.

      3. Stop using the CDM instance represented by the mediaKeys attribute to decrypt media data and remove the association with the media element.

      4. If the preceding step failed, let this object's attaching media keys value be false and reject promise with the appropriate error name.

    3. If mediaKeys is not null, run the following steps:

      1. Associate the CDM instance represented by mediaKeys with the media element for decrypting media data.

      2. If the preceding step failed, run the following steps:

        1. Set the mediaKeys attribute to null.

        2. Let this object's attaching media keys value be false.

        3. Reject promise with a new DOMException whose name is the appropriate error name.

      3. Queue a task to run the Attempt to Resume Playback If Necessary algorithm on the media element.

    4. Set the mediaKeys attribute to mediaKeys.

    5. Let this object's attaching media keys value be false.

    6. Resolve promise.

  6. Return promise.

7.1 MediaEncryptedEvent

The MediaEncryptedEvent object is used for the encrypted event.

Events are constructed as defined in Constructing events [DOM].

[Constructor(DOMString type, optional MediaEncryptedEventInit eventInitDict)]
interface MediaEncryptedEvent : Event {
    readonly attribute DOMString    initDataType;
    readonly attribute ArrayBuffer? initData;
};

Constructors

MediaEncryptedEvent
Parameter Type Nullable Optional Description
type DOMString ✘ ✘
eventInitDict MediaEncryptedEventInit ✘ ✔

Attributes

initDataType of type DOMString, readonly
Indicates the Initialization Data Type of the Initialization Data contained in the initData attribute.
initData of type ArrayBuffer, readonly , nullable
The Initialization Data for the event.

7.1.1 MediaEncryptedEventInit

dictionary MediaEncryptedEventInit : EventInit {
    DOMString    initDataType = "";
    ArrayBuffer? initData = null;
};
Dictionary MediaEncryptedEventInit Members
initDataType of type DOMString, defaulting to ""
The Initialization Data Type.
initData of type ArrayBuffer, nullable, defaulting to null
The Initialization Data.

7.2 Event Summary

This section is non-normative.

Event name Interface Dispatched when... Preconditions
encrypted MediaEncryptedEvent The user agent encounters Initialization Data in the media data. The element's readyState is equal to or greater than HAVE_METADATA.
Note

It is possible that the element is playing or has played.
waitingforkey Event Playback is blocked waiting for a key. The readyState is equal to or less than HAVE_CURRENT_DATA. The element's playback blocked waiting for key value is newly true.

7.3 Algorithms

7.3.1 Media Data May Contain Encrypted Blocks

The Media Data May Contain Encrypted Blocks algorithm pauses playback if the user agent requires specification of a MediaKeys object before playing the media data. Requests to run this algorithm include a target HTMLMediaElement object.

The following steps are run:

  1. Let the media element be the specified HTMLMediaElement object.

  2. If the media element's mediaKeys attribute is null and the implementation requires specification of a MediaKeys object before decoding potentially-encrypted media data, run the following steps:

    Note

    These steps may be reached when the application provides media data before calling setMediaKeys() to provide a MediaKeys object. Selecting a CDM may affect the pipeline and/or decoders used, so some implementations may delay playback of media data that may contain encrypted blocks until a CDM is specified by passing a MediaKeys object to setMediaKeys().

    1. Run the Wait for Key algorithm on the media element.

    2. Wait for a signal to resume playback.

7.3.2 Initialization Data Encountered

The Initialization Data Encountered algorithm queues an encrypted event for Initialization Data encounterd in the media data. Requests to run this algorithm include a target HTMLMediaElement object.

The following steps are run:

  1. Let the media element be the specified HTMLMediaElement object.

  2. Let initDataType be the empty string.

  3. Let initData be null.

  4. If the media data is CORS-same-origin and not mixed content, run the following steps:

    1. Let initDataType be the string representing the Initialization Data Type of the Initialization Data.

    2. Let initData be the Initialization Data.

    Note

    While the media element may allow loading of "Optionally-blockable Content" [MIXED-CONTENT], the user agent MUST NOT expose Initialization Data from such media data to the application.

  5. Queue a task to create an event named encrypted that does not bubble and is not cancellable using the MediaEncryptedEvent interface with its type attribute set to encrypted and its isTrusted attribute initialized to true, and dispatch it at the media element.

    The event interface MediaEncryptedEvent has:

    Note

    readyState is not changed and no algorithms are aborted. This event merely provides information.

    Note

    The initData attribute will be null if the media data is not CORS-same-origin or is mixed content. Applications may retrieve the Initialization Data from an alternate source.

7.3.3 Encrypted Block Encountered

The Encrypted Block Encountered algorithm queues a block of encrypted media data for decryption and attempts to decrypt if possible. Requests to run this algorithm include a target HTMLMediaElement object.

The following steps are run:

  1. Let the media element be the specified HTMLMediaElement object.

  2. Let block be the block of encrypted media data.

  3. Add block to the end of the media element's encrypted block queue.

  4. If the media element's decryption blocked waiting for key value is false, run the Attempt to Decrypt algorithm.

7.3.4 Attempt to Decrypt

The Attempt to Decrypt algorithm attempts to decrypt media data that is queued for decryption. Requests to run this algorithm include a target HTMLMediaElement object.

The following steps are run:

  1. Let the media element be the specified HTMLMediaElement object.

  2. If the media element's encrypted block queue is empty, abort these steps.

  3. If the media element's mediaKeys attribute is not null, run the following steps:

    1. Let media keys be the MediaKeys object referenced by that attribute.

    2. Let cdm be the CDM instance represented by media keys's cdm instance value.

    3. If cdm is no longer usable for any reason, run the following steps:

      Note

      These steps are intended to be run on unrecoverable failures of the CDM.

      1. Run the media data is corrupted steps of the resource fetch algorithm.

      2. Run the CDM Unavailable algorithm on media keys.

      3. Abort these steps.

    4. If there is at least one MediaKeySession created by the media keys that is not closed, run the following steps:

      Note

      This check ensures the cdm has finished loading and is a prerequisite for a matching key being available.

      1. Let block be the first entry in the media element's encrypted block queue.

      2. Let the block key ID be the key ID of block.

        Note

        The key ID is generally specified by the container.

      3. Use the cdm to execute the following steps:

        1. Let available keys be the union of keys in sessions that were created by the media keys.

        2. Let block key be null.

        3. If any of the available keys corresponds to the block key ID and is usable for decryption, let session be a MediaKeySession object containing that key and let block key be that key.

          Note

          If multiple sessions contain a key that is usable for decryption for the block key ID, which session and key to use is Key System-dependent.

        4. If the status of any of the available keys changed as the result of running the preceding step, queue a task to run the Update Key Statuses algorithm on each affected session, providing all key ID(s) in the session along with the appropriate MediaKeyStatus value(s) for each.

        5. If block key is not null, run the following steps:

          1. Use the cdm to decrypt block using block key.

          2. Follow the steps for the first matching condition from the following list:

            If decryption fails

            1. Run the media data is corrupted steps of the resource fetch algorithm.

            2. If cdm is no longer usable for any reason then run the CDM Unavailable algorithm on media keys.

            3. Abort these steps.

            Otherwise

            1. Remove block from the front of the media element's encrypted block queue.

            2. Process the decrypted block as normal.

              Note

              In other words, decode the block.

            3. Return to the beginning of this algorithm.

            Note

            Not all decryption problems (e.g., using the wrong key) will result in a decryption failure. In such cases, no error is fired here but one may be fired during decode.

          Note

          Otherwise, there is no key for the block key ID in any session so continue.

  4. Set the media element's decryption blocked waiting for key value to true.

    Note

    This step is reached when there is no key that is usable for decryption for block.

    Note

    Once the user agent has rendered the blocks preceding the block that cannot be decrypted (as much as it can, such as, all complete video frames), it will run the Wait for Key algorithm.

    That algorithm is not run directly here in order to allow implementations to decrypt and decode media data ahead of the ahead of the current playback position without affecting the visible behavior.

Note

For frame-based encryption, this may be implemented as follows when the media element attempts to decode a frame as part of the resource fetch algorithm:

  1. Let encrypted be false.

  2. Detect whether the frame is encrypted.

    If the frame is encrypted
    Run the steps above.
    Otherwise
    Continue.

  3. Decode the frame.

  4. Provide the frame for rendering.

7.3.5 Wait for Key

The Wait for Key algorithm queues a waitingforkey event and updates readyState. It should only be called when the HTMLMediaElement object is potentially playing and its readyState is equal to HAVE_FUTURE_DATA or greater. Requests to run this algorithm include a target HTMLMediaElement object.

The following steps are run:

  1. Let the media element be the specified HTMLMediaElement object.

  2. If the media element's playback blocked waiting for key value is true, abort these steps.

  3. Set the media element's playback blocked waiting for key value to true.

    Note

    As a result of the above step, the media element will become a blocked media element if it wasn't already. In that case, the media element will stop playback.

  4. Follow the steps for the first matching condition from the following list:

    If data for the immediate current playback position is available

    Set the readyState of media element to HAVE_CURRENT_DATA.

    Otherwise

    Set the readyState of media element to HAVE_METADATA.

    Note

    In other words, if the video frame and audio data for the current playback position have been decoded because they were unencrypted and/or successfully decrypted, set readyState to HAVE_CURRENT_DATA. Otherwise, including if this was previously the case but the data is no longer available, set readyState to HAVE_METADATA.

  5. Queue a task to fire a simple event named waitingforkey at the media element.

  6. Suspend playback.

7.3.6 Attempt to Resume Playback If Necessary

The Attempt to Resume Playback If Necessary algorithm resumes playback if the media element is blocked waiting for a key and necessary key is currently usable for decryption Requests to run this algorithm include a target HTMLMediaElement object.

The following steps are run:

  1. Let the media element be the specified HTMLMediaElement object.

  2. If the media element's playback blocked waiting for key is false, abort these steps.

  3. Run the Attempt to Decrypt algorithm on the media element.

  4. If the user agent can advance the current playback position in the direction of playback:

    1. Set the media element's decryption blocked waiting for key value to false.

    2. Set the media element's playback blocked waiting for key value to false.

      Note

      As a result of the above step, the media element may no longer be a blocked media element and thus playback may resume.

    3. Set the media element's readyState value to HAVE_CURRENT_DATA, HAVE_FUTURE_DATA or HAVE_ENOUGH_DATA as appropriate.

      Note

      States beyond HAVE_CURRENT_DATA and the canplaythrough event do not (or are unlikely to) consider key availability beyond the current key.

      The change in ready state may also cause HTMLMediaElement events to be fired as described here.

7.4 Media Element Restrictions

This section is non-normative.

Media data processed by a CDM MAY be unavailable through web platform APIs in the usual way (for example using the CanvasRenderingContext2D drawImage() method and the AudioContext MediaElementAudioSourceNode). This specification does not define conditions for such non-availability of media data, however, if media data is not available to through such APIs then they MAY behave as if no media data was present at all.

Where media rendering is not performed by the UA, for example in the case of a hardware-based media pipeline, the full set of HTML rendering capabilities, for example CSS Transforms, MAY be unavailable. One likely restriction is that video media MAY be constrained to appear only in rectangular regions with sides parallel to the edges of the window and with normal orientation.

8. Implementation Requirements

This section defines implementation requirements - for both user agents and Key Systems, including the CDM and server(s) - that may not be explicitly addressed in the algorithms. The requirements here and throughout the spec apply to all implementations, regardless of whether the CDM is separate from or a part of the user agent.

8.1 CDM Constraints

User agent implementers MUST ensure that CDMs do not access any information, storage or system capabilities that are not reasonably required for playback of protected media using the features of this specification. Specifically, the CDM SHALL NOT:

User Agent implementers may use various techniques to meet the above requirements. For example, a User Agent implementer also implementing their own CDM may include the above as design requirements for that component. A User Agent implementer making use of a third party CDM may ensure that it executes in a constrained environment (e.g., "sandbox") without access to the prohibited information and components.

8.2 Messages and Communication

All messages and communication to and from the CDM, such as between the CDM and a license server, MUST be passed through the user agent. The CDM MUST NOT make direct out-of band network requests. All messages and communication other than those described in Direct Individualization MUST be passed through the application via the APIs defined in this specification. Specifically, all communication that contains application-, origin-, or content-specific information or is sent to a URL specified by the application or based on its origin, MUST pass through the APIs. This includes all license exchange messages.

8.3 Persistent Data

Persistent Data includes all data stored by the CDM, or by the User Agent on behalf of the CDM, that exists after the destruction of the MediaKeys object. Specifically, it includes any identifiers (including Distinctive Identifier(s)), licenses, keys, key IDs, or records of license destruction stored by the CDM or by the User Agent on behalf of the CDM.

8.3.1 Use origin-specific and browsing profile-specific Key System storage

Persistent Data that might impact messages or behavior in an application- or license server-visible way MUST be stored in an origin-specific and browsing profile-specific way and MUST NOT leak to or from private browsing sessions. Specifically but not exhaustively, session data, licenses, keys and per-origin identifiers MUST be stored per-origin and per-browsing profile.

See Session Storage and Persistence.

8.3.2 Allow Persistent Data to Be Cleared

Implementations that use Persistent Data MUST allow the user to clear that data such that it is no longer retrievable both outside, such as via the APIs defined in this specification, and on the client device.

User Agents SHOULD:

  • Treat Persistent Data like other site data, such as cookies [COOKIES]. Specifically:

    • Allow users to clear Persistent Data along with cookies [COOKIES] and other site data.

    • Allow users to clear Persistent Data as part of user agent features to clear browsing history.

    • Include Persistent Data in "remove all data" features.

    • Present Persistent Data in the same UI locations as other site data.

  • Allow users to clear Persistent Data on a per-origin and per-browsing profile basis, particularly as part of a "Forget about this site" feature that forgets cookies [COOKIES], databases, etc. associated with a particular site.

  • Ensure that operations which clear Persistent Data are sufficiently atomic to prevent a "cookie resurrection" type of recorrelation of a new identifier with the old by relying on another type of locally stored data that did not get cleared at the same time. See incomplete clearing of data.

  • Present these interfaces in a way that helps users to understand the possibility of incomplete clearing of data and enables them to delete data associated with all features that persist data, including cookies [COOKIES] and web storage, simultaneously.

  • Present the interfaces for disabling and re-enabling a Key System in a way that helps users to understand the possibility of incomplete clearing of data and enables them to delete all such data in all persistent storage features simultaneously.

  • Allow users to specifically delete Persistent Data, by origin and/or for all origins.

8.3.3 Encrypt or obfuscate Persistent Data

User agents SHOULD treat Persistent Data as potentially sensitive; it is quite possible for user privacy to be compromised by the release of this information. To this end, user agents SHOULD ensure that Persistent Data is securely stored and when deleting data, it is promptly deleted from the underlying storage.

8.4 Values Exposed to the Application

Values exposed to or inferable by, such as via its use by the CDM, the application could be used to identify the client or user, regardless of whether they are designed to be identifiers. This section defines requirements for avoiding or at least mitigating such concerns. There are additional requirements for Identifiers.

8.4.1 Use Per-Origin Per-Profile Values

All distinctive values exposed to or inferable by the application MUST be unique per origin and browsing profile. That is, the value(s) used for one origin using the APIs defined in this specification MUST be different from those used for any other origin using the APIs, and value(s) used in one browsing profile MUST be different from those used for any other profile, regardless of origin. Such values MUST NOT leak to or from private browsing sessions.

Values across origins and profiles MUST be non-associable by applications, meaning it MUST NOT be possible to correlate values from multiple origins or profiles, such as to determine that they came from the same client or user. Specifically, implementations that derive per-origin values from an origin-independent and/or profile-independent value, MUST do so in a way that ensures the above non-associability property, such as by using derivation functions with appropriate non-reversible properties.

8.4.2 Allow Values to Be Cleared

As a consequence of the requirements in Allow Persistent Data to Be Cleared, all persisted values exposed to the application MUST be clearable such that the values are no longer retrievable, observable, or inferable both outside, such as via the APIs defined in this specification, and on the client device.

Once cleared, new non-associable by applications value(s) MUST be generated when values are subsequently needed.

8.5 Identifiers

The use of identifiers, especially Distinctive Identifier(s) or Distinctive Permanent Identifier(s), by implementations presents a privacy concern. This section defines requirements for avoiding or at least mitigating such concerns. The requirements for Values Exposed to the Application also apply to identifiers exposed to the application.

Note

In summary:

8.5.1 Limit or Avoid use of Distinctive Identifiers and Permanent Identifiers

8.5.2 Encrypt Identifiers

Distinctive Identifiers and Distinctive Permanent Identifiers MUST be encrypted at the message exchange level when exposed outside the client. All other identifiers SHOULD be encrypted at the message exchange level when exposed outside the client. The encryption MUST ensure that any two instances of the identifier ciphertext are associable only by an entity in possession of the decryption key.

Note

Identifiers may be exposed in the following ways:

The CDM MUST verify that the encryption key belongs to a valid server for its Key System. For identifers exposed to the application, this MAY be implemented using a server certificate.

The server MUST NOT expose a Distinctive Identifier to any entity other than the CDM that sent it.

Note

Specifically, it should not be provided to the application or included unencrypted in messages to the CDM. This can be accomplished by encrypting the identifier or message with the identifier or such that it is only decryptable by that specific CDM.

Note

Among other things, this means that:

  • Every signature made with device-specific or user-specific keys MUST be different, even given the same plaintext.

  • Identifiers, keys, or certificates relating to device-specific or user-specific keys MUST be encrypted for the license or individualization server.

  • Messages from the license server to the CDM MUST NOT expose recipient-unique identifiers, such as the ID of the intended decryption key, on the outside of the encryption envelope.

8.5.3 Use Per-Origin Per-Profile Identifiers

All identifiers except Distinctive Permanent Identifiers MUST be unique per origin and browsing profile. See 8.4.1 Use Per-Origin Per-Profile Values.

Note

This includes but is not limited to Distinctive Identifiers.

Distinctive Permanent Identifiers MUST NOT be exposed to the application or origin.

8.5.4 Use Non-Associable Identifiers

All identifiers, including Distinctive Identifiers, exposed by the implementation to applications, even in encrypted form, MUST be non-associable by application(s) across origins, browsing profiles, and clearing of identifiers.

Note

For all such identifiers, it MUST NOT be possible for one or more applications, including related license or other servers to achieve such correlation or association.

8.5.5 Allow Identifiers to Be Cleared

As a consequence of the requirements in Allow Persistent Data to Be Cleared, all potential identifiers or distinctive values except Distinctive Permanent Identifiers MUST be clearable such that the values are no longer retrievable, observable, or inferable both outside, such as via the APIs defined in this specification, and on the client device.

Implementations that use Distinctive Identifier(s) MUST allow the user to clear the Distinctive Identifier(s). Implementations that use Distinctive Permanent Identifier(s) MUST allow the user to clear values associated with the Distinctive Permanent Identifier(s).

Once cleared, new non-associable by applications value(s) MUST be generated when values, such as Distinctive Identifiers, are subsequently needed.

8.6 Individualization

Identifiers, especially Distinctive Identifiers, are sometimes generated or obtained via a process called individualization or provisioning. The resulting identifier(s) MUST be non-associable by applications and use of them MUST only be exposed to a single origin from a single profile. This process MAY be performed multiple times, such as after identifier(s) are cleared.

This process MUST be performed either directly by the user agent or through the application. The mechanisms, flow, and restrictions for the two types of individualization are different, as described in the following sections. Which method is used depends on the CDM implementation and application of the requirements of this specification, especially those below.

Note

distinctiveIdentifier controls whether Distinctive Identifiers and Distinctive Permanent Identifiers may be used, including for individualization. Specifically, such identifiers may only be used when the value of the distinctiveIdentifier member of the MediaKeySystemAccess used to create the MediaKeys object is "required".

8.6.1 Direct Individualization

Direct Individualization is performed between the CDM and an origin- and application-independent server. Although the server is origin-independent, the result of the individualization enables the CDM to provide origin-specific identifiers per the other requirements of this specification. The process MUST be performed by the user agent and MUST NOT use the APIs defined in this specification.

Note

For example, such a process may initialize a client device and/or obtain a per-origin clearable identifier for a single browsing profile by communicating with a pre-determined server hosted by the user agent or CDM vendor, possibly using Distinctive Permanent Identifier(s) or other Permanent Identifier(s) from the client device.

For such individualization, all message exchanges:

  • MUST be handled by the user agent and performed by the user agent via the user agent's network stack.

  • MUST NOT be performed directly by the CDM.

  • MUST NOT be passed to or through the application via the APIs defined in this specification.

  • MUST be sent to a URL selected independently of any origin and application.

  • MUST encrypt all Distinctive Identifiers and Distinctive Permanent Identifiers.

  • MUST use TLS.

Implementations MUST NOT expose, even in encrypted form, origin(s), origin- or application-specific information, or values that are associable with origin(s) to centralized servers since this could create a central record of all origins visited by a user or device.

8.6.2 App-Assisted Individualization

App-Assisted Individualization is performed between the CDM and the application, including an application-selected server, and results in a per-origin identifier. The process MUST be performed via the APIs defined in this specification and MUST NOT involve other methods of communication. As with all other uses of the APIs, the process MAY use one or more Distinctive Identifier(s), but it MUST NOT use Distinctive Permanent Identifier(s) or non-origin-specific values, even in encrypted form. If the process use one or more Distinctive Identifier(s), the resulting identifier is by definition also a Distinctive Identifier.

For such individualization, all message exchanges:

When associable values, including Distinctive Identifier(s), are used in the process, implementations MUST NOT expose, even in encrypted form, origin(s)-, origin- or application-specific information, or values that are associable with origin(s) to centralized servers since this could create a central record of all origins visited by a user or device.

With appropriate precautions, such individualization can provide better privacy than Direct Individualization, though not as good as models that do not use Distinctive Identifier(s). To preserve the benefits of such a design and to avoid introducing other privacy concerns, such implementations and the applications that support them SHOULD avoid deferring or forwarding individualization messages to a central server or other server not controlled by the application author.

8.7 Support Multiple Keys

Implementations MUST support multiple keys in each MediaKeySession object.

Note

The mechanics of how multiple keys are supported is an implementation detail, but it MUST be transparent to the application and the APIs defined in this specification.

Implementations MUST support seamless switching between keys during playback. This includes both keys in the same MediaKeySession and keys in separate MediaKeySession objects.

8.8 Initialization Data Type Support

8.8.1 Licenses Generated are Independent of Content Type

Implementations SHOULD allow licenses generated with any Initialization Data Type they support to be used with any content type.

Note

Otherwise, the requestMediaKeySystemAccess() algorithm might, for example, reject a MediaKeySystemConfiguration because one of the initDataTypes is not supported with one of the videoCapabilities.

8.8.2 Support Extraction From Media Data

For any supported Initialization Data Type that may appear in a supported container, the user agents MUST support extracting that type of Initialization Data from each such supported container.

Note

In other words, indicating support for an Initialization Data Type implies both CDM support for generating license requests and, for container-specific types, user agent support for extracting it from the container. This does not mean that implementations must be able to parse any supported Initialization Data from any supported content type.

8.9 Supported Media

This section defines properties of content (media resource) supported by implementations of this specification.

8.9.1 Unencrypted Container

The media container MUST NOT be encrypted. This specification relies on the user agent's ability to parse the media container without having to decrypt any of the media data. This includes the Encrypted Block Encountered and Initialization Data Encountered algorithms as well as supporting standard HTMLMediaElement [HTML51] functionality, such as seeking.

8.9.2 Interoperably Encrypted

Media resources, including all tracks, MUST be encrypted and packaged per a container-specific "common encryption" specification that allows the content to be decrypted in a fully specified and compatible way when a key or keys are provided.

Note

The Encrypted Media Extensions Stream Format and Initialization Data Format Registry [EME-STREAM-REGISTRY] provides references to such stream formats.

8.9.3 Unencrypted In-band Support Content

In-band support content, such as captions, described audio, and transcripts, SHOULD NOT be encrypted.

Note

Decryption of such tracks - especially such that they can be provided back the user agent - is not generally supported by implementations. Thus, encrypting such tracks would prevent them from being widely available for use with accessibility features in user agent implementations.

To ensure accessibility information is available in usable form, for implementations that choose to support encrypted in-band support content: a) the CDM MUST provide the decrypted data to the user agent and b) the user agent MUST process it in the same way as equivalent unencrypted support content. For example, to be exposed as timed text tracks [HTML51].

9. Common Key Systems

All user agents MUST support the common key systems described in this section.

Note

This ensures that there is a common baseline level of functionality that is guaranteed to be supported in all user agents, including those that are entirely open source. Thus, content providers that need only basic decryption can build simple applications that will work on all platforms without needing to work with any content protection providers.

9.1 Clear Key

The "org.w3.clearkey" Key System uses plain-text clear (unencrypted) key(s) to decrypt the source. No additional client-side content protection is required. This Key System is described below.

9.1.1 Capabilities

The following describe how Clear Key supports key system-specific capabilities:

9.1.2 Behavior

The following describe how Clear Key implements key system-specific behaviors:

  • In the generateRequest() algorithm:

    • The generated message is a JSON object encoded in UTF-8 as described in License Request Format.

    • The request is generated by extracting the key IDs from the sanitized init data.

    • The "type" member value is the value of the sessionType parameter.

  • The sessionId attribute is a numerical value representable by a 32-bit integer.

  • The expiration attribute is always NaN.

  • In the update() algorithm:

    • The response parameter is either a JWK Set as described in License Format, or a JSON object encoded in UTF-8 as described in License Release Acknowledgement Format.

    • In the first case, sanitized response is considered invalid if it is not a valid JWK Set with at least one valid JWK key of a valid length for the audio/video type. In the second case sanitized response is considered invalid if it is not a valid JSON object.

  • For sessions of type "persistent-license", in the remove() algorithm, the message reflecting the record of license destruction is a JSON object encoded in UTF-8 as described in License Release Format.

  • The keyStatuses attribute method initially contains all key IDs that have been provided via update(), with status "usable". When the remove() algorithm is executed, the keyStatuses attribute will be set to an empty list.

  • Initialization Data: Implementations MAY support any combination of registered Initialization Data Types [EME-INITDATA-REGISTRY]. Implementations SHOULD support the "keyids" type [EME-INITDATA-KEYIDS] and other types appropriate for content types supported by the user agent.

9.1.3 License Request Format

This section describes the format of the license request provided to the application via the message attribute of the message event.

The format is a JSON object containing the following members:

"kids"
An array of key IDs. Each element of the array is the base64url encoding of the octet sequence containing the key ID value.
"type"
The requested MediaKeySessionType

When contained in the ArrayBuffer message attribute of a MediaKeyMessageEvent object, the JSON string is encoded in UTF-8 as specified in the Encoding specification [ENCODING]. Applications MAY decode the contents of the ArrayBuffer to a JSON string using the TextDecoder interface [ENCODING].

9.1.3.1 Example

This section is non-normative.

The following example is a license request for a temporary license for two key IDs. (Line breaks are for readability only.)

Example 1
{
  "kids":
    [
     "LwVHf8JLtPrv2GUXFW2v_A",
     "0DdtU9od-Bh5L3xbv0Xf_A"
    ],
  "type":"temporary"
}

9.1.4 License Format

This section describes the format of the license to be provided via the response parameter of the update() method.

The format is a JSON Web Key (JWK) Set containing representation of the symmetric key to be used for decryption, as defined in the JSON Web Key (JWK) specification [RFC7517].

For each JWK in the set, the parameter values are as follows:

"kty" (key type)
"oct" (octet sequence)
"k" (key value)
The base64url encoding of the octet sequence containing the symmetric key value
"kid" (key ID)
The base64url encoding of the octet sequence containing the key ID value

The JSON object MAY have an optional "type" member value, which MUST be one of the MediaKeySessionType values. If not specified, the default value of "temporary" is used. The update() algorithm compares this value to the sessionType.

When passed to the update() method as the ArrayBuffer response parameter, the JSON string MUST be encoded in UTF-8 as specified in the Encoding specification [ENCODING]. Applications MAY encode the JSON string using the TextEncoder interface [ENCODING].

9.1.4.1 Example

This section is non-normative.

The following example is a JWK Set containing a single symmetric key. (Line breaks are for readability only.)

Example 2
{
  "keys":
    [{
      "kty":"oct",
      "k":"tQ0bJVWb6b0KPL6KtZIy_A",
      "kid":"LwVHf8JLtPrv2GUXFW2v_A"
    }],
  'type':"temporary"
}

9.1.5 License Release Format

This section describes the format of the license release message to be provided via the message attribute of the message event.

The format is a JSON object. For sessions of type "persistent-license", the object shall contain the following member:

"kids"
An array of key IDs. Each element of the array is the base64url encoding of the octet sequence containing the key ID value.

When contained in the ArrayBuffer message attribute of a MediaKeyMessageEvent object, the JSON string is encoded in UTF-8 as specified in the Encoding specification [ENCODING]. Applications MAY decode the contents of the ArrayBuffer to a JSON string using the TextDecoder interface [ENCODING].

9.1.5.1 Example message reflecting a record of license destruction

This section is non-normative.

The following example is a license release for a "persistent-license" session that contained two keys. (Line breaks are for readability only.)

Example 3
{
  "kids": [ "LwVHf8JLtPrv2GUXFW2v_A", "0DdtU9od-Bh5L3xbv0Xf_A" ]
}

9.1.6 License Release Acknowledgement Format

This section describes the format of the license release acknowledgement provided via the response parameter of the update() method.

The format is a JSON object containing the following members:

"kids"
An array of key IDs. Each element of the array is the base64url encoding of the octet sequence containing the key ID value.

When passed to the update() method as the ArrayBuffer response parameter, the JSON string MUST be encoded in UTF-8 as specified in the Encoding specification [ENCODING]. Applications MAY encode the JSON string using the TextEncoder interface [ENCODING].

9.1.6.1 Example

This section is non-normative.

The following example is a license request for a temporary license for two key IDs. (Line breaks are for readability only.)

Example 4
{
  "kids":
    [
     "LwVHf8JLtPrv2GUXFW2v_A",
     "0DdtU9od-Bh5L3xbv0Xf_A"
    ]
}

9.1.7 Using base64url

This section is non-normative.

For more information on base64url and working with it, see the "Base64url Encoding" terminology definition and "Notes on implementing base64url encoding without padding" in [RFC7515]. Specifically, there is no '=' padding, and the characters '-' and '_' MUST be used instead of '+' and '/', respectively.

10. Security

10.1 Input Data Attacks and Vulnerabilities

User Agent and Key System implementations MUST consider media data, Initialization Data, data passed to update(), licenses, key data, and all other data provided by the application as untrusted content and potential attack vectors. They MUST use appropriate safeguards to mitigate any associated threats and take care to safely parse, decrypt, etc. such data. User Agents SHOULD validate data before passing it to the CDM.

Note

Such validation is especially important if the CDM does not run in the same (sandboxed) context as, for example, the DOM.

Implementations MUST NOT return active content or passive content that affects program control flow to the application.

Note

For example, it is not safe to expose URLs or other information that may have come from media data, such as is the case for the Initialization Data passed to generateRequest(). Applications must determine the URLs to use. The messageType attribute of the message event can be used by the application to select among a set of URLs if applicable.

10.2 CDM Attacks and Vulnerabilities

User Agents are responsible for providing users with a secure way to browse the web. This responsibility applies to any functionality used by User Agents, including functionalities from third parties. User agent implementers MUST obtain sufficient information from Key System implementers to enable them to properly assess the security implications of integrating with the Key System. User agent implementers MUST ensure CDM implementations provide and/or support sufficient controls for the user agent to provide security for the user. User agent implementers MUST ensure CDM implementations can and will be quickly and proactively updated in the event of security vulnerabilities.

Exploiting a CDM implementation that is not fully sandboxed and/or uses platform features may allow an attacker to access OS or platform features, elevate privilege (e.g., to run as system or root), and/or access drivers, kernel, firmware, hardware, etc. Such features, software, and hardware may not be written to be robust against hostile software or web-based attacks and may not be updated with security fixes, especially compared to the user agent. Lack of, infrequent, or slow updates for fixes to security vulnerabilities in CDM implementations increases the risk. Such CDM implementations and UAs that expose them MUST be especially careful in all areas of security, including parsing of all data.

Note

User agents should be especially diligent when using a CDM or underlying mechanism that is part of or provided by the client OS, platform and/or hardware.

If a user agent chooses to support a Key System implementation that cannot be sufficiently sandboxed or otherwise secured, the user agent SHOULD ensure that users are fully informed and/or give explicit consent before loading or invoking it.

Note

Granting permissions to unauthenticated origins is equivalent to granting the permissions to any origin in the presence of a network attacker. See abuse of persisted consent.

10.3 Network Attacks

10.3.1 Potential Attacks

This section is non-normative.

Potential network attacks and their implications include:

  • DNS spoofing attacks: One cannot guarantee that a host claiming to be in a certain domain (origin) really is from that domain.

  • Passive network attacks: One cannot guarantee that data, including Distinctive Identifiers and Distinctive Permanent Identifiers, transmitted between the client and server is not viewed by other entities. See User Tracking.

  • Active network attacks: One cannot guarantee that Additional scripts or iframes are not injected into pages (both those that use the APIs defined in this specification for legitimate purposes and pages that do not use them). The consequences are that:

    • Calls to the APIs defined in this specification can be injected into any page.

    • Calls to the APIs defined in this specification from pages using them for legitimate reasons can be manipulated, including modifying the requested functionality, modifying or adding calls, and modifying or injecting data. See also Input Data Attacks and Vulnerabilities

    • Data, including Distinctive Identifiers and Distinctive Permanent Identifiers, transmitted between the client and server can be viewed and/or modified by other entities. See User Tracking.

  • Abuse of persisted consent: One cannot guarantee that the host requesting use of the APIs defined in this specification is the host to which the user previously provided consent. The consequences are that granting permissions to unauthenticated origins is equivalent to granting the permissions to any origin in the presence of a network attacker.

10.3.2 Mitigations

The following techniques may mitigate the risks:

Use TLS

Applications using TLS can be sure that only the user, software working on behalf of the user, and other pages using TLS that have certificates identifying them as being from the same domain, can interact with that application. Furthermore, origin-specific permissions in combination with a secure origin, ensure that permissions granted to an application cannot be abused by a network attacker.

The APIs defined in this specification are only exposed on secure contexts. See also Secure Origin and Transport.

Block Mixed Content

User agents MUST properly handle Mixed Content [MIXED-CONTENT], including blocking "Blockable Content" [MIXED-CONTENT] to avoid potential exposure to insecure content. Such exposure could compromise other mitigations, such as use of TLS.

User agents MAY choose to block all Mixed Content, including "Optionally-blockable Content" [MIXED-CONTENT] to further increase security by preventing untrusted media data from being passed to the CDM (see CDM Attacks and Vulnerabilities).

User agents SHOULD ensure that users are fully informed and/or give explicit consent before a Key System that presents security concerns that are greater than other user agent features (e.g., DOM content) may be accessed by an origin.

Such mechanisms MUST be per origin to avoid valid uses enabling subsequent malicious access and MUST be per browsing profile.

Note

The restriction of the APIs defined in this specification to secure contexts ensures that a network attacker cannot exploit permissions granted to an unauthenticated origin. See abuse of persisted consent.

10.4 iframe Attacks

10.4.1 Potential Attacks

This section is non-normative.

Malicious pages could host legitimate applications in an iframe in an attempt hide an attack or deceive the user as to the source, such as making the use appear to be from a legitimate content provider. This is especially relevent for implementations that inform the user or require consent, such as for security and/or privacy reasons. In addition to Network Attacks, attackers could try to exploit legitimate uses of the APIs defined in this specification by hosting them in an iframe. By having the legitimate application performing the actions, the attacker can reuse existing granted permissions (or whitelisting) and/or appear to be a legitimate request or use.

10.4.2 Mitigations

User agents that inform the user or require consent, including for security and/or privacy reasons, SHOULD base the UI and persistence of consent on the combination of origin of the top-level Document and the origin using the APIs defined in this specification. This ensures that users are informed of the main document making the request and that persisting a permission for one (legitimate) combination does not inadvertently allow malicious use to go undetected.

Authors SHOULD prevent other entities from hosting their applications in iframes. Applications that must support being hosted for legitimate application-design reasons SHOULD NOT allow hosting documents to provide any data to be passed to the CDM - either via the APIs defined in this specification or as media data - and SHOULD NOT allow hosting frames to invoke the APIs defined in this specification.

10.5 Cross-Directory Attacks

This section is non-normative.

Different authors sharing one host name, for example users hosting content on geocities.com, all share one origin. User agents do not provide features to restrict access to APIs by pathname.

Using the APIs defined in this specification on shared hosts compromises origin-based security and privacy mitigations implemented by user agents. For example, per-origin Distinctive Identifiers are shared by all authors on one host name, and peristed data may be accessed and manipulated by any author on the host. The latter is especially important if, for example, modification or deletion of such data could erase a user's right to specific content.

Note

Even if a path-restriction feature was made available by user agents, the usual DOM scripting security model would make it trivial to bypass this protection and access the data from any path.

Authors on shared hosts are therefore RECOMMENDED to avoid using the APIs defined in this specification because doing so compromises origin-based security and privacy mitigations in user agents.

11. Privacy

The presence or use of Key System(s) on a user's device raises a number of privacy issues, falling into two categories: (a) user-specific information that may be disclosed by the EME interface itself or within Key System messages and (b) user-specific information that may be persistently stored on the user's device.

User Agents MUST take responsibility for providing users with adequate control over their own privacy. Since User Agents may integrate with third party CDM implementations, CDM implementers MUST provide sufficient information and controls to user agent implementers to enable them to implement appropriate techniques to ensure users have control over their privacy, including but not limited to the techniques described below.

11.1 Information Disclosed by EME and Key Systems

Concerns regarding information disclosed by EME and Key Systems fall into two categories: (a) concerns about non-specific information that may nevertheless contribute to the possibility of fingerprinting a user agent or device and (b) user-specific information that may be used directly for user tracking.

11.2 Fingerprinting

Malicious applications may be able to fingerprint users or user agents by detecting or enumerating the list of Key Systems that are supported and related information. If proper origin protections are not provided this could include detection of sites that have been visited and information stored for those sites. In particular, Key Systems MUST not share key or other data between origins.

11.3 Information Leakage

11.3.1 Concerns

This section is non-normative.

CDMs, especially those implemented outside the user agent, may not have the same fundamental isolations as the web platform. It is important that steps be taken to avoid information leakage, especially across origins. This includes both in-memory and stored data. Failure to do so could lead to information leakage to/from private browsing sessions, across browsing profiles (including across operating system user accounts) and even across different browsers or applications.

11.3.2 Mitigations

To avoid such issues, user agent and CDM implementations MUST ensure that:

  • CDMs have a concept of a CDM instance that is associated one-to-one with a MediaKeys object.

  • Keys, licenses, other session data, and the presence of sessions are restricted to the CDM instance associated with the MediaKeys object that created the session.

  • Session data is not shared between MediaKeys objects or CDM instances.

  • Session data is not shared with media elements not associated with the MediaKeys object that created the session. Among other things, this means a session's keys MUST not be used to decrypt content loaded by a media element whose mediaKeys attribute is not that MediaKeys object.

  • MediaKeys objects and the underlying implementation do not expose information outside the origin.

  • Persisted session data, if applicable, is stored on a per-origin basis.

  • Only data stored by the requesting origin may be loaded.

  • It is not possible to extract, derive or infer information from the CDM that is not either explicitly described in this specification or available to the page through other web platform APIs without user permission. This applies to any information that is exposed outside the client device or to the application, including, for example, in CDM messages.

    Note

    The type of information covered by this requirement includes but is not limited to:

    • Location, including geolocation

    • Credentials or identifiers other than Distinctive Identifiers

    • OS account name and other potential PII

    • Local directory paths, which may contain similar information.

    • Local network details (for example, the device's local IP address)

    • Local devices, including but not limited to Bluetooth, USB, and user media.

    • User state not associated with or stored as a result of the APIs defined in this specification.

11.4 User Tracking

11.4.1 Concerns

This section is non-normative.

A third-party host (or any entity, such as an advertiser, capable of getting content distributed to multiple sites) could use a Distinctive Identifier or persistent data, including licenses, keys, key IDs, or records of license destruction, stored by or on behalf of the CDM to track a user across multiple sessions (including across origins and browsing profiles), building a profile of the user's activities or interests. Such tracking would undermine the privacy protections provided by the rest of the web platform and could, for example, enable highly-targeted advertising not otherwise possible. In conjunction with a site that is aware of the user's real identity (for example, a content provider or e-commerce site that requires authenticated credentials), this could allow oppressive groups to target individuals with greater accuracy than in a world with purely anonymous web usage.

User- or client-specific information that could be obtained via implementations of the APIs in this specification includes:

This specification presents a specific concern because such information is commonly stored outside the user agent (and associated browsing profile storage), often in the CDM.

Since the content of licenses and records of license destruction are Key System-specific and since key IDs may contain any value, these data items could be abused to store user-identifying information.

Key Systems may access or create persistent or semi-persistent identifier(s) for a device or user of a device. In some cases these identifiers may be bound to a specific device in a secure manner. If these identifiers are present in Key System messages, then devices and/or users may be tracked. If the mitigations below are not applied, this could include both tracking of users / devices over time and associating multiple users of a given device.

It is important to note that such identifiers, especially those that are non-clearable, non-origin-specific, or permanent, exceed the tracking impact of existing techniques such as cookies [COOKIES] or session identifiers embedded in URLs.

If not mitigated, such tracking may take three forms depending on the design of the Key System:

  • In all cases, such identifiers are expected to be available to sites and/or servers that fully support the Key System (and thus can interpret Key System messages) enabling tracking by such sites.

  • If identifiers exposed by Key Systems are not origin-specific, then two sites and/or servers that fully support the Key System may collude to track the user.

  • If Key System messages contain information derived from a user identifier in a consistent manner, for example such that a portion of the initial Key System message for a specific content item does not change over time and is dependent on the user identifier, then this information could be used by any application to track the device or user over time.

In addition, if a Key System permits keys or other data to be stored and to be re-used between origins, then it may be possible for two origins to collude and track a unique user by recording their ability to access a common key.

Finally, if any user interface for user control of Key Systems presents data separately from data in HTTP session cookies [COOKIES] or persistent storage, then users are likely to modify site authorization or delete data in one and not the others. This would allow sites to use the various features as redundant backup for each other, defeating a user's attempts to protect his or her privacy.

In addition to the potential for sites and other third-parties to track users, the user agent implementer, CDM vendor, or device vendor could build a profile of the user's activities or interests, such as sites using the APIs defined in this specification that the user visits. Such tracking would undermine the privacy protections provided by the rest of the web platform, especially those related to isolation of origins.

Identifiers, such as Distinctive Identifiers, may be obtained from a server operated or provided by the CDM vendor, such as via an individualization process. The process may include providing client identifier(s), including Distinctive Permanent Identifier(s), to the server. In order to generate a per-origin identifier, a value representing the origin may also be provided.

In such an implementation, the CDM vendor may be able to track the activity of the user, such as number of origins visited or number of times a new identifier is required. If the origin or a value associable with the origin is provided in the identifier request, the CDM vendor could track the sites visited by the user or user(s) of a device.

The following section describes techniques that may mitigate the risks of tracking without user consent.

11.4.2 Mitigations

Do not use Distinctive Identifiers or Distinctive Permanent Identifiers

Key System implementations SHOULD avoid using Distinctive Identifiers and Distinctive Permanent Identifiers whenever possible and only use them when they meaningfully contribute to the robustness of the implementation. See Limit or Avoid use of Distinctive Identifiers and Permanent Identifiers.

Do not expose Distinctive Permanent Identifiers to the application

Implementations MUST NOT expose Distinctive Permanent Identifiers to the application or origin.

Encrypt Distinctive Identifiers

Distinctive Identifiers in Key System messages MUST be encrypted, together with a timestamp or nonce, such that the Key System messages are always different. This prevents the use of Key System messages for tracking except by servers fully supporting the Key System. See Encrypt Identifiers.

Treat Distinctive Identifiers and Key System stored data like cookies / web storage

User agents SHOULD present the presence of Distinctive Identifiers and data stored by Key Systems to the user in a way that associates them strongly with HTTP session cookies [COOKIES], including it in "remove all data", and presenting it in the same UI locations. This might encourage users to view such identifiers with healthy suspicion. User agents SHOULD help the user avoid Incomplete Clearing of Data.

Do not expose per-origin information to unrelated entities

Do not provide origin(s) or values associable with origins to individualization servers or other entities not related to the origin. Follow the requirements and recommendations in the Individualization section if such a process is used by the implementation.

Use non-associable per-origin per-profile values and identifiers

For all distinctive values exposed to the application, implementations MUST use a different non-associable by applications value for each origin and browsing profile. See 8.4.1 Use Per-Origin Per-Profile Values.

This is especially important for implementations that use Distinctive Identifier(s). See 8.5.3 Use Per-Origin Per-Profile Identifiers.

Use origin-specific and browsing profile-specific Key System storage

Any data used by the CDM that might impact messages or behavior in an application- or license server-visible way MUST be partitioned by origin and browsing profile and MUST NOT leak to or from private browsing sessions. This includes both in-memory and persisted data. Specifically but not exhaustively, session data, licenses, keys, and per-origin identifiers MUST be partitioned per-origin and per-browsing profile. See 8.3.1 Use origin-specific and browsing profile-specific Key System storage and 8.4.1 Use Per-Origin Per-Profile Values.

Provide user deletion of persistent data, including Distinctive Identifiers

User agents MUST provide users with the ability to clear any persistent data, including Distinctive Identifiers, maintained by Key Systems. See Allow Persistent Data to Be Cleared.

Expire stored data

User agents MAY, possibly in a manner configured by the user, automatically delete Distinctive Identifiers and/or other Key System data after a period of time.

Note

For example, a user agent could be configured to store such data as session-only storage, deleting the data once the user had closed all the browsing contexts that could access it.

This can restrict the ability of a site to track a user, as the site would then only be able to track the user across multiple sessions when the user authenticates with the site itself (e.g., by making a purchase or signing in to a service).

However, this can also put the user's access to content, especially purchased or rented content, at risk if the user does not fully understand the implications of such expiration.

Block third-party access

User agents MAY restrict access to Key Systems and/or features to scripts originating at the origin of the top-level Document of the browsing context. For example, requestMediaKeySystemAccess() may deny requests for certain configurations for pages from other origins running in iframes.

User agents MUST ensure that users are fully informed and/or give explicit consent before using Distinctive Identifier(s) and Distinctive Permanent Identifier(s).

Such mechanisms MUST be per origin to avoid valid uses enabling subsequent malicious access and MUST be per browsing profile.

Note

The restriction of the APIs defined in this specification to secure contexts ensures that a network attacker cannot exploit permissions granted to an unauthenticated origin. See abuse of persisted consent.

Provide user controls to disable Key Systems or Key System use of identifiers

User Agents SHOULD provide users with a global control of whether a Key System is enabled and/or whether Key System use of Distinctive Identifier(s) and Distinctive Permanent Identifier(s) is enabled (if supported by the Key System). User agents SHOULD help the user avoid Incomplete Clearing of Data.

Require site-specific whitelisting of access to each Key System

User agents MAY require the user to explicitly authorize access to each Key System - and/or certain features - before a site can use it. User agents SHOULD enable users to revoke this authorization either temporarily or permanently.

Use shared blacklists

User agents MAY allow users to share blacklists of origins and/or Key Systems. This would allow communities to act together to protect their privacy.

Note

While these suggestions prevent trivial use of the APIs defined in this specification for user tracking, they do not block it altogether. Within a single origin, a site can continue to track the user during a session, and can then pass all this information to a third party along with any identifying information (names, credit card numbers, addresses) obtained by the site. If a third party cooperates with multiple sites to obtain such information, and if identifiers are not unique per origin and profile, then a profile can still be created.

11.5 Information Stored on User Devices

11.5.1 Concerns

This section is non-normative.

Key Systems may store information on a user's device, or user agents may store information on behalf of Key Systems. Potentially, this could reveal information about a user to another user of the same device, including potentially the origins that have used a particular Key System (i.e., sites visited) or even the content that has been decrypted using a Key System.

If information stored by one origin affects the operation of the Key System for another origin, then potentially the sites visited or content viewed by a user on one site may be revealed to another, potentially malicious, site.

If information stored for one browsing profile on the client device affects the operation of the Key System for other browsing profiles, or browsers, then potentially the sites visited or content viewed in one may be revealed by or correlatable with another browsing profile, even including for different operating system user accounts or browsers.

11.5.2 Mitigations

Requirements mitigating these concerns are defined in 8.3 Persistent Data.

11.6 Incomplete Clearing of Data

11.6.1 Concerns

This section is non-normative.

A user's attempts to protect his or her privacy by clearing Distinctive Identifiers and stored data and/or disabling a Key System may be defeated if all such data and functionality as well as cookies [COOKIES] and other site data are not cleared and/or disabled at the same time. For example:

  • If a user clears cookies or other persistent storage without also clearing Distinctive Identifiers and data stored by Key Systems, sites can defeat those attempts by using the various features as redundant backup for each other.

  • If a user clears Distinctive Identifiers without also clearing data stored by Key Systems, including persistent sessions, as well as cookies and other persistent storage, sites can defeat those attempts by using the remaining data to associate the old and new identifiers.

  • If a user disables a key system, especially for a specific origin, without also clearing cookies or other persistent storage, sites can defeat those attempts by using the remaining features.

  • If a user disables a key system, then later decide to enable the key system, without also clearing clearing cookies or other persistent storage, Distinctive Identifiers, and data stored by Key Systems, sites may be able to associate data prior to the disabling with data and behavior after the key system is re-enabled.

11.6.2 Mitigations

Recommendations mitigating these concerns are defined in 8.3 Persistent Data.

11.7 Private Browsing Modes

User agents may support a mode (e.g., private browsing) of operation intended to preserve user anonymity and/or ensure records of browsing activity are not persisted on the client. The privacy concerns discussed in previous sections may be especially concerning for users employing such modes.

User agent implementers that support such mode(s) SHOULD carefully consider whether access to Key Systems should be disabled in these mode(s). For example, such modes MAY prohibit creation of MediaKeySystemAccess objects that support or use persistentState or a distinctiveIdentifier (either as part of the CDM implementation or because the application indicated they were "required"). If implementations do not prohibit such creation, they SHOULD inform the user of the implications and potential consequences for the expected privacy properties of such modes before allowing their use.

11.8 Secure Origin and Transport

The APIs defined in this specification are only supported on secure origins, protecting information discussed in previous sections. Identifiers are additionally encrypted as specified in Encrypt Identifiers.

Applications, including the servers they use, SHOULD use secure transport for all traffic involving or containing data or messages from the CDM, including but is not limited to all data passed from message events and to update().

All user agents MUST properly handle Mixed Content [MIXED-CONTENT] to avoid exposure to insecure content or transport when the user agent or application wish to enforce secure origin and transport.

12. Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key words MAY, MUST, MUST NOT, OPTIONAL, RECOMMENDED, REQUIRED, SHALL, SHALL NOT, SHOULD, and SHOULD NOT are to be interpreted as described in [RFC2119].

13. Examples

This section is non-normative.

This section contains example solutions for various use cases using the proposed extensions. These are not the only solutions to these use cases. Video elements are used in the examples, but the same would apply to all media elements. In some cases, such as using synchronous XHR, the examples are simplified to keep the focus on the extensions.

13.1 Source and Key Known at Page Load (Clear Key)

In this simple example, the source file and clear-text license are hard-coded in the page. Only one session will ever be created.

Example 5
<script>
  function onLoad() {
    var video = document.getElementById('video');

    if (!video.mediaKeys) {
      navigator.requestMediaKeySystemAccess('org.w3.clearkey', [
        { initDataTypes: ['webm'],
          videoCapabilities: [{ contentType: 'video/webm; codecs="vp8"' }] }
      ]).then(
        function(keySystemAccess) {
          var promise =  keySystemAccess.createMediaKeys();
          promise.catch(
            console.error.bind(console, 'Unable to create MediaKeys')
          );
          promise.then(
            function(createdMediaKeys) {
              return video.setMediaKeys(createdMediaKeys);
            }
          ).catch(
            console.error.bind(console, 'Unable to set MediaKeys')
          );
          promise.then(
            function(createdMediaKeys) {
              var te = new TextEncoder();
              var initData = te.encode( '{"kids":["LwVHf8JLtPrv2GUXFW2v_A"]}');
              var keySession = createdMediaKeys.createSession();
              keySession.addEventListener("message", handleMessage, false);
              return keySession.generateRequest('keyids', initData);
            }
          ).catch(
            console.error.bind(console, 'Unable to create or initialize key session')
          );
        }
      );
    }
  }

  function handleMessage(event) {
    var keySession = event.target;
    var te = new TextEncoder();
    var license = te.encode('{"keys":[{"kty":"oct","k":"tQ0bJVWb6b0KPL6KtZIy_A","kid":"LwVHf8JLtPrv2GUXFW2v_A"}],"type":"temporary"}');
    keySession.update(license).catch(
      console.error.bind(console, 'update() failed')
    );
  }
</script>

<body onload='onLoad()'>
  <video src='foo.webm' autoplay id='video'></video>
</body>

13.2 Selecting a Supported Key System and Using Initialization Data from the "encrypted" Event

This example selects a supported Key System using the requestMediaKeySystemAccess() method then uses the Initialization Data from the media data to generate the license request and send it to the appropriate license server. One of the supported key systems uses a serverCertificate, which is provided proactively.

Example 6
<script>
  var licenseUrl;
  var serverCertificate;

  // Returns a Promise<MediaKeys>.
  function createSupportedKeySystem() {
    someSystemOptions = [
     { initDataTypes: ['keyids', 'webm'],
       audioCapabilities: [
         { contentType: 'audio/webm; codecs="opus"' },
         { contentType: 'audio/webm; codecs="vorbis"' }
       ],
       videoCapabilities: [
         { contentType: 'video/webm; codecs="vp9"' },
         { contentType: 'video/webm; codecs="vp8"' }
       ]
     }
    ];
    clearKeyOptions = [
     { initDataTypes: ['keyids', 'webm'],
       audioCapabilities: [
         { contentType: 'audio/webm; codecs="opus"' },
         { contentType: 'audio/webm; codecs="vorbis"' }
       ],
       videoCapabilities: [
         { contentType: 'video/webm; codecs="vp9"',
           robustness: 'foo' },
         { contentType: 'video/webm; codecs="vp9"',
           robustness: 'bar' },
         { contentType: 'video/webm; codecs="vp8"',
           robustness: 'bar' },
       ]
     }
    ];

    return navigator.requestMediaKeySystemAccess('com.example.somesystem', someSystemOptions).then(
      function(keySystemAccess) {
        // Not shown:
        // 1. Use both attributes of keySystemAccess.getConfiguration().audioCapabilities[0]
        //    and both attributes of keySystemAccess.getConfiguration().videoCapabilities[0]
        //    to retrieve appropriate stream(s).
        // 2. Set video.src.

        licenseUrl = 'https://license.example.com/getkey';
        serverCertificate = new Uint8Array([ ... ]);
        return keySystemAccess.createMediaKeys();
      }
    ).catch(
      function(error) {
        // Try the next key system.
        navigator.requestMediaKeySystemAccess('org.w3.clearkey', clearKeyOptions).then(
          function(keySystemAccess) {
            // Not shown:
            // 1. Use keySystemAccess.getConfiguration().audioCapabilities[0].contentType
            //    and keySystemAccess.getConfiguration().videoCapabilities[0].contentType
            //    to retrieve appropriate stream(s).
            // 2. Set video.src.

            licenseUrl = 'https://license.example.com/clearkey/request';
            return keySystemAccess.createMediaKeys();
          }
        );
      }
    ).catch(
      console.error.bind(console, 'Unable to instantiate a key system supporting the required combinations')
    );
  }

  function handleInitData(event) {
    var video = event.target;
    if (video.mediaKeysObject === undefined) {
      video.mediaKeysObject = null; // Prevent entering this path again.
      video.pendingSessionData = []; // Will store all initData until the MediaKeys is ready.
      createSupportedKeySystem().then(
        function(createdMediaKeys) {
          video.mediaKeysObject = createdMediaKeys;

          if (serverCertificate)
            createdMediaKeys.setServerCertificate(serverCertificate);

          for (var i = 0; i < video.pendingSessionData.length; i++) {
            var data = video.pendingSessionData[i];
            makeNewRequest(video.mediaKeysObject, data.initDataType, data.initData);
          }
          video.pendingSessionData = [];

          return video.setMediaKeys(createdMediaKeys);
        }
      ).catch(
        console.error.bind(console, 'Failed to create and initialize a MediaKeys object')
      );
    }
    addSession(video, event.initDataType, event.initData);
  }

  function addSession(video, initDataType, initData) {
    if (video.mediaKeysObject) {
      makeNewRequest(video.mediaKeysObject, initDataType, initData);
    } else {
      video.pendingSessionData.push({initDataType: initDataType, initData: initData});
    }
  }

  function makeNewRequest(mediaKeys, initDataType, initData) {
    var keySession = mediaKeys.createSession();
    keySession.addEventListener("message", licenseRequestReady, false);
    keySession.generateRequest(initDataType, initData).catch(
      console.error.bind(console, 'Unable to create or initialize key session')
    );
  }

  function licenseRequestReady(event) {
    var request = event.message;

    var xmlhttp = new XMLHttpRequest();
    xmlhttp.keySession = event.target;
    xmlhttp.open("POST", licenseUrl);
    xmlhttp.onreadystatechange = function() {
      if (xmlhttp.readyState == 4) {
        var license = new Uint8Array(xmlhttp.response);
        xmlhttp.keySession.update(license).catch(
          console.error.bind(console, 'update() failed')
        );
      }
    }
    xmlhttp.send(request);
  }
</script>

<video autoplay onencrypted='handleInitData(event)'></video>

13.3 Create MediaKeys Before Loading Media

Initialization is much simpler if encrypted events do not need to be handled during MediaKeys initialization. This can be accomplished either by providing the Initialization Data in other ways or setting the source after the MediaKeys object has been created. This example does the latter.

Example 7
<script>
  var licenseUrl;
  var serverCertificate;
  var mediaKeys;

  // See the previous example for implementations of these functions.
  function createSupportedKeySystem() { ... }
  function makeNewRequest(mediaKeys, initDataType, initData) { ... }
  function licenseRequestReady(event) { ... }

  function handleInitData(event) {
    makeNewRequest(mediaKeys, event.initDataType, event.initData);
  }

  createSupportedKeySystem().then(
    function(createdMediaKeys) {
      mediaKeys = createdMediaKeys;
      var video = document.getElementById("v");
      video.src = 'foo.webm';
      if (serverCertificate)
        mediaKeys.setServerCertificate(serverCertificate);
      return video.setMediaKeys(mediaKeys);
    }
  ).catch(
    console.error.bind(console, 'Failed to create and initialize a MediaKeys object')
  );
</script>

<video id="v" autoplay onencrypted='handleInitData(event)'></video>

13.4 Using All Events

This is a more complete example showing all events being used.

Note that handleMessage() could be called multiple times, including in response to the update() call if multiple round trips are required and for any other reason the Key System might need to send a message.

Example 8
<script>
  var licenseUrl;
  var serverCertificate;
  var mediaKeys;

  // See previous examples for implementations of these functions.
  // createSupportedKeySystem() additionally sets renewalUrl.
  function createSupportedKeySystem() { ... }
  function handleInitData(event) { ... }

  // This replaces the implementation in the previous example.
  function makeNewRequest(mediaKeys, initDataType, initData) {
    var keySession = mediaKeys.createSession();
    keySession.addEventListener('message', handleMessage, false);
    keySession.addEventListener('keystatuseschange', handlekeyStatusesChange, false);
    keySession.closed.then(
      console.log.bind(console, 'Session closed')
    );
    keySession.generateRequest(initDataType, initData).catch(
      console.error.bind(console, 'Unable to create or initialize key session')
    );
  }

  function handleMessageResponse(keySession, response) {
    var license = new Uint8Array(response);
    keySession.update(license).catch(
      function(err) {
        console.error('update() failed: ' + err);
      }
    );
  }

  function sendMessage(type, message, keySession) {
    var url = licenseUrl;
    if (type == "license-renewal")
      url = renewalUrl;
    xmlhttp = new XMLHttpRequest();
    xmlhttp.keySession = keySession;
    xmlhttp.open('POST', url);
    xmlhttp.onreadystatechange = function() {
      if (xmlhttp.readyState == 4)
        handleMessageResponse(xmlhttp.keySession, xmlhttp.response);
    }
    xmlhttp.send(message);
  }

  function handleMessage(event) {
    sendMessage(event.messageType, event.message, event.target);
  }

  function handlekeyStatusesChange(event) {
    // Evaluate the current state using one of the map-like methods exposed by
    // event.target.keyStatuses.
    // For example:
    event.target.keyStatuses.forEach(function(status, keyId) {
      switch (status) {
        case "usable":
          break;
        case "expired":
          // Report an expired key.
          break;
        case "status-pending":
          // The status is not yet known. Consider the key unusable until the status is updated.
          break;
        default:
          // Do something with |keyId| and |status|.
      }
    })
  }

  createSupportedKeySystem().then(
    function(createdMediaKeys) {
      mediaKeys = createdMediaKeys;
      var video = document.getElementById("v");
      video.src = 'foo.webm';
      if (serverCertificate)
        mediaKeys.setServerCertificate(serverCertificate);
      return video.setMediaKeys(mediaKeys);
    }
  ).catch(
    console.error.bind(console, 'Failed to create and initialize a MediaKeys object')
  );
</script>

<video id="v" autoplay onencrypted='handleInitData(event)'></video>

13.5 Stored License

This example requests a persistent license for future use and stores it. It also provides functions for later retrieving the license and for destroying it.

Example 9
<script>
  var licenseUrl;
  var serverCertificate;
  var mediaKeys;

  // See the previous examples for implementations of these functions.
  // createSupportedKeySystem() additionally sets persistentState: "required" in each options dictionary.
  function createSupportedKeySystem() { ... }
  function sendMessage(message, keySession) { ... }
  function handleMessage(event) { ... }

  // Called if the application does not have a stored sessionId for the media resource.
  function makeNewRequest(mediaKeys, initDataType, initData) {
    var keySession = mediaKeys.createSession("persistent-license");
    keySession.addEventListener('message', handleMessage, false);
    keySession.closed.then(
      function() {
        console.log('Session ' + this.sessionId + ' closed');
      }.bind(keySession)
    );
    keySession.generateRequest(initDataType, initData).then(
      function() {
        // Store this.sessionId in the application.
      }.bind(keySession)
    ).catch(
      console.error.bind(console, 'Unable to request a persistent license')
    );
  }

  // Called if the application has a stored sessionId for the media resource.
  function loadStoredSession(mediaKeys, sessionId) {
    var keySession = mediaKeys.createSession("persistent-license");
    keySession.addEventListener('message', handleMessage, false);
    keySession.closed.then(
      console.log.bind(console, 'Session closed')
    );
    keySession.load(sessionId).then(
      function(loaded) {
        if (!loaded) {
          console.error('No stored session with the ID ' + sessionId + ' was found.');
          // The application should remove its record of |sessionId|.
          return;
        }
      }
    ).catch(
      console.error.bind(console, 'Unable to load or initialize the stored session with the ID ' + sessionId)
    );
  }

  // Called when the application wants to stop using the session without removing the stored license.
  function closeSession(keySession) {
    keySession.close();
  }

  // Called when the application wants to remove the stored license.
  // The stored session data has not been completely removed until the promise returned by remove() is fulfilled.
  // The remove() call may initiate a series of messages to/from the server that must be completed before this occurs.
  function removeStoredSession(keySession) {
    keySession.remove().then(
      function() {
        console.log('Session ' + this.sessionId + ' removed');
        // The application should remove its record of this.sessionId.
      }.bind(keySession)
    ).catch(
      console.error.bind(console, 'Failed to remove the session')
    );
  }

  // This replaces the implementation in the previous example.
  function handleMessageResponse(keySession, response) {
    var license = new Uint8Array(response);
    keySession.update(license).then(
      function() {
        // If this was the last required message from the server, the license is
        // now stored. Update the application state as appropriate.
      }
    ).catch(
      console.error.bind(console, 'update() failed')
    );
  }

  createSupportedKeySystem().then(
    function(createdMediaKeys) {
      mediaKeys = createdMediaKeys;
      var video = document.getElementById("v");
      if (serverCertificate)
        mediaKeys.setServerCertificate(serverCertificate);
      return video.setMediaKeys(mediaKeys);
    }
  ).catch(
    console.error.bind(console, 'Failed to create and initialize a MediaKeys object')
  );
</script>

<video id='v' src='foo.webm' autoplay></video>

14. Acknowledgments

The editors would like to thank Aaron Colwell, Alex Russell, Anne van Kesteren, Bob Lund, Boris Zbarsky, Chris Pearce, David Singer, Domenic Denicola, Frank Galligan, Glenn Adams, Henri Sivonen, Jer Noble, Joe Steele, Joey Parrish, John Simmons, Mark Vickers, Pavel Pergamenshchik, Philip Jägenstedt, Pierre Lemieux, Robert O'Callahan, Ryan Sleevi, Steve Heffernan, Steven Robertson, Thomás Inskip, Travis Leithead, and Xiaohan Wang for their contributions to this specification. Thank you also to the many others who contributed to the specification, including through their participation on the mailing list and in the issues.

A. References

A.1 Normative references

[COOKIES]
HTTP State Management Mechanism. A. Barth. IETF. April 2011. Proposed Standard. URL: https://tools.ietf.org/html/rfc6265
[DOM]
W3C DOM4. Anne van Kesteren; Aryeh Gregor; Ms2ger; Alex Russell; Robin Berjon. 19 November 2015. W3C Recommendation. URL: https://www.w3.org/TR/2015/REC-dom-20151119/
[ECMA-262]
ECMAScript Language Specification. Ecma International. URL: https://tc39.github.io/ecma262/
[ENCODING]
Encoding. Anne van Kesteren; Joshua Bell; Addison Phillips. 13 April 2017. W3C Candidate Recommendation. URL: https://www.w3.org/TR/2017/CR-encoding-20170413/
[HTML51]
HTML 5.1 2nd Edition. Steve Faulkner; Arron Eicholz; Travis Leithead; Alex Danilo. W3C. 3 August 2017. W3C Proposed Recommendation. URL: https://www.w3.org/TR/html51/
[MIXED-CONTENT]
Mixed Content. Mike West. W3C. 2 August 2016. W3C Candidate Recommendation. URL: https://www.w3.org/TR/mixed-content/
[RFC2119]
Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. IETF. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119
[RFC6381]
The 'Codecs' and 'Profiles' Parameters for "Bucket" Media Types. R. Gellens; D. Singer; P. Frojdh. IETF. August 2011. Proposed Standard. URL: https://tools.ietf.org/html/rfc6381
[RFC7517]
JSON Web Key (JWK). M. Jones. IETF. May 2015. Proposed Standard. URL: https://tools.ietf.org/html/rfc7517
[WebIDL]
Web IDL. Cameron McCormack; Boris Zbarsky; Tobie Langel. W3C. 15 December 2016. W3C Recommendation. URL: https://www.w3.org/TR/WebIDL-1/

A.2 Informative references

[EME-INITDATA-KEYIDS]
"keyids" Initialization Data Format. David Dorwin; Adrian Bateman; Mark Watson; Jerry Smith. W3C. URL: https://www.w3.org/TR/eme-initdata-keyids/
[EME-INITDATA-REGISTRY]
Encrypted Media Extensions Initialization Data Format Registry. David Dorwin; Adrian Bateman; Mark Watson. W3C. URL: https://www.w3.org/TR/eme-initdata-registry/
[EME-STREAM-REGISTRY]
Encrypted Media Extensions Stream Format Registry. David Dorwin; Adrian Bateman; Mark Watson. W3C. URL: https://www.w3.org/TR/eme-stream-registry/
[MEDIA-SOURCE]
Media Source Extensions™. Matthew Wolenetz; Jerry Smith; Mark Watson; Aaron Colwell; Adrian Bateman. W3C. 17 November 2016. W3C Recommendation. URL: https://www.w3.org/TR/media-source/
[RFC6838]
Media Type Specifications and Registration Procedures. N. Freed; J. Klensin; T. Hansen. IETF. January 2013. Best Current Practice. URL: https://tools.ietf.org/html/rfc6838
[RFC7515]
JSON Web Signature (JWS). M. Jones; J. Bradley; N. Sakimura. IETF. May 2015. Proposed Standard. URL: https://tools.ietf.org/html/rfc7515
[SECURE-CONTEXTS]
Secure Contexts. Mike West. W3C. 15 September 2016. W3C Candidate Recommendation. URL: https://www.w3.org/TR/secure-contexts/