Data Integrity EdDSA Cryptosuites v1.0

Achieving Data Integrity using EdDSA with Edwards curves

W3C Candidate Recommendation Draft

More details about this document
This version:
https://www.w3.org/TR/2024/CRD-vc-di-eddsa-20240303/
Latest published version:
https://www.w3.org/TR/vc-di-eddsa/
Latest editor's draft:
https://w3c.github.io/vc-di-eddsa/
History:
https://www.w3.org/standards/history/vc-di-eddsa/
Commit history
Implementation report:
https://w3c.github.io/vc-data-integrity/implementations/
Editors:
Manu Sporny (Digital Bazaar)
Dmitri Zagidulin (MIT Digital Credentials Consortium)
Greg Bernstein (Invited Expert)
Sebastian Crane (Invited Expert)
Authors:
Dave Longley (Digital Bazaar)
Manu Sporny (Digital Bazaar)
Feedback:
GitHub w3c/vc-di-eddsa (pull requests, new issue, open issues)
Related Specifications
The Verifiable Credentials Data Model v2.0
Verifiable Credential Data Integrity v1.0
The Elliptic Curve Digital Signature Algorithm Cryptosuites v1.0
The BBS Digital Signature Algorithm Cryptosuites v1.0

Copyright © 2024 World Wide Web Consortium. W3C® liability, trademark and permissive document license rules apply.

Abstract

This specification describes a Data Integrity cryptographic suite for use when creating or verifying a digital signature using the twisted Edwards Curve Digital Signature Algorithm (EdDSA) and Curve25519 (ed25519).

Status of This Document

This section describes the status of this document at the time of its publication. 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/.

The Working Group is actively seeking implementation feedback for this specification. In order to exit the Candidate Recommendation phase, the Working Group has set the requirement of at least two independent implementations for each mandatory feature in the specification. For details on the conformance testing process, see the test suites listed in the implementation report.

This document was published by the Verifiable Credentials Working Group as a Candidate Recommendation Draft using the Recommendation track.

Publication as a Candidate Recommendation does not imply endorsement by W3C and its Members. A Candidate Recommendation Draft integrates changes from the previous Candidate Recommendation that the Working Group intends to include in a subsequent Candidate Recommendation Snapshot.

This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 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 03 November 2023 W3C Process Document.

1. Introduction

This specification defines a cryptographic suite for the purpose of creating, verifying proofs for Ed25519 EdDSA signatures in conformance with the Data Integrity [VC-DATA-INTEGRITY] specification. The approach is accepted by the U.S. National Institute of Standards in the latest FIPS 186-5 publication and meets U.S. Federal Information Processing requirements when using cryptography to secure digital information.

The suites described in this specification use the RDF Dataset Normalization Algorithm [RDF-CANON] or the JSON Canonicalization Scheme [RFC8785] to transform an input document into its canonical form. The canonical representation is then hashed and signed with a detached signature algorithm.

1.1 Terminology

Terminology used throughout this document is defined in the Terminology section of the Verifiable Credential Data Integrity 1.0 specification.

1.2 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, and MUST NOT in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

A conforming proof is any concrete expression of the data model that complies with the normative statements in this specification. Specifically, all relevant normative statements in Sections 2. Data Model and 3. Algorithms of this document MUST be enforced.

A conforming processor is any algorithm realized as software and/or hardware that generates or consumes a conforming proof. Conforming processors MUST produce errors when non-conforming documents are consumed.

This document contains examples of JSON and JSON-LD data. Some of these examples are invalid JSON, as they include features such as inline comments (//) explaining certain portions and ellipses (...) indicating the omission of information that is irrelevant to the example. These parts would have to be removed in order to treat the examples as valid JSON or JSON-LD.

2. Data Model

The following sections outline the data model that is used by this specification to express verification methods, such as cryptographic public keys, and data integrity proofs, such as digital signatures.

2.1 Verification Methods

This cryptographic suite is used to verify Data Integrity Proofs [VC-DATA-INTEGRITY] produced using Edwards Curve cryptographic key material. The encoding formats for those key types are provided in this section. Lossless cryptographic key transformation processes that result in equivalent cryptographic key material MAY be used for the processing of digital signatures.

2.1.1 Multikey

The Multikey format, defined in [VC-DATA-INTEGRITY], is used to express public keys for the cryptographic suites defined in this specification.

The publicKeyMultibase value of the verification method MUST start with the base-58-btc prefix (z), as defined in the Multibase section of [VC-DATA-INTEGRITY]. A Multibase-encoded Multikey value follows, which MUST consist of a binary value that starts with the two-byte prefix 0xed01, which is the Multikey header for an Ed25519 public key, followed by the 32-byte public key data, all of which is then encoded using base-58-btc. Any other encoding MUST NOT be allowed.

Developers are advised to not accidentally publish a representation of a private key. Implementations of this specification will raise errors if they encounter a Multikey prefix value other than 0xed01 in a publicKeyMultibase value.

Example 1: An Ed25519 public key encoded as a Multikey 
{
  "id": "https://example.com/issuer/123#key-0",
  "type": "Multikey",
  "controller": "https://example.com/issuer/123",
  "publicKeyMultibase": "z6Mkf5rGMoatrSj1f4CyvuHBeXJELe9RPdzo2PKGNCKVtZxP"
}
Example 2: An Ed25519 public key encoded as a Multikey in a controller document 
{
  "@context": [
    "https://www.w3.org/ns/did/v1",
    "https://w3id.org/security/data-integrity/v1"
  ],
  "id": "did:example:123",
  "verificationMethod": [{
    "id": "did:example:123#key-0",
    "type": "Multikey",
    "controller": "did:example:123",
    "publicKeyMultibase": "z6Mkf5rGMoatrSj1f4CyvuHBeXJELe9RPdzo2PKGNCKVtZxP"
  }],
  "authentication": [
    "did:example:123#key-0"
  ],
  "assertionMethod": [
    "did:example:123#key-0"
  ],
  "capabilityDelegation": [
    "did:example:123#key-0"
  ],
  "capabilityInvocation": [
    "did:example:123#key-0"
  ]
}

The secretKeyMultibase property represents a Multibase-encoded Multikey expression of an Ed25519 secret key (sometimes also referred to as a private key). The value starts with the two-byte prefix 0x8026, followed by the 32-byte Ed25519 secret key data. The combined 34-byte value is then base58-btc encoded and z is added as the prefix on the encoded value.

Developers are advised to prevent accidental publication of a representation of a secret key, and to not export the secretKeyMultibase property by default, when serializing key pairs to Multikey.

2.2 Proof Representations

This section details the proof representation formats that are defined by this specification.

2.2.1 DataIntegrityProof

The verificationMethod property of the proof MUST be a URL. Dereferencing the verificationMethod MUST result in an object containing a type property with the value set to Multikey.

The type property of the proof MUST be DataIntegrityProof.

The cryptosuite property of the proof MUST be eddsa-rdfc-2022 or eddsa-jcs-2022.

The created property of the proof MUST be an [XMLSCHEMA11-2] formatted date string.

The proofPurpose property of the proof MUST be a string, and MUST match the verification relationship expressed by the verification method controller.

The proofValue property of the proof MUST be a detached EdDSA produced according to [RFC8032], encoded using the base-58-btc header and alphabet as described in the Multibase section of [VC-DATA-INTEGRITY].

Example 3: An Ed25519 digital signature expressed as a DataIntegrityProof 
{
  "@context": [
    {"myWebsite": "https://vocabulary.example/myWebsite"},
    "https://www.w3.org/ns/credentials/v2"
  ],
  "myWebsite": "https://hello.world.example/",
  "proof": {
    "type": "DataIntegrityProof",
    "cryptosuite": "eddsa-rdfc-2022",
    "created": "2023-02-24T23:36:38Z",
    "verificationMethod": "https://vc.example/issuers/5678#z6MkrJVnaZkeFzdQyMZu1
      cgjg7k1pZZ6pvBQ7XJPt4swbTQ2",
    "proofPurpose": "assertionMethod",
    "proofValue": "z5C5b1uzYJN6pDR3aWgAqUMoSB1JY29epA74qyjaie9qh4okm9DZP6y77eTNq
      5NfYyMwNu9bpQQWUHKH5zAmEtszK"
  }
}

3. Algorithms

The following section describes multiple Data Integrity cryptographic suites that utilize the twisted Edwards Curve Digital Signature Algorithm.

3.1 eddsa-rdfc-2022

The eddsa-rdfc-2022 cryptographic suite takes an input document, canonicalizes the document using the Universal RDF Dataset Canonicalization Algorithm [RDF-CANON], and then cryptographically hashes and signs the output resulting in the production of a data integrity proof. The algorithms in this section also include the verification of such a data integrity proof.

When the RDF Dataset Canonicalization Algorithm [RDF-CANON] is used, implementations will detect dataset poisoning by default, and abort processing upon such detection.

3.1.1 Add Proof (eddsa-rdfc-2022)

To generate a proof, the algorithm in Section 4.1: Add Proof in the Data Integrity [VC-DATA-INTEGRITY] specification MUST be executed. For that algorithm, the cryptographic suite specific transformation algorithm is defined in Section 3.1.3 Transformation (eddsa-rdfc-2022), the hashing algorithm is defined in Section 3.1.4 Hashing (eddsa-rdfc-2022), and the proof serialization algorithm is defined in Section 3.1.6 Proof Serialization (eddsa-rdfc-2022).

3.1.2 Verify Proof (eddsa-rdfc-2022)

To verify a proof, the algorithm in Section 4.2: Verify Proof in the Data Integrity [VC-DATA-INTEGRITY] specification MUST be executed. For that algorithm, the cryptographic suite specific transformation algorithm is defined in Section 3.1.3 Transformation (eddsa-rdfc-2022), the hashing algorithm is defined in Section 3.1.4 Hashing (eddsa-rdfc-2022), and the proof verification algorithm is defined in Section 3.1.7 Proof Verification (eddsa-rdfc-2022).

3.1.3 Transformation (eddsa-rdfc-2022)

The following algorithm specifies how to transform an unsecured input document into a transformed document that is ready to be provided as input to the hashing algorithm in Section 3.1.4 Hashing (eddsa-rdfc-2022).

Required inputs to this algorithm are an unsecured data document (unsecuredDocument) and transformation options (options). The transformation options MUST contain a type identifier for the cryptographic suite (type) and a cryptosuite identifier (cryptosuite). A transformed data document is produced as output. Whenever this algorithm encodes strings, it MUST use UTF-8 encoding.

  1. If options.type is not set to the string DataIntegrityProof and options.cryptosuite is not set to the string eddsa-rdfc-2022 then a PROOF_TRANSFORMATION_ERROR MUST be raised.
  2. Let canonicalDocument be the result of applying the Universal RDF Dataset Canonicalization Algorithm [RDF-CANON] to the unsecuredDocument.
  3. Return canonicalDocument as the transformed data document.

3.1.4 Hashing (eddsa-rdfc-2022)

The following algorithm specifies how to cryptographically hash a transformed data document and proof configuration into cryptographic hash data that is ready to be provided as input to the algorithms in Section 3.1.6 Proof Serialization (eddsa-rdfc-2022) or Section 3.1.7 Proof Verification (eddsa-rdfc-2022).

The required inputs to this algorithm are a transformed data document (transformedDocument) and canonical proof configuration (canonicalProofConfig). A single hash data value represented as series of bytes is produced as output.

  1. Let transformedDocumentHash be the result of applying the SHA-256 (SHA-2 with 256-bit output) cryptographic hashing algorithm [RFC6234] to the transformedDocument. transformedDocumentHash will be exactly 32 bytes in size.
  2. Let proofConfigHash be the result of applying the SHA-256 (SHA-2 with 256-bit output) cryptographic hashing algorithm [RFC6234] to the canonicalProofConfig. proofConfigHash will be exactly 32 bytes in size.
  3. Let hashData be the result of joining proofConfigHash (the first hash) with transformedDocumentHash (the second hash).
  4. Return hashData as the hash data.

3.1.5 Proof Configuration (eddsa-rdfc-2022)

The following algorithm specifies how to generate a proof configuration from a set of proof options that is used as input to the proof hashing algorithm.

The required inputs to this algorithm are proof options (options). The proof options MUST contain a type identifier for the cryptographic suite (type) and MUST contain a cryptosuite identifier (cryptosuite). A proof configuration object is produced as output.

  1. Let proofConfig be an empty object.
  2. Set proofConfig.type to options.type.
  3. If options.cryptosuite is set, set proofConfig.cryptosuite to its value.
  4. If options.type is not set to DataIntegrityProof and proofConfig.cryptosuite is not set to eddsa-rdfc-2022, an INVALID_PROOF_CONFIGURATION error MUST be raised.
  5. Set proofConfig.created to options.created. If the value is not a valid [XMLSCHEMA11-2] datetime, an INVALID_PROOF_DATETIME error MUST be raised.
  6. Set proofConfig.verificationMethod to options.verificationMethod.
  7. Set proofConfig.proofPurpose to options.proofPurpose.
  8. Set proofConfig.@context to unsecuredDocument.@context
  9. Let canonicalProofConfig be the result of applying the Universal RDF Dataset Canonicalization Algorithm [RDF-CANON] to the proofConfig.
  10. Return canonicalProofConfig.

3.1.6 Proof Serialization (eddsa-rdfc-2022)

The following algorithm specifies how to serialize a digital signature from a set of cryptographic hash data. This algorithm is designed to be used in conjunction with the algorithms defined in the Data Integrity [VC-DATA-INTEGRITY] specification, Section 4: Algorithms. Required inputs are cryptographic hash data (hashData) and proof options (options). The proof options MUST contain a type identifier for the cryptographic suite (type) and MAY contain a cryptosuite identifier (cryptosuite). A single digital proof value represented as series of bytes is produced as output.

  1. Let privateKeyBytes be the result of retrieving the private key bytes associated with the options.verificationMethod value as described in the Data Integrity [VC-DATA-INTEGRITY] specification, Section 4: Retrieving Cryptographic Material.
  2. Let proofBytes be the result of applying the Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032], using the Ed25519 variant (Pure EdDSA), with hashData as the data to be signed using the private key specified by privateKeyBytes. proofBytes will be exactly 64 bytes in size.
  3. Return proofBytes as the digital proof.

3.1.7 Proof Verification (eddsa-rdfc-2022)

The following algorithm specifies how to verify a digital signature from a set of cryptographic hash data. This algorithm is designed to be used in conjunction with the algorithms defined in the Data Integrity [VC-DATA-INTEGRITY] specification, Section 4: Algorithms. Required inputs are cryptographic hash data (hashData), a digital signature (proofBytes) and proof options (options). A verification result represented as a boolean value is produced as output.

  1. Let publicKeyBytes be the result of retrieving the public key bytes associated with the options.verificationMethod value as described in the Data Integrity [VC-DATA-INTEGRITY] specification, Section 4: Retrieving Cryptographic Material.
  2. Let verificationResult be the result of applying the verification algorithm for the Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032], using the Ed25519 variant (Pure EdDSA), with hashData as the data to be verified against the proofBytes using the public key specified by publicKeyBytes.
  3. Return verificationResult as the verification result.

3.2 eddsa-jcs-2022

The eddsa-jcs-2022 cryptographic suite takes an input document, canonicalizes the document using the JSON Canonicalization Scheme [RFC8785], and then cryptographically hashes and signs the output resulting in the production of a data integrity proof. The algorithms for this cryptographic suite are the same as the ones in Section 3.1 eddsa-rdfc-2022 except for the following modifications:

In Section 3.1.3 Transformation (eddsa-rdfc-2022), step 1) and step 2) are replaced by the following text:

  1. If options.type is not set to the string DataIntegrityProof and options.cryptosuite is not set to the string eddsa-jcs-2022 then a PROOF_TRANSFORMATION_ERROR MUST be raised.
  2. Let canonicalDocument be the result of applying the JSON Canonicalization Scheme [RFC8785] to the unsecuredDocument.

In Section 3.1.5 Proof Configuration (eddsa-rdfc-2022), step 8) is not performed, and steps 4) and 9) are replaced by the following text:

4) If options.type is not set to DataIntegrityProof and proofConfig.cryptosuite is not set to eddsa-jcs-2022, an INVALID_PROOF_CONFIGURATION error MUST be raised.

9) Let canonicalProofConfig be the result of applying the JSON Canonicalization Scheme [RFC8785] to the proofConfig.

4. Security Considerations

Before reading this section, readers are urged to familiarize themselves with general security advice provided in the Security Considerations section of the Data Integrity specification.

The following section describes security considerations that developers implementing this specification should be aware of in order to create secure software.

4.1 Security Properties of Ed25519 Implementations

This section is non-normative.

Ed25519 signatures (EdDSA algorithm with edwards25519 curve) have been widely adopted, due both to the compact size of the keys and signatures and to the speed at which signatures can be produced and verified. Many libraries exist that can create and verify Ed25519 signatures. Since the publication of [RFC8032], security properties of Ed25519 signatures have been rigorously proven (see [Provable_Ed25519] and [Taming_EdDSAs]). However, it has been observed that a significant number of libraries do not achieve these security levels, due to missing input validity checks during the signature verification process. In this section, we summarize the security levels achievable with Ed25519 signatures, and indicate how one can determine whether a library will support those levels.

4.1.1 Signature Security Properties

Digital signatures may exhibit a number of desirable cryptographic properties [Taming_EdDSAs] among these are:

EUF-CMA (existential unforgeability under chosen message attacks) is usually the minimal security property required of a signature scheme. It guarantees that any efficient adversary who has the public key p k of the signer and received an arbitrary number of signatures on messages of its choice (in an adaptive manner): { m i , σ i } i = 1 N , cannot output a valid signature σ ∗ for a new message m ∗ ∉ { m i } i = 1 N (except with negligible probability). In case the attacker outputs a valid signature on a new message: ( m ∗ , σ ∗ ) , it is called an existential forgery.

SUF-CMA (strong unforgeability under chosen message attacks) is a stronger notion than EUF-CMA. It guarantees that for any efficient adversary who has the public key p k of the signer and received an arbitrary number of signatures on messages of its choice: { m i , σ i } i = 1 N , it cannot output a new valid signature pair ( m ∗ , σ ∗ ) , such that ( m ∗ , σ ∗ ) ∉ { m i , σ i } i = 1 N (except with negligible probability). Strong unforgeability implies that an adversary cannot only sign new messages, but also cannot find a new signature on an old message. See [Provable_Ed25519] for a real world attack that would have been circumvented with SUF-CMA security over EUF-CMA security.

Binding signature (BS) We say that a signature scheme is binding if no efficient signer can output a tuple [ p k , m , m ′ , σ ] , where both ( m , σ ) and ( m ′ , σ ) are valid message signature pairs under the public key p k and m ≠ m ′ (except with negligible probability). A binding signature makes it impossible for the signer to claim later that it has signed a different message, the signature binds the signer to the message.

Strongly Binding signature (SBS) Certain applications may require a signature to not only be binding to the message but also be binding to the public key. We say that a signature scheme is strongly-binding if any efficient signer can not output a tuple [ p k , m , p k ′ , m ′ , σ ] , where ( m , σ ) is a valid signature for the public key p k and ( m ′ , σ ) is a valid signature for the public key p k ′ and either m ′ ≠ m or p k ≠ p k ′ , or both (except with negligible probability). See [Provable_Ed25519] for real world attacks that would have been circumvented with the SBS property.

Note that the BS and SBS properties are forms of non-repudiation.

4.1.2 Achieving Ed25519 Security Properties

As pointed on in [Taming_EdDSAs] flaws in Ed25519 libraries primarily occur on the signature verification side where sometimes edge cases are not properly checked. An Ed25519 signature library that is in conformance with [RFC8032] or [FIPS-186-5], i.e., one that performs all specified validation checks, will have the SUF-CMA property in addition to EUF-CMA.

Reference [Taming_EdDSAs] achieves the BS and SBS properties along with SUF-CMA in their "signature verification algorithm 2" where an additional check is performed against the public key A to make sure that it is not one of eight "small order points". These additional checks incur minimal processing overhead.

Reference [Taming_EdDSAs] included a set of twelve test vectors to test various Ed25519 libraries available at the time of publication. They found that a significant portion missed edge cases and hence did not achieve SUF-CMA (just EUF-CMA) and only two libraries out of sixteen achieved all the security properties. Since the time of publication more Ed25519 libraries have been created and some of the libraries have been updated to include all verification checks. Implementers are recommended to test the Ed25519 library they are using against the test vectors of [Taming_EdDSAs].

5. Privacy Considerations

Before reading this section, readers are urged to familiarize themselves with general privacy advice provided in the Privacy Considerations section of the Data Integrity specification.

The following section describes privacy considerations that developers implementing this specification should be aware of in order to avoid violating privacy assumptions.

Issue 1

This cryptography suite does not provide for selective disclosure or unlinkability. If signatures are re-used, they can be used as correlatable data.

A. The Ed25519Signature2020 Suite

Ed25519Signature2020 is an earlier version of a cryptographic suite for the usage of the EdDSA algorithm and Curve25519. While it has been used in production systems, new implementations should use edssa-2022 instead. It has been kept in this specification to provide a stable reference.

A.1 Data Model

A.1.1 Verification Methods

A.1.1.1 Ed25519VerificationKey2020
Issue 2

We need to add documentation to note that this key format is deployed and widely used in production, but is deprecated. Multikey and JsonWebKey2020 supersede it.

The type of the verification method MUST be Ed25519VerificationKey2020.

The controller of the verification method MUST be a URL.

The publicKeyMultibase value of the verification method MUST start with the base-58-btc prefix (z), as defined in the Multibase section of [VC-DATA-INTEGRITY]. A Multibase-encoded Multikey value follows, which MUST consist of a binary value that starts with the two-byte prefix 0xed01, which is the Multikey header for an Ed25519 public key, followed by the 32-byte public key data, all of which is then encoded using base-58-btc. Any other encoding MUST NOT be allowed.

Developers are advised to not accidentally publish a representation of a private key. Implementations of this specification will raise errors in the event of a Multikey header value other than 0xed01 being used in a publicKeyMultibase value.

Example 4: An Ed25519 public key encoded as an Ed25519VerificationKey2020 
{
  "id": "https://example.com/issuer/123#key-0",
  "type": "Ed25519VerificationKey2020",
  "controller": "https://example.com/issuer/123",
  "publicKeyMultibase": "z6Mkf5rGMoatrSj1f4CyvuHBeXJELe9RPdzo2PKGNCKVtZxP"
}
Example 5: An Ed25519 public key encoded as an Ed25519VerificationKey2020 in a controller document. 
{
  "@context": [
    "https://www.w3.org/ns/did/v1",
    "https://w3id.org/security/suites/ed25519-2020/v1"
  ],
  "id": "did:example:123",
  "verificationMethod": [{
    "id": "did:example:123#key-0",
    "type": "Ed25519VerificationKey2020",
    "controller": "did:example:123",
    "publicKeyMultibase": "z6Mkf5rGMoatrSj1f4CyvuHBeXJELe9RPdzo2PKGNCKVtZxP"
  }],
  "authentication": [
    "did:example:123#key-0"
  ],
  "assertionMethod": [
    "did:example:123#key-0"
  ],
  "capabilityDelegation": [
    "did:example:123#key-0"
  ],
  "capabilityInvocation": [
    "did:example:123#key-0"
  ]
}

A.1.2 Proof representations

A.1.2.1 Ed25519Signature2020

The verificationMethod property of the proof MUST be a URL. Dereferencing the verificationMethod MUST result in an object containing a type property with the value set to Ed25519VerificationKey2020.

The type property of the proof MUST be Ed25519Signature2020.

The created property of the proof MUST be an [XMLSCHEMA11-2] formatted date string.

The proofPurpose property of the proof MUST be a string, and MUST match the verification relationship expressed by the verification method controller.

The proofValue property of the proof MUST be a detached EdDSA produced according to [RFC8032], encoded using the base-58-btc header and alphabet as described in the Multibase section of [VC-DATA-INTEGRITY].

Example 6: An Ed25519 digital signature expressed as a Ed25519Signature2020 
{
  "@context": [
    {"myWebsite": "https://vocabulary.example/myWebsite"},
    "https://w3id.org/security/data-integrity/v1"
  ],
  "myWebsite": "https://hello.world.example/",
  "proof": {
    "type": "Ed25519Signature2020",
    "created": "2020-11-05T19:23:24Z",
    "verificationMethod": "https://di.example/issuer#z6MkjLrk3gKS2nnkeWcmcxiZPGskmesDpuwRBorgHxUXfxnG",
    "proofPurpose": "assertionMethod",
    "proofValue": "z4oey5q2M3XKaxup3tmzN4DRFTLVqpLMweBrSxMY2xHX5XTYVQeVbY8nQAVHMrXFkXJpmEcqdoDwLWxaqA3Q1geV6"
  }
}

A.2 Algorithms

A.2.1 Ed25519Signature2020

The Ed25519Signature2020 cryptographic suite takes an input document, canonicalizes the document using the Universal RDF Dataset Canonicalization Algorithm [RDF-CANON], and then cryptographically hashes and signs the output resulting in the production of a data integrity proof. The algorithms in this section also include the verification of such a data integrity proof.

A.2.1.1 Add Proof (Ed25519Signature2020)

To generate a proof, the algorithm in Section 4.1: Add Proof in the Data Integrity [VC-DATA-INTEGRITY] specification MUST be executed. For that algorithm, the cryptographic suite specific transformation algorithm is defined in Section A.2.1.3 Transformation (Ed25519Signature2020), the hashing algorithm is defined in Section A.2.1.4 Hashing (Ed25519Signature2020), and the proof serialization algorithm is defined in Section A.2.1.6 Proof Serialization (Ed25519Signature2020).

A.2.1.2 Verify Proof (Ed25519Signature2020)

To verify a proof, the algorithm in Section 4.2: Verify Proof in the Data Integrity [VC-DATA-INTEGRITY] specification MUST be executed. For that algorithm, the cryptographic suite specific transformation algorithm is defined in Section A.2.1.3 Transformation (Ed25519Signature2020), the hashing algorithm is defined in Section A.2.1.4 Hashing (Ed25519Signature2020), and the proof verification algorithm is defined in Section A.2.1.7 Proof Verification (Ed25519Signature2020).

A.2.1.3 Transformation (Ed25519Signature2020)

The following algorithm specifies how to transform an unsecured input document into a transformed document that is ready to be provided as input to the hashing algorithm in Section A.2.1.4 Hashing (Ed25519Signature2020).

Required inputs to this algorithm are an unsecured data document (unsecuredDocument) and transformation options (options). The transformation options MUST contain a type identifier for the cryptographic suite (type) and a cryptosuite identifier (cryptosuite). A transformed data document is produced as output. Whenever this algorithm encodes strings, it MUST use UTF-8 encoding.

  1. If options.type is not set to the string Ed25519Signature2020, then a PROOF_TRANSFORMATION_ERROR MUST be raised.
  2. Let canonicalDocument be the result of applying the Universal RDF Dataset Canonicalization Algorithm [RDF-CANON] to the unsecuredDocument.
  3. Set output to the value of canonicalDocument.
  4. Return canonicalDocument as the transformed data document.
A.2.1.4 Hashing (Ed25519Signature2020)

The following algorithm specifies how to cryptographically hash a transformed data document and proof configuration into cryptographic hash data that is ready to be provided as input to the algorithms in Section A.2.1.6 Proof Serialization (Ed25519Signature2020) or Section A.2.1.7 Proof Verification (Ed25519Signature2020).

The required inputs to this algorithm are a transformed data document (transformedDocument) and proof configuration (proofConfig). The proof configuration MUST contain a type identifier for the cryptographic suite (type) and MAY contain a cryptosuite identifier (cryptosuite). A single hash data value represented as series of bytes is produced as output.

  1. Let transformedDocumentHash be the result of applying the SHA-256 (SHA-2 with 256-bit output) cryptographic hashing algorithm [RFC6234] to the transformedDocument. transformedDocumentHash will be exactly 32 bytes in size.
  2. Let proofConfigHash be the result of applying the SHA-256 (SHA-2 with 256-bit output) cryptographic hashing algorithm [RFC6234] to the canonicalProofConfig. proofConfigHash will be exactly 32 bytes in size.
  3. Let hashData be the result of joining proofConfigHash (the first hash) with transformedDocumentHash (the second hash).
  4. Return hashData as the hash data.
A.2.1.5 Proof Configuration (Ed25519Signature2020)

The following algorithm specifies how to generate a proof configuration from a set of proof options that is used as input to the proof hashing algorithm.

The required inputs to this algorithm are proof options (options). The proof options MUST contain a type identifier for the cryptographic suite (type) and MAY contain a cryptosuite identifier (cryptosuite). A proof configuration object is produced as output.

  1. Let proofConfig be an empty object.
  2. Set proofConfig.type to options.type.
  3. If options.cryptosuite is set, set proofConfig.cryptosuite to its value.
  4. If options.type is not set to Ed25519Signature2020, an INVALID_PROOF_CONFIGURATION error MUST be raised.
  5. Set proofConfig.created to options.created. If the value is not a valid [XMLSCHEMA11-2] datetime, an INVALID_PROOF_DATETIME error MUST be raised.
  6. Set proofConfig.verificationMethod to options.verificationMethod.
  7. Set proofConfig.proofPurpose to options.proofPurpose.
  8. Set proofConfig.@context to unsecuredDocument.@context
  9. Let canonicalProofConfig be the result of applying the Universal RDF Dataset Canonicalization Algorithm [RDF-CANON] to the proofConfig.
  10. Return canonicalProofConfig.
A.2.1.6 Proof Serialization (Ed25519Signature2020)

The following algorithm specifies how to serialize a digital signature from a set of cryptographic hash data. This algorithm is designed to be used in conjunction with the algorithms defined in the Data Integrity [VC-DATA-INTEGRITY] specification, Section 4: Algorithms. Required inputs are cryptographic hash data (hashData) and proof options (options). The proof options MUST contain a type identifier for the cryptographic suite (type) and MAY contain a cryptosuite identifier (cryptosuite). A single digital proof value represented as series of bytes is produced as output.

  1. Let privateKeyBytes be the result of retrieving the private key bytes associated with the options.verificationMethod value as described in the Data Integrity [VC-DATA-INTEGRITY] specification, Section 4: Retrieving Cryptographic Material.
  2. Let proofBytes be the result of applying the Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032], using the Ed25519 variant (Pure EdDSA), with hashData as the data to be signed using the private key specified by privateKeyBytes. proofBytes will be exactly 64 bytes in size.
  3. Return proofBytes as the digital proof.
A.2.1.7 Proof Verification (Ed25519Signature2020)

The following algorithm specifies how to verify a digital signature from a set of cryptographic hash data. This algorithm is designed to be used in conjunction with the algorithms defined in the Data Integrity [VC-DATA-INTEGRITY] specification, Section 4: Algorithms. Required inputs are cryptographic hash data (hashData), a digital signature (proofBytes) and proof options (options). A verification result represented as a boolean value is produced as output.

  1. Let publicKeyBytes be the result of retrieving the public key bytes associated with the options.verificationMethod value as described in the Data Integrity [VC-DATA-INTEGRITY] specification, Section 4: Retrieving Cryptographic Material.
  2. Let verificationResult be the result of applying the verification algorithm for the Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032], using the Ed25519 variant (Pure EdDSA), with hashData as the data to be verified against the proofBytes using the public key specified by publicKeyBytes.
  3. Return verificationResult as the verification result.

B. Test Vectors

This section is non-normative.

B.1 Representation: eddsa-rdfc-2022

The signer needs to generate a private/public key pair with the private key used for signing and the public key made available for verification. The representation of the public key and the representation of the private key are shown below.

Example 7: Private and Public keys for Signature 
{
    publicKeyMultibase: "z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2",
    privateKeyMultibase: "z3u2en7t5LR2WtQH5PfFqMqwVHBeXouLzo6haApm8XHqvjxq"
}

Signing begins with a credential without an attached proof, which is converted to canonical form, and then hashed, as shown in the following three examples.

Example 8: Credential without Proof 
{
    "@context": [
        "https://www.w3.org/ns/credentials/v2",
        "https://www.w3.org/ns/credentials/examples/v2"
    ],
    "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
    "type": ["VerifiableCredential", "AlumniCredential"],
    "name": "Alumni Credential",
    "description": "A minimum viable example of an Alumni Credential.",
    "issuer": "https://vc.example/issuers/5678",
    "validFrom": "2023-01-01T00:00:00Z",
    "credentialSubject": {
        "id": "did:example:abcdefgh",
        "alumniOf": "The School of Examples"
    }
}
Example 9: Canonical Credential without Proof 
<did:example:abcdefgh> <https://www.w3.org/ns/credentials/examples#alumniOf> "The School of Examples" .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <https://www.w3.org/2018/credentials#VerifiableCredential> .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <https://www.w3.org/ns/credentials/examples#AlumniCredential> .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <https://schema.org/description> "A minimum viable example of an Alumni Credential." .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <https://schema.org/name> "Alumni Credential" .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <https://www.w3.org/2018/credentials#credentialSubject> <did:example:abcdefgh> .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <https://www.w3.org/2018/credentials#issuer> <https://vc.example/issuers/5678> .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <https://www.w3.org/2018/credentials#validFrom> "2023-01-01T00:00:00Z"^^<http://www.w3.org/2001/XMLSchema#dateTime> .
Example 10: Hash of Canonical Credential without Proof (hex) 
517744132ae165a5349155bef0bb0cf2258fff99dfe1dbd914b938d775a36017

The next step is to take the proof options document, convert it to canonical form, and obtain its hash, as shown in the next three examples.

Example 11: Proof Options Document 
{
  "type": "DataIntegrityProof",
  "cryptosuite": "eddsa-rdfc-2022",
  "created": "2023-02-24T23:36:38Z",
  "verificationMethod": "https://vc.example/issuers/5678#z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2",
  "proofPurpose": "assertionMethod",
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ]
}
Example 12: Canonical Proof Options Document 
_:c14n0 <http://purl.org/dc/terms/created> "2023-02-24T23:36:38Z"^^<http://www.w3.org/2001/XMLSchema#dateTime> .
_:c14n0 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <https://w3id.org/security#DataIntegrityProof> .
_:c14n0 <https://w3id.org/security#cryptosuite> "eddsa-rdfc-2022"^^<https://w3id.org/security#cryptosuiteString> .
_:c14n0 <https://w3id.org/security#proofPurpose> <https://w3id.org/security#assertionMethod> .
_:c14n0 <https://w3id.org/security#verificationMethod> <https://vc.example/issuers/5678#z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2> .
Example 13: Hash of Canonical Proof Options Document (hex) 
4c4d3890a157f8d611b13c265c2c22f39aa0a567c7c7dd9ba3e45cd579784eeb

Finally, we concatenate the hash of the proof options followed by the hash of the credential without proof, use the private key with the combined hash to compute the Ed25519 signature, and then base58-btc encode the signature.

Example 14: Combine hashes of Proof Options and Credential (hex) 
4c4d3890a157f8d611b13c265c2c22f39aa0a567c7c7dd9ba3e45cd579784eeb517744132ae165a5349155bef0bb0cf2258fff99dfe1dbd914b938d775a36017
Example 15: Signature of Combined Hashes (hex) 
3237ba3b695c09e199540507ead17a58300cc4efe91ce19d582ad7e001455190f1ea3d13bdeff2cbaf7f30da7fe9f24b475511ef3875b6efe7cc9f49d3f55b02
Example 16: Signature of Combined Hashes base58-btc 
z21EVs3eXERqTn4acNHT9viboqgzUaQ3kTmhPT3eA8qrVPE7CrQq78WkzctnMX5W4CrzcKnHw8V6dvy5pgWYCU5e9

Assemble the signed credential with the following two steps:

  1. Add the proofValue field with the previously computed base58-btc value to the proof options document.
  2. Set the proof field of the credential to the augmented proof option document.
Example 17: Signed Credential 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
  "type": [
    "VerifiableCredential",
    "AlumniCredential"
  ],
  "name": "Alumni Credential",
  "description": "A minimum viable example of an Alumni Credential.",
  "issuer": "https://vc.example/issuers/5678",
  "validFrom": "2023-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:abcdefgh",
    "alumniOf": "The School of Examples"
  },
  "proof": {
    "type": "DataIntegrityProof",
    "cryptosuite": "eddsa-rdfc-2022",
    "created": "2023-02-24T23:36:38Z",
    "verificationMethod": "https://vc.example/issuers/5678#z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2",
    "proofPurpose": "assertionMethod",
    "proofValue": "z21EVs3eXERqTn4acNHT9viboqgzUaQ3kTmhPT3eA8qrVPE7CrQq78WkzctnMX5W4CrzcKnHw8V6dvy5pgWYCU5e9"
  }
}

B.2 Representation: eddsa-jcs-2022

The signer needs to generate a private/public key pair with the private key used for signing and the public key made available for verification. The representation of the public key, and the representation of the private key are shown below.

Example 18: Private and Public keys for Signature 
{
  publicKeyMultibase: "z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2",
  privateKeyMultibase: "z3u2en7t5LR2WtQH5PfFqMqwVHBeXouLzo6haApm8XHqvjxq"
}

Signing begins with a credential without an attached proof, which is converted to canonical form, and then hashed, as shown in the following three examples.

Example 19: Credential without Proof 
{
    "@context": [
        "https://www.w3.org/ns/credentials/v2",
        "https://www.w3.org/ns/credentials/examples/v2"
    ],
    "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
    "type": ["VerifiableCredential", "AlumniCredential"],
    "name": "Alumni Credential",
    "description": "A minimum viable example of an Alumni Credential.",
    "issuer": "https://vc.example/issuers/5678",
    "validFrom": "2023-01-01T00:00:00Z",
    "credentialSubject": {
        "id": "did:example:abcdefgh",
        "alumniOf": "The School of Examples"
    }
}
Example 20: Canonical Credential without Proof 
{"@context":["https://www.w3.org/ns/credentials/v2","https://www.w3.org/ns/credentials/examples/v2"],"credentialSubject":{"alumniOf":"The School of Examples","id":"did:example:abcdefgh"},"description":"A minimum viable example of an Alumni Credential.","id":"urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33","issuer":"https://vc.example/issuers/5678","name":"Alumni Credential","type":["VerifiableCredential","AlumniCredential"],"validFrom":"2023-01-01T00:00:00Z"}
Example 21: Hash of Canonical Credential without Proof (hex) 
59b7cb6251b8991add1ce0bc83107e3db9dbbab5bd2c28f687db1a03abc92f19

The next step is to take the proof options document, convert it to canonical form, and obtain its hash, as shown in the next three examples.

Example 22: Proof Options Document 
{
  "type": "DataIntegrityProof",
  "cryptosuite": "eddsa-jcs-2022",
  "created": "2023-02-24T23:36:38Z",
  "verificationMethod": "https://vc.example/issuers/5678#z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2",
  "proofPurpose": "assertionMethod"
}
Example 23: Canonical Proof Options Document 
{"created":"2023-02-24T23:36:38Z","cryptosuite":"eddsa-jcs-2022","proofPurpose":"assertionMethod","type":"DataIntegrityProof","verificationMethod":"https://vc.example/issuers/5678#z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2"}
Example 24: Hash of Canonical Proof Options Document (hex) 
56d860737b1bc788da1f5c5a506115278314559a680f37976502c9b3ed1f38f4

Finally, we concatenate the hash of the proof options followed by the hash of the credential without proof, use the private key with the combined hash to compute the Ed25519 signature, and then base58-btc encode the signature.

Example 25: Combine hashes of Proof Options and Credential (hex) 
56d860737b1bc788da1f5c5a506115278314559a680f37976502c9b3ed1f38f459b7cb6251b8991add1ce0bc83107e3db9dbbab5bd2c28f687db1a03abc92f19
Example 26: Signature of Combined Hashes (hex) 
7717cab27b6a4d91a472922d0ec071ead8297ce65c47436ca95b98c646d109abbd0c52cab09e83af605e2d896f29a30bbf81cbe0c2089a7193d908c96eaf6106
Example 27: Signature of Combined Hashes base58-btc 
z3P6rHMUaWG6e3Ac6xYFht8aEvoVXndgKTtEY8kzWYXzk8dKmAo2GJeZiJw4qoZ2PGp4ugdaHx3oQiLpeFBLDqP2M

Assemble the signed credential with the following two steps:

  1. Add the proofValue field with the previously computed base58-btc value to the proof options document.
  2. Set the proof field of the credential to the augmented proof option document.
Example 28: Signed Credential 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
  "type": [
    "VerifiableCredential",
    "AlumniCredential"
  ],
  "name": "Alumni Credential",
  "description": "A minimum viable example of an Alumni Credential.",
  "issuer": "https://vc.example/issuers/5678",
  "validFrom": "2023-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:abcdefgh",
    "alumniOf": "The School of Examples"
  },
  "proof": {
    "type": "DataIntegrityProof",
    "cryptosuite": "eddsa-jcs-2022",
    "created": "2023-02-24T23:36:38Z",
    "verificationMethod": "https://vc.example/issuers/5678#z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2",
    "proofPurpose": "assertionMethod",
    "proofValue": "z3P6rHMUaWG6e3Ac6xYFht8aEvoVXndgKTtEY8kzWYXzk8dKmAo2GJeZiJw4qoZ2PGp4ugdaHx3oQiLpeFBLDqP2M"
  }
}

B.3 Representation: Ed25519Signature2020

The signer needs to generate a private/public key pair with the private key used for signing and the public key made available for verification. The representation of the public key, and the representation of the private key, are shown below.

Example 29: Private and Public keys for Signature 
{
    publicKeyMultibase: "z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2",
    privateKeyMultibase: "z3u2en7t5LR2WtQH5PfFqMqwVHBeXouLzo6haApm8XHqvjxq"
}

Signing begins with a credential without an attached proof, which is converted to canonical form, and then hashed, as shown in the following three examples.

Example 30: Credential without Proof 
{
    "@context": [
        "https://www.w3.org/ns/credentials/v2",
        "https://www.w3.org/ns/credentials/examples/v2"
    ],
    "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
    "type": ["VerifiableCredential", "AlumniCredential"],
    "name": "Alumni Credential",
    "description": "A minimum viable example of an Alumni Credential.",
    "issuer": "https://vc.example/issuers/5678",
    "validFrom": "2023-01-01T00:00:00Z",
    "credentialSubject": {
        "id": "did:example:abcdefgh",
        "alumniOf": "The School of Examples"
    }
}
Example 31: Canonical Credential without Proof 
<did:example:abcdefgh> <https://www.w3.org/ns/credentials/examples#alumniOf> "The School of Examples" .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <https://www.w3.org/2018/credentials#VerifiableCredential> .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <https://www.w3.org/ns/credentials/examples#AlumniCredential> .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <https://schema.org/description> "A minimum viable example of an Alumni Credential." .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <https://schema.org/name> "Alumni Credential" .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <https://www.w3.org/2018/credentials#credentialSubject> <did:example:abcdefgh> .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <https://www.w3.org/2018/credentials#issuer> <https://vc.example/issuers/5678> .
<urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33> <https://www.w3.org/2018/credentials#validFrom> "2023-01-01T00:00:00Z"^^<http://www.w3.org/2001/XMLSchema#dateTime> .
Example 32: Hash of Canonical Credential without Proof (hex) 
517744132ae165a5349155bef0bb0cf2258fff99dfe1dbd914b938d775a36017

The next step is to take the proof options document, convert it to canonical form, and obtain its hash, as shown in the next three examples.

Example 33: Proof Options Document 
{
  "type": "Ed25519Signature2020",
  "created": "2023-02-24T23:36:38Z",
  "verificationMethod": "https://vc.example/issuers/5678#z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2",
  "proofPurpose": "assertionMethod",
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2",
    "https://w3id.org/security/suites/ed25519-2020/v1"
  ]
}
Example 34: Canonical Proof Options Document 
_:c14n0 <http://purl.org/dc/terms/created> "2023-02-24T23:36:38Z"^^<http://www.w3.org/2001/XMLSchema#dateTime> .
_:c14n0 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <https://w3id.org/security#Ed25519Signature2020> .
_:c14n0 <https://w3id.org/security#proofPurpose> <https://w3id.org/security#assertionMethod> .
_:c14n0 <https://w3id.org/security#verificationMethod> <https://vc.example/issuers/5678#z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2> .
Example 35: Hash of Canonical Proof Options Document (hex) 
5e41905a6915396ff4eb426ce26c322d0e1d870b3d75cef95612cc94e4f8bad7

Finally, we concatenate the hash of the proof options followed by the hash of the credential without proof, use the private key with the combined hash to compute the Ed25519 signature, and then base58-btc encode the signature.

Example 36: Combine hashes of Proof Options and Credential (hex) 
5e41905a6915396ff4eb426ce26c322d0e1d870b3d75cef95612cc94e4f8bad7517744132ae165a5349155bef0bb0cf2258fff99dfe1dbd914b938d775a36017
Example 37: Signature of Combined Hashes (hex) 
d6310be6e26c28c327abc6f9e392c9f91c4e5f71252a8a3bc6acfedcc62a1c216e8979afdbb1badaa57e4ed8ad362af447ac6e649a074d5ea99788e3343b980b
Example 38: Signature of Combined Hashes base58-btc 
z5HNuvc5WbWYsRRt97kXJ6SoKgb1tMwtkQND4pnobZE26JGnohdWVpzashF9d8FRzhzm8oYRSivKACTakeE4DzdHL

Assemble the signed credential with the following two steps:

  1. Add the proofValue field with the previously computed base58-btc value to the proof options document.
  2. Set the proof field of the credential to the augmented proof option document.
Example 39: Signed Credential 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2",
    "https://w3id.org/security/suites/ed25519-2020/v1"
  ],
  "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
  "type": [
    "VerifiableCredential",
    "AlumniCredential"
  ],
  "name": "Alumni Credential",
  "description": "A minimum viable example of an Alumni Credential.",
  "issuer": "https://vc.example/issuers/5678",
  "validFrom": "2023-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:abcdefgh",
    "alumniOf": "The School of Examples"
  },
  "proof": {
    "type": "Ed25519Signature2020",
    "created": "2023-02-24T23:36:38Z",
    "verificationMethod": "https://vc.example/issuers/5678#z6MkrJVnaZkeFzdQyMZu1cgjg7k1pZZ6pvBQ7XJPt4swbTQ2",
    "proofPurpose": "assertionMethod",
    "proofValue": "z5HNuvc5WbWYsRRt97kXJ6SoKgb1tMwtkQND4pnobZE26JGnohdWVpzashF9d8FRzhzm8oYRSivKACTakeE4DzdHL"
  }
}

B.4 Proof Sets and Chains

Proof sets and chains are defined in the [VC-DATA-INTEGRITY]. We provide test vectors showing the creation of proof sets and chains with the eddsa-rdfc-2022 cryptosuite. Multiple signers can be involved in the generation of proof sets and chains so multiple public/private key pairs are needed. These are shown below.

Example 40: Public and Private Key Pairs 
{
  "keyPair1": {
    "publicKeyMultibase": "z6MktgKTsu1QhX6QPbyqG6geXdw6FQCZBPq7uQpieWbiQiG7",
    "privateKeyMultibase": "z3u2W4YnTstS1nSSBAgZcYSJF43JuZ9uLV6bF38B1Bf8NugW"
  },
  "keyPair2": {
    "publicKeyMultibase": "z6MkhWqdDBPojHA7cprTGTt5yHv5yUi1B8cnXn8ReLumkw6E",
    "privateKeyMultibase": "z3u2cfp4Q17kMGhNCh348a3yw3cUBiWK6RXRzyJE54sixMFn"
  },
  "keyPair3": {
    "publicKeyMultibase": "z6MkmEq87wkHCYnWnNZkigeDMGTN7oUw1upkhzd77KuXERS1",
    "privateKeyMultibase": "z3u2Zr3tcDLBDQKGxVa9SRDFNLqNqPWsa8p9rWPvCEH6bADB"
  },
  "keyPair4": {
    "publicKeyMultibase": "z6Mkm1S51iPHJvDEkJ9MRtxJmT8Pqo6wHipAFwBAjN83vntT",
    "privateKeyMultibase": "z3u2ZTWiFwM17veUR7sXniY66Gf14SqMdpMLy7SW9x4EDdmw"
  }
}

The original unsigned credential is shown below:

Example 41: Unsigned Credential 
{
    "@context": [
        "https://www.w3.org/ns/credentials/v2",
        "https://www.w3.org/ns/credentials/examples/v2"
    ],
    "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
    "type": ["VerifiableCredential", "AlumniCredential"],
    "name": "Alumni Credential",
    "description": "A minimum viable example of an Alumni Credential.",
    "issuer": "https://vc.example/issuers/5678",
    "validFrom": "2023-01-01T00:00:00Z",
    "credentialSubject": {
        "id": "did:example:abcdefgh",
        "alumniOf": "The School of Examples"
    }
}

B.4.1 Proof Set

To demonstrate creating a proof set, we start with a document containing a single proof and add another proof to it. The starting document is shown below and contains a proof signed with keyPair1.

Example 42: Starting Document for Proof Set 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
  "type": [
    "VerifiableCredential",
    "AlumniCredential"
  ],
  "name": "Alumni Credential",
  "description": "A minimum viable example of an Alumni Credential.",
  "issuer": "https://vc.example/issuers/5678",
  "validFrom": "2023-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:abcdefgh",
    "alumniOf": "The School of Examples"
  },
  "proof": {
    "type": "DataIntegrityProof",
    "id": "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
    "cryptosuite": "eddsa-rdfc-2022",
    "created": "2023-02-24T23:36:38Z",
    "verificationMethod": "https://vc.example/issuers/56781#z6MktgKTsu1QhX6QPbyqG6geXdw6FQCZBPq7uQpieWbiQiG7",
    "proofPurpose": "assertionMethod",
    "proofValue": "z5KTX5yikM4eUukZW9qh66LGT3KZEUCACGpWcT2t4Yd54NMoFRchGmH4778omyNFAD3weSt6sNk5fuaMQmhhzNmEC"
  }
}

The options input to Section 4.4: Add Proof Set/Chain in [VC-DATA-INTEGRITY] is shown below. Note that it does not include a previousProof attribute since we are constructing a proof set and not a chain. In addition, we will be using keyPair2 for signing.

Example 43: Proof Options for Set 
{
  "type": "DataIntegrityProof",
  "id": "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54",
  "cryptosuite": "eddsa-rdfc-2022",
  "created": "2023-02-24T23:36:38Z",
  "verificationMethod": "https://vc.example/issuers/56782#z6MkhWqdDBPojHA7cprTGTt5yHv5yUi1B8cnXn8ReLumkw6E",
  "proofPurpose": "assertionMethod"
}

Per the algorithm of Section 4.4: Add Proof Set/Chain in [VC-DATA-INTEGRITY], we create an array variable, allProofs, and add the proof from the starting document to it. Since there is no previousProof attribute, no modification of unsignedDocument is needed prior to computing the signed proof in step 6 of Section 4.4: Add Proof Set/Chain in [VC-DATA-INTEGRITY]. The signed proof configuration is shown below.

Example 44: Signed Proof Options 
{
  "type": "DataIntegrityProof",
  "id": "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54",
  "cryptosuite": "eddsa-rdfc-2022",
  "created": "2023-02-24T23:36:38Z",
  "verificationMethod": "https://vc.example/issuers/56782#z6MkhWqdDBPojHA7cprTGTt5yHv5yUi1B8cnXn8ReLumkw6E",
  "proofPurpose": "assertionMethod",
  "proofValue": "z5KXNyXDcm822dHS37tmS6Xc7FFNo8c73AfeqmfHoywPxnXWNjWKYK3VQzt3CMUoK9uAqsboVHKJXxuYwbdnfxZeA"
}

The signed proof options above gets appended to the allProofs variable, which then gets set as the proof attribute of the unsigned document to produce the final signed document as shown below.

Example 45: Signed Proof Set 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
  "type": [
    "VerifiableCredential",
    "AlumniCredential"
  ],
  "name": "Alumni Credential",
  "description": "A minimum viable example of an Alumni Credential.",
  "issuer": "https://vc.example/issuers/5678",
  "validFrom": "2023-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:abcdefgh",
    "alumniOf": "The School of Examples"
  },
  "proof": [
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56781#z6MktgKTsu1QhX6QPbyqG6geXdw6FQCZBPq7uQpieWbiQiG7",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KTX5yikM4eUukZW9qh66LGT3KZEUCACGpWcT2t4Yd54NMoFRchGmH4778omyNFAD3weSt6sNk5fuaMQmhhzNmEC"
    },
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56782#z6MkhWqdDBPojHA7cprTGTt5yHv5yUi1B8cnXn8ReLumkw6E",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KXNyXDcm822dHS37tmS6Xc7FFNo8c73AfeqmfHoywPxnXWNjWKYK3VQzt3CMUoK9uAqsboVHKJXxuYwbdnfxZeA"
    }
  ]
}

B.4.2 Proof Chain with Multiple Dependencies

This collection of test vectors demonstrates the construction a proof chain. We start with a document containing a proof set, i.e., our previous example, and then add a new proof to the credential that has a dependency on the existing proofs. This example also demonstrates the case where the previousProofs attribute is an array. This example uses keyPair3 and the starting document is given below.

Example 46: Starting Document for Proof Chain 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
  "type": [
    "VerifiableCredential",
    "AlumniCredential"
  ],
  "name": "Alumni Credential",
  "description": "A minimum viable example of an Alumni Credential.",
  "issuer": "https://vc.example/issuers/5678",
  "validFrom": "2023-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:abcdefgh",
    "alumniOf": "The School of Examples"
  },
  "proof": [
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56781#z6MktgKTsu1QhX6QPbyqG6geXdw6FQCZBPq7uQpieWbiQiG7",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KTX5yikM4eUukZW9qh66LGT3KZEUCACGpWcT2t4Yd54NMoFRchGmH4778omyNFAD3weSt6sNk5fuaMQmhhzNmEC"
    },
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56782#z6MkhWqdDBPojHA7cprTGTt5yHv5yUi1B8cnXn8ReLumkw6E",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KXNyXDcm822dHS37tmS6Xc7FFNo8c73AfeqmfHoywPxnXWNjWKYK3VQzt3CMUoK9uAqsboVHKJXxuYwbdnfxZeA"
    }
  ]
}

The options input to Section 4.4: Add Proof Set/Chain in [VC-DATA-INTEGRITY] is shown below. Note that it includes a previousProof attribute since we are constructing a proof chain.

Example 47: Options for Proof Chain 
{
  "type": "DataIntegrityProof",
  "id": "urn:uuid:d94f792a-c546-4d06-b38a-da070ab56c23",
  "cryptosuite": "eddsa-rdfc-2022",
  "created": "2023-02-26T22:06:38Z",
  "verificationMethod": "https://vc.example/issuers/56783#z6MkmEq87wkHCYnWnNZkigeDMGTN7oUw1upkhzd77KuXERS1",
  "proofPurpose": "assertionMethod",
  "previousProof": [
    "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
    "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54"
  ]
}

Per the algorithm of Section 4.4: Add Proof Set/Chain in [VC-DATA-INTEGRITY], we create an array variable, allProofs, and add the proofs from the starting document to it. Since the options contains the previousProof attribute, we compute the matchingProofs variable per step 4 of Section 4.4: Add Proof Set/Chain, and we set the unsecuredDocument.proof equal to the matchingProofs. This produces the document shown below.

Example 48: Temporary Unsecured Document for Binding Previous Proofs 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
  "type": [
    "VerifiableCredential",
    "AlumniCredential"
  ],
  "name": "Alumni Credential",
  "description": "A minimum viable example of an Alumni Credential.",
  "issuer": "https://vc.example/issuers/5678",
  "validFrom": "2023-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:abcdefgh",
    "alumniOf": "The School of Examples"
  },
  "proof": [
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56781#z6MktgKTsu1QhX6QPbyqG6geXdw6FQCZBPq7uQpieWbiQiG7",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KTX5yikM4eUukZW9qh66LGT3KZEUCACGpWcT2t4Yd54NMoFRchGmH4778omyNFAD3weSt6sNk5fuaMQmhhzNmEC"
    },
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56782#z6MkhWqdDBPojHA7cprTGTt5yHv5yUi1B8cnXn8ReLumkw6E",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KXNyXDcm822dHS37tmS6Xc7FFNo8c73AfeqmfHoywPxnXWNjWKYK3VQzt3CMUoK9uAqsboVHKJXxuYwbdnfxZeA"
    }
  ]
}

In step 6, we use the previous document (unsecured document with previous proofs added to it) to compute the proofValue attribute. This gives the signed configuration options (proof) shown below:

Example 49: Signed Configuration Options (proof) 
{
  "type": "DataIntegrityProof",
  "id": "urn:uuid:d94f792a-c546-4d06-b38a-da070ab56c23",
  "cryptosuite": "eddsa-rdfc-2022",
  "created": "2023-02-26T22:06:38Z",
  "verificationMethod": "https://vc.example/issuers/56783#z6MkmEq87wkHCYnWnNZkigeDMGTN7oUw1upkhzd77KuXERS1",
  "proofPurpose": "assertionMethod",
  "previousProof": [
    "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
    "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54"
  ],
  "proofValue": "z2hcFbMaj3BJufikuLZQ36gAXVT9J3ZiwB9rqN3j7VdqyT1GaQPbMTaF1Q2gn7h75ZcJ6JpV9pvNoDumvcjtmSRAV"
}

The signed proof options above gets appended to the allProofs variable, which then gets set as the proof attribute of the unsigned document to produce the final signed document as shown below.

Example 50: Signed Proof Chain 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
  "type": [
    "VerifiableCredential",
    "AlumniCredential"
  ],
  "name": "Alumni Credential",
  "description": "A minimum viable example of an Alumni Credential.",
  "issuer": "https://vc.example/issuers/5678",
  "validFrom": "2023-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:abcdefgh",
    "alumniOf": "The School of Examples"
  },
  "proof": [
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56781#z6MktgKTsu1QhX6QPbyqG6geXdw6FQCZBPq7uQpieWbiQiG7",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KTX5yikM4eUukZW9qh66LGT3KZEUCACGpWcT2t4Yd54NMoFRchGmH4778omyNFAD3weSt6sNk5fuaMQmhhzNmEC"
    },
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56782#z6MkhWqdDBPojHA7cprTGTt5yHv5yUi1B8cnXn8ReLumkw6E",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KXNyXDcm822dHS37tmS6Xc7FFNo8c73AfeqmfHoywPxnXWNjWKYK3VQzt3CMUoK9uAqsboVHKJXxuYwbdnfxZeA"
    },
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:d94f792a-c546-4d06-b38a-da070ab56c23",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-26T22:06:38Z",
      "verificationMethod": "https://vc.example/issuers/56783#z6MkmEq87wkHCYnWnNZkigeDMGTN7oUw1upkhzd77KuXERS1",
      "proofPurpose": "assertionMethod",
      "previousProof": [
        "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
        "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54"
      ],
      "proofValue": "z2hcFbMaj3BJufikuLZQ36gAXVT9J3ZiwB9rqN3j7VdqyT1GaQPbMTaF1Q2gn7h75ZcJ6JpV9pvNoDumvcjtmSRAV"
    }
  ]
}

B.4.3 Extended Proof Chain

This collection of test vectors demonstrates construction of an extended proof chain. We start with the output of the previous section and add an additional proof that is dependent on one of the existing proofs. This example uses keyPair4, and the starting document is given below.

Example 51: Starting Document for Extended Proof Chain 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
  "type": [
    "VerifiableCredential",
    "AlumniCredential"
  ],
  "name": "Alumni Credential",
  "description": "A minimum viable example of an Alumni Credential.",
  "issuer": "https://vc.example/issuers/5678",
  "validFrom": "2023-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:abcdefgh",
    "alumniOf": "The School of Examples"
  },
  "proof": [
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56781#z6MktgKTsu1QhX6QPbyqG6geXdw6FQCZBPq7uQpieWbiQiG7",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KTX5yikM4eUukZW9qh66LGT3KZEUCACGpWcT2t4Yd54NMoFRchGmH4778omyNFAD3weSt6sNk5fuaMQmhhzNmEC"
    },
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56782#z6MkhWqdDBPojHA7cprTGTt5yHv5yUi1B8cnXn8ReLumkw6E",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KXNyXDcm822dHS37tmS6Xc7FFNo8c73AfeqmfHoywPxnXWNjWKYK3VQzt3CMUoK9uAqsboVHKJXxuYwbdnfxZeA"
    },
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:d94f792a-c546-4d06-b38a-da070ab56c23",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-26T22:06:38Z",
      "verificationMethod": "https://vc.example/issuers/56783#z6MkmEq87wkHCYnWnNZkigeDMGTN7oUw1upkhzd77KuXERS1",
      "proofPurpose": "assertionMethod",
      "previousProof": [
        "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
        "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54"
      ],
      "proofValue": "z2hcFbMaj3BJufikuLZQ36gAXVT9J3ZiwB9rqN3j7VdqyT1GaQPbMTaF1Q2gn7h75ZcJ6JpV9pvNoDumvcjtmSRAV"
    }
  ]
}

The options input to Section 4.4: Add Proof Set/Chain in [VC-DATA-INTEGRITY] is shown below. Note that it includes a previousProof attribute since we are constructing a proof chain, however this time it is a single value.

Example 52: Options for Extended Proof Chain 
{
  "type": "DataIntegrityProof",
  "cryptosuite": "eddsa-rdfc-2022",
  "created": "2023-02-26T22:16:38Z",
  "verificationMethod": "https://vc.example/issuers/56784#z6MkmEq87wkHCYnWnNZkigeDMGTN7oUw1upkhzd77KuXERS1",
  "proofPurpose": "assertionMethod",
  "previousProof": "urn:uuid:d94f792a-c546-4d06-b38a-da070ab56c23"
}

Per the algorithm of Section 4.4: Add Proof Set/Chain in [VC-DATA-INTEGRITY], we create an array variable, allProofs, and add the proofs from the starting document to it. Since the options contains the previousProof attribute, we compute the matchingProofs variable per step 4 of Section 4.4: Add Proof Set/Chain, and we set the unsecuredDocument.proof equal to the matchingProofs. This produces the document shown below.

Example 53: Temporary Unsecured Document for Binding Previous Proofs (Extended Chain) 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
  "type": [
    "VerifiableCredential",
    "AlumniCredential"
  ],
  "name": "Alumni Credential",
  "description": "A minimum viable example of an Alumni Credential.",
  "issuer": "https://vc.example/issuers/5678",
  "validFrom": "2023-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:abcdefgh",
    "alumniOf": "The School of Examples"
  },
  "proof": [
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:d94f792a-c546-4d06-b38a-da070ab56c23",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-26T22:06:38Z",
      "verificationMethod": "https://vc.example/issuers/56783#z6MkmEq87wkHCYnWnNZkigeDMGTN7oUw1upkhzd77KuXERS1",
      "proofPurpose": "assertionMethod",
      "previousProof": [
        "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
        "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54"
      ],
      "proofValue": "z2hcFbMaj3BJufikuLZQ36gAXVT9J3ZiwB9rqN3j7VdqyT1GaQPbMTaF1Q2gn7h75ZcJ6JpV9pvNoDumvcjtmSRAV"
    }
  ]
}

In step 6, we use the previous document (unsecured document with previous proofs added to it) to compute the proofValue attribute. This gives the signed configuration options (proof) shown below:

Example 54: Signed Configuration Options (Extended) 
{
  "type": "DataIntegrityProof",
  "cryptosuite": "eddsa-rdfc-2022",
  "created": "2023-02-26T22:16:38Z",
  "verificationMethod": "https://vc.example/issuers/56784#z6MkmEq87wkHCYnWnNZkigeDMGTN7oUw1upkhzd77KuXERS1",
  "proofPurpose": "assertionMethod",
  "previousProof": "urn:uuid:d94f792a-c546-4d06-b38a-da070ab56c23",
  "proofValue": "z6f4Lx4xiwWq8sucv6pg2vVvD5R4bxr58q2TagpwDXCxPVVS28S1iFwhor4ikhG6u4RKrNx7uSkYrCHdiiw5Js3d"
}

The signed proof options above gets appended to the allProofs variable, which then gets set as the proof attribute of the unsigned document to produce the final signed document as shown below.

Example 55: Signed Proof Chain (Extended) 
{
  "@context": [
    "https://www.w3.org/ns/credentials/v2",
    "https://www.w3.org/ns/credentials/examples/v2"
  ],
  "id": "urn:uuid:58172aac-d8ba-11ed-83dd-0b3aef56cc33",
  "type": [
    "VerifiableCredential",
    "AlumniCredential"
  ],
  "name": "Alumni Credential",
  "description": "A minimum viable example of an Alumni Credential.",
  "issuer": "https://vc.example/issuers/5678",
  "validFrom": "2023-01-01T00:00:00Z",
  "credentialSubject": {
    "id": "did:example:abcdefgh",
    "alumniOf": "The School of Examples"
  },
  "proof": [
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56781#z6MktgKTsu1QhX6QPbyqG6geXdw6FQCZBPq7uQpieWbiQiG7",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KTX5yikM4eUukZW9qh66LGT3KZEUCACGpWcT2t4Yd54NMoFRchGmH4778omyNFAD3weSt6sNk5fuaMQmhhzNmEC"
    },
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-24T23:36:38Z",
      "verificationMethod": "https://vc.example/issuers/56782#z6MkhWqdDBPojHA7cprTGTt5yHv5yUi1B8cnXn8ReLumkw6E",
      "proofPurpose": "assertionMethod",
      "proofValue": "z5KXNyXDcm822dHS37tmS6Xc7FFNo8c73AfeqmfHoywPxnXWNjWKYK3VQzt3CMUoK9uAqsboVHKJXxuYwbdnfxZeA"
    },
    {
      "type": "DataIntegrityProof",
      "id": "urn:uuid:d94f792a-c546-4d06-b38a-da070ab56c23",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-26T22:06:38Z",
      "verificationMethod": "https://vc.example/issuers/56783#z6MkmEq87wkHCYnWnNZkigeDMGTN7oUw1upkhzd77KuXERS1",
      "proofPurpose": "assertionMethod",
      "previousProof": [
        "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
        "urn:uuid:8cc9022b-6b14-4cf3-8571-74972c5feb54"
      ],
      "proofValue": "z2hcFbMaj3BJufikuLZQ36gAXVT9J3ZiwB9rqN3j7VdqyT1GaQPbMTaF1Q2gn7h75ZcJ6JpV9pvNoDumvcjtmSRAV"
    },
    {
      "type": "DataIntegrityProof",
      "cryptosuite": "eddsa-rdfc-2022",
      "created": "2023-02-26T22:16:38Z",
      "verificationMethod": "https://vc.example/issuers/56784#z6MkmEq87wkHCYnWnNZkigeDMGTN7oUw1upkhzd77KuXERS1",
      "proofPurpose": "assertionMethod",
      "previousProof": "urn:uuid:d94f792a-c546-4d06-b38a-da070ab56c23",
      "proofValue": "z6f4Lx4xiwWq8sucv6pg2vVvD5R4bxr58q2TagpwDXCxPVVS28S1iFwhor4ikhG6u4RKrNx7uSkYrCHdiiw5Js3d"
    }
  ]
}

B.5 Revision History

This section is non-normative.

This section contains the substantive changes that have been made to this specification over time.

Changes since the First Public Working Draft:

C. References

C.1 Normative references

[RDF-CANON]
RDF Dataset Canonicalization. Dave Longley; Gregg Kellogg; Dan Yamamoto. W3C. 30 November 2023. W3C Candidate Recommendation. URL: https://www.w3.org/TR/rdf-canon/
[RFC2119]
Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. IETF. March 1997. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc2119
[RFC6234]
US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF). D. Eastlake 3rd; T. Hansen. IETF. May 2011. Informational. URL: https://www.rfc-editor.org/rfc/rfc6234
[RFC8032]
Edwards-Curve Digital Signature Algorithm (EdDSA). S. Josefsson; I. Liusvaara. IETF. January 2017. Informational. URL: https://www.rfc-editor.org/rfc/rfc8032
[RFC8174]
Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words. B. Leiba. IETF. May 2017. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc8174
[RFC8785]
JSON Canonicalization Scheme (JCS). A. Rundgren; B. Jordan; S. Erdtman. IETF. June 2020. Informational. URL: https://www.rfc-editor.org/rfc/rfc8785
[VC-DATA-INTEGRITY]
Verifiable Credential Data Integrity 1.0. Manu Sporny; Dave Longley; Greg Bernstein; Dmitri Zagidulin; Sebastian Crane. W3C. 10 December 2023. W3C Candidate Recommendation. URL: https://www.w3.org/TR/vc-data-integrity/
[XMLSCHEMA11-2]
W3C XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes. David Peterson; Sandy Gao; Ashok Malhotra; Michael Sperberg-McQueen; Henry Thompson; Paul V. Biron et al. W3C. 5 April 2012. W3C Recommendation. URL: https://www.w3.org/TR/xmlschema11-2/

C.2 Informative references

[FIPS-186-5]
FIPS PUB 186-5: Digital Signature Standard (DSS). U.S. Department of Commerce/National Institute of Standards and Technology. 3 February 2023. National Standard. URL: https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-5.pdf
[Provable_Ed25519]
The Provable Security of Ed25519: Theory and Practice. Jacqueline Brendel; Cas Cremers; Dennis Jackson; Mang Zhao. Cryptology ePrint Archive, Paper 2020/823. 2020. URL: https://eprint.iacr.org/2020/823
[Taming_EdDSAs]
Taming the many EdDSAs. Konstantinos Chalkias; François Garillot; Valeria Nikolaenko. Cryptology ePrint Archive, Paper 2020/1244. 2020. URL: https://eprint.iacr.org/2020/1244