Cryptography Introduction

Hash (fingerprint, digest): evenly and randomly maps variable length data into a smaller fixed size such that it's "one-way" (hard to find a data object for a given hash result) and "collision-free" (hard to find two data objects with the same hash result).

Secret Key Cryptography (symmetric): the key used for processing is kept as a secret.

Public Key Cryptography (asymmetric): a private/public key pair (inverse of each other) are used to sign (via the private key) and encrypt (via the public key).

Signature: a private key is applied to some data (or its hash)

• authenticity (a specific key was used),
• integrity (the document has been changed),
• and non-repudiation (possessor of the key can not deny it was used.)

Encryption: One often uses a public key (easy to obtain) to send a symmetric key (efficient) for a "session" of communication.