HMAC: keyed-hash message authentication code (RFC 2104) #47

Phase 5: Pure Rust Crypto#

Implement HMAC (Hash-based Message Authentication Code) per RFC 2104 in the crypto crate.

Dependencies#

• Requires SHA-2 implementation (SHA-256, SHA-384, SHA-512)

Requirements#

• Generic over hash function (HMAC-SHA-256, HMAC-SHA-384, HMAC-SHA-512)
• Hmac::new(key), update(&[u8]), finalize() -> Vec<u8>
• One-shot: hmac_sha256(key, data) -> [u8; 32], etc.
• Key handling: keys longer than block size are hashed; shorter keys are zero-padded
• Inner and outer padding (ipad/opad) per RFC 2104 §2

Acceptance Criteria#

• Generic HMAC implementation parameterized over hash function
• HMAC-SHA-256, HMAC-SHA-384, HMAC-SHA-512 variants
• Pass RFC 4231 test vectors (Test Cases 1-7)
• Handles keys shorter than, equal to, and longer than block size
• cargo test -p we-crypto passes
• cargo clippy -p we-crypto -- -D warnings clean