hmac_sha1.nx

hmac_sha1.nx -- HMAC with SHA-1 (RFC 2104 + FIPS 198-1). Interop-only primitive, like sha1.nx itself. HMAC does not rely on its inner hash's collision resistance (only pseudo- randomness of the keyed mix), so HMAC-SHA1 remains safe for authentication even though plain SHA-1 is broken for signatures. Still widely used: - TOTP / HOTP (RFC 4226 / 6238 default) - OAuth 1.0 HMAC-SHA1 signatures - AWS SigV2 / legacy API auth - PBKDF2-HMAC-SHA1 (WPA2, older WebCrypto key derivation) - Older JWT HS1 tokens Algorithm (RFC 2104): block_size = 64 bytes for SHA-1 if len(key) > block_size: key = SHA1(key) key = key || zeros to block_size ipad = key XOR 0x36 repeated opad = key XOR 0x5C repeated tag = SHA1(opad || SHA1(ipad || msg)) Composes sha1.nx. Output is 20 bytes. Invariants: HS1 Output = 20 bytes always (HMAC-SHA1 tag length). HS2 Matches RFC 2202 test vectors (not checked in smoke, but the algorithm is textbook).