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Cryptography

SHA-256 digests and keyed HMAC-SHA-256 MACs, implemented from scratch in plain C (no OpenSSL or third-party code) and returned as lowercase-hex ABS_STR values.

#include "abscom/abs.h"

API

Function Description
var sha256(const char *input) The SHA-256 digest of a NUL-terminated string, as a 64-char hex string.
var hmac_sha256(const char *key, const char *msg) The HMAC-SHA-256 MAC of msg under key, as a 64-char hex string. 
var h = sha256("password");
print(h);   /* 5e884898da28047151d0e56f8dc6292773603d0d6aabbdd62a11ef721d1542d8 */

var mac = hmac_sha256("secret", "message");
print(mac); /* 64 lowercase hex chars */

Notes

  • The SHA-256 core is a compact FIPS 180-4 implementation; HMAC follows RFC 2104. Keys longer than the 64-byte block are pre-hashed, per the RFC.
  • Output is always lowercase hex, 64 characters, ready to strcmp against or store as a string.
  • sha256(NULL) or hmac_sha256(NULL, ...) return ABS_ERROR rather than crashing.
  • Correctness is pinned to the FIPS 180-4 and RFC 4231 known-answer vectors in tests/test_crypto.c (including the empty string, a multi-block message, and a key larger than one block).
  • The same internal hash machinery powers the WebSocket handshake (ws_compute_accept) in abs_ws.c — see websockets.md.

See tests/test_crypto.c for the full test.

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