lib/hmac.c

/* hmac.c -- hashed message authentication codes
   Copyright (C) 2005-2006, 2009-2026 Free Software Foundation, Inc.

   This file is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation; either version 2.1 of the
   License, or (at your option) any later version.

   This file is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <string.h>

#include "memxor.h"

#define IPAD 0x36
#define OPAD 0x5c

/* Concatenate two preprocessor tokens.  */
#define _GLHMAC_CONCAT_(prefix, suffix) prefix##suffix
#define _GLHMAC_CONCAT(prefix, suffix) _GLHMAC_CONCAT_ (prefix, suffix)

#if GL_HMAC_NAME == 5
# define HMAC_ALG md5
#else
# define HMAC_ALG _GLHMAC_CONCAT (sha, GL_HMAC_NAME)
#endif

#define GL_HMAC_CTX _GLHMAC_CONCAT (HMAC_ALG, _ctx)
#define GL_HMAC_FN _GLHMAC_CONCAT (hmac_, HMAC_ALG)
#define GL_HMAC_FN_INIT _GLHMAC_CONCAT (HMAC_ALG, _init_ctx)
#define GL_HMAC_FN_BLOC _GLHMAC_CONCAT (HMAC_ALG, _process_block)
#define GL_HMAC_FN_PROC _GLHMAC_CONCAT (HMAC_ALG, _process_bytes)
#define GL_HMAC_FN_FINI _GLHMAC_CONCAT (HMAC_ALG, _finish_ctx)

static void
hmac_hash (const void *key, size_t keylen,
           const void *in, size_t inlen,
           int pad, void *resbuf)
{
  char block[GL_HMAC_BLOCKSIZE];

  memset (block, pad, sizeof block);
  memxor (block, key, keylen);

  struct GL_HMAC_CTX hmac_ctx;
  GL_HMAC_FN_INIT (&hmac_ctx);
  GL_HMAC_FN_BLOC (block, sizeof block, &hmac_ctx);
  GL_HMAC_FN_PROC (in, inlen, &hmac_ctx);
  GL_HMAC_FN_FINI (&hmac_ctx, resbuf);
}

int
GL_HMAC_FN (const void *key, size_t keylen,
            const void *in, size_t inlen, void *resbuf)
{
  char optkeybuf[GL_HMAC_HASHSIZE];

  /* Ensure key size is <= block size.  */
  if (keylen > GL_HMAC_BLOCKSIZE)
    {
      struct GL_HMAC_CTX keyhash;

      GL_HMAC_FN_INIT (&keyhash);
      GL_HMAC_FN_PROC (key, keylen, &keyhash);
      GL_HMAC_FN_FINI (&keyhash, optkeybuf);

      key = optkeybuf;
      /* zero padding of the key to the block size
         is implicit in the memxor.  */
      keylen = sizeof optkeybuf;
    }

  /* Compute INNERHASH from KEY and IN.  */
  char innerhash[GL_HMAC_HASHSIZE];
  hmac_hash (key, keylen, in, inlen, IPAD, innerhash);

  /* Compute result from KEY and INNERHASH.  */
  hmac_hash (key, keylen, innerhash, sizeof innerhash, OPAD, resbuf);

  return 0;
}