lib/hmac-sha256.c

   1 /* hmac-sha256.c -- hashed message authentication codes
   2    Copyright (C) 2005-2006, 2009-2017 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, see <http://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Simon Josefsson.  */
  18
  19 #include <config.h>
  20
  21 #include "hmac.h"
  22
  23 #include "memxor.h"
  24 #include "sha256.h"
  25
  26 #include <string.h>
  27
  28 #define IPAD 0x36
  29 #define OPAD 0x5c
  30
  31 int
  32 hmac_sha256 (const void *key, size_t keylen,
  33              const void *in, size_t inlen, void *resbuf)
  34 {
  35   struct sha256_ctx inner;
  36   struct sha256_ctx outer;
  37   char optkeybuf[32];
  38   char block[64];
  39   char innerhash[32];
  40
  41   /* Reduce the key's size, so that it becomes <= 64 bytes large.  */
  42
  43   if (keylen > 64)
  44     {
  45       struct sha256_ctx keyhash;
  46
  47       sha256_init_ctx (&keyhash);
  48       sha256_process_bytes (key, keylen, &keyhash);
  49       sha256_finish_ctx (&keyhash, optkeybuf);
  50
  51       key = optkeybuf;
  52       keylen = 32;
  53     }
  54
  55   /* Compute INNERHASH from KEY and IN.  */
  56
  57   sha256_init_ctx (&inner);
  58
  59   memset (block, IPAD, sizeof (block));
  60   memxor (block, key, keylen);
  61
  62   sha256_process_block (block, 64, &inner);
  63   sha256_process_bytes (in, inlen, &inner);
  64
  65   sha256_finish_ctx (&inner, innerhash);
  66
  67   /* Compute result from KEY and INNERHASH.  */
  68
  69   sha256_init_ctx (&outer);
  70
  71   memset (block, OPAD, sizeof (block));
  72   memxor (block, key, keylen);
  73
  74   sha256_process_block (block, 64, &outer);
  75   sha256_process_bytes (innerhash, 32, &outer);
  76
  77   sha256_finish_ctx (&outer, resbuf);
  78
  79   return 0;
  80 }