src/ccchmac.c

   1 /*
   2
   3 ccchmac.c -- compatibility implemenation of CCHmac functions for MD5
   4 Copyright (c) 2014 Kyle J. McKay.  All rights reserved.
   5
   6 This program is free software; you can redistribute it and/or
   7 modify it under the terms of the GNU General Public License
   8 as published by the Free Software Foundation; either version 2
   9 of the License, or (at your option) any later version.
  10
  11 This program is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with this program; if not, write to the Free Software
  18 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  19
  20 */
  21
  22 #include <CommonCrypto/CommonDigest.h>
  23 #include <string.h>
  24
  25 #define kCCHmacAlgMD5 1
  26
  27 typedef struct {
  28   CC_MD5_CTX md5ctx;
  29   unsigned char keydata[CC_MD5_BLOCK_BYTES];
  30 } CCHmacContext;
  31
  32 /*
  33  * RFC 2104 defines the HMAC computation
  34  * We only support H = MD5 (B=CC_MD5_BLOCK_BYTES)
  35  */
  36
  37 extern void die(const char *err, ...);
  38
  39 void cCCHmacInit(CCHmacContext *ctx, int alg, const void *k, size_t kl)
  40 {
  41   size_t i;
  42
  43   if (alg != kCCHmacAlgMD5)
  44     die("cCCHmacInit requires kCCHmacAlgMD5");
  45
  46   /* 1. Get CC_MD5_BLOCK_BYTES byte key */
  47   if (kl > CC_MD5_BLOCK_BYTES)
  48     kl = CC_MD5_BLOCK_BYTES;
  49   memcpy(ctx->keydata, k, kl);
  50   if (kl < CC_MD5_BLOCK_BYTES)
  51     memset(&ctx->keydata[kl], 0, CC_MD5_BLOCK_BYTES - kl);
  52
  53   /* 2. XOR step 1 key with 0x36 */
  54   for (i=0; i<CC_MD5_BLOCK_BYTES; ++i)
  55     ctx->keydata[i] ^= 0x36;
  56
  57   /* 3. Append text to the result of step 2 */
  58   /* 4. Compute MD5 of result of step 3 */
  59   CC_MD5_Init(&ctx->md5ctx);
  60   CC_MD5_Update(&ctx->md5ctx, ctx->keydata, CC_MD5_BLOCK_BYTES);
  61 }
  62
  63 void cCCHmacUpdate(CCHmacContext *ctx, const void *d, size_t dl)
  64 {
  65   /* 3. Append text to the result of step 2 */
  66   /* 4. Compute MD5 of result of step 3 */
  67   CC_MD5_Update(&ctx->md5ctx, d, (CC_LONG)dl);
  68 }
  69
  70 void cCCHmacFinal(CCHmacContext *ctx, void *m)
  71 {
  72   size_t i;
  73   unsigned char md5[CC_MD5_DIGEST_LENGTH];
  74
  75   /* 4. Compute MD5 of result of step 3 */
  76   CC_MD5_Final(md5, &ctx->md5ctx);
  77
  78   /* 5. XOR step 1 key with 0x5c */
  79   for (i=0; i<CC_MD5_BLOCK_BYTES; ++i)
  80     ctx->keydata[i] ^= (0x36 ^ 0x5c);
  81
  82   /* 6. Append MD5 result from step 4 to result of step 5 */
  83   /* 7. Compute MD5 of result of step 6 and output the result */
  84   CC_MD5_Init(&ctx->md5ctx);
  85   CC_MD5_Update(&ctx->md5ctx, ctx->keydata, CC_MD5_BLOCK_BYTES);
  86   CC_MD5_Update(&ctx->md5ctx, md5, CC_MD5_DIGEST_LENGTH);
  87   CC_MD5_Final(m, &ctx->md5ctx);
  88 }