hmac.c

   1 /*
   2  * S-nail - a mail user agent derived from Berkeley Mail.
   3  *
   4  * Copyright (c) 2000-2004 Gunnar Ritter, Freiburg i. Br., Germany.
   5  * Copyright (c) 2012 Steffen "Daode" Nurpmeso.
   6  */
   7 /*
   8  * Derived from:
   9
  10 Network Working Group                                       H. Krawczyk
  11 Request for Comments: 2104                                          IBM
  12 Category: Informational                                      M. Bellare
  13                                                                    UCSD
  14                                                              R. Canetti
  15                                                                     IBM
  16                                                           February 1997
  17
  18
  19              HMAC: Keyed-Hashing for Message Authentication
  20
  21 Status of This Memo
  22
  23    This memo provides information for the Internet community.  This memo
  24    does not specify an Internet standard of any kind.  Distribution of
  25    this memo is unlimited.
  26
  27 Appendix -- Sample Code
  28
  29    For the sake of illustration we provide the following sample code for
  30    the implementation of HMAC-MD5 as well as some corresponding test
  31    vectors (the code is based on MD5 code as described in [MD5]).
  32 */
  33
  34 #include "rcv.h"
  35 #include "md5.h"
  36
  37 #ifndef USE_MD5
  38 typedef int avoid_empty_file_compiler_warning;
  39 #else
  40
  41 /*
  42 ** Function: hmac_md5
  43 */
  44
  45 void
  46 hmac_md5 (
  47     unsigned char *text,                /* pointer to data stream */
  48     int text_len,       /* length of data stream */
  49     unsigned char *key,         /* pointer to authentication key */
  50     int key_len,        /* length of authentication key */
  51     void *digest        /* caller digest to be filled in */
  52 )
  53
  54 {
  55         MD5_CTX context;
  56         unsigned char k_ipad[65];    /* inner padding -
  57                                       * key XORd with ipad
  58                                       */
  59         unsigned char k_opad[65];    /* outer padding -
  60                                       * key XORd with opad
  61                                       */
  62         unsigned char tk[16];
  63         int i;
  64         /* if key is longer than 64 bytes reset it to key=MD5(key) */
  65         if (key_len > 64) {
  66
  67                 MD5_CTX      tctx;
  68
  69                 MD5Init(&tctx);
  70                 MD5Update(&tctx, key, key_len);
  71                 MD5Final(tk, &tctx);
  72
  73                 key = tk;
  74                 key_len = 16;
  75         }
  76
  77         /*
  78          * the HMAC_MD5 transform looks like:
  79          *
  80          * MD5(K XOR opad, MD5(K XOR ipad, text))
  81          *
  82          * where K is an n byte key
  83          * ipad is the byte 0x36 repeated 64 times
  84          * opad is the byte 0x5c repeated 64 times
  85          * and text is the data being protected
  86          */
  87
  88         /* start out by storing key in pads */
  89         memset(k_ipad, 0, sizeof k_ipad);
  90         memset(k_opad, 0, sizeof k_opad);
  91         memcpy(k_ipad, key, key_len);
  92         memcpy(k_opad, key, key_len);
  93
  94         /* XOR key with ipad and opad values */
  95         for (i=0; i<64; i++) {
  96                 k_ipad[i] ^= 0x36;
  97                 k_opad[i] ^= 0x5c;
  98         }
  99         /*
 100          * perform inner MD5
 101          */
 102         MD5Init(&context);                   /* init context for 1st
 103                                               * pass */
 104         MD5Update(&context, k_ipad, 64);             /* start with inner pad */
 105         MD5Update(&context, text, text_len); /* then text of datagram */
 106         MD5Final(digest, &context);          /* finish up 1st pass */
 107         /*
 108          * perform outer MD5
 109          */
 110         MD5Init(&context);                   /* init context for 2nd
 111                                               * pass */
 112         MD5Update(&context, k_opad, 64);     /* start with outer pad */
 113         MD5Update(&context, digest, 16);     /* then results of 1st
 114                                               * hash */
 115         MD5Final(digest, &context);          /* finish up 2nd pass */
 116 }
 117 #endif /* USE_MD5 */