hmac.c

   1 /*
   2  * Heirloom mailx - a mail user agent derived from Berkeley Mail.
   3  *
   4  * Copyright (c) 2000-2004 Gunnar Ritter, Freiburg i. Br., Germany.
   5  */
   6 /*
   7  * Derived from:
   8
   9 Network Working Group                                       H. Krawczyk
  10 Request for Comments: 2104                                          IBM
  11 Category: Informational                                      M. Bellare
  12                                                                    UCSD
  13                                                              R. Canetti
  14                                                                     IBM
  15                                                           February 1997
  16
  17
  18              HMAC: Keyed-Hashing for Message Authentication
  19
  20 Status of This Memo
  21
  22    This memo provides information for the Internet community.  This memo
  23    does not specify an Internet standard of any kind.  Distribution of
  24    this memo is unlimited.
  25
  26 Appendix -- Sample Code
  27
  28    For the sake of illustration we provide the following sample code for
  29    the implementation of HMAC-MD5 as well as some corresponding test
  30    vectors (the code is based on MD5 code as described in [MD5]).
  31 */
  32
  33 /*      Sccsid @(#)hmac.c       1.8 (gritter) 3/4/06    */
  34
  35 #include "rcv.h"
  36 #include "md5.h"
  37
  38 /*
  39 ** Function: hmac_md5
  40 */
  41
  42 void
  43 hmac_md5 (
  44     unsigned char *text,                /* pointer to data stream */
  45     int text_len,       /* length of data stream */
  46     unsigned char *key,         /* pointer to authentication key */
  47     int key_len,        /* length of authentication key */
  48     void *digest        /* caller digest to be filled in */
  49 )
  50
  51 {
  52         MD5_CTX context;
  53         unsigned char k_ipad[65];    /* inner padding -
  54                                       * key XORd with ipad
  55                                       */
  56         unsigned char k_opad[65];    /* outer padding -
  57                                       * key XORd with opad
  58                                       */
  59         unsigned char tk[16];
  60         int i;
  61         /* if key is longer than 64 bytes reset it to key=MD5(key) */
  62         if (key_len > 64) {
  63
  64                 MD5_CTX      tctx;
  65
  66                 MD5Init(&tctx);
  67                 MD5Update(&tctx, key, key_len);
  68                 MD5Final(tk, &tctx);
  69
  70                 key = tk;
  71                 key_len = 16;
  72         }
  73
  74         /*
  75          * the HMAC_MD5 transform looks like:
  76          *
  77          * MD5(K XOR opad, MD5(K XOR ipad, text))
  78          *
  79          * where K is an n byte key
  80          * ipad is the byte 0x36 repeated 64 times
  81          * opad is the byte 0x5c repeated 64 times
  82          * and text is the data being protected
  83          */
  84
  85         /* start out by storing key in pads */
  86         memset(k_ipad, 0, sizeof k_ipad);
  87         memset(k_opad, 0, sizeof k_opad);
  88         memcpy(k_ipad, key, key_len);
  89         memcpy(k_opad, key, key_len);
  90
  91         /* XOR key with ipad and opad values */
  92         for (i=0; i<64; i++) {
  93                 k_ipad[i] ^= 0x36;
  94                 k_opad[i] ^= 0x5c;
  95         }
  96         /*
  97          * perform inner MD5
  98          */
  99         MD5Init(&context);                   /* init context for 1st
 100                                               * pass */
 101         MD5Update(&context, k_ipad, 64);             /* start with inner pad */
 102         MD5Update(&context, text, text_len); /* then text of datagram */
 103         MD5Final(digest, &context);          /* finish up 1st pass */
 104         /*
 105          * perform outer MD5
 106          */
 107         MD5Init(&context);                   /* init context for 2nd
 108                                               * pass */
 109         MD5Update(&context, k_opad, 64);     /* start with outer pad */
 110         MD5Update(&context, digest, 16);     /* then results of 1st
 111                                               * hash */
 112         MD5Final(digest, &context);          /* finish up 2nd pass */
 113 }