/**
 * This codes comes from RFC 2104, and was just cleaned up.
 */

#include <string.h>

#include "md5.h"
#include "hmac-md5.h"

/*
** Function: hmac_md5
*/

void
hmac_md5 (text, text_len, key, key_len, digest)
  unsigned char  *text;                /* pointer to data stream */
  int             text_len;            /* length of data stream */
  unsigned char  *key;                 /* pointer to authentication key */
  int             key_len;             /* length of authentication key */
  unsigned char  *digest;              /* caller digest to be filled in */
{
  MD5_CTX       context;
  unsigned char k_ipad[65];    /* inner padding -
                                * key XORd with ipad
                                */
  unsigned char k_opad[65];    /* outer padding -
                                * key XORd with opad
                                */
  unsigned char tk[16];
  int           i;


  /* if key is longer than 64 bytes reset it to key=MD5(key) */
  if (key_len > 64) {

    MD5_CTX      tctx;

    MD5Init (&tctx);
    MD5Update (&tctx, key, key_len);
    MD5Final (tk, &tctx);

    key     = tk;
    key_len = 16;
  }

  /*
   * the HMAC_MD5 transform looks like:
   *
   * MD5(K XOR opad, MD5(K XOR ipad, text))
   *
   * where K is an n byte key
   * ipad is the byte 0x36 repeated 64 times
   * opad is the byte 0x5c repeated 64 times
   * and text is the data being protected
   */

  /* start out by storing key in pads */
  memset (k_ipad, '\0', sizeof (k_ipad));
  memset (k_opad, '\0', sizeof (k_opad));
  memcpy (k_ipad, key, key_len);
  memcpy (k_opad, key, key_len);

  /* XOR key with ipad and opad values */
  for (i = 0; i < 64; i++) {
    k_ipad[i] ^= 0x36;
    k_opad[i] ^= 0x5c;
  }

  /*
   * perform inner MD5
   */
  MD5Init (&context);                   /* init context for 1st
                                         * pass */
  MD5Update (&context, k_ipad, 64);     /* start with inner pad */
  MD5Update (&context, text, text_len); /* then text of datagram */
  MD5Final (digest, &context);          /* finish up 1st pass */
  /*
   * perform outer MD5
   */
  MD5Init (&context);                   /* init context for 2nd
                                         * pass */
  MD5Update (&context, k_opad, 64);     /* start with outer pad */
  MD5Update (&context, digest, 16);     /* then results of 1st
                                         * hash */
  MD5Final (digest, &context);          /* finish up 2nd pass */
}