#include "rsa_hmac_md5.h"

/*
** Function: hmac_md5
*/

void
hmac_md5(text, text_len, key, key_len, digest)
POINTER         text;                /* pointer to data stream */
unsigned int    text_len;            /* length of data stream */
POINTER         key;                 /* pointer to authentication key */
unsigned int    key_len;             /* length of authentication key */
POINTER         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 */
}