/*
   For the sake of illustration we provide the following sample code for
   the implementation of HMAC-MD5 as well as some corresponding test
   vectors (the code is based on MD5 code as described in [MD5]).
*/

/*
** Function: hmac_md5
*/

#include <string.h>
#include "md5.h"
#include "libradius.h"

/*
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
*/

void
lrad_hmac_md5(const unsigned char *text, int text_len,
	      const unsigned char *key, int key_len,
	      unsigned char *digest)
{
        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 */
}

/*
Test Vectors (Trailing '\0' of a character string not included in test):

  key =         0x0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b
  key_len =     16 bytes
  data =        "Hi There"
  data_len =    8  bytes
  digest =      0x9294727a3638bb1c13f48ef8158bfc9d

  key =         "Jefe"
  data =        "what do ya want for nothing?"
  data_len =    28 bytes
  digest =      0x750c783e6ab0b503eaa86e310a5db738

  key =         0xAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

  key_len       16 bytes
  data =        0xDDDDDDDDDDDDDDDDDDDD...
                ..DDDDDDDDDDDDDDDDDDDD...
                ..DDDDDDDDDDDDDDDDDDDD...
                ..DDDDDDDDDDDDDDDDDDDD...
                ..DDDDDDDDDDDDDDDDDDDD
  data_len =    50 bytes
  digest =      0x56be34521d144c88dbb8c733f0e8b3f6
*/

#ifdef TESTING
/*
 *  cc -DTESTING -I ../include/ hmac.c md5.c -o hmac
 *
 *  ./hmac Jefe "what do ya want for nothing?"
 */

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
  unsigned char digest[16];
  char *key;
  int key_len;
  char *text;
  int text_len;
  int i;

  key = argv[1];
  key_len = strlen(key);

  text = argv[2];
  text_len = strlen(text);

  lrad_hmac_md5(text, text_len, key, key_len, digest);
  
  for (i = 0; i < 16; i++) {
    printf("%02x", digest[i]);
  }
  printf("\n");
  
  exit(0);
  return 0;
}

#endif
