hmac_md5.c

#include "md5.h"

#define bzero(b,l) memset(b,0,l)
#define bcopy(s, d, l) memcpy(d, s, l)


/* Function: hmac_md5, sample code from rfc2104 */
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_context 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_context tctx;

                md5_starts(&tctx);
                md5_update(&tctx, key, key_len);
                md5_finish(&tctx, tk);

                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 */
        bzero( k_ipad, sizeof(k_ipad));
        bzero( k_opad, sizeof(k_opad));
        bcopy( key, k_ipad, key_len);
        bcopy( key, k_opad, 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 */
        md5_starts(&context);      /* init context for 1st * pass */
        md5_update(&context, k_ipad, 64);  	/* start with inner pad */
        md5_update(&context, text, text_len); 	/* then text of datagram */
        md5_finish(&context, digest);          	/* finish up 1st pass */

	  /* perform outer MD5 */
        md5_starts(&context); 			/* init context for 2nd * pass */
        md5_update(&context, k_opad, 64);     	/* start with outer pad */
        md5_update(&context, digest, 16);     	/* then results of 1st * hash */
        md5_finish(&context, digest);          	/* finish up 2nd pass */
}