/*
** Function: hmac_md5
*/

#include <string.h>
#include "md5.h"
#include "hmac_md5.h"

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

		MD5_Init(&tctx);
		MD5_Update(&tctx, key, key_len);
		MD5_Final(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 */
	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_Init(&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_Final(digest, &context);  /* finish up 1st pass */
	/*
	 * perform outer MD5
	 */
	MD5_Init(&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_Final(digest, &context); /* finish up 2nd pass */
}