meillo@0: /*
meillo@211: hmac_md5 -- implements RFC 2104
meillo@211: 
meillo@211: Copyright 2010, markus schnalke <meillo@marmaro.de>
meillo@211: 
meillo@211: Permission to use, copy, modify, and/or distribute this software for any
meillo@211: purpose with or without fee is hereby granted, provided that the above
meillo@211: copyright notice and this permission notice appear in all copies.
meillo@211: 
meillo@211: THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
meillo@211: WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
meillo@211: MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
meillo@211: ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
meillo@211: WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
meillo@211: ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
meillo@211: OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
meillo@211: 
meillo@211: 
meillo@211: My motivation to write this code was the lack of a nicely licensed
meillo@211: hmac_md5 function in C. I programmed it following the RFC's text.
meillo@211: Obviously this code is highly similar to the sample code of the RFC.
meillo@211: The code is tested against the test vectors of the RFC. Wikipedia's
meillo@211: HMAC page helped me to understand the algorithm better.
meillo@211: 
meillo@211: This hmac_md5 function requires an OpenSSL-compatible MD5
meillo@211: implementation. There are Public Domain MD5 implementations by Colin
meillo@211: Plumb and by Solar Designer. You probably want to use one of these.
meillo@0: */
meillo@0: 
meillo@0: #include <string.h>
meillo@0: #include "md5.h"
meillo@0: 
meillo@211: 
meillo@211: const int blocksize = 64;
meillo@211: const int hashsize = 16;
meillo@211: 
meillo@211: 
meillo@211: /*
meillo@211: The computed HMAC will be written to `digest'.
meillo@211: Ensure digest points to hashsize bytes of allocated memory.
meillo@211: */
meillo@10: void
meillo@366: hmac_md5(unsigned char *text, int textlen, unsigned char *key, int keylen, unsigned char *digest)
meillo@10: {
meillo@211: 	int i;
meillo@10: 	MD5_CTX context;
meillo@211: 	unsigned char ipad[blocksize];
meillo@211: 	unsigned char opad[blocksize];
meillo@0: 
meillo@211: 	/* too long keys are replaced by their hash value */
meillo@211: 	if (keylen > blocksize) {
meillo@211: 		MD5_Init(&context);
meillo@211: 		MD5_Update(&context, key, keylen);
meillo@211: 		MD5_Final(digest, &context);
meillo@211: 		key = digest;
meillo@211: 		keylen = hashsize;
meillo@10: 	}
meillo@0: 
meillo@211:         /* copy the key into the pads */
meillo@211: 	memset(ipad, 0, sizeof(ipad));
meillo@211: 	memcpy(ipad, key, keylen);
meillo@0: 
meillo@211: 	memset(opad, 0, sizeof(opad));
meillo@211: 	memcpy(opad, key, keylen);
meillo@0: 
meillo@211:         /* xor the pads with their ``basic'' value */
meillo@211: 	for (i=0; i<blocksize; i++) {
meillo@211: 		ipad[i] ^= 0x36;
meillo@211: 		opad[i] ^= 0x5c;
meillo@10: 	}
meillo@211: 
meillo@211: 	/* inner pass (ipad ++ message) */
meillo@211: 	MD5_Init(&context);
meillo@211: 	MD5_Update(&context, ipad, sizeof(ipad));
meillo@211: 	MD5_Update(&context, text, textlen);
meillo@211: 	MD5_Final(digest, &context);
meillo@211: 
meillo@211: 	/* outer pass (opad ++ result of inner pass) */
meillo@211: 	MD5_Init(&context);
meillo@211: 	MD5_Update(&context, opad, sizeof(opad));
meillo@211: 	MD5_Update(&context, digest, hashsize);
meillo@211: 	MD5_Final(digest, &context);
meillo@0: }