hmac_sha1.c

/**
 * @file hmac_sha1.c  Implements HMAC-SHA1 as of RFC 2202
 *
 * Copyright (C) 2010 Creytiv.com
 */
#include <string.h>
#include <re_types.h>
#ifdef USE_OPENSSL
#include <openssl/sha.h>
#include <openssl/hmac.h>
#include <openssl/err.h>
#else
#include <re_sha.h>
#endif
#include <re_hmac.h>


/** SHA-1 Block size */
#ifndef SHA_BLOCKSIZE
#define SHA_BLOCKSIZE   64
#endif


/**
 * Function to compute the digest
 *
 * @param k   Secret key
 * @param lk  Length of the key in bytes
 * @param d   Data
 * @param ld  Length of data in bytes
 * @param out Digest output
 * @param t   Size of digest output
 */
void hmac_sha1(const uint8_t *k,  /* secret key */
	       size_t   lk,       /* length of the key in bytes */
	       const uint8_t *d,  /* data */
	       size_t   ld,       /* length of data in bytes */
	       uint8_t *out,      /* output buffer, at least "t" bytes */
	       size_t   t)
{
#ifdef USE_OPENSSL
	(void)t;

	if (!HMAC(EVP_sha1(), k, (int)lk, d, ld, out, NULL))
		ERR_clear_error();
#else
	SHA_CTX ictx, octx;
	uint8_t isha[SHA_DIGEST_LENGTH], osha[SHA_DIGEST_LENGTH];
	uint8_t key[SHA_DIGEST_LENGTH];
	uint8_t buf[SHA_BLOCKSIZE];
	size_t  i;

	if (lk > SHA_BLOCKSIZE) {
		SHA_CTX tctx;

		SHA1_Init(&tctx);
		SHA1_Update(&tctx, k, lk);
		SHA1_Final(key, &tctx);

		k = key;
		lk = SHA_DIGEST_LENGTH;
	}

	/**** Inner Digest ****/

	SHA1_Init(&ictx);

	/* Pad the key for inner digest */
	for (i = 0 ; i < lk ; ++i)
		buf[i] = k[i] ^ 0x36;
	for (i = lk ; i < SHA_BLOCKSIZE ; ++i)
		buf[i] = 0x36;

	SHA1_Update(&ictx, buf, SHA_BLOCKSIZE);
	SHA1_Update(&ictx, d, ld);

	SHA1_Final(isha, &ictx);

	/**** Outer Digest ****/

	SHA1_Init(&octx);

	/* Pad the key for outter digest */

	for (i = 0 ; i < lk ; ++i)
		buf[i] = k[i] ^ 0x5c;
	for (i = lk ; i < SHA_BLOCKSIZE ; ++i)
		buf[i] = 0x5c;

	SHA1_Update(&octx, buf, SHA_BLOCKSIZE);
	SHA1_Update(&octx, isha, SHA_DIGEST_LENGTH);

	SHA1_Final(osha, &octx);

	/* truncate and print the results */
	t = t > SHA_DIGEST_LENGTH ? SHA_DIGEST_LENGTH : t;
	memcpy(out, osha, t);
#endif
}