src/crypto/sha1-tlsprf.c

/*
 * TLS PRF (SHA1 + MD5)
 * Copyright (c) 2003-2005, Jouni Malinen <j@w1.fi>
 *
 * This software may be distributed under the terms of the BSD license.
 * See README for more details.
 */

#include "includes.h"

#include "common.h"
#include "sha1.h"
#include "md5.h"


/**
 * tls_prf_sha1_md5 - Pseudo-Random Function for TLS (TLS-PRF, RFC 2246)
 * @secret: Key for PRF
 * @secret_len: Length of the key in bytes
 * @label: A unique label for each purpose of the PRF
 * @seed: Seed value to bind into the key
 * @seed_len: Length of the seed
 * @out: Buffer for the generated pseudo-random key
 * @outlen: Number of bytes of key to generate
 * Returns: 0 on success, -1 on failure.
 *
 * This function is used to derive new, cryptographically separate keys from a
 * given key in TLS. This PRF is defined in RFC 2246, Chapter 5.
 */
int tls_prf_sha1_md5(const u8 *secret, size_t secret_len, const char *label,
		     const u8 *seed, size_t seed_len, u8 *out, size_t outlen)
{
	size_t L_S1, L_S2, i;
	const u8 *S1, *S2;
	u8 A_MD5[MD5_MAC_LEN], A_SHA1[SHA1_MAC_LEN];
	u8 P_MD5[MD5_MAC_LEN], P_SHA1[SHA1_MAC_LEN];
	int MD5_pos, SHA1_pos;
	const u8 *MD5_addr[3];
	size_t MD5_len[3];
	const unsigned char *SHA1_addr[3];
	size_t SHA1_len[3];

	if (secret_len & 1)
		return -1;

	MD5_addr[0] = A_MD5;
	MD5_len[0] = MD5_MAC_LEN;
	MD5_addr[1] = (unsigned char *) label;
	MD5_len[1] = os_strlen(label);
	MD5_addr[2] = seed;
	MD5_len[2] = seed_len;

	SHA1_addr[0] = A_SHA1;
	SHA1_len[0] = SHA1_MAC_LEN;
	SHA1_addr[1] = (unsigned char *) label;
	SHA1_len[1] = os_strlen(label);
	SHA1_addr[2] = seed;
	SHA1_len[2] = seed_len;

	/* RFC 2246, Chapter 5
	 * A(0) = seed, A(i) = HMAC(secret, A(i-1))
	 * P_hash = HMAC(secret, A(1) + seed) + HMAC(secret, A(2) + seed) + ..
	 * PRF = P_MD5(S1, label + seed) XOR P_SHA-1(S2, label + seed)
	 */

	L_S1 = L_S2 = (secret_len + 1) / 2;
	S1 = secret;
	S2 = secret + L_S1;
	if (secret_len & 1) {
		/* The last byte of S1 will be shared with S2 */
		S2--;
	}

	hmac_md5_vector(S1, L_S1, 2, &MD5_addr[1], &MD5_len[1], A_MD5);
	hmac_sha1_vector(S2, L_S2, 2, &SHA1_addr[1], &SHA1_len[1], A_SHA1);

	MD5_pos = MD5_MAC_LEN;
	SHA1_pos = SHA1_MAC_LEN;
	for (i = 0; i < outlen; i++) {
		if (MD5_pos == MD5_MAC_LEN) {
			hmac_md5_vector(S1, L_S1, 3, MD5_addr, MD5_len, P_MD5);
			MD5_pos = 0;
			hmac_md5(S1, L_S1, A_MD5, MD5_MAC_LEN, A_MD5);
		}
		if (SHA1_pos == SHA1_MAC_LEN) {
			hmac_sha1_vector(S2, L_S2, 3, SHA1_addr, SHA1_len,
					 P_SHA1);
			SHA1_pos = 0;
			hmac_sha1(S2, L_S2, A_SHA1, SHA1_MAC_LEN, A_SHA1);
		}

		out[i] = P_MD5[MD5_pos] ^ P_SHA1[SHA1_pos];

		MD5_pos++;
		SHA1_pos++;
	}

	return 0;
}