sha1-tlsprf.c revision 351611 
1/*
2 * TLS PRF (SHA1 + MD5)
3 * Copyright (c) 2003-2005, Jouni Malinen <j@w1.fi>
4 *
5 * This software may be distributed under the terms of the BSD license.
6 * See README for more details.
7 */
8
9#include "includes.h"
10
11#include "common.h"
12#include "sha1.h"
13#include "md5.h"
14
15
16/**
17 * tls_prf_sha1_md5 - Pseudo-Random Function for TLS (TLS-PRF, RFC 2246)
18 * @secret: Key for PRF
19 * @secret_len: Length of the key in bytes
20 * @label: A unique label for each purpose of the PRF
21 * @seed: Seed value to bind into the key
22 * @seed_len: Length of the seed
23 * @out: Buffer for the generated pseudo-random key
24 * @outlen: Number of bytes of key to generate
25 * Returns: 0 on success, -1 on failure.
26 *
27 * This function is used to derive new, cryptographically separate keys from a
28 * given key in TLS. This PRF is defined in RFC 2246, Chapter 5.
29 */
30int tls_prf_sha1_md5(const u8 *secret, size_t secret_len, const char *label,
31		     const u8 *seed, size_t seed_len, u8 *out, size_t outlen)
32{
33	size_t L_S1, L_S2, i;
34	const u8 *S1, *S2;
35	u8 A_MD5[MD5_MAC_LEN], A_SHA1[SHA1_MAC_LEN];
36	u8 P_MD5[MD5_MAC_LEN], P_SHA1[SHA1_MAC_LEN];
37	int MD5_pos, SHA1_pos;
38	const u8 *MD5_addr[3];
39	size_t MD5_len[3];
40	const unsigned char *SHA1_addr[3];
41	size_t SHA1_len[3];
42
43	MD5_addr[0] = A_MD5;
44	MD5_len[0] = MD5_MAC_LEN;
45	MD5_addr[1] = (unsigned char *) label;
46	MD5_len[1] = os_strlen(label);
47	MD5_addr[2] = seed;
48	MD5_len[2] = seed_len;
49
50	SHA1_addr[0] = A_SHA1;
51	SHA1_len[0] = SHA1_MAC_LEN;
52	SHA1_addr[1] = (unsigned char *) label;
53	SHA1_len[1] = os_strlen(label);
54	SHA1_addr[2] = seed;
55	SHA1_len[2] = seed_len;
56
57	/* RFC 2246, Chapter 5
58	 * A(0) = seed, A(i) = HMAC(secret, A(i-1))
59	 * P_hash = HMAC(secret, A(1) + seed) + HMAC(secret, A(2) + seed) + ..
60	 * PRF = P_MD5(S1, label + seed) XOR P_SHA-1(S2, label + seed)
61	 */
62
63	L_S1 = L_S2 = (secret_len + 1) / 2;
64	S1 = secret;
65	S2 = secret + L_S1;
66	if (secret_len & 1) {
67		/* The last byte of S1 will be shared with S2 */
68		S2--;
69	}
70
71	hmac_md5_vector(S1, L_S1, 2, &MD5_addr[1], &MD5_len[1], A_MD5);
72	hmac_sha1_vector(S2, L_S2, 2, &SHA1_addr[1], &SHA1_len[1], A_SHA1);
73
74	MD5_pos = MD5_MAC_LEN;
75	SHA1_pos = SHA1_MAC_LEN;
76	for (i = 0; i < outlen; i++) {
77		if (MD5_pos == MD5_MAC_LEN) {
78			hmac_md5_vector(S1, L_S1, 3, MD5_addr, MD5_len, P_MD5);
79			MD5_pos = 0;
80			hmac_md5(S1, L_S1, A_MD5, MD5_MAC_LEN, A_MD5);
81		}
82		if (SHA1_pos == SHA1_MAC_LEN) {
83			hmac_sha1_vector(S2, L_S2, 3, SHA1_addr, SHA1_len,
84					 P_SHA1);
85			SHA1_pos = 0;
86			hmac_sha1(S2, L_S2, A_SHA1, SHA1_MAC_LEN, A_SHA1);
87		}
88
89		out[i] = P_MD5[MD5_pos] ^ P_SHA1[SHA1_pos];
90
91		MD5_pos++;
92		SHA1_pos++;
93	}
94
95	forced_memzero(A_MD5, MD5_MAC_LEN);
96	forced_memzero(P_MD5, MD5_MAC_LEN);
97	forced_memzero(A_SHA1, SHA1_MAC_LEN);
98	forced_memzero(P_SHA1, SHA1_MAC_LEN);
99
100	return 0;
101}
102