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+/*
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+ * TLS PRF (SHA1 + MD5)
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+ * Copyright (c) 2003-2005, Jouni Malinen <j@w1.fi>
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+ *
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+ * This program is free software; you can redistribute it and/or modify
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+ * it under the terms of the GNU General Public License version 2 as
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+ * published by the Free Software Foundation.
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+ *
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+ * Alternatively, this software may be distributed under the terms of BSD
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+ * license.
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+ *
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+ * See README and COPYING for more details.
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+ */
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+
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+#include "includes.h"
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+
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+#include "common.h"
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+#include "sha1.h"
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+#include "md5.h"
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+#include "crypto.h"
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+
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+
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+/**
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+ * tls_prf - Pseudo-Random Function for TLS (TLS-PRF, RFC 2246)
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+ * @secret: Key for PRF
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+ * @secret_len: Length of the key in bytes
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+ * @label: A unique label for each purpose of the PRF
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+ * @seed: Seed value to bind into the key
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+ * @seed_len: Length of the seed
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+ * @out: Buffer for the generated pseudo-random key
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+ * @outlen: Number of bytes of key to generate
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+ * Returns: 0 on success, -1 on failure.
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+ *
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+ * This function is used to derive new, cryptographically separate keys from a
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+ * given key in TLS. This PRF is defined in RFC 2246, Chapter 5.
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+ */
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+int tls_prf(const u8 *secret, size_t secret_len, const char *label,
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+ const u8 *seed, size_t seed_len, u8 *out, size_t outlen)
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+{
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+ size_t L_S1, L_S2, i;
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+ const u8 *S1, *S2;
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+ u8 A_MD5[MD5_MAC_LEN], A_SHA1[SHA1_MAC_LEN];
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+ u8 P_MD5[MD5_MAC_LEN], P_SHA1[SHA1_MAC_LEN];
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+ int MD5_pos, SHA1_pos;
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+ const u8 *MD5_addr[3];
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+ size_t MD5_len[3];
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+ const unsigned char *SHA1_addr[3];
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+ size_t SHA1_len[3];
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+
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+ if (secret_len & 1)
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+ return -1;
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+
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+ MD5_addr[0] = A_MD5;
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+ MD5_len[0] = MD5_MAC_LEN;
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+ MD5_addr[1] = (unsigned char *) label;
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+ MD5_len[1] = os_strlen(label);
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+ MD5_addr[2] = seed;
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+ MD5_len[2] = seed_len;
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+
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+ SHA1_addr[0] = A_SHA1;
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+ SHA1_len[0] = SHA1_MAC_LEN;
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+ SHA1_addr[1] = (unsigned char *) label;
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+ SHA1_len[1] = os_strlen(label);
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+ SHA1_addr[2] = seed;
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+ SHA1_len[2] = seed_len;
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+
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+ /* RFC 2246, Chapter 5
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+ * A(0) = seed, A(i) = HMAC(secret, A(i-1))
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+ * P_hash = HMAC(secret, A(1) + seed) + HMAC(secret, A(2) + seed) + ..
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+ * PRF = P_MD5(S1, label + seed) XOR P_SHA-1(S2, label + seed)
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+ */
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+
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+ L_S1 = L_S2 = (secret_len + 1) / 2;
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+ S1 = secret;
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+ S2 = secret + L_S1;
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+ if (secret_len & 1) {
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+ /* The last byte of S1 will be shared with S2 */
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+ S2--;
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+ }
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+
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+ hmac_md5_vector(S1, L_S1, 2, &MD5_addr[1], &MD5_len[1], A_MD5);
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+ hmac_sha1_vector(S2, L_S2, 2, &SHA1_addr[1], &SHA1_len[1], A_SHA1);
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+
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+ MD5_pos = MD5_MAC_LEN;
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+ SHA1_pos = SHA1_MAC_LEN;
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+ for (i = 0; i < outlen; i++) {
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+ if (MD5_pos == MD5_MAC_LEN) {
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+ hmac_md5_vector(S1, L_S1, 3, MD5_addr, MD5_len, P_MD5);
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+ MD5_pos = 0;
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+ hmac_md5(S1, L_S1, A_MD5, MD5_MAC_LEN, A_MD5);
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+ }
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+ if (SHA1_pos == SHA1_MAC_LEN) {
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+ hmac_sha1_vector(S2, L_S2, 3, SHA1_addr, SHA1_len,
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+ P_SHA1);
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+ SHA1_pos = 0;
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+ hmac_sha1(S2, L_S2, A_SHA1, SHA1_MAC_LEN, A_SHA1);
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+ }
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+
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+ out[i] = P_MD5[MD5_pos] ^ P_SHA1[SHA1_pos];
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+
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+ MD5_pos++;
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+ SHA1_pos++;
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+ }
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+
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+ return 0;
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+}
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Johannes Berg