Line data    Source code

       1             : /*
       2             :  * TLS PRF P_SHA256
       3             :  * Copyright (c) 2011, 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 "sha256.h"
      13             : 
      14             : 
      15             : /**
      16             :  * tls_prf_sha256 - Pseudo-Random Function for TLS v1.2 (P_SHA256, RFC 5246)
      17             :  * @secret: Key for PRF
      18             :  * @secret_len: Length of the key in bytes
      19             :  * @label: A unique label for each purpose of the PRF
      20             :  * @seed: Seed value to bind into the key
      21             :  * @seed_len: Length of the seed
      22             :  * @out: Buffer for the generated pseudo-random key
      23             :  * @outlen: Number of bytes of key to generate
      24             :  * Returns: 0 on success, -1 on failure.
      25             :  *
      26             :  * This function is used to derive new, cryptographically separate keys from a
      27             :  * given key in TLS. This PRF is defined in RFC 2246, Chapter 5.
      28             :  */
      29           0 : void tls_prf_sha256(const u8 *secret, size_t secret_len, const char *label,
      30             :                     const u8 *seed, size_t seed_len, u8 *out, size_t outlen)
      31             : {
      32             :         size_t clen;
      33             :         u8 A[SHA256_MAC_LEN];
      34             :         u8 P[SHA256_MAC_LEN];
      35             :         size_t pos;
      36             :         const unsigned char *addr[3];
      37             :         size_t len[3];
      38             : 
      39           0 :         addr[0] = A;
      40           0 :         len[0] = SHA256_MAC_LEN;
      41           0 :         addr[1] = (unsigned char *) label;
      42           0 :         len[1] = os_strlen(label);
      43           0 :         addr[2] = seed;
      44           0 :         len[2] = seed_len;
      45             : 
      46             :         /*
      47             :          * RFC 5246, Chapter 5
      48             :          * A(0) = seed, A(i) = HMAC(secret, A(i-1))
      49             :          * P_hash = HMAC(secret, A(1) + seed) + HMAC(secret, A(2) + seed) + ..
      50             :          * PRF(secret, label, seed) = P_SHA256(secret, label + seed)
      51             :          */
      52             : 
      53           0 :         hmac_sha256_vector(secret, secret_len, 2, &addr[1], &len[1], A);
      54             : 
      55           0 :         pos = 0;
      56           0 :         while (pos < outlen) {
      57           0 :                 hmac_sha256_vector(secret, secret_len, 3, addr, len, P);
      58           0 :                 hmac_sha256(secret, secret_len, A, SHA256_MAC_LEN, A);
      59             : 
      60           0 :                 clen = outlen - pos;
      61           0 :                 if (clen > SHA256_MAC_LEN)
      62           0 :                         clen = SHA256_MAC_LEN;
      63           0 :                 os_memcpy(out + pos, P, clen);
      64           0 :                 pos += clen;
      65             :         }
      66           0 : }