1 /* 2 * HMAC-SHA256 KDF (RFC 5295) 3 * Copyright (c) 2014, Jouni Malinen <j (at) 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 * hmac_sha256_kdf - HMAC-SHA256 based KDF (RFC 5295) 17 * @secret: Key for KDF 18 * @secret_len: Length of the key in bytes 19 * @label: A unique label for each purpose of the KDF 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 ERP. This KDF is defined in RFC 5295, Chapter 3.1.2. 28 */ 29 int hmac_sha256_kdf(const u8 *secret, size_t secret_len, 30 const char *label, const u8 *seed, size_t seed_len, 31 u8 *out, size_t outlen) 32 { 33 u8 T[SHA256_MAC_LEN]; 34 u8 iter = 1; 35 const unsigned char *addr[4]; 36 size_t len[4]; 37 size_t pos, clen; 38 39 addr[0] = T; 40 len[0] = SHA256_MAC_LEN; 41 addr[1] = (const unsigned char *) label; 42 len[1] = os_strlen(label) + 1; 43 addr[2] = seed; 44 len[2] = seed_len; 45 addr[3] = &iter; 46 len[3] = 1; 47 48 if (hmac_sha256_vector(secret, secret_len, 3, &addr[1], &len[1], T) < 0) 49 return -1; 50 51 pos = 0; 52 for (;;) { 53 clen = outlen - pos; 54 if (clen > SHA256_MAC_LEN) 55 clen = SHA256_MAC_LEN; 56 os_memcpy(out + pos, T, clen); 57 pos += clen; 58 59 if (pos == outlen) 60 break; 61 62 if (iter == 255) { 63 os_memset(out, 0, outlen); 64 os_memset(T, 0, SHA256_MAC_LEN); 65 return -1; 66 } 67 iter++; 68 69 if (hmac_sha256_vector(secret, secret_len, 4, addr, len, T) < 0) 70 { 71 os_memset(out, 0, outlen); 72 os_memset(T, 0, SHA256_MAC_LEN); 73 return -1; 74 } 75 } 76 77 os_memset(T, 0, SHA256_MAC_LEN); 78 return 0; 79 } 80
