1 /* 2 * HMAC-SHA256 KDF (RFC 5295) and HKDF-Expand(SHA256) (RFC 5869) 3 * Copyright (c) 2014-2017, 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 or %NULL to select 20 * RFC 5869 HKDF-Expand() with arbitrary seed (= info) 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 ERP. This KDF is defined in RFC 5295, Chapter 3.1.2. When used 29 * with label = NULL and seed = info, this matches HKDF-Expand() defined in 30 * RFC 5869, Chapter 2.3. 31 */ 32 int hmac_sha256_kdf(const u8 *secret, size_t secret_len, 33 const char *label, const u8 *seed, size_t seed_len, 34 u8 *out, size_t outlen) 35 { 36 u8 T[SHA256_MAC_LEN]; 37 u8 iter = 1; 38 const unsigned char *addr[4]; 39 size_t len[4]; 40 size_t pos, clen; 41 42 addr[0] = T; 43 len[0] = SHA256_MAC_LEN; 44 if (label) { 45 addr[1] = (const unsigned char *) label; 46 len[1] = os_strlen(label) + 1; 47 } else { 48 addr[1] = (const u8 *) ""; 49 len[1] = 0; 50 } 51 addr[2] = seed; 52 len[2] = seed_len; 53 addr[3] = &iter; 54 len[3] = 1; 55 56 if (hmac_sha256_vector(secret, secret_len, 3, &addr[1], &len[1], T) < 0) 57 return -1; 58 59 pos = 0; 60 for (;;) { 61 clen = outlen - pos; 62 if (clen > SHA256_MAC_LEN) 63 clen = SHA256_MAC_LEN; 64 os_memcpy(out + pos, T, clen); 65 pos += clen; 66 67 if (pos == outlen) 68 break; 69 70 if (iter == 255) { 71 os_memset(out, 0, outlen); 72 os_memset(T, 0, SHA256_MAC_LEN); 73 return -1; 74 } 75 iter++; 76 77 if (hmac_sha256_vector(secret, secret_len, 4, addr, len, T) < 0) 78 { 79 os_memset(out, 0, outlen); 80 os_memset(T, 0, SHA256_MAC_LEN); 81 return -1; 82 } 83 } 84 85 os_memset(T, 0, SHA256_MAC_LEN); 86 return 0; 87 } 88
