1 /* 2 * SHA256-based PRF (IEEE 802.11r) 3 * Copyright (c) 2003-2016, 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 #include "crypto.h" 14 15 16 /** 17 * sha256_prf - SHA256-based Pseudo-Random Function (IEEE 802.11r, 8.5.1.5.2) 18 * @key: Key for PRF 19 * @key_len: Length of the key in bytes 20 * @label: A unique label for each purpose of the PRF 21 * @data: Extra data to bind into the key 22 * @data_len: Length of the data 23 * @buf: Buffer for the generated pseudo-random key 24 * @buf_len: 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. 29 */ 30 int sha256_prf(const u8 *key, size_t key_len, const char *label, 31 const u8 *data, size_t data_len, u8 *buf, size_t buf_len) 32 { 33 return sha256_prf_bits(key, key_len, label, data, data_len, buf, 34 buf_len * 8); 35 } 36 37 38 /** 39 * sha256_prf_bits - IEEE Std 802.11-2012, 11.6.1.7.2 Key derivation function 40 * @key: Key for KDF 41 * @key_len: Length of the key in bytes 42 * @label: A unique label for each purpose of the PRF 43 * @data: Extra data to bind into the key 44 * @data_len: Length of the data 45 * @buf: Buffer for the generated pseudo-random key 46 * @buf_len: Number of bits of key to generate 47 * Returns: 0 on success, -1 on failure 48 * 49 * This function is used to derive new, cryptographically separate keys from a 50 * given key. If the requested buf_len is not divisible by eight, the least 51 * significant 1-7 bits of the last octet in the output are not part of the 52 * requested output. 53 */ 54 int sha256_prf_bits(const u8 *key, size_t key_len, const char *label, 55 const u8 *data, size_t data_len, u8 *buf, 56 size_t buf_len_bits) 57 { 58 u16 counter = 1; 59 size_t pos, plen; 60 u8 hash[SHA256_MAC_LEN]; 61 const u8 *addr[4]; 62 size_t len[4]; 63 u8 counter_le[2], length_le[2]; 64 size_t buf_len = (buf_len_bits + 7) / 8; 65 66 addr[0] = counter_le; 67 len[0] = 2; 68 addr[1] = (u8 *) label; 69 len[1] = os_strlen(label); 70 addr[2] = data; 71 len[2] = data_len; 72 addr[3] = length_le; 73 len[3] = sizeof(length_le); 74 75 WPA_PUT_LE16(length_le, buf_len_bits); 76 pos = 0; 77 while (pos < buf_len) { 78 plen = buf_len - pos; 79 WPA_PUT_LE16(counter_le, counter); 80 if (plen >= SHA256_MAC_LEN) { 81 if (hmac_sha256_vector(key, key_len, 4, addr, len, 82 &buf[pos]) < 0) 83 return -1; 84 pos += SHA256_MAC_LEN; 85 } else { 86 if (hmac_sha256_vector(key, key_len, 4, addr, len, 87 hash) < 0) 88 return -1; 89 os_memcpy(&buf[pos], hash, plen); 90 pos += plen; 91 break; 92 } 93 counter++; 94 } 95 96 /* 97 * Mask out unused bits in the last octet if it does not use all the 98 * bits. 99 */ 100 if (buf_len_bits % 8) { 101 u8 mask = 0xff << (8 - buf_len_bits % 8); 102 buf[pos - 1] &= mask; 103 } 104 105 os_memset(hash, 0, sizeof(hash)); 106 107 return 0; 108 } 109
