1 /* 2 * HKDF implementation -- RFC 5869 3 * 4 * Copyright The Mbed TLS Contributors 5 * SPDX-License-Identifier: Apache-2.0 6 * 7 * Licensed under the Apache License, Version 2.0 (the "License"); you may 8 * not use this file except in compliance with the License. 9 * You may obtain a copy of the License at 10 * 11 * http://www.apache.org/licenses/LICENSE-2.0 12 * 13 * Unless required by applicable law or agreed to in writing, software 14 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT 15 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 * See the License for the specific language governing permissions and 17 * limitations under the License. 18 */ 19 #include "common.h" 20 21 #if defined(MBEDTLS_HKDF_C) 22 23 #include <string.h> 24 #include "mbedtls/hkdf.h" 25 #include "mbedtls/platform_util.h" 26 #include "mbedtls/error.h" 27 28 int mbedtls_hkdf(const mbedtls_md_info_t *md, const unsigned char *salt, 29 size_t salt_len, const unsigned char *ikm, size_t ikm_len, 30 const unsigned char *info, size_t info_len, 31 unsigned char *okm, size_t okm_len) 32 { 33 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; 34 unsigned char prk[MBEDTLS_MD_MAX_SIZE]; 35 36 ret = mbedtls_hkdf_extract(md, salt, salt_len, ikm, ikm_len, prk); 37 38 if (ret == 0) { 39 ret = mbedtls_hkdf_expand(md, prk, mbedtls_md_get_size(md), 40 info, info_len, okm, okm_len); 41 } 42 43 mbedtls_platform_zeroize(prk, sizeof(prk)); 44 45 return ret; 46 } 47 48 int mbedtls_hkdf_extract(const mbedtls_md_info_t *md, 49 const unsigned char *salt, size_t salt_len, 50 const unsigned char *ikm, size_t ikm_len, 51 unsigned char *prk) 52 { 53 unsigned char null_salt[MBEDTLS_MD_MAX_SIZE] = { '\0' }; 54 55 if (salt == NULL) { 56 size_t hash_len; 57 58 if (salt_len != 0) { 59 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; 60 } 61 62 hash_len = mbedtls_md_get_size(md); 63 64 if (hash_len == 0) { 65 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; 66 } 67 68 salt = null_salt; 69 salt_len = hash_len; 70 } 71 72 return mbedtls_md_hmac(md, salt, salt_len, ikm, ikm_len, prk); 73 } 74 75 int mbedtls_hkdf_expand(const mbedtls_md_info_t *md, const unsigned char *prk, 76 size_t prk_len, const unsigned char *info, 77 size_t info_len, unsigned char *okm, size_t okm_len) 78 { 79 size_t hash_len; 80 size_t where = 0; 81 size_t n; 82 size_t t_len = 0; 83 size_t i; 84 int ret = 0; 85 mbedtls_md_context_t ctx; 86 unsigned char t[MBEDTLS_MD_MAX_SIZE]; 87 88 if (okm == NULL) { 89 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; 90 } 91 92 hash_len = mbedtls_md_get_size(md); 93 94 if (prk_len < hash_len || hash_len == 0) { 95 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; 96 } 97 98 if (info == NULL) { 99 info = (const unsigned char *) ""; 100 info_len = 0; 101 } 102 103 n = okm_len / hash_len; 104 105 if (okm_len % hash_len != 0) { 106 n++; 107 } 108 109 /* 110 * Per RFC 5869 Section 2.3, okm_len must not exceed 111 * 255 times the hash length 112 */ 113 if (n > 255) { 114 return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; 115 } 116 117 mbedtls_md_init(&ctx); 118 119 if ((ret = mbedtls_md_setup(&ctx, md, 1)) != 0) { 120 goto exit; 121 } 122 123 memset(t, 0, hash_len); 124 125 /* 126 * Compute T = T(1) | T(2) | T(3) | ... | T(N) 127 * Where T(N) is defined in RFC 5869 Section 2.3 128 */ 129 for (i = 1; i <= n; i++) { 130 size_t num_to_copy; 131 unsigned char c = i & 0xff; 132 133 ret = mbedtls_md_hmac_starts(&ctx, prk, prk_len); 134 if (ret != 0) { 135 goto exit; 136 } 137 138 ret = mbedtls_md_hmac_update(&ctx, t, t_len); 139 if (ret != 0) { 140 goto exit; 141 } 142 143 ret = mbedtls_md_hmac_update(&ctx, info, info_len); 144 if (ret != 0) { 145 goto exit; 146 } 147 148 /* The constant concatenated to the end of each T(n) is a single octet. 149 * */ 150 ret = mbedtls_md_hmac_update(&ctx, &c, 1); 151 if (ret != 0) { 152 goto exit; 153 } 154 155 ret = mbedtls_md_hmac_finish(&ctx, t); 156 if (ret != 0) { 157 goto exit; 158 } 159 160 num_to_copy = i != n ? hash_len : okm_len - where; 161 memcpy(okm + where, t, num_to_copy); 162 where += hash_len; 163 t_len = hash_len; 164 } 165 166 exit: 167 mbedtls_md_free(&ctx); 168 mbedtls_platform_zeroize(t, sizeof(t)); 169 170 return ret; 171 } 172 173 #endif /* MBEDTLS_HKDF_C */ 174