1 /* Copyright (c) 2014, Google Inc. 2 * 3 * Permission to use, copy, modify, and/or distribute this software for any 4 * purpose with or without fee is hereby granted, provided that the above 5 * copyright notice and this permission notice appear in all copies. 6 * 7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY 10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION 12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN 13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ 14 15 #include <openssl/hkdf.h> 16 17 #include <assert.h> 18 #include <string.h> 19 20 #include <openssl/err.h> 21 #include <openssl/hmac.h> 22 23 #include "../internal.h" 24 25 26 int HKDF(uint8_t *out_key, size_t out_len, const EVP_MD *digest, 27 const uint8_t *secret, size_t secret_len, const uint8_t *salt, 28 size_t salt_len, const uint8_t *info, size_t info_len) { 29 // https://tools.ietf.org/html/rfc5869#section-2 30 uint8_t prk[EVP_MAX_MD_SIZE]; 31 size_t prk_len; 32 33 if (!HKDF_extract(prk, &prk_len, digest, secret, secret_len, salt, 34 salt_len) || 35 !HKDF_expand(out_key, out_len, digest, prk, prk_len, info, info_len)) { 36 return 0; 37 } 38 39 return 1; 40 } 41 42 int HKDF_extract(uint8_t *out_key, size_t *out_len, const EVP_MD *digest, 43 const uint8_t *secret, size_t secret_len, const uint8_t *salt, 44 size_t salt_len) { 45 // https://tools.ietf.org/html/rfc5869#section-2.2 46 47 // If salt is not given, HashLength zeros are used. However, HMAC does that 48 // internally already so we can ignore it. 49 unsigned len; 50 if (HMAC(digest, salt, salt_len, secret, secret_len, out_key, &len) == NULL) { 51 OPENSSL_PUT_ERROR(HKDF, ERR_R_HMAC_LIB); 52 return 0; 53 } 54 *out_len = len; 55 assert(*out_len == EVP_MD_size(digest)); 56 return 1; 57 } 58 59 int HKDF_expand(uint8_t *out_key, size_t out_len, const EVP_MD *digest, 60 const uint8_t *prk, size_t prk_len, const uint8_t *info, 61 size_t info_len) { 62 // https://tools.ietf.org/html/rfc5869#section-2.3 63 const size_t digest_len = EVP_MD_size(digest); 64 uint8_t previous[EVP_MAX_MD_SIZE]; 65 size_t n, done = 0; 66 unsigned i; 67 int ret = 0; 68 HMAC_CTX hmac; 69 70 // Expand key material to desired length. 71 n = (out_len + digest_len - 1) / digest_len; 72 if (out_len + digest_len < out_len || n > 255) { 73 OPENSSL_PUT_ERROR(HKDF, HKDF_R_OUTPUT_TOO_LARGE); 74 return 0; 75 } 76 77 HMAC_CTX_init(&hmac); 78 if (!HMAC_Init_ex(&hmac, prk, prk_len, digest, NULL)) { 79 goto out; 80 } 81 82 for (i = 0; i < n; i++) { 83 uint8_t ctr = i + 1; 84 size_t todo; 85 86 if (i != 0 && (!HMAC_Init_ex(&hmac, NULL, 0, NULL, NULL) || 87 !HMAC_Update(&hmac, previous, digest_len))) { 88 goto out; 89 } 90 if (!HMAC_Update(&hmac, info, info_len) || 91 !HMAC_Update(&hmac, &ctr, 1) || 92 !HMAC_Final(&hmac, previous, NULL)) { 93 goto out; 94 } 95 96 todo = digest_len; 97 if (done + todo > out_len) { 98 todo = out_len - done; 99 } 100 OPENSSL_memcpy(out_key + done, previous, todo); 101 done += todo; 102 } 103 104 ret = 1; 105 106 out: 107 HMAC_CTX_cleanup(&hmac); 108 if (ret != 1) { 109 OPENSSL_PUT_ERROR(HKDF, ERR_R_HMAC_LIB); 110 } 111 return ret; 112 } 113
