1 /* $OpenBSD: hkdf.c,v 1.5 2021/08/27 16:12:33 tb Exp $ */ 2 /* Copyright (c) 2014, Google Inc. 3 * 4 * Permission to use, copy, modify, and/or distribute this software for any 5 * purpose with or without fee is hereby granted, provided that the above 6 * copyright notice and this permission notice appear in all copies. 7 * 8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY 11 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION 13 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN 14 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 15 */ 16 17 #include <openssl/hkdf.h> 18 19 #include <string.h> 20 21 #include <openssl/err.h> 22 #include <openssl/hmac.h> 23 24 /* https://tools.ietf.org/html/rfc5869#section-2 */ 25 int 26 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 { 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 return 0; 36 if (!HKDF_expand(out_key, out_len, digest, prk, prk_len, info, 37 info_len)) 38 return 0; 39 40 return 1; 41 } 42 43 /* https://tools.ietf.org/html/rfc5869#section-2.2 */ 44 int 45 HKDF_extract(uint8_t *out_key, size_t *out_len, 46 const EVP_MD *digest, const uint8_t *secret, size_t secret_len, 47 const uint8_t *salt, size_t salt_len) 48 { 49 unsigned int len; 50 51 /* 52 * If salt is not given, HashLength zeros are used. However, HMAC does 53 * that internally already so we can ignore it. 54 */ 55 if (HMAC(digest, salt, salt_len, secret, secret_len, out_key, &len) == 56 NULL) { 57 CRYPTOerror(ERR_R_CRYPTO_LIB); 58 return 0; 59 } 60 *out_len = len; 61 return 1; 62 } 63 64 /* https://tools.ietf.org/html/rfc5869#section-2.3 */ 65 int 66 HKDF_expand(uint8_t *out_key, size_t out_len, 67 const EVP_MD *digest, const uint8_t *prk, size_t prk_len, 68 const uint8_t *info, size_t info_len) 69 { 70 const size_t digest_len = EVP_MD_size(digest); 71 uint8_t previous[EVP_MAX_MD_SIZE]; 72 size_t n, done = 0; 73 unsigned int i; 74 int ret = 0; 75 HMAC_CTX hmac; 76 77 /* Expand key material to desired length. */ 78 n = (out_len + digest_len - 1) / digest_len; 79 if (out_len + digest_len < out_len || n > 255) { 80 CRYPTOerror(EVP_R_TOO_LARGE); 81 return 0; 82 } 83 84 HMAC_CTX_init(&hmac); 85 if (!HMAC_Init_ex(&hmac, prk, prk_len, digest, NULL)) 86 goto out; 87 88 for (i = 0; i < n; i++) { 89 uint8_t ctr = i + 1; 90 size_t todo; 91 92 if (i != 0 && (!HMAC_Init_ex(&hmac, NULL, 0, NULL, NULL) || 93 !HMAC_Update(&hmac, previous, digest_len))) 94 goto out; 95 96 if (!HMAC_Update(&hmac, info, info_len) || 97 !HMAC_Update(&hmac, &ctr, 1) || 98 !HMAC_Final(&hmac, previous, NULL)) 99 goto out; 100 101 todo = digest_len; 102 if (done + todo > out_len) 103 todo = out_len - done; 104 105 memcpy(out_key + done, previous, todo); 106 done += todo; 107 } 108 109 ret = 1; 110 111 out: 112 HMAC_CTX_cleanup(&hmac); 113 explicit_bzero(previous, sizeof(previous)); 114 if (ret != 1) 115 CRYPTOerror(ERR_R_CRYPTO_LIB); 116 return ret; 117 } 118