1 /* $OpenBSD: hkdf.c,v 1.4 2019/11/21 20:02:20 tim 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 <assert.h> 20 #include <string.h> 21 22 #include <openssl/err.h> 23 #include <openssl/hmac.h> 24 25 /* https://tools.ietf.org/html/rfc5869#section-2 */ 26 int 27 HKDF(uint8_t *out_key, size_t out_len, const EVP_MD *digest, 28 const uint8_t *secret, size_t secret_len, const uint8_t *salt, 29 size_t salt_len, const uint8_t *info, size_t info_len) 30 { 31 uint8_t prk[EVP_MAX_MD_SIZE]; 32 size_t prk_len; 33 34 if (!HKDF_extract(prk, &prk_len, digest, secret, secret_len, salt, 35 salt_len)) 36 return 0; 37 if (!HKDF_expand(out_key, out_len, digest, prk, prk_len, info, 38 info_len)) 39 return 0; 40 41 return 1; 42 } 43 44 /* https://tools.ietf.org/html/rfc5869#section-2.2 */ 45 int 46 HKDF_extract(uint8_t *out_key, size_t *out_len, 47 const EVP_MD *digest, const uint8_t *secret, size_t secret_len, 48 const uint8_t *salt, size_t salt_len) 49 { 50 unsigned int len; 51 52 /* 53 * If salt is not given, HashLength zeros are used. However, HMAC does 54 * that internally already so we can ignore it. 55 */ 56 if (HMAC(digest, salt, salt_len, secret, secret_len, out_key, &len) == 57 NULL) { 58 CRYPTOerror(ERR_R_CRYPTO_LIB); 59 return 0; 60 } 61 *out_len = len; 62 return 1; 63 } 64 65 /* https://tools.ietf.org/html/rfc5869#section-2.3 */ 66 int 67 HKDF_expand(uint8_t *out_key, size_t out_len, 68 const EVP_MD *digest, const uint8_t *prk, size_t prk_len, 69 const uint8_t *info, size_t info_len) 70 { 71 const size_t digest_len = EVP_MD_size(digest); 72 uint8_t previous[EVP_MAX_MD_SIZE]; 73 size_t n, done = 0; 74 unsigned int i; 75 int ret = 0; 76 HMAC_CTX hmac; 77 78 /* Expand key material to desired length. */ 79 n = (out_len + digest_len - 1) / digest_len; 80 if (out_len + digest_len < out_len || n > 255) { 81 CRYPTOerror(EVP_R_TOO_LARGE); 82 return 0; 83 } 84 85 HMAC_CTX_init(&hmac); 86 if (!HMAC_Init_ex(&hmac, prk, prk_len, digest, NULL)) 87 goto out; 88 89 for (i = 0; i < n; i++) { 90 uint8_t ctr = i + 1; 91 size_t todo; 92 93 if (i != 0 && (!HMAC_Init_ex(&hmac, NULL, 0, NULL, NULL) || 94 !HMAC_Update(&hmac, previous, digest_len))) 95 goto out; 96 97 if (!HMAC_Update(&hmac, info, info_len) || 98 !HMAC_Update(&hmac, &ctr, 1) || 99 !HMAC_Final(&hmac, previous, NULL)) 100 goto out; 101 102 todo = digest_len; 103 if (done + todo > out_len) 104 todo = out_len - done; 105 106 memcpy(out_key + done, previous, todo); 107 done += todo; 108 } 109 110 ret = 1; 111 112 out: 113 HMAC_CTX_cleanup(&hmac); 114 explicit_bzero(previous, sizeof(previous)); 115 if (ret != 1) 116 CRYPTOerror(ERR_R_CRYPTO_LIB); 117 return ret; 118 } 119