| /* Copyright (c) 2014, Google Inc. |
| * |
| * Permission to use, copy, modify, and/or distribute this software for any |
| * purpose with or without fee is hereby granted, provided that the above |
| * copyright notice and this permission notice appear in all copies. |
| * |
| * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES |
| * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF |
| * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY |
| * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES |
| * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION |
| * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN |
| * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ |
| |
| #include <openssl/hkdf.h> |
| |
| #include <assert.h> |
| #include <string.h> |
| |
| #include <openssl/err.h> |
| #include <openssl/hmac.h> |
| |
| |
| int HKDF(uint8_t *out_key, size_t out_len, |
| const EVP_MD *digest, |
| const uint8_t *secret, size_t secret_len, |
| const uint8_t *salt, size_t salt_len, |
| const uint8_t *info, size_t info_len) { |
| /* https://tools.ietf.org/html/rfc5869#section-2.2 */ |
| const size_t digest_len = EVP_MD_size(digest); |
| uint8_t prk[EVP_MAX_MD_SIZE], previous[EVP_MAX_MD_SIZE]; |
| size_t n, done = 0; |
| unsigned i, prk_len; |
| int ret = 0; |
| HMAC_CTX hmac; |
| |
| /* If salt is not given, HashLength zeros are used. However, HMAC does that |
| * internally already so we can ignore it.*/ |
| |
| /* Expand key material to desired length. */ |
| n = (out_len + digest_len - 1) / digest_len; |
| if (out_len + digest_len < out_len || n > 255) { |
| OPENSSL_PUT_ERROR(HKDF, HKDF, HKDF_R_OUTPUT_TOO_LARGE); |
| return 0; |
| } |
| |
| HMAC_CTX_init(&hmac); |
| |
| /* Extract input keying material into pseudorandom key |prk|. */ |
| if (HMAC(digest, salt, salt_len, secret, secret_len, prk, &prk_len) == NULL) { |
| goto out; |
| } |
| assert(prk_len == digest_len); |
| |
| if (!HMAC_Init_ex(&hmac, prk, prk_len, digest, NULL)) { |
| goto out; |
| } |
| |
| for (i = 0; i < n; i++) { |
| uint8_t ctr = i + 1; |
| size_t todo; |
| |
| if (i != 0 && (!HMAC_Init_ex(&hmac, NULL, 0, NULL, NULL) || |
| !HMAC_Update(&hmac, previous, digest_len))) { |
| goto out; |
| } |
| if (!HMAC_Update(&hmac, info, info_len) || |
| !HMAC_Update(&hmac, &ctr, 1) || |
| !HMAC_Final(&hmac, previous, NULL)) { |
| goto out; |
| } |
| |
| todo = digest_len; |
| if (done + todo > out_len) { |
| todo = out_len - done; |
| } |
| memcpy(out_key + done, previous, todo); |
| done += todo; |
| } |
| |
| ret = 1; |
| |
| out: |
| HMAC_CTX_cleanup(&hmac); |
| if (ret != 1) { |
| OPENSSL_PUT_ERROR(HKDF, HKDF, ERR_R_HMAC_LIB); |
| } |
| return ret; |
| } |