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/* 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_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, ERR_R_HMAC_LIB);
}
return ret;
}
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