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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, 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;
- }
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