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