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/* $OpenBSD: hkdf.c,v 1.11 2024/03/25 13:09:13 jsing Exp $ */
/*
* 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 <string.h>
#include <openssl/err.h>
#include <openssl/hmac.h>
#include "bytestring.h"
#include "evp_local.h"
#include "hmac_local.h"
/* https://tools.ietf.org/html/rfc5869#section-2 */
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)
{
uint8_t prk[EVP_MAX_MD_SIZE];
size_t prk_len;
if (!HKDF_extract(prk, &prk_len, digest, secret, secret_len, salt,
salt_len))
return 0;
if (!HKDF_expand(out_key, out_len, digest, prk, prk_len, info,
info_len))
return 0;
return 1;
}
LCRYPTO_ALIAS(HKDF);
/* https://tools.ietf.org/html/rfc5869#section-2.2 */
int
HKDF_extract(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)
{
unsigned int len;
/*
* If salt is not given, HashLength zeros are used. However, HMAC does
* that internally already so we can ignore it.
*/
if (HMAC(digest, salt, salt_len, secret, secret_len, out_key, &len) ==
NULL) {
CRYPTOerror(ERR_R_CRYPTO_LIB);
return 0;
}
*out_len = len;
return 1;
}
LCRYPTO_ALIAS(HKDF_extract);
/* https://tools.ietf.org/html/rfc5869#section-2.3 */
int
HKDF_expand(uint8_t *out_key, size_t out_len,
const EVP_MD *digest, const uint8_t *prk, size_t prk_len,
const uint8_t *info, size_t info_len)
{
const size_t digest_len = EVP_MD_size(digest);
uint8_t out_hmac[EVP_MAX_MD_SIZE];
size_t n, remaining;
uint8_t ctr;
HMAC_CTX *hmac = NULL;
CBB cbb;
int ret = 0;
if (!CBB_init_fixed(&cbb, out_key, out_len))
goto err;
if ((hmac = HMAC_CTX_new()) == NULL)
goto err;
if (!HMAC_Init_ex(hmac, prk, prk_len, digest, NULL))
goto err;
remaining = out_len;
ctr = 0;
/* Expand key material to desired length. */
while (remaining > 0) {
if (++ctr == 0) {
CRYPTOerror(EVP_R_TOO_LARGE);
goto err;
}
if (!HMAC_Update(hmac, info, info_len))
goto err;
if (!HMAC_Update(hmac, &ctr, 1))
goto err;
if (!HMAC_Final(hmac, out_hmac, NULL))
goto err;
if ((n = remaining) > digest_len)
n = digest_len;
if (!CBB_add_bytes(&cbb, out_hmac, n))
goto err;
remaining -= n;
if (remaining > 0) {
if (!HMAC_Init_ex(hmac, NULL, 0, NULL, NULL))
goto err;
if (!HMAC_Update(hmac, out_hmac, digest_len))
goto err;
}
}
ret = 1;
err:
CBB_cleanup(&cbb);
HMAC_CTX_free(hmac);
explicit_bzero(out_hmac, sizeof(out_hmac));
return ret;
}
LCRYPTO_ALIAS(HKDF_expand);
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