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/*
This file is part of GNUnet.
Copyright (C) 2010 GNUnet e.V.
GNUnet is free software: you can redistribute it and/or modify it
under the terms of the GNU Affero General Public License as published
by the Free Software Foundation, either version 3 of the License,
or (at your option) any later version.
GNUnet is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
SPDX-License-Identifier: AGPL3.0-or-later
*/
/**
* @file src/util/crypto_kdf.c
* @brief Key derivation
* @author Nils Durner
* @author Jeffrey Burdges <burdges@gnunet.org>
*/
#include <gcrypt.h>
#include "platform.h"
#include "gnunet_crypto_lib.h"
#define LOG(kind, ...) GNUNET_log_from (kind, "util-crypto-kdf", __VA_ARGS__)
enum GNUNET_GenericReturnValue
GNUNET_CRYPTO_kdf_v (void *result,
size_t out_len,
const void *xts,
size_t xts_len,
const void *skm,
size_t skm_len,
va_list argp)
{
/*
* "Finally, we point out to a particularly advantageous instantiation using
* HMAC-SHA512 as XTR and HMAC-SHA256 in PRF* (in which case the output from SHA-512 is
* truncated to 256 bits). This makes sense in two ways: First, the extraction part is where we need a
* stronger hash function due to the unconventional demand from the hash function in the extraction
* setting. Second, as shown in Section 6, using HMAC with a truncated output as an extractor
* allows to prove the security of HKDF under considerably weaker assumptions on the underlying
* hash function."
*
* http://eprint.iacr.org/2010/264
*/
return GNUNET_CRYPTO_hkdf_v (result,
out_len,
GCRY_MD_SHA512,
GCRY_MD_SHA256,
xts,
xts_len,
skm,
skm_len,
argp);
}
enum GNUNET_GenericReturnValue
GNUNET_CRYPTO_kdf (void *result,
size_t out_len,
const void *xts,
size_t xts_len,
const void *skm,
size_t skm_len, ...)
{
va_list argp;
int ret;
va_start (argp, skm_len);
ret = GNUNET_CRYPTO_kdf_v (result,
out_len,
xts,
xts_len,
skm,
skm_len,
argp);
va_end (argp);
return ret;
}
void
GNUNET_CRYPTO_kdf_mod_mpi (gcry_mpi_t *r,
gcry_mpi_t n,
const void *xts, size_t xts_len,
const void *skm, size_t skm_len,
const char *ctx)
{
gcry_error_t rc;
unsigned int nbits;
size_t rsize;
uint16_t ctr;
nbits = gcry_mpi_get_nbits (n);
/* GNUNET_assert (nbits > 512); */
ctr = 0;
while (1)
{
/* Ain't clear if n is always divisible by 8 */
size_t bsize = (nbits - 1) / 8 + 1;
uint8_t buf[bsize];
uint16_t ctr_nbo = htons (ctr);
rc = GNUNET_CRYPTO_kdf (buf,
bsize,
xts, xts_len,
skm, skm_len,
ctx, strlen (ctx),
&ctr_nbo, sizeof(ctr_nbo),
NULL, 0);
GNUNET_assert (GNUNET_YES == rc);
rc = gcry_mpi_scan (r,
GCRYMPI_FMT_USG,
(const unsigned char *) buf,
bsize,
&rsize);
GNUNET_assert (GPG_ERR_NO_ERROR == rc); /* Allocation error? */
GNUNET_assert (rsize == bsize);
gcry_mpi_clear_highbit (*r,
nbits);
GNUNET_assert (0 ==
gcry_mpi_test_bit (*r,
nbits));
++ctr;
/* We reject this FDH if either *r > n and retry with another ctr */
if (0 > gcry_mpi_cmp (*r, n))
break;
gcry_mpi_release (*r);
}
}
/* end of crypto_kdf.c */
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