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/*
This file is part of GNUnet.
(C) 2010 Christian Grothoff (and other contributing authors)
GNUnet is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published
by the Free Software Foundation; either version 3, 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
General Public License for more details.
You should have received a copy of the GNU General Public License
along with GNUnet; see the file COPYING. If not, write to the
Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.
*/
/**
* @file src/util/crypto_kdf.c
* @brief Key derivation
* @author Nils Durner
*/
#include <gcrypt.h>
#include "platform.h"
#include "gnunet_crypto_lib.h"
#define LOG(kind,...) GNUNET_log_from (kind, "util", __VA_ARGS__)
/**
* @brief Derive key
* @param result buffer for the derived key, allocated by caller
* @param out_len desired length of the derived key
* @param xts salt
* @param xts_len length of xts
* @param skm source key material
* @param skm_len length of skm
* @param argp va_list of void * & size_t pairs for context chunks
* @return GNUNET_YES on success
*/
int
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);
}
/**
* @brief Derive key
* @param result buffer for the derived key, allocated by caller
* @param out_len desired length of the derived key
* @param xts salt
* @param xts_len length of xts
* @param skm source key material
* @param skm_len length of skm
* @param ... void * & size_t pairs for context chunks
* @return GNUNET_YES on success
*/
int
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;
}
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