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bignum-random.c
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Niels Möller authored
work by allocating a fix amount of stack and imposing a hard limit on what can be allocated. Updated all users of alloca. Rev: src/nettle/bignum-random.c:1.4 Rev: src/nettle/cbc.c:1.8 Rev: src/nettle/dsa-keygen.c:1.7 Rev: src/nettle/hmac.c:1.6 Rev: src/nettle/pkcs1-rsa-md5.c:1.3 Rev: src/nettle/pkcs1-rsa-sha1.c:1.3 Rev: src/nettle/rsa-decrypt.c:1.5 Rev: src/nettle/rsa-encrypt.c:1.8 Rev: src/nettle/sexp.c:1.15
Niels Möller authoredwork by allocating a fix amount of stack and imposing a hard limit on what can be allocated. Updated all users of alloca. Rev: src/nettle/bignum-random.c:1.4 Rev: src/nettle/cbc.c:1.8 Rev: src/nettle/dsa-keygen.c:1.7 Rev: src/nettle/hmac.c:1.6 Rev: src/nettle/pkcs1-rsa-md5.c:1.3 Rev: src/nettle/pkcs1-rsa-sha1.c:1.3 Rev: src/nettle/rsa-decrypt.c:1.5 Rev: src/nettle/rsa-encrypt.c:1.8 Rev: src/nettle/sexp.c:1.15
bignum-random.c 2.61 KiB
/* bignum-random.c
*
* Generating big random numbers
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2002 Niels Möller
*
* The nettle library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at your
* option) any later version.
*
* The nettle library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the nettle library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
* MA 02111-1307, USA.
*/
#if HAVE_CONFIG_H
# include "config.h"
#endif
#if HAVE_LIBGMP
#include <stdlib.h>
#include "bignum.h"
#include "nettle-internal.h"
void
nettle_mpz_random_size(mpz_t x,
void *ctx, nettle_random_func random,
unsigned bits)
{
unsigned length = (bits + 7) / 8;
TMP_DECL(data, uint8_t, NETTLE_MAX_BIGNUM_BITS / 8);
TMP_ALLOC(data, length);
random(ctx, length, data);
nettle_mpz_set_str_256_u(x, length, data);
if (bits % 8)
mpz_fdiv_r_2exp(x, x, bits);
}
/* Returns a random number x, 0 <= x < n */
void
nettle_mpz_random(mpz_t x,
void *ctx, nettle_random_func random,
const mpz_t n)
{
/* FIXME: This leaves some bias, which may be bad for DSA. A better
* way might to generate a random number of mpz_sizeinbase(n, 2)
* bits, and loop until one smaller than n is found. */
/* From Daniel Bleichenbacher (via coderpunks):
*
* There is still a theoretical attack possible with 8 extra bits.
* But, the attack would need about 2^66 signatures 2^66 memory and
* 2^66 time (if I remember that correctly). Compare that to DSA,
* where the attack requires 2^22 signatures 2^40 memory and 2^64
* time. And of course, the numbers above are not a real threat for