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/* pkcs1-decrypt.c
*
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2001, 2012 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., 51 Franklin Street, Fifth Floor, Boston,
* MA 02111-1301, USA.
*/
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include <string.h>
#include "pkcs1.h"
#include "bignum.h"
#include "nettle-internal.h"
int
pkcs1_decrypt (unsigned key_size,
const mpz_t m,
unsigned *length, uint8_t *message)
{
TMP_DECL(em, uint8_t, NETTLE_MAX_BIGNUM_SIZE);
uint8_t *terminator;
unsigned padding;
unsigned message_length;
TMP_ALLOC(em, key_size);
nettle_mpz_get_str_256(key_size, em, m);
/* Check format */
if (em[0] || em[1] != 2)
return 0;
terminator = memchr(em + 2, 0, key_size - 2);
if (!terminator)
return 0;
padding = terminator - (em + 2);
if (padding < 8)
return 0;
message_length = key_size - 3 - padding;
if (*length < message_length)
return 0;
memcpy(message, terminator + 1, message_length);
*length = message_length;
return 1;
}
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