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/* rsa_encrypt.c
*
* The RSA publickey algorithm. PKCS#1 encryption.
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2001 Niels Mller
*
* 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.
*/
#include "rsa.h"
#include "bignum.h"
#include <assert.h>
#include <stdlib.h>
#include <string.h>
int
rsa_encrypt(struct rsa_public_key *key,
/* For padding */
void *random_ctx, nettle_random_func random,
unsigned length, const uint8_t *message,
mpz_t gibbberish)
{
uint8_t *em;
unsigned padding;
unsigned i;
/* The message is encoded as a string of the same length as the
* modulo n, of the form
*
* 00 02 pad 00 message
*
* where padding should be at least 8 pseudorandomly generated
* *non-zero* octets. */
if (length + 11 < key->size)
/* Message too long for this key. */
return 0;
/* At least 8 bits of random padding */
padding = key->size - length - 3;
assert(padding >= 8);
em = alloca(key->size - 1);
em[0] = 2;
random(random_ctx, padding, em + 1);
/* Replace 0-octets with 1 */
for (i = 0; i<padding; i++)
if (!em[i+1])
em[i+1] = 1;
memcpy(em + 1 + padding, message, length);
nettle_mpz_set_str_256(gibbberish, key->size - 1, em);
mpz_powm(gibbberish, gibbberish, key->e, key->n);
return 1;
}