release/src/router/nettle/pkcs1-encrypt.c

   1 /* pkcs1-encrypt.c
   2  *
   3  * The RSA publickey algorithm. PKCS#1 encryption.
   4  */
   5
   6 /* nettle, low-level cryptographics library
   7  *
   8  * Copyright (C) 2001, 2012 Niels Möller
   9  *
  10  * The nettle library is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU Lesser General Public License as published by
  12  * the Free Software Foundation; either version 2.1 of the License, or (at your
  13  * option) any later version.
  14  *
  15  * The nettle library is distributed in the hope that it will be useful, but
  16  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  17  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  18  * License for more details.
  19  *
  20  * You should have received a copy of the GNU Lesser General Public License
  21  * along with the nettle library; see the file COPYING.LIB.  If not, write to
  22  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
  23  * MA 02111-1301, USA.
  24  */
  25
  26 #if HAVE_CONFIG_H
  27 # include "config.h"
  28 #endif
  29
  30 #include <assert.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33
  34 #include "pkcs1.h"
  35
  36 #include "bignum.h"
  37 #include "nettle-internal.h"
  38
  39 int
  40 pkcs1_encrypt (unsigned key_size,
  41                /* For padding */
  42                void *random_ctx, nettle_random_func *random,
  43                unsigned length, const uint8_t *message,
  44                mpz_t m)
  45 {
  46   TMP_DECL(em, uint8_t, NETTLE_MAX_BIGNUM_SIZE);
  47   unsigned padding;
  48   unsigned i;
  49
  50   /* The message is encoded as a string of the same length as the
  51    * modulo n, of the form
  52    *
  53    *   00 02 pad 00 message
  54    *
  55    * where padding should be at least 8 pseudorandomly generated
  56    * *non-zero* octets. */
  57
  58   if (length + 11 > key_size)
  59     /* Message too long for this key. */
  60     return 0;
  61
  62   /* At least 8 octets of random padding */
  63   padding = key_size - length - 3;
  64   assert(padding >= 8);
  65
  66   TMP_ALLOC(em, key_size - 1);
  67   em[0] = 2;
  68
  69   random(random_ctx, padding, em + 1);
  70
  71   /* Replace 0-octets with 1 */
  72   for (i = 0; i<padding; i++)
  73     if (!em[i+1])
  74       em[i+1] = 1;
  75
  76   em[padding+1] = 0;
  77   memcpy(em + padding + 2, message, length);
  78
  79   nettle_mpz_set_str_256_u(m, key_size - 1, em);
  80   return 1;
  81 }