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

   1 /* pkcs1-decrypt.c
   2  *
   3  */
   4
   5 /* nettle, low-level cryptographics library
   6  *
   7  * Copyright (C) 2001, 2012 Niels Möller
   8  *
   9  * The nettle library is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU Lesser General Public License as published by
  11  * the Free Software Foundation; either version 2.1 of the License, or (at your
  12  * option) any later version.
  13  *
  14  * The nettle library is distributed in the hope that it will be useful, but
  15  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  16  * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  17  * License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public License
  20  * along with the nettle library; see the file COPYING.LIB.  If not, write to
  21  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
  22  * MA 02111-1301, USA.
  23  */
  24
  25 #if HAVE_CONFIG_H
  26 # include "config.h"
  27 #endif
  28
  29 #include <string.h>
  30
  31 #include "pkcs1.h"
  32
  33 #include "bignum.h"
  34 #include "nettle-internal.h"
  35
  36 int
  37 pkcs1_decrypt (unsigned key_size,
  38                const mpz_t m,
  39                unsigned *length, uint8_t *message)
  40 {
  41   TMP_DECL(em, uint8_t, NETTLE_MAX_BIGNUM_SIZE);
  42   uint8_t *terminator;
  43   unsigned padding;
  44   unsigned message_length;
  45
  46   TMP_ALLOC(em, key_size);
  47   nettle_mpz_get_str_256(key_size, em, m);
  48
  49   /* Check format */
  50   if (em[0] || em[1] != 2)
  51     return 0;
  52
  53   terminator = memchr(em + 2, 0, key_size - 2);
  54
  55   if (!terminator)
  56     return 0;
  57
  58   padding = terminator - (em + 2);
  59   if (padding < 8)
  60     return 0;
  61
  62   message_length = key_size - 3 - padding;
  63
  64   if (*length < message_length)
  65     return 0;
  66
  67   memcpy(message, terminator + 1, message_length);
  68   *length = message_length;
  69
  70   return 1;
  71 }
  72