release/src/router/nettle/pkcs1.c

   1 /* pkcs1.c
   2  *
   3  * PKCS1 embedding.
   4  */
   5
   6 /* nettle, low-level cryptographics library
   7  *
   8  * Copyright (C) 2003 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 <string.h>
  32
  33 #include "pkcs1.h"
  34
  35 /* Formats the PKCS#1 padding, of the form
  36  *
  37  *   0x00 0x01 0xff ... 0xff 0x00 id ...digest...
  38  *
  39  * where the 0xff ... 0xff part consists of at least 8 octets. The
  40  * total size equals the octet size of n.
  41  */
  42 uint8_t *
  43 _pkcs1_signature_prefix(unsigned key_size,
  44                         uint8_t *buffer,
  45                         unsigned id_size,
  46                         const uint8_t *id,
  47                         unsigned digest_size)
  48 {
  49   unsigned j;
  50
  51   if (key_size < 11 + id_size + digest_size)
  52     return NULL;
  53
  54   j = key_size - digest_size - id_size;
  55
  56   memcpy (buffer + j, id, id_size);
  57   buffer[0] = 0;
  58   buffer[1] = 1;
  59   buffer[j-1] = 0;
  60
  61   assert(j >= 11);
  62   memset(buffer + 2, 0xff, j - 3);
  63
  64   return buffer + j + id_size;
  65 }