mdw@git.distorted.org.uk Git - userv-utils/blob - ipif/mech-pkcs5.c

   1 /*
   2  * PKCS#5 padding mechanism for udp tunnel
   3  *
   4  * mechanism: pkcs5
   5  * arguments: block size to pad to, must be power of 2 and <=128
   6  *
   7  * restrictions: none
   8  * encoding: append between 1 and n bytes, all of the same value being
   9  *           the number of bytes appended
  10  */
  11 /*
  12  * Copyright (C) 2000 Ian Jackson
  13  *
  14  * This is free software; you can redistribute it and/or modify it
  15  * under the terms of the GNU General Public License as published by
  16  * the Free Software Foundation; either version 2 of the License, or
  17  * (at your option) any later version.
  18  *
  19  * This program is distributed in the hope that it will be useful, but
  20  * WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  22  * General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU General Public License
  25  * along with userv-utils; if not, write to the Free Software
  26  * Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  27  */
  28
  29 #include "forwarder.h"
  30
  31 struct mechdata {
  32   unsigned mask;
  33 };
  34
  35 static unsigned long setup(struct mechdata **md_r) {
  36   struct mechdata *md;
  37   unsigned long blocksize;
  38
  39   XMALLOC(md);
  40
  41   blocksize= getarg_ulong();
  42   md->mask= blocksize - 1;
  43   arg_assert(!(md->mask & blocksize));
  44   arg_assert(blocksize <= 255);
  45
  46   *md_r= md;
  47   return blocksize;
  48 }
  49
  50 static void mes_pkcs5(struct mechdata **md_r, int *maxprefix_io, int *maxsuffix_io) {
  51   unsigned long blocksize;
  52
  53   blocksize= setup(md_r);
  54   *maxsuffix_io += blocksize + 1;
  55 }
  56
  57 static void mds_pkcs5(struct mechdata **md_r) {
  58   setup(md_r);
  59 }
  60
  61 static void menc_pkcs5(struct mechdata *md, struct buffer *buf) {
  62   unsigned char *pad;
  63   int padlen;
  64
  65                                   /* eg with blocksize=4 mask=3 mask+2=5   */
  66                                   /* msgsize    20    21    22    23   24  */
  67   padlen= md->mask - buf->size;   /*           -17   -18   -19   -16  -17  */
  68   padlen &= md->mask;             /*             3     2     1     0    3  */
  69   padlen++;                       /*             4     3     2     1    4  */
  70
  71   pad= buf_append(buf,padlen);
  72   memset(pad,padlen,padlen);
  73 }
  74
  75 static const char *mdec_pkcs5(struct mechdata *md, struct buffer *buf) {
  76   unsigned char *padp;
  77   unsigned padlen;
  78   int i;
  79
  80   BUF_UNAPPEND(padp,buf,1);
  81   padlen= *padp;
  82   if (!padlen || (padlen > md->mask+1)) return "invalid length";
  83
  84   BUF_UNAPPEND(padp,buf,padlen-1);
  85   for (i=0; i<padlen-1; i++)
  86     if (*++padp != padlen) return "corrupted padding";
  87
  88   return 0;
  89 }
  90
  91 STANDARD_MECHANISMLIST("pkcs5",pkcs5)