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) 2000,2003 Ian Jackson
  13  * This file is part of ipif, part of userv-utils
  14  *
  15  * This is free software; you can redistribute it and/or modify it
  16  * under the terms of the GNU General Public License as published by
  17  * the Free Software Foundation; either version 2 of the License, or
  18  * (at your option) any later version.
  19  *
  20  * This program is distributed in the hope that it will be useful, but
  21  * WITHOUT ANY WARRANTY; without even the implied warranty of
  22  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  23  * General Public License for more details.
  24  *
  25  * You should have received a copy of the GNU General Public License
  26  * along with userv-utils; if not, write to the Free Software
  27  * Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  28  */
  29
  30 #include "forwarder.h"
  31
  32 struct mechdata {
  33   unsigned mask;
  34 };
  35
  36 static unsigned long setup(struct mechdata **md_r) {
  37   struct mechdata *md;
  38   unsigned long blocksize;
  39
  40   XMALLOC(md);
  41
  42   blocksize= getarg_ulong();
  43   md->mask= blocksize - 1;
  44   arg_assert(!(md->mask & blocksize));
  45   arg_assert(blocksize <= 255);
  46
  47   *md_r= md;
  48   return blocksize;
  49 }
  50
  51 static void mes_pkcs5(struct mechdata **md_r, int *maxprefix_io, int *maxsuffix_io) {
  52   unsigned long blocksize;
  53
  54   blocksize= setup(md_r);
  55   *maxsuffix_io += blocksize + 1;
  56 }
  57
  58 static void mds_pkcs5(struct mechdata **md_r) {
  59   setup(md_r);
  60 }
  61
  62 static void menc_pkcs5(struct mechdata *md, struct buffer *buf) {
  63   unsigned char *pad;
  64   int padlen;
  65
  66                                   /* eg with blocksize=4 mask=3 mask+2=5   */
  67                                   /* msgsize    20    21    22    23   24  */
  68   padlen= md->mask - buf->size;   /*           -17   -18   -19   -16  -17  */
  69   padlen &= md->mask;             /*             3     2     1     0    3  */
  70   padlen++;                       /*             4     3     2     1    4  */
  71
  72   pad= buf_append(buf,padlen);
  73   memset(pad,padlen,padlen);
  74 }
  75
  76 static const char *mdec_pkcs5(struct mechdata *md, struct buffer *buf) {
  77   unsigned char *padp;
  78   unsigned padlen;
  79   int i;
  80
  81   BUF_UNAPPEND(padp,buf,1);
  82   padlen= *padp;
  83   if (!padlen || (padlen > md->mask+1)) return "invalid length";
  84
  85   BUF_UNAPPEND(padp,buf,padlen-1);
  86   for (i=0; i<padlen-1; i++)
  87     if (*++padp != padlen) return "corrupted padding";
  88
  89   return 0;
  90 }
  91
  92 STANDARD_MECHANISMLIST("pkcs5",pkcs5)