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

   1 /*
   2  * PKCS#5 padding mechanism for udp tunnel
   3  *
   4  * arguments: block size to pad to, must be power of 2
   5  *
   6  * encoding: append between 1 and n bytes, all of the same value being
   7  *           the number of bytes appended
   8  */
   9 /*
  10  * Copyright (C) 2000 Ian Jackson
  11  *
  12  * This is free software; you can redistribute it and/or modify it
  13  * under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * This program is distributed in the hope that it will be useful, but
  18  * WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  20  * General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with userv-utils; if not, write to the Free Software
  24  * Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  25  */
  26
  27 #include "forwarder.h"
  28
  29 struct mechdata {
  30   unsigned mask;
  31 };
  32
  33 static unsigned long setup(struct mechdata **md_r) {
  34   struct mechdata *md;
  35   unsigned long blocksize;
  36
  37   XMALLOC(md);
  38
  39   blocksize= getarg_ulong();
  40   md->mask= blocksize - 1;
  41   arg_assert(!(md->mask & blocksize));
  42   arg_assert(blocksize <= 255);
  43
  44   *md_r= md;
  45   return blocksize;
  46 }
  47
  48 static void mes_pkcs5(struct mechdata **md_r, int *maxprefix_io, int *maxsuffix_io) {
  49   unsigned long blocksize;
  50
  51   blocksize= setup(md_r);
  52   *maxsuffix_io += blocksize + 1;
  53 }
  54
  55 static void mds_pkcs5(struct mechdata **md_r) {
  56   setup(md_r);
  57 }
  58
  59 static void menc_pkcs5(struct mechdata *md, struct buffer *buf) {
  60   unsigned char *pad;
  61   int padlen;
  62
  63                                   /* eg with blocksize=4 mask=3 mask+2=5   */
  64                                   /* msgsize    20    21    22    23   24  */
  65   padlen= md->mask - buf->size;   /*           -17   -18   -19   -16  -17  */
  66   padlen &= md->mask;             /*             3     2     1     0    3  */
  67   padlen++;                       /*             4     3     2     1    4  */
  68
  69   pad= buf_append(buf,padlen);
  70   memset(pad,padlen,padlen);
  71 }
  72
  73 static const char *mdec_pkcs5(struct mechdata *md, struct buffer *buf) {
  74   unsigned char *padp;
  75   unsigned padlen;
  76   int i;
  77
  78   BUF_UNAPPEND(padp,buf,1);
  79   padlen= *padp;
  80   if (!padlen || (padlen > md->mask+1)) return "invalid length";
  81
  82   BUF_UNAPPEND(padp,buf,padlen-1);
  83   for (i=0; i<padlen-1; i++)
  84     if (*++padp != padlen) return "corrupted padding";
  85
  86   return 0;
  87 }
  88
  89 STANDARD_MECHANISMLIST("pkcs5",pkcs5)