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  * This file is part of ipif, part of userv-utils
  13  *
  14  * Copyright 1996-2013 Ian Jackson <ijackson@chiark.greenend.org.uk>
  15  * Copyright 1998 David Damerell <damerell@chiark.greenend.org.uk>
  16  * Copyright 1999,2003
  17  *    Chancellor Masters and Scholars of the University of Cambridge
  18  * Copyright 2010 Tony Finch <fanf@dotat.at>
  19  *
  20  * This is free software; you can redistribute it and/or modify it
  21  * under the terms of the GNU General Public License as published by
  22  * the Free Software Foundation; either version 3 of the License, or
  23  * (at your option) any later version.
  24  *
  25  * This program is distributed in the hope that it will be useful, but
  26  * WITHOUT ANY WARRANTY; without even the implied warranty of
  27  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  28  * General Public License for more details.
  29  *
  30  * You should have received a copy of the GNU General Public License
  31  * along with userv-utils; if not, see http://www.gnu.org/licenses/.
  32  */
  33
  34 #include "forwarder.h"
  35
  36 struct mechdata {
  37   unsigned mask;
  38 };
  39
  40 static unsigned long setup(struct mechdata **md_r) {
  41   struct mechdata *md;
  42   unsigned long blocksize;
  43
  44   XMALLOC(md);
  45
  46   blocksize= getarg_ulong();
  47   md->mask= blocksize - 1;
  48   arg_assert(!(md->mask & blocksize));
  49   arg_assert(blocksize <= 255);
  50
  51   *md_r= md;
  52   return blocksize;
  53 }
  54
  55 static void mes_pkcs5(struct mechdata **md_r, int *maxprefix_io, int *maxsuffix_io) {
  56   unsigned long blocksize;
  57
  58   blocksize= setup(md_r);
  59   *maxsuffix_io += blocksize + 1;
  60 }
  61
  62 static void mds_pkcs5(struct mechdata **md_r) {
  63   setup(md_r);
  64 }
  65
  66 static void menc_pkcs5(struct mechdata *md, struct buffer *buf) {
  67   unsigned char *pad;
  68   int padlen;
  69
  70                                   /* eg with blocksize=4 mask=3 mask+2=5   */
  71                                   /* msgsize    20    21    22    23   24  */
  72   padlen= md->mask - buf->size;   /*           -17   -18   -19   -16  -17  */
  73   padlen &= md->mask;             /*             3     2     1     0    3  */
  74   padlen++;                       /*             4     3     2     1    4  */
  75
  76   pad= buf_append(buf,padlen);
  77   memset(pad,padlen,padlen);
  78 }
  79
  80 static const char *mdec_pkcs5(struct mechdata *md, struct buffer *buf) {
  81   unsigned char *padp;
  82   unsigned padlen;
  83   int i;
  84
  85   BUF_UNAPPEND(padp,buf,1);
  86   padlen= *padp;
  87   if (!padlen || (padlen > md->mask+1)) return "invalid length";
  88
  89   BUF_UNAPPEND(padp,buf,padlen-1);
  90   for (i=0; i<padlen-1; i++)
  91     if (*++padp != padlen) return "corrupted padding";
  92
  93   return 0;
  94 }
  95
  96 STANDARD_MECHANISMLIST("pkcs5",pkcs5)