gpg-packet.cc

   1 /*
   2  * Copyright (c) 2008, Dave Korn.
   3  *
   4  *     This program is free software; you can redistribute it and/or modify
   5  *     it under the terms of the GNU General Public License as published by
   6  *     the Free Software Foundation; either version 2 of the License, or
   7  *     (at your option) any later version.
   8  *
   9  *     A copy of the GNU General Public License can be found at
  10  *     http://www.gnu.org/
  11  *
  12  *   This module contains support utilities to assist in reading and
  13  * parsing RFC4880-compliant OpenPGP format signature and key files,
  14  * and related constant definitions.
  15  *
  16  *
  17  * Written by Dave Korn <dave.korn.cygwin@gmail.com>
  18  *
  19  */
  20
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <unistd.h>
  24 #include "win32.h"
  25 #include "io_stream.h"
  26 #include "gcrypt.h"
  27 #include "gpg-packet.h"
  28 #include "msg.h"
  29 #include "LogSingleton.h"
  30 #include "resource.h"
  31
  32 #ifndef RFC4880DEBUGGING
  33 #define RFC4880DEBUGGING         (0)
  34 #endif
  35
  36 #if RFC4880DEBUGGING
  37 #define ERRKIND __asm__ __volatile__ (".byte 0xcc"); note
  38 #define MESSAGE LogBabblePrintf
  39 #else  /* !RFC4880DEBUGGING */
  40 #define ERRKIND note
  41 #define MESSAGE while (0) LogBabblePrintf
  42 #endif /* RFC4880DEBUGGING */
  43
  44 #ifndef ARRAYSIZE
  45 #define ARRAYSIZE(_ar) (sizeof (_ar) / sizeof (_ar[0]))
  46 #endif
  47
  48 static const struct { char from; char to; } RFC4880HashCodesToGPGHashCodes[] =
  49 {
  50   { RFC4880_HC_MD5,       GCRY_MD_MD5    },
  51   { RFC4880_HC_SHA1,      GCRY_MD_SHA1   },
  52   { RFC4880_HC_RIPEMD160, GCRY_MD_RMD160 },
  53   { RFC4880_HC_SHA256,    GCRY_MD_SHA256 },
  54   { RFC4880_HC_SHA384,    GCRY_MD_SHA384 },
  55   { RFC4880_HC_SHA512,    GCRY_MD_SHA512 },
  56   { RFC4880_HC_SHA224,    GCRY_MD_SHA224 }
  57 };
  58
  59 char
  60 pkt_convert_hashcode (char rfc_hash)
  61 {
  62   for (unsigned int i = 0; i < ARRAYSIZE(RFC4880HashCodesToGPGHashCodes); i++)
  63     if (RFC4880HashCodesToGPGHashCodes[i].from == rfc_hash)
  64       return RFC4880HashCodesToGPGHashCodes[i].to;
  65   return GCRY_MD_NONE;
  66 }
  67
  68 /*
  69 4.2.2.  New Format Packet Lengths
  70
  71    New format packets have four possible ways of encoding length:
  72
  73    1. A one-octet Body Length header encodes packet lengths of up to 191
  74       octets.
  75
  76    2. A two-octet Body Length header encodes packet lengths of 192 to
  77       8383 octets.
  78
  79    3. A five-octet Body Length header encodes packet lengths of up to
  80       4,294,967,295 (0xFFFFFFFF) octets in length.  (This actually
  81       encodes a four-octet scalar number.)
  82
  83    4. When the length of the packet body is not known in advance by the
  84       issuer, Partial Body Length headers encode a packet of
  85       indeterminate length, effectively making it a stream.
  86
  87 4.2.2.1.  One-Octet Lengths
  88
  89    A one-octet Body Length header encodes a length of 0 to 191 octets.
  90    This type of length header is recognized because the one octet value
  91    is less than 192.  The body length is equal to:
  92
  93        bodyLen = 1st_octet;
  94
  95 4.2.2.2.  Two-Octet Lengths
  96
  97    A two-octet Body Length header encodes a length of 192 to 8383
  98    octets.  It is recognized because its first octet is in the range 192
  99    to 223.  The body length is equal to:
 100
 101        bodyLen = ((1st_octet - 192) << 8) + (2nd_octet) + 192
 102
 103 4.2.2.3.  Five-Octet Lengths
 104
 105    A five-octet Body Length header consists of a single octet holding
 106    the value 255, followed by a four-octet scalar.  The body length is
 107    equal to:
 108
 109        bodyLen = (2nd_octet << 24) | (3rd_octet << 16) |
 110                  (4th_octet << 8)  | 5th_octet
 111
 112    This basic set of one, two, and five-octet lengths is also used
 113    internally to some packets.
 114
 115 */
 116 long
 117 pkt_getlen (io_stream *file)
 118 {
 119   int ch1, ch2;
 120
 121   ch1 = pkt_getch (file);
 122   // Obviously these two conditions fold into one, but since
 123   // one is an error test and the other a range check it's
 124   // nice to write them separately and let the compiler take
 125   // care of it.
 126   if (ch1 < 0)
 127     return ch1;
 128   if (ch1 < 192)
 129     return ch1;
 130
 131   if (ch1 == 255)
 132     return pkt_getdword (file);
 133
 134   ch2 = pkt_getch (file);
 135   if (ch2 < 0)
 136     return ch2;
 137   if (ch1 < 224)
 138     return ((ch1 - 192) << 8) + (ch2) + 192;
 139   return -2;
 140 }
 141
 142 /*
 143 3.2.  Multiprecision Integers
 144
 145    Multiprecision integers (also called MPIs) are unsigned integers used
 146    to hold large integers such as the ones used in cryptographic
 147    calculations.
 148
 149    An MPI consists of two pieces: a two-octet scalar that is the length
 150    of the MPI in bits followed by a string of octets that contain the
 151    actual integer.
 152
 153    These octets form a big-endian number; a big-endian number can be
 154    made into an MPI by prefixing it with the appropriate length.
 155
 156    Examples:
 157
 158    (all numbers are in hexadecimal)
 159
 160    The string of octets [00 01 01] forms an MPI with the value 1.  The
 161    string [00 09 01 FF] forms an MPI with the value of 511.
 162
 163    Additional rules:
 164
 165    The size of an MPI is ((MPI.length + 7) / 8) + 2 octets.
 166
 167    The length field of an MPI describes the length starting from its
 168    most significant non-zero bit.  Thus, the MPI [00 02 01] is not
 169    formed correctly.  It should be [00 01 01].
 170
 171    Unused bits of an MPI MUST be zero.
 172
 173    Also note that when an MPI is encrypted, the length refers to the
 174    plaintext MPI.  It may be ill-formed in its ciphertext.
 175
 176 */
 177 int
 178 pkt_get_mpi (gcry_mpi_t *mpiptr, io_stream *file)
 179 {
 180    /*  "An MPI consists of two pieces: a two-octet scalar that is the
 181    length of the MPI in bits followed by a string of octets that contain
 182    the actual integer."  */
 183
 184   long nbits = pkt_getword (file);
 185
 186   if (nbits < 0)
 187     return nbits;
 188
 189   size_t nbytes = ((nbits + 7) >> 3);
 190
 191   unsigned char *tmpbuf = new unsigned char [nbytes];
 192
 193   if (file->read (tmpbuf, nbytes) != (ssize_t)nbytes)
 194     return -2;
 195
 196   gcry_error_t rv = gcry_mpi_scan (mpiptr, GCRYMPI_FMT_USG, tmpbuf, nbytes, 0UL);
 197
 198   delete[] tmpbuf;
 199
 200   if (rv != GPG_ERR_NO_ERROR)
 201     return -3;
 202
 203   return 0;
 204 }
 205
 206 /*  Walk the packets in an io_stream.  */
 207 static void
 208 walk_packets_1 (struct packet_walker *wlk)
 209 {
 210   long size_left = wlk->size_to_walk;
 211   size_t ostartpos = wlk->startpos;
 212   MESSAGE ("walk $%08x bytes at startpos $%08x\n", wlk->size_to_walk, wlk->startpos);
 213   while (size_left)
 214     {
 215       char packet_type;
 216       long packet_len;
 217       enum pkt_cb_resp rv;
 218       off_t newstartpos;
 219
 220       wlk->pfile->seek (wlk->startpos, IO_SEEK_SET);
 221
 222       if (wlk->is_subpackets)
 223         packet_len = pkt_getlen (wlk->pfile) - 1;
 224       else
 225         packet_len = -1;
 226
 227       int tag = pkt_getch (wlk->pfile);
 228       MESSAGE ("tag $%02x size $%08x\n", tag, size_left);
 229
 230       if (!wlk->is_subpackets && ((tag < 0) || !(tag & 0x80)))
 231         {
 232           ERRKIND (wlk->owner, IDS_CRYPTO_ERROR, tag, "illegal tag.");
 233           return;
 234         }
 235
 236       if (wlk->is_subpackets)
 237         packet_type = tag;
 238       else if (tag & 0x40)
 239         {
 240           packet_type = tag & 0x3f;
 241           packet_len = pkt_getlen (wlk->pfile);
 242         }
 243       else
 244         {
 245           packet_type = (tag >> 2) & 0x0f;
 246           switch (tag & 3)
 247             {
 248               case 0:
 249                 packet_len = pkt_getch (wlk->pfile);
 250                 break;
 251               case 1:
 252                 packet_len = pkt_getword (wlk->pfile);
 253                 break;
 254               case 2:
 255                 packet_len = pkt_getdword (wlk->pfile);
 256                 break;
 257               case 3:
 258                 ERRKIND (wlk->owner, IDS_CRYPTO_ERROR, tag, "illegal old tag.");
 259                 return;
 260             }
 261         }
 262
 263       MESSAGE ("type $%02x len $%08x pos $%08x\n", packet_type, packet_len,
 264         wlk->pfile->tell ());
 265       if (packet_len < 0)
 266         {
 267           ERRKIND (wlk->owner, IDS_CRYPTO_ERROR, packet_len, "invalid packet");
 268           return;
 269         }
 270       else if (packet_len > (size_left - (wlk->pfile->tell () - (long)wlk->startpos)))
 271         {
 272           ERRKIND (wlk->owner, IDS_CRYPTO_ERROR, packet_len, "malformed packet");
 273           return;
 274         }
 275
 276       newstartpos = wlk->pfile->tell () + packet_len;
 277       rv = wlk->func ? wlk->func (wlk, packet_type, packet_len, wlk->startpos)
 278                       : pktCONTINUE;
 279       if (rv == pktHALT)
 280         break;
 281
 282       wlk->startpos = newstartpos;
 283       wlk->pfile->seek (wlk->startpos, IO_SEEK_SET);
 284       size_left = wlk->size_to_walk - (wlk->startpos - ostartpos);
 285       MESSAGE ("remaining $%08x nextpos $%08x\n", size_left, wlk->startpos);
 286     }
 287 }
 288
 289 void *
 290 pkt_walk_packets (io_stream *packet_file, packet_walk_cb func, HWND owner,
 291         size_t startpos, size_t size_to_walk, void *userdata)
 292 {
 293   struct packet_walker wlk;
 294   wlk.pfile = packet_file;
 295   wlk.func = func;
 296   wlk.owner = owner;
 297   wlk.userdata = userdata;
 298   wlk.startpos = startpos;
 299   wlk.size_to_walk = size_to_walk;
 300   wlk.is_subpackets = false;
 301   walk_packets_1 (&wlk);
 302   return wlk.userdata;
 303 }
 304
 305 void *
 306 pkt_walk_subpackets (io_stream *packet_file, packet_walk_cb func, HWND owner,
 307         size_t startpos, size_t size_to_walk, void *userdata)
 308 {
 309   struct packet_walker wlk;
 310   wlk.pfile = packet_file;
 311   wlk.func = func;
 312   wlk.owner = owner;
 313   wlk.userdata = userdata;
 314   wlk.startpos = startpos;
 315   wlk.size_to_walk = size_to_walk;
 316   wlk.is_subpackets = true;
 317   walk_packets_1 (&wlk);
 318   return wlk.userdata;
 319 }
 320