File: pka.c

package info (click to toggle)
gnupg 1.4.18-7+deb8u5
  • links: PTS, VCS
  • area: main
  • in suites: jessie
  • size: 34,476 kB
  • sloc: ansic: 127,074; sh: 7,535; asm: 4,610; makefile: 1,186; yacc: 291; perl: 196; pascal: 72; sed: 16
file content (262 lines) | stat: -rw-r--r-- 6,536 bytes parent folder | download | duplicates (5)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
/* pka.c - DNS Public Key Association RR access
 * Copyright (C) 2005, 2007 Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * GnuPG is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include <config.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifdef USE_DNS_PKA
# include <sys/types.h>
# ifdef _WIN32
#  include <windows.h>
# else
#  include <netinet/in.h>
#  include <arpa/nameser.h>
#  include <arpa/inet.h>
#  include <resolv.h>
   /* Not every installation has gotten around to supporting CERTs yet... */
#  ifndef T_CERT
#   define T_CERT 37
#   ifdef __VMS
#    include "cert_vms.h"
#   endif /* def __VMS */
#  endif
# endif
#endif /* USE_DNS_PKA */

#include "memory.h"
#include "types.h"
#include "util.h"


#ifdef USE_DNS_PKA
/* Parse the TXT resource record. Format is:

   v=pka1;fpr=a4d94e92b0986ab5ee9dcd755de249965b0358a2;uri=string

   For simplicity white spaces are not allowed.  Because we expect to
   use a new RRTYPE for this in the future we define the TXT really
   strict for simplicity: No white spaces, case sensitivity of the
   names, order must be as given above.  Only URI is optional.

   This function modifies BUFFER.  On success 0 is returned, the 20
   byte fingerprint stored at FPR and BUFFER contains the URI or an
   empty string.
*/
static int
parse_txt_record (char *buffer, unsigned char *fpr)
{
  char *p, *pend;
  int i;

  p = buffer;
  pend = strchr (p, ';');
  if (!pend)
    return -1;
  *pend++ = 0;
  if (strcmp (p, "v=pka1"))
    return -1; /* Wrong or missing version. */

  p = pend;
  pend = strchr (p, ';');
  if (pend)
    *pend++ = 0;
  if (strncmp (p, "fpr=", 4))
    return -1; /* Missing fingerprint part. */
  p += 4;
  for (i=0; i < 20 && hexdigitp (p) && hexdigitp (p+1); i++, p += 2)
    fpr[i] = xtoi_2 (p);
  if (i != 20)
    return -1; /* Fingerprint consists not of exactly 40 hexbytes. */

  p = pend;
  if (!p || !*p)
    {
      *buffer = 0;
      return 0; /* Success (no URI given). */
    }
  if (strncmp (p, "uri=", 4))
    return -1; /* Unknown part. */
  p += 4;
  /* There is an URI, copy it to the start of the buffer. */
  while (*p)
    *buffer++ = *p++;
  *buffer = 0;
  return 0;
}


/* For the given email ADDRESS lookup the PKA information in the DNS.

   On success the 20 byte SHA-1 fingerprint is stored at FPR and the
   URI will be returned in an allocated buffer.  Note that the URI
   might be an zero length string as this information is optiobnal.
   Caller must xfree the returned string.

   On error NULL is returned and the 20 bytes at FPR are not
   defined. */
char *
get_pka_info (const char *address, unsigned char *fpr)
{
  union
    {
      signed char p[PACKETSZ];
      HEADER h;
    } answer;
  int anslen;
  int qdcount, ancount;
  int rc;
  unsigned char *p, *pend;
  const char *domain;
  char *name;


  domain = strrchr (address, '@');
  if (!domain || domain == address || !domain[1])
    return NULL; /* invalid mail address given. */

  name = malloc (strlen (address) + 5 + 1);
  memcpy (name, address, domain - address);
  strcpy (stpcpy (name + (domain-address), "._pka."), domain+1);

  anslen = res_query (name, C_IN, T_TXT, answer.p, PACKETSZ);
  xfree (name);
  if (anslen < sizeof(HEADER))
    return NULL; /* DNS resolver returned a too short answer. */
  if ( (rc=answer.h.rcode) != NOERROR )
    return NULL; /* DNS resolver returned an error. */

  /* We assume that PACKETSZ is large enough and don't do dynmically
     expansion of the buffer. */
  if (anslen > PACKETSZ)
    return NULL; /* DNS resolver returned a too long answer */

  qdcount = ntohs (answer.h.qdcount);
  ancount = ntohs (answer.h.ancount);

  if (!ancount)
    return NULL; /* Got no answer. */

  p = answer.p + sizeof (HEADER);
  pend = answer.p + anslen; /* Actually points directly behind the buffer. */

  while (qdcount-- && p < pend)
    {
      rc = dn_skipname (p, pend);
      if (rc == -1)
        return NULL;
      p += rc + QFIXEDSZ;
    }

  if (ancount > 1)
    return NULL; /* more than one possible gpg trustdns record - none used. */

  while (ancount-- && p <= pend)
    {
      unsigned int type, class, txtlen, n;
      char *buffer, *bufp;

      rc = dn_skipname (p, pend);
      if (rc == -1)
        return NULL;
      p += rc;
      if (p >= pend - 10)
        return NULL; /* RR too short. */

      type = *p++ << 8;
      type |= *p++;
      class = *p++ << 8;
      class |= *p++;
      p += 4;
      txtlen = *p++ << 8;
      txtlen |= *p++;
      if (type != T_TXT || class != C_IN)
        return NULL; /* Answer does not match the query. */

      buffer = bufp = xmalloc (txtlen + 1);
      while (txtlen && p < pend)
        {
          for (n = *p++, txtlen--; txtlen && n && p < pend; txtlen--, n--)
            *bufp++ = *p++;
        }
      *bufp = 0;
      if (parse_txt_record (buffer, fpr))
        {
          xfree (buffer);
          return NULL; /* Not a valid gpg trustdns RR. */
        }
      return buffer;
    }

  return NULL;
}
#else /* !USE_DNS_PKA */

/* Dummy version of the function if we can't use the resolver
   functions. */
char *
get_pka_info (const char *address, unsigned char *fpr)
{
  return NULL;
}
#endif /* !USE_DNS_PKA */


#ifdef TEST
int
main(int argc,char *argv[])
{
  unsigned char fpr[20];
  char *uri;
  int i;

  if (argc < 2)
    {
      fprintf (stderr, "usage: pka mail-addresses\n");
      return 1;
    }
  argc--;
  argv++;

  for (; argc; argc--, argv++)
    {
      uri = get_pka_info ( *argv, fpr );
      printf ("%s", *argv);
      if (uri)
        {
          putchar (' ');
          for (i=0; i < 20; i++)
            printf ("%02X", fpr[i]);
          if (*uri)
            printf (" %s", uri);
          xfree (uri);
        }
      putchar ('\n');
    }
  return 0;
}
#endif /* TEST */

/*
Local Variables:
compile-command: "cc -DUSE_DNS_PKA -DTEST -I.. -I../include -Wall -g -o pka pka.c -lresolv libutil.a"
End:
*/