Switch to a hash and CERT record based PKA system.

* util/pka.c: Rewrite.
(get_pka_info): Add arg fprbuflen.  Change callers to pass this.
* util/strgutil.c (ascii_strlwr): New.
* configure.ac: Remove option --disable-dns-pka.
(USE_DNS_PKA): Remove ac_define.
* g10/getkey.c (parse_auto_key_locate): Always include PKA.
--

Note that although PKA is now always build, it will only work if
support for looking up via DNS has not been disabled.

The new PKA only works with the IPGP DNS certtype and shall be used
only to retrieve the fingerprint and optional the key for the first
time.  Due to the security problems with DNSSEC the former assumption
to validate the key using DNSSEC is not anymore justified.  Instead an
additional layer (e.g. Trust-On-First-Use) needs to be implemented to
track change to the key.  Having a solid way of getting a key matching
a mail address is however a must have.

More work needs to go into a redefinition of the --verify-options
pka-lookups and pka-trust-increase.  The auto-key-locate mechanism
should also be able to continue key fetching with another method once
the fingerprint has been retrieved with PKA.

Signed-off-by: Werner Koch <wk@gnupg.org>

This is a backport from master.
(backported from commit 2fc27c8696f5cf2ddf3212397ea49bff115d617b)

configure.ac

@@ -703,18 +703,13 @@ if test x"$try_dns" = xyes ; then
          use_dns_srv=$enableval,use_dns_srv=yes)
    fi
 
-   AC_ARG_ENABLE(dns-pka,
-      AC_HELP_STRING([--disable-dns-pka],
-   	[disable the use of PKA records in DNS]),
-      use_dns_pka=$enableval,use_dns_pka=yes)
-
    AC_ARG_ENABLE(dns-cert,
       AC_HELP_STRING([--disable-dns-cert],
    	[disable the use of CERT records in DNS]),
       use_dns_cert=$enableval,use_dns_cert=yes)
 fi
 
-if test x"$use_dns_pka" = xyes || test x"$use_dns_srv" = xyes || test x"$use_dns_cert" = xyes; then
+if test x"$use_dns_srv" = xyes || test x"$use_dns_cert" = xyes; then
   _dns_save_libs=$LIBS
   LIBS=""
   # the double underscore thing is a glibc-ism?
@@ -762,10 +757,6 @@ if test x"$use_dns_pka" = xyes || test x"$use_dns_srv" = xyes || test x"$use_dns
         AC_DEFINE(USE_DNS_SRV,1,[define to use DNS SRV])
      fi
 
-     if test x"$use_dns_pka" = xyes ; then
-        AC_DEFINE(USE_DNS_PKA,1,[define to use our experimental DNS PKA])
-     fi
-
      if test x"$use_dns_cert" = xyes ; then
         AC_DEFINE(USE_DNS_CERT,1,[define to use DNS CERT])
      fi
@@ -775,7 +766,6 @@ if test x"$use_dns_pka" = xyes || test x"$use_dns_srv" = xyes || test x"$use_dns
      fi
   else
      use_dns_srv=no
-     use_dns_pka=no
      use_dns_cert=no
   fi
 

g10/getkey.c

@@ -3063,10 +3063,8 @@ parse_auto_key_locate(char *options)
       else if(ascii_strcasecmp(tok,"cert")==0)
 	akl->type=AKL_CERT;
 #endif
-#ifdef USE_DNS_PKA
       else if(ascii_strcasecmp(tok,"pka")==0)
 	akl->type=AKL_PKA;
-#endif
       else if((akl->spec=parse_keyserver_uri(tok,1,NULL,0)))
 	akl->type=AKL_SPEC;
       else

g10/keyserver.c

@@ -2229,8 +2229,8 @@ keyserver_import_pka(const char *name,unsigned char **fpr,size_t *fpr_len)
   *fpr=xmalloc(20);
   *fpr_len=20;
 
-  uri = get_pka_info (name, *fpr);
+  uri = get_pka_info (name, *fpr, 20);
-  if (uri)
+  if (uri && *uri)
     {
       struct keyserver_spec *spec;
       spec = parse_keyserver_uri (uri, 1, NULL, 0);
@@ -2239,11 +2239,14 @@ keyserver_import_pka(const char *name,unsigned char **fpr,size_t *fpr_len)
 	  rc=keyserver_import_fprint (*fpr, 20, spec);
 	  free_keyserver_spec (spec);
 	}
-      xfree (uri);
     }
+  xfree (uri);
 
-  if(rc!=0)
+  if (rc)
-    xfree(*fpr);
+    {
+      xfree(*fpr);
+      *fpr = NULL;
+    }
 
   return rc;
 }

g10/mainproc.c

@@ -1443,7 +1443,8 @@ pka_uri_from_sig (PKT_signature *sig)
         {
           char *uri;
 
-          uri = get_pka_info (sig->pka_info->email, sig->pka_info->fpr);
+          uri = get_pka_info (sig->pka_info->email,
+                              sig->pka_info->fpr, sizeof sig->pka_info->fpr);
           if (uri)
             {
               sig->pka_info->valid = 1;

include/util.h

@@ -196,6 +196,7 @@ char *string_to_utf8 (const char *string);
 int ascii_isupper (int c);
 int ascii_islower (int c);
 int ascii_memcasecmp( const char *a, const char *b, size_t n);
+char *ascii_strlwr (char *s);
 
 #ifndef HAVE_STPCPY
 char *stpcpy(char *a,const char *b);
@@ -251,7 +252,7 @@ char *xtryvasprintf (const char *fmt, va_list arg_ptr);
 char *strconcat (const char *s1, ...) GNUPG_GCC_A_SENTINEL(0);
 
 /*-- pka.c --*/
-char *get_pka_info (const char *address, unsigned char *fpr);
+char *get_pka_info (const char *address, void *fprbuf, size_t fprbuflen);
 
 /*-- cert.c --*/
 int get_cert (const char *name, int want_ipgp, size_t max_size, IOBUF *iobuf,

util/pka.c

@@ -1,5 +1,6 @@
-/* pka.c - DNS Public Key Association RR access
+/* pka.c - DNS Public Key Association CERT record access
- * Copyright (C) 2005, 2007 Free Software Foundation, Inc.
+ * Copyright (C) 1998-2015 Free Software Foundation, Inc.
+ * Copyright (C) 1998-2015 Werner Koch
  *
  * This file is part of GnuPG.
  *
@@ -22,241 +23,237 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-
+#include <errno.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 "cipher.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)
+string_has_ctrl_or_space (const char *string)
 {
-  char *p, *pend;
+  for (; *string; string++ )
-  int i;
+    if (!(*string & 0x80) && *string <= 0x20)
-
+      return 1;
-  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;
 }
 
 
+/* Return true if STRING has two consecutive '.' after an '@'
+   sign.  */
+static int
+has_dotdot_after_at (const char *string)
+{
+  string = strchr (string, '@');
+  if (!string)
+    return 0; /* No at-sign.  */
+  string++;
+  return !!strstr (string, "..");
+}
+
+
+/* Return the mailbox (local-part@domain) form a standard user id.
+   Caller must free the result.  Returns NULL if no valid mailbox was
+   found (or we are out of memory). */
+static char *
+mailbox_from_userid (const char *userid)
+{
+  const char *s, *s_end;
+  size_t len;
+  char *result = NULL;
+
+  s = strchr (userid, '<');
+  if (s)
+    {
+      /* Seems to be a standard user id.  */
+      s++;
+      s_end = strchr (s, '>');
+      if (s_end && s_end > s)
+        {
+          len = s_end - s;
+          result = xmalloc (len + 1);
+          strncpy (result, s, len);
+          result[len] = 0;
+          /* Apply some basic checks on the address.  We do not use
+             is_valid_mailbox because those checks are too strict.  */
+          if (string_count_chr (result, '@') != 1  /* Need exactly one '@.  */
+              || *result == '@'           /* local-part missing.  */
+              || result[len-1] == '@'     /* domain missing.  */
+              || result[len-1] == '.'     /* ends with a dot.  */
+              || string_has_ctrl_or_space (result)
+              || has_dotdot_after_at (result))
+            {
+              xfree (result);
+              result = NULL;
+              errno = EINVAL;
+            }
+        }
+      else
+        errno = EINVAL;
+    }
+  else if (is_valid_mailbox (userid))
+    {
+      /* The entire user id is a mailbox.  Return that one.  Note that
+         this fallback method has some restrictions on the valid
+         syntax of the mailbox.  However, those who want weird
+         addresses should know about it and use the regular <...>
+         syntax.  */
+      result = xtrystrdup (userid);
+    }
+  else
+    errno = EINVAL;
+
+  return result? ascii_strlwr (result) : NULL;
+}
+
+
+/* Zooko's base32 variant. See RFC-6189 and
+   http://philzimmermann.com/docs/human-oriented-base-32-encoding.txt
+   Caller must xfree the returned string.  Returns NULL and sets ERRNO
+   on error.  To avoid integer overflow DATALEN is limited to 2^16
+   bytes.  Note, that DATABITS is measured in bits!.  */
+static char *
+zb32_encode (const void *data, unsigned int databits)
+{
+  static char const zb32asc[32] = {'y','b','n','d','r','f','g','8',
+                                   'e','j','k','m','c','p','q','x',
+                                   'o','t','1','u','w','i','s','z',
+                                   'a','3','4','5','h','7','6','9' };
+  const unsigned char *s;
+  char *output, *d;
+  size_t datalen;
+
+  datalen = (databits + 7) / 8;
+  if (datalen > (1 << 16))
+    {
+      errno = EINVAL;
+      return NULL;
+    }
+
+  d = output = xtrymalloc (8 * (datalen / 5)
+                           + 2 * (datalen % 5)
+                           - ((datalen%5)>2)
+                           + 1);
+  if (!output)
+    return NULL;
+
+  /* I use straightforward code.  The compiler should be able to do a
+     better job on optimization than me and it is easier to read.  */
+  for (s = data; datalen >= 5; s += 5, datalen -= 5)
+    {
+      *d++ = zb32asc[((s[0]      ) >> 3)               ];
+      *d++ = zb32asc[((s[0] &   7) << 2) | (s[1] >> 6) ];
+      *d++ = zb32asc[((s[1] &  63) >> 1)               ];
+      *d++ = zb32asc[((s[1] &   1) << 4) | (s[2] >> 4) ];
+      *d++ = zb32asc[((s[2] &  15) << 1) | (s[3] >> 7) ];
+      *d++ = zb32asc[((s[3] & 127) >> 2)               ];
+      *d++ = zb32asc[((s[3] &   3) << 3) | (s[4] >> 5) ];
+      *d++ = zb32asc[((s[4] &  31)     )               ];
+    }
+
+  switch (datalen)
+    {
+    case 4:
+      *d++ = zb32asc[((s[0]      ) >> 3)               ];
+      *d++ = zb32asc[((s[0] &   7) << 2) | (s[1] >> 6) ];
+      *d++ = zb32asc[((s[1] &  63) >> 1)               ];
+      *d++ = zb32asc[((s[1] &   1) << 4) | (s[2] >> 4) ];
+      *d++ = zb32asc[((s[2] &  15) << 1) | (s[3] >> 7) ];
+      *d++ = zb32asc[((s[3] & 127) >> 2)               ];
+      *d++ = zb32asc[((s[3] &   3) << 3)               ];
+      break;
+    case 3:
+      *d++ = zb32asc[((s[0]      ) >> 3)               ];
+      *d++ = zb32asc[((s[0] &   7) << 2) | (s[1] >> 6) ];
+      *d++ = zb32asc[((s[1] &  63) >> 1)               ];
+      *d++ = zb32asc[((s[1] &   1) << 4) | (s[2] >> 4) ];
+      *d++ = zb32asc[((s[2] &  15) << 1)               ];
+      break;
+    case 2:
+      *d++ = zb32asc[((s[0]      ) >> 3)               ];
+      *d++ = zb32asc[((s[0] &   7) << 2) | (s[1] >> 6) ];
+      *d++ = zb32asc[((s[1] &  63) >> 1)               ];
+      *d++ = zb32asc[((s[1] &   1) << 4)               ];
+      break;
+    case 1:
+      *d++ = zb32asc[((s[0]      ) >> 3)               ];
+      *d++ = zb32asc[((s[0] &   7) << 2)               ];
+      break;
+    default:
+      break;
+    }
+  *d = 0;
+
+  /* Need to strip some bytes if not a multiple of 40.  */
+  output[(databits + 5 - 1) / 5] = 0;
+  return output;
+}
+
+
+
 /* 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
+   On success the fingerprint is stored at FPRBUF and the URI will be
-   URI will be returned in an allocated buffer.  Note that the URI
+   returned in an allocated buffer.  Note that the URI might be a zero
-   might be an zero length string as this information is optiobnal.
+   length string as this information is optional.  Caller must xfree
-   Caller must xfree the returned string.
+   the returned string.  FPRBUFLEN gives the size of the expected
+   fingerprint (usually 20).
 
    On error NULL is returned and the 20 bytes at FPR are not
    defined. */
 char *
-get_pka_info (const char *address, unsigned char *fpr)
+get_pka_info (const char *address, void *fprbuf, size_t fprbuflen)
 {
-  union
+  char *result = NULL;
+  char *mbox;
+  char *domain;  /* Points to mbox.  */
+  char hashbuf[20];
+  char *hash = NULL;
+  char *name = NULL;
+  unsigned char *fpr = NULL;
+  size_t fpr_len;
+  char *url = NULL;
+
+  mbox = mailbox_from_userid (address);
+  if (!mbox)
+    goto leave;
+  domain = strchr (mbox, '@');
+  if (!domain)
+    goto leave;
+  *domain++ = 0;
+
+  sha1_hash_buffer (hashbuf, mbox, strlen (mbox));
+  hash = zb32_encode (hashbuf, 8*20);
+  if (!hash)
+    goto leave;
+  name = strconcat (hash, "._pka.", domain, NULL);
+  if (!name)
+    goto leave;
+  if (get_cert (name, 1, 16384, NULL, &fpr, &fpr_len, &url))
+    goto leave;
+  if (!fpr)
+    goto leave;
+
+  /* Return the fingerprint.  */
+  if (fpr_len != fprbuflen)
     {
-      signed char p[PACKETSZ];
+      /* fprintf (stderr, "get_dns_cert failed: fprlen (%zu/%zu)\n", */
-      HEADER h;
+      /*          fpr_len, fprbuflen); */
-    } answer;
+      goto leave;
-  int anslen;
+    }
-  int qdcount, ancount;
+  memcpy (fprbuf, fpr, fpr_len);
-  int rc;
+  /* We return the URL or an empty string.  */
-  unsigned char *p, *pend;
+  if (!url)
-  const char *domain;
+    url = xcalloc (1, 1);
-  char *name;
+  result = url;
+  url = NULL;
 
-
+ leave:
-  domain = strrchr (address, '@');
+  xfree (fpr);
-  if (!domain || domain == address || !domain[1])
+  xfree (url);
-    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))
+  xfree (hash);
-    return NULL; /* DNS resolver returned a too short answer. */
+  xfree (mbox);
-  if ( (rc=answer.h.rcode) != NOERROR )
+  return result;
-    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:
-*/

util/strgutil.c

@@ -1297,6 +1297,18 @@ ascii_memcasecmp( const char *a, const char *b, size_t n )
     return 0;
 }
 
+/* Lowercase all ASCII characters in S.  */
+char *
+ascii_strlwr (char *s)
+{
+  char *p;
+
+  for (p = s; *p; p++ )
+    if (isascii (*p) && *p >= 'A' && *p <= 'Z')
+      *p |= 0x20;
+
+  return s;
+}
 
 
 /*********************************************