[PATCH] anti-forgery

[Billy D. <bi...@da...>]

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Here's a patch to do forgery checks.  They are enabled by default.
You'll need to get String::Approx from CPAN for this to work.
I've been testing it out and it's working really well.
I hope GPG doesn't mangle my patch..


diff --exclude Makefile --exclude blib --exclude CVS -ru pgpenvelope.orig/Makefile.PL pgpenvelope/Makefile.PL
- --- pgpenvelope.orig/Makefile.PL	Tue Oct  3 06:32:54 2000
+++ pgpenvelope/Makefile.PL	Tue Oct  3 06:30:53 2000
@@ -14,6 +14,7 @@
 		       'Term::ReadLine::Gnu' => 1.01,
 		       'GnuPG::Interface'    => 0.10,
 		       'Class::MethodMaker'  => 0.96,
+		       'String::Approx'      => 3.13,
 		      };
 
 print
diff --exclude Makefile --exclude blib --exclude CVS -ru pgpenvelope.orig/lib/PGPEnvelope/Config.pm pgpenvelope/lib/PGPEnvelope/Config.pm
- --- pgpenvelope.orig/lib/PGPEnvelope/Config.pm	Tue Oct  3 06:32:54 2000
+++ pgpenvelope/lib/PGPEnvelope/Config.pm	Tue Oct  3 06:21:56 2000
@@ -171,6 +171,16 @@
        'signing-key'
        => PGPEnvelope::Config::Definition->new
        ( ARGCOUNT => 1 ),
+
+       'forgery-warning'
+       => PGPEnvelope::Config::Definition->new
+       ( ARGCOUNT => 1,
+         DEFAULT => '[WARNING:not from pgpenvelope]',
+       ),
+
+       'do-forgery-check'
+       => PGPEnvelope::Config::Definition->new
+       ( DEFAULT => 1 ),
        
       );
     
@@ -321,6 +331,17 @@
 #top-border          = $defs{'top-border'}->{DEFAULT}
 #info-top-border     = $defs{'info-top-border'}->{DEFAULT}
 #info-bottom-Border  = $defs{'info-bottom-border'}->{DEFAULT}
+
+# An attacker could try to send you a forged message that looks as
+# though it had been passed through pgpenvelope_decrypt
+# and been verified.
+# If pgpenvelope_decrypt detects an input line matching any of your
+# pgpenvelope message borders, it will prepend a warning message
+# to those lines to warn you of a possible forgery unless you disable 
+# the forgery-warning option by setting do-forgery-check to 0.
+
+#forgery-warning = $defs{'forgery-warning'}->{DEFAULT}
+#do-forgery-check = $defs{'do-forgery-check'}->{DEFAULT}
 
 # This specifies if you only want to see the first uid and
 # subkey information for keys to encrypt to when encrypting
diff --exclude Makefile --exclude blib --exclude CVS -ru pgpenvelope.orig/pgpenvelope pgpenvelope/pgpenvelope
- --- pgpenvelope.orig/pgpenvelope	Tue Oct  3 06:32:54 2000
+++ pgpenvelope/pgpenvelope	Tue Oct  3 06:51:35 2000
@@ -121,7 +121,7 @@
     * ^-----BEGIN PGP
     pgpenvelope-backup
      
- -    :0 abfw
+    :0 bfw
     | (path_to)/pgpenvelope_decrypt --filter
 
 
diff --exclude Makefile --exclude blib --exclude CVS -ru pgpenvelope.orig/pgpenvelope_decrypt pgpenvelope/pgpenvelope_decrypt
- --- pgpenvelope.orig/pgpenvelope_decrypt	Tue Oct  3 06:32:54 2000
+++ pgpenvelope/pgpenvelope_decrypt	Tue Oct  3 06:22:46 2000
@@ -32,6 +32,8 @@
 use IO::File;
 use IO::Seekable;
 use FindBin;
+use String::Approx qw( aindex );
+
 use sigtrap 'handler' => 'die_signal_handler', 'normal-signals';
 
 use GnuPG::Interface 0.10;
@@ -96,8 +98,14 @@
 $gnupg->options->meta_interactive( not $is_filter );
 $gnupg->gnupg_call( $program_call );
 
+my $do_forgery_check = $config->get('do-forgery-check');
+
 PGP_MESSAGE: while ( <STDIN> )
 {
+    if($do_forgery_check and &detect_forged_borders($_)){
+        $_ = $config->get('forgery-warning').$_;
+    }
+
     unless ( /^-----BEGIN PGP / )
     {
 	print STDOUT $_;
@@ -301,4 +309,30 @@
     {
 	print $fh $zeros;
     }
+} 
+
+#
+#  Detect forged pgpenvelope borders.
+#
+# Check a line of data.
+# Perform an approximate match against the pgpenvelope border messages.
+# If the match is not flush against the left side, then there is no
+# cause for alarm, and a 0 is returned
+#
+# return 1 if any lines were within a 10% margin. (User should be warned).
+#            This means that up to 9 characters in 10 correctly matched
+#            his border string without any edits.
+# return 0 if everything is okay.
+#
+sub detect_forged_borders
+{
+        my ($line) = @_;
+        my @bordernames = qw( top-border info-top-border info-bottom-border);
+        my @borders = map { $config->get($_) } @bordernames;
+
+        for my $b (@borders) {
+                return 1 if aindex($b, $line) == 0;
+        }
+        return 0;
 }
+

- --
"The Funk, the whole Funk, and nothing but the Funk."
Linux barcode software mirror: http://dadadada.net/cuecat
Billy Donahue <mailto:bi...@da...>
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Comment: pgpenvelope 2.9.0 - http://pgpenvelope.sourceforge.net/

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