[Nmh-workers] whitelisting by In-Reply-To

[Michael Richardson]

I have my MH's send: set up to generate message IDs itself.
  send: -msgid

It produces message IDs like:

Message-ID: <address@hidden>

When people reply to me, they often have In-Reply-To: headers,
like:

In-Reply-To: Message from Michael Richardson <address@hidden
a> of "Sat, 21 Aug 2004 22:37:08 EDT." <address@hidden> 


(and RFC2822 mandates all of this)

What's I'd like to do is to change the message ID generation code such
it takes a unique 32-bit value (derive it from time), encrypts it
with some minor check built in, and then base64 encodes it into the
message-Id.

I then want to use pick (maybe eventually procmail) to sort real replies
to me into a higher precedence folder.

I think that I can code all of this. I just wanted to run the idea by
people.

I would verify that the message id decrypted is right by encrypting
a single block with time|(time^0xffffffff). 

It produces msgid's like:
   <address@hidden> msgid is good

I prototyped it in perl. 

#!/usr/bin/perl
# cryptomsgid.pl

use MIME::Base64;
use Crypt::DES_EDE3;
use Data::Dumper;

$Data::Dumper::Useqq = 1;

$MAILDIR="$ENV{'HOME'}/Mail";

$msgidfile="$MAILDIR/.msgid";
$msgidkeyfile="$MAILDIR/.msgidkey";

$msgidunique=time();

if(open(MSGID, "$msgidfile")) {
    chop($lastmsgid=<MSGID>);

    if($msgidunique <= $lastmsgid) {
        $msgidunique = $lastmsgid+1;
    }
    close(MSGID);
} 

open(MSGID, ">$msgidfile") || die "Can not write to $msgidfile: $!\n";
print MSGID $msgidunique."\n";
close(MSGID);

if(open(KEYFILE, "$msgidkeyfile")) {
    #print STDERR "Reusing old keyfile\n";
    sysread(KEYFILE, $key, 24);
    close(KEYFILE);
} else {
    open(KEYFILE, "/dev/random") || die "can not open /dev/random: $!\n";
    open(KEYFILE2, ">$msgidkeyfile") || die "can not write to $msgidkeyfile: 
$!\n";
    sysread(KEYFILE, $key, 24);
    syswrite(KEYFILE2, $key, 24);
    close(KEYFILE);
    close(KEYFILE2);
}

my $ede3 = Crypt::DES_EDE3->new($key);

$invert = ($msgidunique ^ 0xffffffff);
#printf(STDERR "msgid: %08x invert: %08x\n",$msgidunique, $invert);

$block = pack("NN",
              ($msgidunique & 0xffffffff),
              ($invert & 0xffffffff));

#print STDERR "plain: ".Dumper($block);

$newblock = $ede3->encrypt($block);

#print STDERR "enc: ".Dumper($newblock);

$base64 = MIME::Base64::encode($newblock."|", "");

#print STDERR "base64: ".Dumper($base64);

chop($hostname=`hostname`);

print "<address@hidden>\n";

===
#!/usr/bin/perl
# checkmsgid.pl

use MIME::Base64;
use Crypt::DES_EDE3;
use Data::Dumper;

$Data::Dumper::Useqq = 1;

$MAILDIR="$ENV{'HOME'}/Mail";

$msgidfile="$MAILDIR/.msgid";
$msgidkeyfile="$MAILDIR/.msgidkey";

open(KEYFILE, "$msgidkeyfile") || die "No message key file: $msgidkeyfile\n";
sysread(KEYFILE, $key, 24);
close(KEYFILE);

my $ede3 = Crypt::DES_EDE3->new($key);
chop($hostname=`hostname`);

while(<>) {
    chop;
    $all = $_;

    if(/.*\<(.*)address@hidden>.*/) {
        $id = $1;
        
        # verify it 

        #print STDERR "ID: ".Dumper($id);

        $decoded = MIME::Base64::decode($id);
        if(substr($decoded, 8, 1) != "|") {
            print "$all is trivially not valid\n";
            next;
        }

        $encblock = substr($decoded, 0, 8);

        #print STDERR "ENC: ".Dumper($encblock);

        $plainblock=$ede3->decrypt($encblock);
        #print STDERR "plain: ".Dumper($plainblock);

        ($msgidnum, $msgidinvert) = unpack("NN", $plainblock);
        
        $msgid2 = $msgidinvert ^ 0xffffffff;

        #printf(STDERR "msgidnum: %08x invert: %08x (%08x)\n",
        #       $msgidnum, $msgidinvert, $msgid2); 
        if($msgidnum == $msgid2) {
            print "$all msgid is good\n";
        } else {
            print "$all msgid is bad\n";
        }
    } else {
        print "$all is not formatted correctly\n";
    }
}