CDR: anonymous PGP-only remailers

4 Oct 2000

      "cypherpunks write code", wasn't it? :)

here's my first proposal. a simple perl script that should find out
whether any given message (piped from stdin) is a PGP message or not. it
does NOT accept messages with more than 10 non-blank, non-encrypted
lines. why? well, you might have a few lines of .sig, but we don't want
to accept your spam simple because you have three fake PGP-lines at the
bottom, right?

I'm not a perl-guru, so this can most likely be reduced to less than
half the space. :)

and no, it's NOT an algorithm that can check whether something is plain-
or ciphertext. it's for PGP messages ONLY. please tell me whether or not
you find a way to make it accept spam as legitimate, or deny a PGP mail.

#!/usr/bin/perl

$is_crypted=false;
$stage=0;
$body=0;
$lines=0;
$lines_fit=0;
$other_lines=0;

while (<>) {
    if ($body==0&&/^$/) {
        $body=1;
    }
    if ($body==0) { next; }

    if ($stage==0&&/^-----BEGIN PGP MESSAGE-----$/) {
        $stage=1;
        next;
    }
    if ($stage==1&&//) {
        $stage=2;
        next;
    }
    if ($stage==2&&/^-----END PGP MESSAGE-----$/) {
        if ($lines_fit+3>$lines) {
            $stage=3;
        } else {
            print "malformed PGP message\n";
            exit 1;
        }
    }
    if ($stage==2&&/^(.*)$/) {
        $line=$1;
        $line =~ s/ //g;
        if (length($line)>0) { $lines++; }
        if (length($line)==64) { $lines_fit++; }
        next;
    }
    $other_lines++;
}
if ($other_lines>10) {
    print "too many non-encrypted lines\n";
    exit 1;
}
if ($stage==3) {
    exit 0;
} else {
    print "not a PGP message\n";
    exit 1;
}

CDR: anonymous PGP-only remailers

Tom Vogt