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17 Dec 2003

      ##
In-reply-to: <199711020051.QAA23884@sirius.infonex.com> (message from Mix on
	Sat, 1 Nov 1997 16:51:19 -0800 (PST))
Subject: Re: cute.

-----BEGIN PGP SIGNED MESSAGE-----

Monty says
...
What would be really nice is if the mailing list machines time stamped
messages.
That would be nice.  I wonder, could one of our list hosts add a
script to sign outgoing majordomo traffic?

Here's a script to do it:

- --------------------8<--------------------
#!/usr/local/bin/perl
$userID="cypherpunks\@algebra.com";
$pgp="/usr/local/bin/pgp";
$tmp="/tmp/.sig$$";
undef($/);
$post = <STDIN>;
($headers,@body) = split(/\n\n/,$post);$body = join("\n\n",@body);
open(PIPE,"|$pgp -satf +batchmode +verbose=0 -u $userID > $tmp");
print PIPE $body;
close(PIPE);
open(SIGNED,"<$tmp");$signed=<SIGNED>;close(SIGNED);
print "$headers\n\n$signed";
unlink($tmp);
- --------------------8<--------------------

It handles one mail only.  If you want to run it on a mail folder, use
formail.
...
This would also prevent an attack where somebody forges mail from a
cypherpunks list machine to flush out identities.  If the attacker
sends a unique message to every person, he or she will be able to
break an identity if the message is replied to on the list.
You could do something similar with independent parties posting hashes
of messages in the feed they got to the list, or to subscribers to the
service.

The list bot signing is more convenient to check though with existing
software.  Also, unfortunately, most MUA pgp software doesn't check
nested signatures, so a signature from the list would break ability to
auto check signatures from posters.

Here's another script to check the list added signature on receipt:

- --------------------8<--------------------
#!/usr/local/bin/perl
$userID="cypherpunks\@algebra.com";
$pgp="/usr/local/bin/pgp";
$tmp="/tmp/.sig$$";$in="/tmp/.in$$";$msg="/tmp/.msg$$";
undef($/);
$post = <STDIN>;
($headers,@body) = split(/\n\n/,$post);$body = join("\n\n",@body);
open(BODY,">$in");print BODY $body;close(BODY);
$res = system("$pgp -f +batchmode +verbose=0 -u $userID < $in > $tmp 2> $msg");
open(SIGNED,"<$tmp");$signed=<SIGNED>;close(SIGNED);
open(ERR,"<$msg");$err=<ERR>;close(ERR);
if ($res==0) {
    ($who) = ($err =~ m/Good signature from user "(.*)"\./);
    if ($who !~ m/$userID/) { $res=1; }
}
$headers =~ s/\[FORGERY\]//g;
if ($res) {
    $headers =~ s/(Subject: )([^\n]*)/\1\[FORGERY\] \2/g;
}
print "$headers\n";
print "X-Signature: ", $res ? "forgery" : "ok $who", "\n";
print "\n\n$signed\n";
unlink($tmp,$in,$msg);
- --------------------8<--------------------
...
I'm not sure a timestamp matters that much for "authenticating" your
key.  After all, you don't own "Amad3us", you own key 0x4D162BBE1.
Yes.  Except for minor nit: 0x4D162BBE1 is susceptible to a 0xdeadbeef
attack, anyone can generate another key with that keyID.  Even the
fingerprint is spoofable.  But the combination is truly hard to spoof,
and this I do own: 0xa11a8a18bf6dbe8362926e9458a3616d/0x4d162bbe1
(fingerprint/keyID).

Amad3us (0xa11a8a18bf6dbe8362926e9458a3616d/0x4d162bbe1)

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iQCVAwUBNFwjxvKMuKFNFivhAQGYnAQA33Ss68TKF+QfDGweQZ7TAkbmlOeqPC/J
iBoV5zA+skqdgs+PD2afLAhQn5otm7xbx7rBEnBgMOYff9GyKB6Bfs/po7juwqs5
dACGPZhc5kNf4f18V04jv5sr6PWLWdwsoVegshVsiHmQgWtG9UlnZ0wKe2ORKzxf
sQkJsIe3/jA=
=naXX
-----END PGP SIGNATURE-----

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nobody＠REPLAY.COM