Automatic Key retrieval in procmail

This is some procmail code and a shell script to collect pgp keys that are used to sign or encrypt mail that you recieve.

Right now, it only collects keys that are on the key servers, although it would be easy to look for finger near pgp, and extract keys there. I haven't written that code because I think that finger for pgp key is philisophically wrong. Anyone (behind firewalls, over UUCP links) can use this code just as well as someone on a T3.

I've been thinking of adding an http mode that uses netcat to grab keys, but its a lot of complexity, and since I'm sorting mail into boxes anyway, I've found that the email retreival is fast enough to get keys before I get to see most messages.

The code

This rule set exists becuase I often made mistakes, and got sent the whole damn ring. Also, I don't need to see failures, except by looking at my procmail log files. The key handling is before the key retreival to avoid loops when a key comes in.

:0
* From bal@swissnet.ai.mit.edu
{
   :0 h
   * >10000
   /dev/null

   :0 h
   *^Subject:.*no keys match
   /dev/null

	# This doesn't belong here.  Its for when I send in a key, but
	# it protects the next rule from barfing.  
   :0:
   *Subject: Your command, ADD
   $DEFAULT

   :0E
   | pgp +batchmode -fka
}

# auto key retreival

:0BW
* -----BEGIN PGP
*!^FROM_DAEMON
KEYID=|/home/adam/bin/sender_unknown

#
# I have an elm alias, pgp, points to a keyserver
# The logfile gets unset briefly to keep the elm lines out of my
# logfile.

:0 ahc	# added h 8 jan 95
* ! ^X-Loop: Adams autokey retreival.
| formail -a"X-Loop: Adams akr" |elm -s"mget $KEYID" pgp

This line could replace the elm line above, but I haven't tested it. nc is netcat. Ask your vendor why its not included, and get it yourself. FTP netcat

| echo "GET /pks/lookup?op=get&exact=on&search=$KEYID" | nc big-screw.mit.edu 11371

This next bit is the sender unknown script. Its longer than it strictly needs to be for readability.

#!/bin/sh
# sender_unknown returns a keyid, exits 1 if the key is known
# $output is to get the exit status. Othierwise, this would be a one
liner.
OUTPUT=`pgp -f +VERBOSE=0 +batchmode  -o /dev/null`
echo $OUTPUT | egrep -s 'not found in file'
EV=$? 
if [ $EV -eq 0 ]; then 
        echo $OUTPUT | awk '{print $6}' 
fi
exit $EV