#!/bin/bash
#
# firma v0.2: simple encrypted mailing list aliases
# feedback: rhatto@riseup.net luis@riseup.net | GPL
#
# list configuration is passed thru the config file,
# where you put PARAMETER=value (whithout spaces)
#
# MAIL= path for mail program
# GPG= path for gnupg binary
# TMP= where you want the temp files
# LISTNAME= list email
# LISTADMIN= list administrator email addresses (space separated)
# GPGDIR= gpg dir for the lists' keyring
# PASSWD= passwd for the lists' keyring

# eval the config file
source $1

# declare GPG variables
GPGCOMMAND="$GPG --quiet --homedir $GPGDIR --batch --no-tty --no-use-agent --no-permission-warning"
GPGLIST="$GPGCOMMAND --list-keys"
GPGDECRYPT="$GPGCOMMAND --passphrase-fd 0 --decrypt"
GPGENCRYPT="$GPGCOMMAND --passphrase-fd 0 --always-trust --encrypt --sign --armor --recipient"

# declare functions
# discard $GPGDECRYPT STDOUT and get its STDERR instead, for signature checking
function GPGSTDERR {
  echo "$PASSWD" | ($GPGDECRYPT --status-fd 2 $TMP.gpg 1> /dev/null) 2>&1 ;
}

# get list susbscriber addresses
function SUBSCRIBERS {
  $GPGLIST | sed -n "/$LISTNAME/d;/pub/p" | grep -o '<.*>' | sed -e 's/[<>]//g' ;
}

# create the temporary files and restrict their permissions
rm -f $TMP $TMP.gpg
touch $TMP; chmod 600 $TMP;
touch $TMP.gpg; chmod 600 $TMP.gpg;

# todo: use an array
while read STDIN; do
  echo $STDIN >> $TMP
done

# get the message headers
# todo: find a better place for $FROMADD since its not part of the message headers
FROM=$(grep -m 1 ^From: $TMP | cut -f 2 -d :)
FROMADD=$(echo $FROMADD | if grep -q '<' ; then echo $FROMADD | grep -o '<.*>' | sed -e 's/[<>]//g' ; else echo $FROMADD ; fi)
DATE=$(grep -m 1 ^Date: $TMP)
SUBJECT=$(grep -m 1 ^Subject: $TMP | cut -f 2 -d :)

# get the encrypted message
sed -n '/-----BEGIN PGP MESSAGE-----/,/-----END PGP MESSAGE-----/p' $TMP >> $TMP.gpg

# if signature is OK, encrypt and send it for each list subscriber
# todo: declare a function to decrypt, re-encrypt and send the list messages
if (GPGSTDERR | grep -q 'GOODSIG') ; then

  for EMAIL in $(SUBSCRIBERS); do 

    echo "$PASSWD
    Message from: $FROM
    Subject: $SUBJECT
    $DATE

    $(GPGSTDERR | grep 'gpg: Signature made')
    $(GPGSTDERR | grep 'gpg: Good signature from')

$(echo "$PASSWD" | $GPGDECRYPT $TMP.gpg 2> /dev/null)" | sed -e 's/=20$//' | $GPGENCRYPT $EMAIL | $MAIL -r $LISTNAME $EMAIL

  done

# else, if signature is BAD, email it back to sender and to list admins
elif (GPGSTDERR | grep -q 'BADSIG') ; then

    echo "$PASSWD
    Message from: $FROM
    Subject: [BAD SIGNATURE] $SUBJECT
    $DATE

    $(GPGSTDERR | grep 'gpg: Signature made')
    $(GPGSTDERR | grep 'gpg: BAD signature from')

$(echo "$PASSWD" | $GPGDECRYPT $TMP.gpg 2> /dev/null)" | sed -e 's/=20$//' | $GPGENCRYPT $LISTADMIN $FROMADD | $MAIL -r $LISTNAME $LISTADMIN $FROMADD

# else, probably either the message was not signed or the sender is not subscribed to the list
# email the message back to sender including a note about this
# todo: parse STDERR to find out why the signature couldn't be checked and send more specific errors back to sender
else

    echo "
    Message from: $FROM
    Subject: [RETURNED MAIL] $SUBJECT
    $DATE

    [ It was not possible to process this message. Either or both
      the message was not encrypted and/or signed, or you are not
      subscribed to this list.  Contact the list administrator if
      you have any questions. ]

    -- 
    firma v0.2" | $MAIL -r $LISTNAME $FROMADD

fi
 
rm -f $TMP $TMP.gpg