#!/bin/bash
#
# firma v0.2.2: 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

# if the configuration file exists, disable "sourcepath" and evaluate the parameters
if [ -f $1 ]; then
  shopt -u sourcepath && source $1
else
  echo -e "\nConfiguration file \"$1\" could not be found.\n"
  exit
fi

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

# check configuration file parameters
# todo: check if $TMP directory/files exist
if [ ! -f $GPG -o ! -x $GPG ]; then
  echo -e "\n$1: GPG binary ($GPG) could not be found.\n"
  exit
elif [ ! -f $MAIL -o ! -x $MAIL ]; then
  echo -e "\n$1: Mail program ($MAIL) could not be found.\n"
  exit
elif [ ! -d $GPGDIR -o ! -f $GPGDIR/pubring.gpg -o ! -f $GPGDIR/secring.gpg ]; then
  echo -e "\n$1: GPG home directory ($GPGDIR) or the GPG keyrings could not be found.\n"
  exit
elif [ -z "$(cat $1 | grep -o ^PASSWD=\'[^\']*\'$)" -o \
       -z "$(echo -n $PASSWD)" -o \
       "$(echo -n $PASSWD | wc -m)" -lt "25" -o \
       -z "$(echo -n $PASSWD | grep -o [[:lower:][:upper:]])" -o \
       -z "$(echo -n $PASSWD | grep -o [[:digit:]])" -o \
       "$(echo -n $PASSWD | grep -o [[:punct:]] | wc -l)" -lt "5" ]; then
  echo -e "\n$1: PASSWD is empty or does not meet the minimum complexity requirements."
  echo "$1: Please set a new passphrase for the list's private key. Make it at least"
  echo "$1: 25 characters long (using a combination of letters, numbers and at least"
  echo "$1: 5 special characters) and enclose it in 'single quotes'. The passphrase"
  echo -e "$1: itself, though, cannot contain any single quote.\n"
  exit
elif [ -z "$($GPGLIST | grep ^pub | cut -d : -f 10 | grep -i \<$LISTNAME\>$)" ]; then
  echo -e "\n$1: GPG key for list \"$LISTNAME\" could not be found."
  echo -e "$1: Note that this parameter expects an email address.\n"
  exit
else
  for ADMIN in $LISTADMIN; do {
    if [ -z "$($GPGLIST | grep ^pub | cut -d : -f 10 | grep -i \<$ADMIN\>$)" ]; then
      echo -e "\n$1: GPG key for list administrator \"$ADMIN\" could not be found."
      echo -e "$1: Note that this parameter expects one or more space separated email addresses.\n"
      exit
    fi; }
  done
fi

# 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 {
  $GPGLIST | sed -ne "/$LISTNAME/Id" -e '/pub/p' | cut -d : -f 10 | 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 and the sender's email address
FROM=$(grep -m 1 ^From: $TMP | cut -d : -f 2- | sed -e 's/^ //')
FROMADD=$(if [ -z "$(echo $FROM | grep '>$')" ] ; then echo $FROM ; else echo $FROM | grep -o '<[^<>]*>$' | sed -e 's/[<>]//g' ; fi)
DATE=$(grep -m 1 ^Date: $TMP)
SUBJECT=$(grep -m 1 ^Subject: $TMP | cut -d : -f 2- | sed -e 's/^ //')

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

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

  for EMAIL in $(SUBSCRIBERS); do 

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

    $(GPGSTDERR | grep -F 'gpg: Signature made')
    $(GPGSTDERR | grep -F '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 the list admins and to sender
elif (GPGSTDERR | grep -Fq BADSIG) ; then

  for EMAIL in $(echo $LISTADMIN $FROMADD); do

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

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

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

  done

# 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 v0.2.2" | $MAIL -r $LISTNAME $FROMADD

fi
 
rm -f $TMP $TMP.gpg