#!/bin/bash
#
# .---.                  .              .
# |                      |              |
# |--- .--. .-.  .-.  .-.|  .-. .--.--. |.-.  .-. .--.  .-.
# |    |   (.-' (.-' (   | (   )|  |  | |   )(   )|  | (.-'
# '    '     --'  --'  -' -  -' '  '   -' -'   -' '   -  --'
#
#                    Freedom in the Cloud
#
# A script which splits a user's gpg key into fragments which
# may then be shared

# To get a random fragment
# get a random fragment
#     fragment_files=($FRAGMENTS_DIR/*)
#     FRAGMENT_FILE="${files[RANDOM % ${#files[@]}]}"

# License
# =======
#
# Copyright (C) 2015 Bob Mottram <bob@robotics.uk.to>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.

KEY_FRAGMENTS=3
MY_USERNAME=
MY_EMAIL_ADDRESS=
PASSPHRASE=

function show_help {
    echo ''
    echo 'freedombone-splitkey -u [username] -n [number of fragments] -e [email address] -p [passphrase]'
    echo ''
    exit 0
}

while [[ $# > 1 ]]
do
key="$1"

case $key in
    -h|--help)
    show_help
    ;;
    -u|--user)
    shift
    MY_USERNAME="$1"
    ;;
    -n|--fragments)
    shift
    KEY_FRAGMENTS=$1
    ;;
    -e|--email)
    shift
    MY_EMAIL_ADDRESS=$1
    ;;
    -p|--passphrase)
    shift
    PASSPHRASE=$1
    ;;
    *)
    # unknown option
    ;;
esac
shift
done

if [ ! $MY_USERNAME ]; then
    show_help
fi
if [ ! -d /home/$MY_USERNAME ]; then
    echo "User $MY_USERNAME does not exist on the system"
    exit 7270
fi

if [ ! -d /home/$MY_USERNAME/.gnupg ]; then
    echo 'No gpg key found'
    exit 5393
fi

FRAGMENTS_DIR=/home/$MY_USERNAME/.gnupg_fragments
if [ -d $FRAGMENTS_DIR ]; then
    exit 0
fi

# get the gpg key ID
if [ ! $MY_EMAIL_ADDRESS ]; then
    MY_EMAIL_ADDRESS=$MY_USERNAME@$HOSTNAME
fi
KEYID=$(su -c "gpg --list-keys $MY_EMAIL_ADDRESS | grep 'pub '" - \
        $MY_USERNAME | awk -F ' ' '{print $2}' | awk -F '/' '{print $2}')

# create the key file
KEYS_FILE=/home/$MY_USERNAME/tempdatafile.asc
gpg --output /home/$MY_USERNAME/pubkey.txt --armor --export $KEYID
if [ ! "$?" = "0" ]; then
    echo "Unable to extract public key for $KEYID"
    exit 7835
fi
gpg --output /home/$MY_USERNAME/privkey.txt --armor --export-secret-key $KEYID
if [ ! "$?" = "0" ]; then
    echo "Unable to extract private key for $KEYID"
    exit 7823
fi
cat /home/$MY_USERNAME/pubkey.txt /home/$MY_USERNAME/privkey.txt > $KEYS_FILE
shred -zu /home/$MY_USERNAME/privkey.txt
shred -zu /home/$MY_USERNAME/pubkey.txt

# generate a random passphrase if one isn't supplied
if [ ! $PASSPHRASE ]; then
    PASSPHRASE="$(openssl rand -base64 100)"
fi

# encrypt the keys file with a passphrase
echo "$PASSPHRASE" | gpg --passphrase-fd 0 --output $KEYS_FILE.gpg --symmetric $KEYS_FILE
if [ ! "$?" = "0" ]; then
    echo "Unable to encrypt the data prior to splitting"
    exit 7352
fi
shred -zu $KEYS_FILE

# split the passphrase into shares
echo "$PASSPHRASE" | ssss-split -q -t $KEY_FRAGMENTS -n $KEY_FRAGMENTS > \
                                /home/$MY_USERNAME/.gnupg_fragments/shares.txt

# (maybe) overwrite passphrase after use
PASSPHRASE="$(openssl rand -base64 100)"

# check that passphrase shares were created
if [ ! -f /home/$MY_USERNAME/.gnupg_fragments/shares.txt ]; then
    echo 'Passphrase for key fragments could not be split'
    shred -zu $KEYS_FILE.gpg
    exit 74549
fi

# generate fragments
GPG_KEYS_SIZE_BYTES=$(wc -c <"$KEYS_FILE.gpg")
GPG_BYTES_PER_FRAGMENT=$((GPG_KEYS_SIZE_BYTES / KEY_FRAGMENTS))
GPG_BYTES_PER_FRAGMENT=$((GPG_BYTES_PER_FRAGMENT + 1))
mkdir -p $FRAGMENTS_DIR
split --bytes=$GPG_BYTES_PER_FRAGMENT $KEYS_FILE.gpg $FRAGMENTS_DIR/data
chown -R $MY_USERNAME:$MY_USERNAME $FRAGMENTS_DIR
chmod -R 600 $FRAGMENTS_DIR

# delete the keys file
shred -zu $KEYS_FILE.gpg

echo "$KEY_FRAGMENTS key fragments created"

exit 0