Wrapper around ssh-keygen, openssl, and base64 to exchange small asymmetric encrypted messages

enc_wrapper.sh

#!/bin/bash

# Copyright 2016 icasdri
#
# 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/>.


improper_usage() {
    echo 'Usage: enc_wrapper.sh (encrypt|decrypt) KEY'
    echo '    where KEY is an OpenSSH RSA key (public/private as appropriate)'
    echo
    echo 'Example: '
    echo '    To encrypt: enc_wrapper.sh enc ~/.ssh/id_rsa.pub'
    echo '    To decrypt: enc_wrapper.sh dec ~/.ssh/id_rsa'
    exit 2
}

if [ "$#" -ne 2 ]; then
    improper_usage
fi

KEY_TARGET='/tmp/enc_wrapper.pub'

umask 077
case "$1" in
    e*)
        if [ -f "$2" ]; then
            echo "Reading ssh-rsa public key from $2..."
            echo "Converting to PKCS8 format..."
            ssh-keygen -e -f "$2" -m PKCS8 > "$KEY_TARGET"
            echo "Enter message then press Return followed by Ctrl-D to end stream: "
            openssl rsautl -encrypt -inkey "$KEY_TARGET" -pubin -pkcs | base64 -w0
            echo
            echo "The last printed line is your encrypted message."
        else
            echo "Failed to read key: no such file $2"
        fi
        ;;
    d*)
        if [ -f "$2" ]; then
            echo "Reading PEM private key from $2"
            echo "Enter encrypted message then press Return followed by Ctrl-D to end stream: "
            base64 -dw0 | openssl rsautl -decrypt -inkey "$2" -pkcs
        else
            echo "Failed to read key: no such file $2"
        fi
        ;;
    *)
        improper_usage
        ;;
esac