#!/bin/bash
# auth2aes wraps "openssl enc" protect a file with a password
# with aes-256-cbc, with a pbkdf2-derived key.
# This file could be a ~/.bash_aliases or source'd from another script.

# 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 <https://www.gnu.org/licenses/>.

# Copyright © 2021 Ludovic Pouzenc <ludovic@pouzenc.fr>

alias auth2aes="_auth2aes e"
alias aes2auth="_auth2aes d"
_auth2aes() {
	local aespass
	local aespass2
	local res
	local out
	local status=0
	local iterations=XXX #TODO Choose a number > 800000 here, should be ~1 sec of CPU workload
	local action="$1"; shift
	
	# Minimal "usage" / help if called without any args
	if [[ $# -eq 0 || ( "e" != "$action" && "d" != "$action" ) ]]; then
		echo "Usage: auth2aes <filepath-to-encrypt>..." >&2
		echo "       aes2auth <filepath-to-decrypt>..." >&2
		return 1
	fi
	# Interactive password input (2 times if encrypt)
	read -sp "Please enter the password to derive the key from (undisplayed): " aespass
	res=$?; echo
	if [[ $res -ne 0 || -z "$aespass" ]]; then
		echo "Wrong input" >&2
		return 2
	fi
	if [ "e" == "$action" ]; then
		read -sp "Please confirm by typing it again: " aespass2
		res=$?; echo
		if [[ $res -ne 0 || "$aespass" != "$aespass2" ]]; then
			echo "Wrong input" >&2
			return 3
		fi
	fi
	# for each command-line arg 
	while [ -n "$1" ]; do
		# skip file if unreadable
		if [ ! -r "$1" ]; then
			echo "Unreadable file: '$1'" >&2
			status=$((status|4))
			shift; continue
		fi
		# Append or remove .aes output file extension according to $action
		[ "e" == "$action" ] && out="$1.aes" || out="${1%.aes}"

		# Encode or decode verbosely
		[ "d" == "$action" ] && echo "Decrypting '$1' => '$out'"
		echo $aespass | openssl enc -$action -pass stdin -aes-256-cbc -pbkdf2 -iter $iterations -in "$1" -out "$out"

		if [ $? -eq 0 ]; then
		       [ "e" == "$action" ] && echo "File '$1' encrypted with aes-256-cbc pbkdf2 $iterations iterations => '$out'"
		       [ "d" == "$action" ] && echo "Success"
		else
		    echo "failure with openssl enc -$action" >&2
			status=$((status|8))
		fi
		shift
	done
	return $status
}