Shell script to decode and encode TP-LINK router config files

tlrecode.sh

#!/usr/bin/env bash

# tlrecode.sh
# Decode and encode TP-LINK router config files.
# Mod for TD-W8970B(DE)
#
# Creative Commons CC0 License:
# http://creativecommons.org/publicdomain/zero/1.0/
#
# To the extent possible under law, the person who associated CC0 with this
# work has waived all copyright and related or neighboring rights to this work.

in=""
out=""
mode=""

# See http://teknoraver.net/software/hacks/tplink/
key="478DA50BF9E3D2CF"

tmp_template="tlrecode.XXXXXXXXXX"
tmp=""
tmp2=""
tmp3=""

usage() {
    cat <<EOF
tlrecode.sh
Decode and encode TP-LINK router config files.

Usage: tlrecode.sh (-e|-d) [-i] INPUT [-o] OUTPUT

    -i, --input    Input file name.
    -o, --output   Output file name.
    -d, --decode   Decoding mode (default).
    -e, --encode   Encoding mode.
    -h, --help     Print this message.

EOF
}

error() {
    echo "Error: $1" >&2
    exit 1
}

decode() {
    openssl enc -d -des-ecb -K "${key}" -nopad -in "${in}" -out "${tmp}" &&
        tail -c +17 "${tmp}" > "${tmp2}" &&
        tr -d "\000" < "${tmp2}" > "${out}"
}

encode() {
    cat "${in}" > "${tmp}" &&
    truncate -s +1 "${tmp}" &&
    openssl md5 -binary "${tmp}" > "${tmp2}" && 
        cat "${tmp2}" "${tmp}" > "${tmp3}" && truncate -s %8 "${tmp3}" &&
        openssl enc -e -des-ecb -K "${key}" -nopad -in "${tmp3}" -out "${out}"
}

while [ $# -gt 0 ]; do
    case "$1" in
        -i|--input)
            [ -z "${in}" ] || error "input file '${in}' is already set."
            [ $# -gt 1 ] || error "option '$1' needs an argument."
            in="$2"
            shift 2
            ;;
        -o|--output)
            [ -z "${out}" ] || error "output file '${out}' is already set."
            [ $# -gt 1 ] || error "option '$1' needs an argument."
            out="$2"
            shift 2
            ;;
        -d|--decode)
            [ -z "${mode}" ] || error "mode '${mode}' is already set."
            mode="decode"
            shift 1
            ;;
        -e|--encode)
            [ -z "${mode}" ] || error "mode '${mode}' is already set."
            mode="encode"
            shift 1
            ;;
        -h|--help)
            usage
            exit 0
            ;;
        *)
            if [ -z "${in}" ]; then
                in="$1"
            elif [ -z "${out}" ]; then
                out="$1"
            else
                error "unexpected argument '$1'"
            fi
            shift 1
            ;;
    esac
done

[ -z "${in}" ] && error "no input file given."
[ -f "${in}" ] || error "input file '${in}' does not exist."
[ -z "${out}" ] && error "no output file given."
[ -z "${mode}" ] && mode="decode"

tmp="$(mktemp ${tmp_template})"
tmp2="$(mktemp ${tmp_template})"
tmp3="$(mktemp ${tmp_template})"

if [ "${mode}" == "decode" ]; then
    decode
else
    encode
fi

result=$?
rm "${tmp}" "${tmp2}"
exit ${result}