#!/bin/bash -e

# Copyright 2020 Pyckle
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

IMG_TO_SIGN=$1
SIGNED_IMG_OUT=${2:-"$IMG_TO_SIGN.signed.bin"}

SALT_SIG_1="57c5375741c30ca9ebcb36713db4ba51"
SALT_SIG_2="ab0dff19af8842cdb70a86b4b68d23f7"
MAGIC_COFFEE=00c0ffee

if [ -z "$IMG_TO_SIGN" ] || [ ! -f "$IMG_TO_SIGN" ] ; then
    echo "Usage $0 <image to sign> <out img>"
    exit
fi
if [ -f "$SIGNED_IMG_OUT" ] ; then
    echo "Cowardly refusing to clobber $SIGNED_IMG_OUT"
    exit
fi

SECOND_TO_LAST_COFFEE=$(tail -c 24 "$IMG_TO_SIGN"|head -c4|xxd -p)
LAST_COFFEE=$(tail -c 4 "$IMG_TO_SIGN"|xxd -p)

INPUT_SIZE="$(stat --printf="%s" "$IMG_TO_SIGN")"
if [ "$LAST_COFFEE" == "$MAGIC_COFFEE" ] ; then
    echo "Image is already single signed. Removing first signature."
    INPUT_SIZE=$(expr $INPUT_SIZE - 20)
    if [ $SECOND_TO_LAST_COFFEE == "$MAGIC_COFFEE" ] ; then
        echo "Image is already double signed. Removing second signature."
        INPUT_SIZE=$(expr $INPUT_SIZE - 20)
    fi
else
    echo "Image is unsigned. Adding both signatures."
fi

head -c "$INPUT_SIZE" "$IMG_TO_SIGN" > "$SIGNED_IMG_OUT"

# add some extra padding. This is done on all of the firmware that is on D-link's site.
# if it is already there, it hopefully shouldn't hurt things
echo -n "c0ffeesign" >> "$SIGNED_IMG_OUT"

function addSignature()
{
    SALT="$1"
    SIGNATURE=$( (echo "$SALT" | xxd -r -p ; cat "$SIGNED_IMG_OUT") | md5sum -b | awk '{print $1}')
    echo "Salted MD5 Signature is $SIGNATURE"
    echo -n "$SIGNATURE$MAGIC_COFFEE" | xxd -r -p >> "$SIGNED_IMG_OUT"
}

addSignature $SALT_SIG_1
addSignature $SALT_SIG_2

echo "Signing complete. Signed firmware written to $SIGNED_IMG_OUT"