prependKey

#!/usr/bin/env bash
# Jacob Alexander 2017
# Prepends a 64 bit value to the beginning of a file
# Used to add/modify security key for the Kiibohd Bootloader

# Error out on issues
set -e

# Check for an argument
if [ $# -eq 0 ]; then
	echo "Requires at least one argument."
	echo "$0 <filename> [<key1> <key2>]"
fi

# Detect which OS
case "$OSTYPE" in
# macOS
"darwin"*)
	echo "${OSTYPE}/macOS uses gsed instead of sed."
	SED=gsed
	;;
*)
	SED=sed
	;;
esac

input_file=${1}
tmp_file=newbin.bin
CLEARKEY=${CLEARKEY:-false}
STRIPKEY=${STRIPKEY:-false}
BLOCK_SIZE=${BLOCK_SIZE:-1024}
KEY_SIZE=${KEY_SIZE:-8}

# Check for 2nd argument, then convert to an base 10 integer
if [ $# -eq 2 ]; then
	key=$((${2}))

# Otherwise, use a zero'd key
else
	key=0
fi

# If PREPENDKEY is set, use that
if [ ! -z "${PREPENDKEY}" ]; then
	key=$((${PREPENDKEY}))
fi

# Check if valid file
if [ ! -e ${input_file} ]; then
	echo "${input_file} is not a valid file"
	exit 1
fi

# Read the first 4 bytes to determine if this is a valid file
# XXX (HaaTa) This check may not always be valid
cur_key=$(head -c 4 ${input_file} | hexdump -C | cut -b9- | cut -d"|" -f1 | tr -d ' \t\n\r')

# Check if key is unset
# 00200020 - mk20dx128vlf5
# 00400020 - mk20dx128vlh7
# 00800020 - mk20dx256vlh7
# 00000120 - mk22fx512avlh12
# d8650020 - sam4s8b
if [ "${cur_key}" = "00800020" ] \
		|| [ "${cur_key}" = "00200020" ] \
		|| [ "${cur_key}" = "00000120" ] \
		|| [ "${cur_key}" = "00400020" ] \
		|| [ "${cur_key}" = "908b0020" ]; then
	echo "Setting new key"
else
	# Check if CLEARKEY was set to true
	if ${CLEARKEY} || ${STRIPKEY}; then
		# Strip first 1024 bytes
		dd bs=${BLOCK_SIZE} skip=1 if=${input_file} of=${tmp_file} &> /dev/null
		# Overwrite old file
		mv ${tmp_file} ${input_file}

		# Do not prepend a new key
		if ${STRIPKEY}; then
			exit 0
		fi
	else
		echo "Key already set!: ${cur_key}"
		exit 1
	fi
fi

# Generate printf key
# XXX (HaaTa) Currently only the mk20dx256vlh7 is supported
# The key must sit in it's own block (which is 1024 bytes)
# This means we have to pad 1016 bytes in addition to the 8 bytes to the beginning of the file
#    8 * 2 = 16 digits
# 1016 * 2 = 2032 digits
PAD_LENGTH=$(( (${BLOCK_SIZE}-${KEY_SIZE}) * 2 ))
output_key=$(printf "%016X" ${key})
echo "Key Prepended: ${output_key}"

# 4 bytes at a time, then re-order to Little-Endian
# XXX (HaaTa) This seems to not work on macOS (removing the tailing I breaks the formatting...)
echo ${output_key}$(printf "%0${PAD_LENGTH}X" 0) | ${SED} 's/\([0-9A-F]\{2\}\)\([0-9A-F]\{2\}\)\([0-9A-F]\{2\}\)\([0-9A-F]\{2\}\)/\\\\\\x\4\\\\\\x\3\\\\\\x\2\\\\\\x\1/gI' | xargs printf > ${tmp_file}

# Append old file onto new one
cat ${input_file} >> ${tmp_file}

# Overwrite old file
mv ${tmp_file} ${input_file}