eg : "This is the key"
...this would not work : "this is the key"
By processing encrypt.php you overwrite string.txt
...so protect the page encrypt.php by setting a password.
Warning : If you connect from a public Pc, or from any occasional Pc, do not forget to make proper settings in order not to memorize you key when you access your encript-decrypt pages. If you feel you might overlook this precaution, then you better change the input type of the key field into password, you will then view just ***** while typing your key and will leave nothing in the occasional Pc you will be using.