This web application uses RIJNDAEL-256 Block Cipher with a Symetric Key algorithm in CTR mode and base 64 encodes your message. Nothing is stored on this server except the functions for encrypting and decrypting. The Secret Key and Messages are your responsibility. You and the message recepient agree on a secret key and use this app to encrypt and decrypt the notes you pass to each other. Andrew Johnson has a Fantastic Tutorial & Class if you would like to learn more about using libmcrypt with PHP.