Crypt Class is a wrapper around libmcrypt_ functions, it greatly simplifies the interface and adds new features like embedded IV. It provides an easy way to encrypt and decrypt data, it automatically creates the IV and extracts it for you later.
Crypt Class stores the IV with the encrypted string so every time you encrypt a string it will look different but decrypt to the original value.
Crypt Class uses libmcrypt so twofish, blowfish, aes, and many other "real" encryption ciphers are available.
Crypt Class also makes it easy to switch between encryption modes and ciphers.