Encryption/Decryption of a string

I’m using as3crypto classes for encryption/decryption of a string. The encryption is ok (I’m using the following encryption method):

var cut:ByteArray = new ByteArray(); 
var key:ByteArray = new ByteArray(); 
var random:Random = new Random(); 
random.nextBytes(key, 8); 
var aes:ICipher = Crypto.getCipher("blowfish-ecb", key, Crypto.getPad("pkcs5"));

Now, I’m trying to decrypt the encrypted string using the same method, but I can’t and I don’t know why. Every time I’m debugging my air application I’m receiving an error (something about the decrypt() and IPad).
Can you help me to solve this problem? How to use the same method to decrypt?
Thanks in advance,