Java using AES 256 and 128 Symmetric-key encryption

Question

I am new in cipher technology. I found this code to do Symmetric Encryption.

byte[] key = //... secret sequence of bytes
byte[] dataToSend = ...
Cipher c = C         


        

Answer 1

From Java's docs for Cipher.init(...):

public final void init(int opmode, Key key)

Throws: InvalidKeyException - if the given key is inappropriate for initializing this cipher, or if this cipher is being initialized for decryption and requires algorithm parameters that cannot be determined from the given key, or if the given key has a keysize that exceeds the maximum allowable keysize (as determined from the configured jurisdiction policy files).

To me, this means that, as Martijn Courteaux said in his comment, you should use a key of 256 bits (i.e. initialize the SecretKeySpec with a byte array containing 32 bytes), and the cipher will accept it and use it, or reject it and throw an exception if its size is not acceptable.

If you get an exception, it's probably because you have not installed the unlimited strength crypto files, (the default JDK install allows 128 bit keys as documented in this crypto spec document). Download unlimited strength crypto package here.