AES Cipher in Java

How to implementing AES cipher in JAVA and main problems you may find in this challenge.

When I started, I tried to do a parallel between my 3Des implementation and AES, so I discovered the first difference:

I tried to generate a SecretKey from a pass-phrase for AES in the following way,

KeySpec aesSpec = new KeySpec(key.getBytes(), "AES");
SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("AES");
SecretKey secretKey = keyFactory.generateSecret(aesSpec);

This is the very similar how I do with 3Des:

KeySpec TDesSpec = new DESKeySpec(key.getBytes());
SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DESede");
SecretKey secretKey = keyFactory.generateSecret(aesSpec);

However when I tested, it threw an exception "AES SecretKeyFactory not available".

So the solution was made some small change:

SecretKey secretKey = new SecretKeySpec(key.getBytes(), "AES");

There are two hints here:

• The key needs be multiples of 16;
• AES works with those keys sizes: 128, 192 and 256 bits.

Then, you can use the key to encrypt/decrypt, for instance, the encryption code is as follows,

// Initialize the cipher

Cipher cipher = Cipher.getInstance("AES/ECB/NoPadding");




// Define the mode [Cipher.ENCRYPT_MODE|Cipher.DECRYPT_MODE]

cipher.init(Cipher.ENCRYPT_MODE, secretKey);

cryptogram = cipher.doFinal(data);