AES key size in Java

Question

Testing RSA to encrypt an AES key, I realized that RSA has only 1 block with a limited size (settable by the programmer) do store the encrypted key. The question is, when I use:

KeyGenerator.getInstance("AES").generateKey()

the AES keys will have a constant size in every computer and jvm implementation?

Answer 1

There is an init method in the KeyGenerator that allows you to specify the number of bits.

KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
keyGenerator.init(128);
SecretKey key = keyGenerator.generateKey();

Will that do what you need?

The default appears to be 128 bits, but I would not assume that all JVM's use the same default, or that it will always be the default.