Reading and Writing a SecretKey to a file

Question

I'm looking to be able to save a DES SecretKey to a file, so you can import and use it later on. I've looked at a few routes, but they all seem a bit long winded, is there no conscise simple way of doing this?

Answer 1

The most "natural" way to save a SecretKey into a file in Java is to use a KeyStore: that's exactly what it's for (although you can save certificates too, of course).

The example in the documentation shows how to save a private key and a secret key. It will also encrypt it with a protection parameter (password here).

Answer 2

javax.crypto.SecretKey extends java.security.Key

java.security.Key extends java.io.Serializable

So if you trust the file-system to which you're storing keys, you can write out a key using java.io.ObjectOutputStream and read it in using java.io.ObjectInputStream.

ObjectOutputStream oout = new ObjectOutputStream(outputStream);
try {
  oout.writeObject(myKey);
} finally {
  oout.close();
}

and the input looks similar

Key key;
ObjectInputStream oin = new ObjectInputStream(inputStream);
try {
  key = (Key) oin.readObject();
} finally {
  oin.close();
}

To generate a key, you need a KeyFactory or SecretKeyFactory

SecretKeyFactory factory = SecretKeyFactory.getInstance(algorithm);

and then to generate a secret

factory.generateSecret(keySpec);

given a key spec that is appropriate to the algorithm. See the KeySpec javadoc for pointers to algorithm specific KeySpec implementations.

For DES, see DESKeySpec though you might want something more modern.