Digital signatures in Java

We needed this for work, so while learning I wrote this very small program.

package digisign;

import java.security.InvalidKeyException;

import java.security.KeyFactory;

import java.security.KeyPair;

import java.security.KeyPairGenerator;

import java.security.NoSuchAlgorithmException;

import java.security.PrivateKey;

import java.security.PublicKey;

import java.security.Signature;

import java.security.SignatureException;

import java.security.spec.InvalidKeySpecException;

import java.security.spec.X509EncodedKeySpec;

/*

 * http://java.sun.com/docs/books/tutorial/security/apisign/index.html

 */

public class Main {

    public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeyException, SignatureException, InvalidKeySpecException {

// create some keys

KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");

keyPairGenerator.initialize(1024);

KeyPair keyPair = keyPairGenerator.generateKeyPair();

PrivateKey privateKey = keyPair.getPrivate();

PublicKey publicKey = keyPair.getPublic();

// sign some data

byte[] data = "Hello, world!\n".getBytes();

Signature signature = Signature.getInstance("SHA1withRSA");

signature.initSign(privateKey);

signature.update(data);

byte[] sign = signature.sign();

// serialize public key and hand it over

byte[] pubKey = publicKey.getEncoded();

// store to disk, read in etc...

X509EncodedKeySpec encodedKeySpec = new X509EncodedKeySpec(pubKey);

KeyFactory keyFactory = KeyFactory.getInstance("RSA");

publicKey = keyFactory.generatePublic(encodedKeySpec);

// verify signature

signature = Signature.getInstance("SHA1withRSA");

signature.initVerify(publicKey);

signature.update(data);

boolean b = signature.verify(sign);

System.out.println("signature " + (b ? "ok." : "invalid!"));

    }

}