I cannot find any good (complete) documentation on how to exchange a public/private key signed message in Java.
I have yet to find a concise document on the minimum steps needed to generate a public key and private key using DSA, sign a byte[], and verify it.
The documentation from Oracle is too broken up and requires running across multiple JVMs.
I have successfully signed a byte array with a private key and verified it with a public key.
Example.
byte[] data = "hello.".getBytes();
/* Test generating and verifying a DSA signature */
try {
/* generate a key pair */
KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA");
keyGen.initialize(1024, new SecureRandom());
KeyPair pair = keyGen.generateKeyPair();
/* create a Signature object to use
* for signing and verifying */
Signature dsa = Signature.getInstance("SHA/DSA");
/* initialize the Signature object for signing */
PrivateKey priv = pair.getPrivate();
dsa.initSign(priv);
/* Update and sign the data */
dsa.update(data);
/* Now that all the data to be signed
* has been read in, sign it */
byte[] sig = dsa.sign();
/* Verify the signature */
/* Initialize the Signature object for verification */
PublicKey pub = pair.getPublic();
dsa.initVerify(pub);
/* Update and verify the data */
dsa.update(data);
boolean verifies = dsa.verify(sig);
Assert.assertTrue(verifies);
} catch (Exception e) {
System.err.println("Caught exception " + e.toString());
}
In this version, I serialize the public key into a byte array and then create a PublicKey from that byte array.
byte[] data = "hello.".getBytes();
/* Test generating and verifying a DSA signature */
try {
/* generate a key pair */
KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DSA");
keyGen.initialize(1024, new SecureRandom());
KeyPair pair = keyGen.generateKeyPair();
/* create a Signature object to use
* for signing and verifying */
Signature dsa = Signature.getInstance("SHA/DSA");
/* initialize the Signature object for signing */
PrivateKey priv = pair.getPrivate();
dsa.initSign(priv);
/* Update and sign the data */
dsa.update(data);
/* Now that all the data to be signed
* has been read in, sign it */
byte[] sig = dsa.sign();
/* Verify the signature */
/* Initialize the Signature object for verification */
PublicKey pub = pair.getPublic();
/* Encode the public key into a byte array */
byte[] encoded = pub.getEncoded();
/* Get the public key from the encoded byte array */
PublicKey fromEncoded = KeyFactory.getInstance("DSA", "SUN").generatePublic(new X509EncodedKeySpec(encoded));
dsa.initVerify(fromEncoded);
/* Update and verify the data */
dsa.update(data);
boolean verifies = dsa.verify(sig);
Assert.assertTrue(verifies);
} catch (Exception e) {
System.err.println("Caught exception " + e.toString());
}