Message Signature
Cryptographic signatures are based on public/private key pairs. In contrast
to MACs they allow anyone to verify the
integrity of a message with the public key. Signatures are the core building
blocks in cryptography to create chains of trust. For example SSL
certificates are signed by certification authorities. By knowing the public
keys of the trusted certification authorities a web browser can verify the
certificates offered by a web site.
Since Java 1.1
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.Signature;
public class MessageSignature {
public static void main(String[] args) throws Exception {
KeyPair keypair = KeyPairGenerator.getInstance("RSA").genKeyPair();
Signature signature = Signature.getInstance("SHA256withRSA");
// Sign a message with the private key:
signature.initSign(keypair.getPrivate());
signature.update("The price is 39.99€".getBytes());
byte[] signed = signature.sign();
// Verify the message with the public key:
signature.initVerify(keypair.getPublic());
signature.update("The price is 39.99€".getBytes());
System.out.println(signature.verify(signed));
// When the message is altered the signature cannot be verified:
signature.initVerify(keypair.getPublic());
signature.update("The price is 29.99€".getBytes());
System.out.println(signature.verify(signed));
}
}
This snippet at GitHub
