How can I get the signature of a string using SHA1withRSA
if I already have the Private Key as byte[]
or String
?
I guess what you say is you know the key pair before hand and want to sign/verify with that.
Please see the following code.
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.Signature;
import sun.misc.BASE64Encoder;
public class MainClass {
public static void main(String[] args) throws Exception {
KeyPair keyPair = getKeyPair();
byte[] data = "test".getBytes("UTF8");
Signature sig = Signature.getInstance("SHA1WithRSA");
sig.initSign(keyPair.getPrivate());
sig.update(data);
byte[] signatureBytes = sig.sign();
System.out.println("Signature:" + new BASE64Encoder().encode(signatureBytes));
sig.initVerify(keyPair.getPublic());
sig.update(data);
System.out.println(sig.verify(signatureBytes));
}
private static KeyPair getKeyPair() throws NoSuchAlgorithmException {
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(1024);
return kpg.genKeyPair();
}
}
Here you need to change the method getKeyPair() to supply your known key pair. You may load it from a java key store [JKS].
You can't just have an arbitrary byte array either as your public key or private key. They should be generated in relation.