KeyPairChecker.java

import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertTrue;

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.util.Map;

import org.junit.jupiter.api.Test;

public class KeyPairChecker {

	private static Map<String, String> SIGNATURE_ALGOS = Map.of( //
			"DSA", "SHA256WithDSA", //
			"RSA", "SHA256WithRSA", //
			"EC", "SHA256WithECDSA");

	boolean isKeyPair(PrivateKey privateKey, PublicKey publicKey) throws Exception {
		if (!privateKey.getAlgorithm().equals(publicKey.getAlgorithm())) {
			return false;
		}
		var signature = Signature.getInstance(SIGNATURE_ALGOS.get(privateKey.getAlgorithm()));
		signature.initSign(privateKey);
		var signed = signature.sign();
		signature.initVerify(publicKey);
		return signature.verify(signed);
	}

	// Testing

	private KeyPair createKeyPair(String algo, int size) throws NoSuchAlgorithmException {
		var kpg = KeyPairGenerator.getInstance(algo);
		kpg.initialize(size);
		return kpg.generateKeyPair();
	}

	@Test
	void dsa_match() throws Exception {
		var pair = createKeyPair("DSA", 1024);
		assertTrue(isKeyPair(pair.getPrivate(), pair.getPublic()));
	}

	@Test
	void dsa_no_match() throws Exception {
		var pair1 = createKeyPair("DSA", 1024);
		var pair2 = createKeyPair("DSA", 1024);
		assertFalse(isKeyPair(pair1.getPrivate(), pair2.getPublic()));
	}

	@Test
	void rsa_match() throws Exception {
		var pair = createKeyPair("RSA", 1024);
		assertTrue(isKeyPair(pair.getPrivate(), pair.getPublic()));
	}

	@Test
	void rsa_no_match() throws Exception {
		var pair1 = createKeyPair("RSA", 1024);
		var pair2 = createKeyPair("RSA", 1024);
		assertFalse(isKeyPair(pair1.getPrivate(), pair2.getPublic()));
	}

	@Test
	void ec_match() throws Exception {
		var pair = createKeyPair("EC", 256);
		assertTrue(isKeyPair(pair.getPrivate(), pair.getPublic()));
	}

	@Test
	void ec_no_match() throws Exception {
		var pair1 = createKeyPair("EC", 256);
		var pair2 = createKeyPair("EC", 256);
		assertFalse(isKeyPair(pair1.getPrivate(), pair2.getPublic()));
	}

	@Test
	void algo_no_match() throws Exception {
		var pair1 = createKeyPair("RSA", 1024);
		var pair2 = createKeyPair("EC", 256);
		assertFalse(isKeyPair(pair1.getPrivate(), pair2.getPublic()));
	}

}