Elliptic curve Diffie–Hellman using Bouncy Castle v1.50 example code

ECDH_BC.java

import java.math.BigInteger;
import java.security.PublicKey;
import java.security.PrivateKey;
import java.security.KeyFactory;
import java.security.Security;
import java.security.KeyPairGenerator;
import java.security.KeyPair;
import java.security.SecureRandom;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.ECGenParameterSpec;
import javax.crypto.KeyAgreement;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.jce.interfaces.ECPublicKey;
import org.bouncycastle.jce.interfaces.ECPrivateKey;
import org.bouncycastle.jce.ECNamedCurveTable;
import org.bouncycastle.jce.spec.ECParameterSpec;
import org.bouncycastle.jce.spec.ECPublicKeySpec;
import org.bouncycastle.jce.spec.ECPrivateKeySpec;
import org.bouncycastle.math.ec.ECPoint;

public class ECDH_BC
{
	final protected static char[] hexArray = "0123456789abcdef".toCharArray();
	public static String bytesToHex(byte[] bytes) {
		char[] hexChars = new char[bytes.length * 2];
		for ( int j = 0; j < bytes.length; j++ ) {
			int v = bytes[j] & 0xFF;
			hexChars[j * 2] = hexArray[v >>> 4];
			hexChars[j * 2 + 1] = hexArray[v & 0x0F];
		}
		return new String(hexChars);
	}

	public static byte [] savePublicKey (PublicKey key) throws Exception
	{
		//return key.getEncoded();

		ECPublicKey eckey = (ECPublicKey)key;
		return eckey.getQ().getEncoded(true);
	}

	public static PublicKey loadPublicKey (byte [] data) throws Exception
	{
		/*KeyFactory kf = KeyFactory.getInstance("ECDH", "BC");
		return kf.generatePublic(new X509EncodedKeySpec(data));*/

		ECParameterSpec params = ECNamedCurveTable.getParameterSpec("prime192v1");
		ECPublicKeySpec pubKey = new ECPublicKeySpec(
				params.getCurve().decodePoint(data), params);
		KeyFactory kf = KeyFactory.getInstance("ECDH", "BC");
		return kf.generatePublic(pubKey);
	}

	public static byte [] savePrivateKey (PrivateKey key) throws Exception
	{
		//return key.getEncoded();

		ECPrivateKey eckey = (ECPrivateKey)key;
		return eckey.getD().toByteArray();
	}

	public static PrivateKey loadPrivateKey (byte [] data) throws Exception
	{
		//KeyFactory kf = KeyFactory.getInstance("ECDH", "BC");
		//return kf.generatePrivate(new PKCS8EncodedKeySpec(data));

		ECParameterSpec params = ECNamedCurveTable.getParameterSpec("prime192v1");
		ECPrivateKeySpec prvkey = new ECPrivateKeySpec(new BigInteger(data), params);
		KeyFactory kf = KeyFactory.getInstance("ECDH", "BC");
		return kf.generatePrivate(prvkey);
	}

	public static void doECDH (String name, byte[] dataPrv, byte[] dataPub) throws Exception
	{
		KeyAgreement ka = KeyAgreement.getInstance("ECDH", "BC");
		ka.init(loadPrivateKey(dataPrv));
		ka.doPhase(loadPublicKey(dataPub), true);
		byte [] secret = ka.generateSecret();
		System.out.println(name + bytesToHex(secret));
	}

	public static void main (String [] args) throws Exception
	{
		Security.addProvider(new BouncyCastleProvider());

		KeyPairGenerator kpgen = KeyPairGenerator.getInstance("ECDH", "BC");
		kpgen.initialize(new ECGenParameterSpec("prime192v1"), new SecureRandom());
		KeyPair pairA = kpgen.generateKeyPair();
		KeyPair pairB = kpgen.generateKeyPair();
		System.out.println("Alice: " + pairA.getPrivate());
		System.out.println("Alice: " + pairA.getPublic());
		System.out.println("Bob:   " + pairB.getPrivate());
		System.out.println("Bob:   " + pairB.getPublic());
		byte [] dataPrvA = savePrivateKey(pairA.getPrivate());
		byte [] dataPubA = savePublicKey(pairA.getPublic());
		byte [] dataPrvB = savePrivateKey(pairB.getPrivate());
		byte [] dataPubB = savePublicKey(pairB.getPublic());
		System.out.println("Alice Prv: " + bytesToHex(dataPrvA));
		System.out.println("Alice Pub: " + bytesToHex(dataPubA));
		System.out.println("Bob Prv:   " + bytesToHex(dataPrvB));
		System.out.println("Bob Pub:   " + bytesToHex(dataPubB));

		doECDH("Alice's secret: ", dataPrvA, dataPubB);
		doECDH("Bob's secret:   ", dataPrvB, dataPubA);
	}
}

output

$ javac -cp .:bcprov-jdk15on-150.jar ECDH_BC.java
$ java -cp .:bcprov-jdk15on-150.jar ECDH_BC
Alice: EC Private Key
             S: 7b957721204d4290edcb5f1420988ddd9ab9ffc97c8905dd

Alice: EC Public Key
            X: 4384a964ca4840b4a085054764fa2f597a16a42ea822896
            Y: 62e33641881715e624851242fd7ab360dd8a908dc35d3a7a

Bob:   EC Private Key
             S: f8ec571d10500474e577633e75342319d779f2ad345ac3f7

Bob:   EC Public Key
            X: 8dcaf55783a679ae29d0cd93a236187988e3f43636e8ec8f
            Y: 7c7613d284c0b054fea567a6790c91a91cde96d1178d9a3d

Alice Prv: 7b957721204d4290edcb5f1420988ddd9ab9ffc97c8905dd
Alice Pub: 0204384a964ca4840b4a085054764fa2f597a16a42ea822896
Bob Prv:   00f8ec571d10500474e577633e75342319d779f2ad345ac3f7
Bob Pub:   038dcaf55783a679ae29d0cd93a236187988e3f43636e8ec8f
Alice's secret: 15e53462327effedb5da725bfe9610a3d106088d73e522e4
Bob's secret:   15e53462327effedb5da725bfe9610a3d106088d73e522e4