Diffie-Hellman with Elliptic Curve : Diffie Hellman « Security « Java Tutorial

1. Java Tutorial
2. Security
3. Diffie Hellman

import java.math.BigInteger;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.MessageDigest;
import java.security.SecureRandom;
import java.security.Security;
import java.security.spec.ECFieldFp;
import java.security.spec.ECParameterSpec;
import java.security.spec.ECPoint;
import java.security.spec.EllipticCurve;

import javax.crypto.KeyAgreement;

public class MainClass {
  public static void main(String[] args) throws Exception {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());

    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("ECDH", "BC");
    EllipticCurve curve = new EllipticCurve(new ECFieldFp(new BigInteger(
        "fffffffffffffffffffffffffffffffeffffffffffffffff", 16)), new BigInteger(
        "fffffffffffffffffffffffffffffffefffffffffffffffc", 16), new BigInteger(
        "fffffffffffffffffffffffffffffffefffffffffffffffc", 16));

    ECParameterSpec ecSpec = new ECParameterSpec(curve, new ECPoint(new BigInteger(
        "fffffffffffffffffffffffffffffffefffffffffffffffc", 16), new BigInteger(
        "fffffffffffffffffffffffffffffffefffffffffffffffc", 16)), new BigInteger(
        "fffffffffffffffffffffffffffffffefffffffffffffffc", 16), 1);

    keyGen.initialize(ecSpec, new SecureRandom());

    KeyAgreement aKeyAgree = KeyAgreement.getInstance("ECDH", "BC");
    KeyPair aPair = keyGen.generateKeyPair();
    KeyAgreement bKeyAgree = KeyAgreement.getInstance("ECDH", "BC");
    KeyPair bPair = keyGen.generateKeyPair();

    aKeyAgree.init(aPair.getPrivate());
    bKeyAgree.init(bPair.getPrivate());

    aKeyAgree.doPhase(bPair.getPublic(), true);
    bKeyAgree.doPhase(aPair.getPublic(), true);

    MessageDigest hash = MessageDigest.getInstance("SHA1", "BC");

    System.out.println(new String(hash.digest(aKeyAgree.generateSecret())));
    System.out.println(new String(hash.digest(bKeyAgree.generateSecret())));
  }
}