Java Tutorial/Security/Diffie Hellman

Diffie-Hellman Key Agreement

   <source lang="java">

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 javax.crypto.KeyAgreement; import javax.crypto.spec.DHParameterSpec; public class MainClass {

 private static BigInteger g512 = new BigInteger("1234567890", 16);
 private static BigInteger p512 = new BigInteger("1234567890", 16);
 public static void main(String[] args) throws Exception {
   Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
   DHParameterSpec dhParams = new DHParameterSpec(p512, g512);
   KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DH", "BC");
   keyGen.initialize(dhParams, new SecureRandom());
   KeyAgreement aKeyAgree = KeyAgreement.getInstance("DH", "BC");
   KeyPair aPair = keyGen.generateKeyPair();
   KeyAgreement bKeyAgree = KeyAgreement.getInstance("DH", "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())));
 }

}</source>

Diffie-Hellman with Elliptic Curve

   <source lang="java">

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())));
 }

}</source>

Generating a Parameter Set for the Diffie-Hellman Key Agreement Algorithm

   <source lang="java">

import java.security.AlgorithmParameterGenerator; import java.security.AlgorithmParameters; import javax.crypto.spec.DHParameterSpec; public class Main {

 public static void main(String[] argv) throws Exception {
   AlgorithmParameterGenerator paramGen = AlgorithmParameterGenerator.getInstance("DH");
   paramGen.init(1024);
   AlgorithmParameters params = paramGen.generateParameters();
   DHParameterSpec dhSpec = (DHParameterSpec) params.getParameterSpec(DHParameterSpec.class);
   System.out.println("" + dhSpec.getP() + "," + dhSpec.getG() + "," + dhSpec.getL());
 }

}</source>

Implementing the Diffie-Hellman key exchange

   <source lang="java">

import java.math.BigInteger; import java.security.KeyFactory; import java.security.KeyPair; import java.security.KeyPairGenerator; import java.security.SecureRandom; import javax.crypto.spec.DHParameterSpec; import javax.crypto.spec.DHPublicKeySpec; public class MainClass {

 public final static int pValue = 47;
 public final static int gValue = 71;
 public final static int XaValue = 9;
 public final static int XbValue = 14;
 public static void main(String[] args) throws Exception {
   BigInteger p = new BigInteger(Integer.toString(pValue));
   BigInteger g = new BigInteger(Integer.toString(gValue));
   BigInteger Xa = new BigInteger(Integer.toString(XaValue));
   BigInteger Xb = new BigInteger(Integer.toString(XbValue));
   createKey();
   int bitLength = 512; // 512 bits
   SecureRandom rnd = new SecureRandom();
   p = BigInteger.probablePrime(bitLength, rnd);
   g = BigInteger.probablePrime(bitLength, rnd);
   
   createSpecificKey(p, g);
 }
 public static void createKey() throws Exception {
   KeyPairGenerator kpg = KeyPairGenerator.getInstance("DiffieHellman");
   kpg.initialize(512);
   KeyPair kp = kpg.generateKeyPair();
   KeyFactory kfactory = KeyFactory.getInstance("DiffieHellman");
   DHPublicKeySpec kspec = (DHPublicKeySpec) kfactory.getKeySpec(kp.getPublic(),
       DHPublicKeySpec.class);
 }
 public static void createSpecificKey(BigInteger p, BigInteger g) throws Exception {
   KeyPairGenerator kpg = KeyPairGenerator.getInstance("DiffieHellman");
   DHParameterSpec param = new DHParameterSpec(p, g);
   kpg.initialize(param);
   KeyPair kp = kpg.generateKeyPair();
   KeyFactory kfactory = KeyFactory.getInstance("DiffieHellman");
   DHPublicKeySpec kspec = (DHPublicKeySpec) kfactory.getKeySpec(kp.getPublic(),
       DHPublicKeySpec.class);
 }

}</source>