package org.bouncycastle.crypto.examples;
import java.math.BigInteger;
import java.security.SecureRandom;
import org.bouncycastle.crypto.CryptoException;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.agreement.jpake.JPAKEPrimeOrderGroup;
import org.bouncycastle.crypto.agreement.jpake.JPAKEPrimeOrderGroups;
import org.bouncycastle.crypto.agreement.jpake.JPAKEParticipant;
import org.bouncycastle.crypto.agreement.jpake.JPAKERound1Payload;
import org.bouncycastle.crypto.agreement.jpake.JPAKERound2Payload;
import org.bouncycastle.crypto.agreement.jpake.JPAKERound3Payload;
import org.bouncycastle.crypto.digests.SHA256Digest;
/**
* An example of a J-PAKE exchange.
* <p>
*
* In this example, both Alice and Bob are on the same computer (in the same JVM, in fact).
* In reality, Alice and Bob would be in different locations,
* and would be sending their generated payloads to each other.
*/
public class JPAKEExample
{
public static void main(String args[]) throws CryptoException
{
/*
* Initialization
*
* Pick an appropriate prime order group to use throughout the exchange.
* Note that both participants must use the same group.
*/
JPAKEPrimeOrderGroup group = JPAKEPrimeOrderGroups.NIST_3072;
BigInteger p = group.getP();
BigInteger q = group.getQ();
BigInteger g = group.getG();
String alicePassword = "password";
String bobPassword = "password";
System.out.println("********* Initialization **********");
System.out.println("Public parameters for the cyclic group:");
System.out.println("p (" + p.bitLength() + " bits): " + p.toString(16));
System.out.println("q (" + q.bitLength() + " bits): " + q.toString(16));
System.out.println("g (" + p.bitLength() + " bits): " + g.toString(16));
System.out.println("p mod q = " + p.mod(q).toString(16));
System.out.println("g^{q} mod p = " + g.modPow(q, p).toString(16));
System.out.println("");
System.out.println("(Secret passwords used by Alice and Bob: " +
"\"" + alicePassword + "\" and \"" + bobPassword + "\")\n");
/*
* Both participants must use the same hashing algorithm.
*/
Digest digest = new SHA256Digest();
SecureRandom random = new SecureRandom();
JPAKEParticipant alice = new JPAKEParticipant("alice", alicePassword.toCharArray(), group, digest, random);
JPAKEParticipant bob = new JPAKEParticipant("bob", bobPassword.toCharArray(), group, digest, random);
/*
* Round 1
*
* Alice and Bob each generate a round 1 payload, and send it to each other.
*/
JPAKERound1Payload aliceRound1Payload = alice.createRound1PayloadToSend();
JPAKERound1Payload bobRound1Payload = bob.createRound1PayloadToSend();
System.out.println("************ Round 1 **************");
System.out.println("Alice sends to Bob: ");
System.out.println("g^{x1}=" + aliceRound1Payload.getGx1().toString(16));
System.out.println("g^{x2}=" + aliceRound1Payload.getGx2().toString(16));
System.out.println("KP{x1}={" + aliceRound1Payload.getKnowledgeProofForX1()[0].toString(16) + "};{" + aliceRound1Payload.getKnowledgeProofForX1()[1].toString(16) + "}");
System.out.println("KP{x2}={" + aliceRound1Payload.getKnowledgeProofForX2()[0].toString(16) + "};{" + aliceRound1Payload.getKnowledgeProofForX2()[1].toString(16) + "}");
System.out.println("");
System.out.println("Bob sends to Alice: ");
System.out.println("g^{x3}=" + bobRound1Payload.getGx1().toString(16));
System.out.println("g^{x4}=" + bobRound1Payload.getGx2().toString(16));
System.out.println("KP{x3}={" + bobRound1Payload.getKnowledgeProofForX1()[0].toString(16) + "};{" + bobRound1Payload.getKnowledgeProofForX1()[1].toString(16) + "}");
System.out.println("KP{x4}={" + bobRound1Payload.getKnowledgeProofForX2()[0].toString(16) + "};{" + bobRound1Payload.getKnowledgeProofForX2()[1].toString(16) + "}");
System.out.println("");
/*
* Each participant must then validate the received payload for round 1
*/
alice.validateRound1PayloadReceived(bobRound1Payload);
System.out.println("Alice checks g^{x4}!=1: OK");
System.out.println("Alice checks KP{x3}: OK");
System.out.println("Alice checks KP{x4}: OK");
System.out.println("");
bob.validateRound1PayloadReceived(aliceRound1Payload);
System.out.println("Bob checks g^{x2}!=1: OK");
System.out.println("Bob checks KP{x1},: OK");
System.out.println("Bob checks KP{x2},: OK");
System.out.println("");
/*
* Round 2
*
* Alice and Bob each generate a round 2 payload, and send it to each other.
*/
JPAKERound2Payload aliceRound2Payload = alice.createRound2PayloadToSend();
JPAKERound2Payload bobRound2Payload = bob.createRound2PayloadToSend();
System.out.println("************ Round 2 **************");
System.out.println("Alice sends to Bob: ");
System.out.println("A=" + aliceRound2Payload.getA().toString(16));
System.out.println("KP{x2*s}={" + aliceRound2Payload.getKnowledgeProofForX2s()[0].toString(16) + "},{" + aliceRound2Payload.getKnowledgeProofForX2s()[1].toString(16) + "}");
System.out.println("");
System.out.println("Bob sends to Alice");
System.out.println("B=" + bobRound2Payload.getA().toString(16));
System.out.println("KP{x4*s}={" + bobRound2Payload.getKnowledgeProofForX2s()[0].toString(16) + "},{" + bobRound2Payload.getKnowledgeProofForX2s()[1].toString(16) + "}");
System.out.println("");
/*
* Each participant must then validate the received payload for round 2
*/
alice.validateRound2PayloadReceived(bobRound2Payload);
System.out.println("Alice checks KP{x4*s}: OK\n");
bob.validateRound2PayloadReceived(aliceRound2Payload);
System.out.println("Bob checks KP{x2*s}: OK\n");
/*
* After round 2, each participant computes the keying material.
*/
BigInteger aliceKeyingMaterial = alice.calculateKeyingMaterial();
BigInteger bobKeyingMaterial = bob.calculateKeyingMaterial();
System.out.println("********* After round 2 ***********");
System.out.println("Alice computes key material \t K=" + aliceKeyingMaterial.toString(16));
System.out.println("Bob computes key material \t K=" + bobKeyingMaterial.toString(16));
System.out.println();
/*
* You must derive a session key from the keying material applicable
* to whatever encryption algorithm you want to use.
*/
BigInteger aliceKey = deriveSessionKey(aliceKeyingMaterial);
BigInteger bobKey = deriveSessionKey(bobKeyingMaterial);
/*
* At this point, you can stop and use the session keys if you want.
* This is implicit key confirmation.
*
* If you want to explicitly confirm that the key material matches,
* you can continue on and perform round 3.
*/
/*
* Round 3
*
* Alice and Bob each generate a round 3 payload, and send it to each other.
*/
JPAKERound3Payload aliceRound3Payload = alice.createRound3PayloadToSend(aliceKeyingMaterial);
JPAKERound3Payload bobRound3Payload = bob.createRound3PayloadToSend(bobKeyingMaterial);
System.out.println("************ Round 3 **************");
System.out.println("Alice sends to Bob: ");
System.out.println("MacTag=" + aliceRound3Payload.getMacTag().toString(16));
System.out.println("");
System.out.println("Bob sends to Alice: ");
System.out.println("MacTag=" + bobRound3Payload.getMacTag().toString(16));
System.out.println("");
/*
* Each participant must then validate the received payload for round 3
*/
alice.validateRound3PayloadReceived(bobRound3Payload, aliceKeyingMaterial);
System.out.println("Alice checks MacTag: OK\n");
bob.validateRound3PayloadReceived(aliceRound3Payload, bobKeyingMaterial);
System.out.println("Bob checks MacTag: OK\n");
System.out.println();
System.out.println("MacTags validated, therefore the keying material matches.");
}
private static BigInteger deriveSessionKey(BigInteger keyingMaterial)
{
/*
* You should use a secure key derivation function (KDF) to derive the session key.
*
* For the purposes of this example, I'm just going to use a hash of the keying material.
*/
SHA256Digest digest = new SHA256Digest();
byte[] keyByteArray = keyingMaterial.toByteArray();
byte[] output = new byte[digest.getDigestSize()];
digest.update(keyByteArray, 0, keyByteArray.length);
digest.doFinal(output, 0);
return new BigInteger(output);
}
}