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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8 with debug enabled.

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package org.bouncycastle.crypto.agreement;

import java.math.BigInteger;

import org.bouncycastle.crypto.BasicAgreement;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.params.AsymmetricKeyParameter;
import org.bouncycastle.crypto.params.DHParameters;
import org.bouncycastle.crypto.params.DHPrivateKeyParameters;
import org.bouncycastle.crypto.params.DHPublicKeyParameters;
import org.bouncycastle.crypto.params.ParametersWithRandom;

/**
 * a Diffie-Hellman key agreement class.
 * 

* note: This is only the basic algorithm, it doesn't take advantage of * long term public keys if they are available. See the DHAgreement class * for a "better" implementation. */ public class DHBasicAgreement implements BasicAgreement { private static final BigInteger ONE = BigInteger.valueOf(1); private DHPrivateKeyParameters key; private DHParameters dhParams; public void init( CipherParameters param) { AsymmetricKeyParameter kParam; if (param instanceof ParametersWithRandom) { ParametersWithRandom rParam = (ParametersWithRandom)param; kParam = (AsymmetricKeyParameter)rParam.getParameters(); } else { kParam = (AsymmetricKeyParameter)param; } if (!(kParam instanceof DHPrivateKeyParameters)) { throw new IllegalArgumentException("DHEngine expects DHPrivateKeyParameters"); } this.key = (DHPrivateKeyParameters)kParam; this.dhParams = key.getParameters(); } public int getFieldSize() { return (key.getParameters().getP().bitLength() + 7) / 8; } /** * given a short term public key from a given party calculate the next * message in the agreement sequence. */ public BigInteger calculateAgreement( CipherParameters pubKey) { DHPublicKeyParameters pub = (DHPublicKeyParameters)pubKey; if (!pub.getParameters().equals(dhParams)) { throw new IllegalArgumentException("Diffie-Hellman public key has wrong parameters."); } BigInteger p = dhParams.getP(); BigInteger peerY = pub.getY(); if (peerY == null || peerY.compareTo(ONE) <= 0 || peerY.compareTo(p.subtract(ONE)) >= 0) { throw new IllegalArgumentException("Diffie-Hellman public key is weak"); } BigInteger result = peerY.modPow(key.getX(), p); if (result.equals(ONE)) { throw new IllegalStateException("Shared key can't be 1"); } return result; } }





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