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The FIPS 140-2 Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms certified to FIPS 140-2 level 1. This jar contains the debug version JCE provider and low-level API for the BC-FJA version 1.0.2.3, FIPS Certificate #3514. Please note the debug jar is not certified.

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package org.bouncycastle.crypto.fips;

import java.math.BigInteger;

import org.bouncycastle.crypto.IllegalKeyException;
import org.bouncycastle.crypto.internal.BasicAgreement;
import org.bouncycastle.crypto.internal.CipherParameters;
import org.bouncycastle.crypto.internal.params.DhParameters;
import org.bouncycastle.crypto.internal.params.DhPrivateKeyParameters;
import org.bouncycastle.crypto.internal.params.DhPublicKeyParameters;

/**
 * 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.
 */
class DhBasicAgreement
    implements BasicAgreement
{
    private DhPrivateKeyParameters key;
    private DhParameters dhParams;

    public void init(
        CipherParameters param)
    {
        DhPrivateKeyParameters kParam = (DhPrivateKeyParameters)param;

        this.key = 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;
        DhParameters pubParams = pub.getParameters();

        if (!pubParams.getG().equals(dhParams.getG()) || !pubParams.getP().equals(dhParams.getP()))
        {
            throw new IllegalKeyException("DH public key has wrong domain parameters");
        }

        return pub.getY().modPow(key.getX(), dhParams.getP());
    }
}