BouncyECIESAgreementEngine.java

/*
 * GordianKnot: Security Suite
 * Copyright 2026. Tony Washer
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License.  You may obtain a copy
 * of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package io.github.tonywasher.joceanus.gordianknot.impl.bc.agree;

import io.github.tonywasher.joceanus.gordianknot.api.base.GordianException;
import io.github.tonywasher.joceanus.gordianknot.impl.bc.keypair.BouncyEllipticKeyPair.BouncyECPrivateKey;
import io.github.tonywasher.joceanus.gordianknot.impl.bc.keypair.BouncyEllipticKeyPair.BouncyECPublicKey;
import io.github.tonywasher.joceanus.gordianknot.impl.core.agree.GordianCoreAgreementFactory;
import io.github.tonywasher.joceanus.gordianknot.impl.core.exc.GordianIOException;
import io.github.tonywasher.joceanus.gordianknot.impl.core.spec.agree.GordianCoreAgreementSpec;
import org.bouncycastle.crypto.DerivationFunction;
import org.bouncycastle.crypto.SecretWithEncapsulation;
import org.bouncycastle.crypto.kems.ECIESKEMExtractor;
import org.bouncycastle.crypto.kems.ECIESKEMGenerator;

import javax.security.auth.DestroyFailedException;

/**
 * EC Agreement Engine.
 */
public class BouncyECIESAgreementEngine
        extends BouncyAgreementBase {
    /**
     * Key Length.
     */
    private static final int KEYLEN = 32;

    /**
     * Derivation function.
     */
    private final DerivationFunction theDerivation;

    /**
     * Constructor.
     *
     * @param pFactory the security factory
     * @param pSpec    the agreementSpec
     * @throws GordianException on error
     */
    BouncyECIESAgreementEngine(final GordianCoreAgreementFactory pFactory,
                               final GordianCoreAgreementSpec pSpec) throws GordianException {
        /* Initialize underlying class */
        super(pFactory, pSpec);

        /* Initialise the derivation function */
        theDerivation = newDerivationFunction();
    }

    @Override
    public void buildClientHello() throws GordianException {
        /* Protect against exceptions */
        try {
            /* Create encapsulation */
            final BouncyECPublicKey myPublic = (BouncyECPublicKey) getPublicKey(getServerKeyPair());
            final ECIESKEMGenerator myGenerator = new ECIESKEMGenerator(KEYLEN, theDerivation, getRandom());
            final SecretWithEncapsulation myResult = myGenerator.generateEncapsulated(myPublic.getPublicKey());

            /* Store the encapsulation */
            setEncapsulated(myResult.getEncapsulation());

            /* Store secret and create initVector */
            storeSecret(myResult.getSecret());
            myResult.destroy();

        } catch (DestroyFailedException e) {
            throw new GordianIOException("Failed to destroy secret", e);
        }
    }

    @Override
    public void processClientHello() throws GordianException {
        /* Create encapsulation */
        final BouncyECPrivateKey myPrivate = (BouncyECPrivateKey) getPrivateKey(getServerKeyPair());
        final ECIESKEMExtractor myExtractor = new ECIESKEMExtractor(myPrivate.getPrivateKey(), KEYLEN, theDerivation);

        /* Parse encapsulated message and store secret */
        final byte[] myMessage = getEncapsulated();
        storeSecret(myExtractor.extractSecret(myMessage));
    }
}