org.bouncycastle.crypto.ec.ECElGamalEncryptor.java Source code

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Here is the source code for org.bouncycastle.crypto.ec.ECElGamalEncryptor.java

Source

package org.bouncycastle.crypto.ec;

import java.math.BigInteger;
import java.security.SecureRandom;

import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.CryptoServicesRegistrar;
import org.bouncycastle.crypto.params.ECDomainParameters;
import org.bouncycastle.crypto.params.ECPublicKeyParameters;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.math.ec.ECAlgorithms;
import org.bouncycastle.math.ec.ECMultiplier;
import org.bouncycastle.math.ec.ECPoint;
import org.bouncycastle.math.ec.FixedPointCombMultiplier;

/**
 * this does your basic ElGamal encryption algorithm using EC
 */
public class ECElGamalEncryptor implements ECEncryptor {
    private ECPublicKeyParameters key;
    private SecureRandom random;

    /**
     * initialise the encryptor.
     *
     * @param param the necessary EC key parameters.
     */
    public void init(CipherParameters param) {
        if (param instanceof ParametersWithRandom) {
            ParametersWithRandom p = (ParametersWithRandom) param;

            if (!(p.getParameters() instanceof ECPublicKeyParameters)) {
                throw new IllegalArgumentException("ECPublicKeyParameters are required for encryption.");
            }
            this.key = (ECPublicKeyParameters) p.getParameters();
            this.random = p.getRandom();
        } else {
            if (!(param instanceof ECPublicKeyParameters)) {
                throw new IllegalArgumentException("ECPublicKeyParameters are required for encryption.");
            }

            this.key = (ECPublicKeyParameters) param;
            this.random = CryptoServicesRegistrar.getSecureRandom();
        }
    }

    /**
     * Process a single EC point using the basic ElGamal algorithm.
     *
     * @param point the EC point to process.
     * @return the result of the Elgamal process.
     */
    public ECPair encrypt(ECPoint point) {
        if (key == null) {
            throw new IllegalStateException("ECElGamalEncryptor not initialised");
        }

        ECDomainParameters ec = key.getParameters();
        BigInteger k = ECUtil.generateK(ec.getN(), random);

        ECMultiplier basePointMultiplier = createBasePointMultiplier();

        ECPoint[] gamma_phi = new ECPoint[] { basePointMultiplier.multiply(ec.getG(), k),
                key.getQ().multiply(k).add(ECAlgorithms.cleanPoint(ec.getCurve(), point)) };

        ec.getCurve().normalizeAll(gamma_phi);

        return new ECPair(gamma_phi[0], gamma_phi[1]);
    }

    protected ECMultiplier createBasePointMultiplier() {
        return new FixedPointCombMultiplier();
    }
}