/**
 *
 */
package ch.ethz.ssh2.crypto.dh;

import java.io.IOException;
import java.math.BigInteger;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.interfaces.ECPrivateKey;
import java.security.interfaces.ECPublicKey;
import java.security.spec.ECParameterSpec;
import java.security.spec.ECPoint;
import java.security.spec.ECPublicKeySpec;
import java.security.spec.InvalidKeySpecException;

import javax.crypto.KeyAgreement;

import ch.ethz.ssh2.signature.ECDSASHA2Verify;

/**
 * @author kenny
 *
 */
public class EcDhExchange extends GenericDhExchange {

    /* Client public and private */

    private ECPrivateKey clientPrivate;
    private ECPublicKey clientPublic;

    /* Server public */

    private ECPublicKey serverPublic;
    private byte[] f;

    @Override
    public void init(String name) throws IOException {
        final ECParameterSpec spec;

        if ("ecdh-sha2-nistp256".equals(name)) {
            spec = ECDSASHA2Verify.EllipticCurves.nistp256;
        }
        else if ("ecdh-sha2-nistp384".equals(name)) {
            spec = ECDSASHA2Verify.EllipticCurves.nistp384;
        }
        else if ("ecdh-sha2-nistp521".equals(name)) {
            spec = ECDSASHA2Verify.EllipticCurves.nistp521;
        }
        else {
            throw new IllegalArgumentException("Unknown EC curve " + name);
        }

        KeyPairGenerator kpg;

        try {
            kpg = KeyPairGenerator.getInstance("EC");
            kpg.initialize(spec);
            KeyPair pair = kpg.generateKeyPair();
            clientPrivate = (ECPrivateKey) pair.getPrivate();
            clientPublic = (ECPublicKey) pair.getPublic();
        }
        catch (NoSuchAlgorithmException e) {
            throw(IOException) new IOException("No DH keypair generator").initCause(e);
        }
        catch (InvalidAlgorithmParameterException e) {
            throw(IOException) new IOException("Invalid DH parameters").initCause(e);
        }
    }

    @Override
    public byte[] getE() {
        return ECDSASHA2Verify.encodeECPoint(clientPublic.getW(), clientPublic.getParams()
                                             .getCurve());
    }

    @Override
    protected byte[] getServerE() {
        return ECDSASHA2Verify.encodeECPoint(serverPublic.getW(), serverPublic.getParams()
                                             .getCurve());
    }

    @Override
    public byte[] getF() {
        return f;
    }

    @Override
    public void setF(byte[] f) throws IOException {
        if (clientPublic == null)
            throw new IllegalStateException("DhDsaExchange not initialized!");

        final KeyAgreement ka;

        try {
            KeyFactory kf = KeyFactory.getInstance("EC");
            ECParameterSpec params = clientPublic.getParams();
            ECPoint serverPoint = ECDSASHA2Verify.decodeECPoint(f, params.getCurve());
            this.f = f;
            this.serverPublic = (ECPublicKey) kf.generatePublic(new ECPublicKeySpec(serverPoint,
                                params));
            ka = KeyAgreement.getInstance("ECDH");
            ka.init(clientPrivate);
            ka.doPhase(serverPublic, true);
        }
        catch (NoSuchAlgorithmException e) {
            throw(IOException) new IOException("No ECDH key agreement method").initCause(e);
        }
        catch (InvalidKeyException e) {
            throw(IOException) new IOException("Invalid ECDH key").initCause(e);
        }
        catch (InvalidKeySpecException e) {
            throw(IOException) new IOException("Invalid ECDH key").initCause(e);
        }

        sharedSecret = new BigInteger(ka.generateSecret());
    }

    @Override
    public String getHashAlgo() {
        return ECDSASHA2Verify.getDigestAlgorithmForParams(clientPublic.getParams());
    }
}