/*

 * Copyright 2009 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package sun.security.ec;

import java.security.*;

import java.security.interfaces.*;

import java.security.spec.*;

import javax.crypto.*;

import javax.crypto.spec.*;

/**

 * KeyAgreement implementation for ECDH.

 *

 * @since   1.7

 */

public final class ECDHKeyAgreement extends KeyAgreementSpi {

    // flag indicating whether the native ECC implementation is present

    private static boolean implementationPresent = true;

    static {

        try {

            AccessController.doPrivileged(new PrivilegedAction<Void>() {

                public Void run() {

                    System.loadLibrary("sunecc");

                    return null;

                }

            });

        } catch (UnsatisfiedLinkError e) {

            implementationPresent = false;

        }

    }

    // private key, if initialized

    private ECPrivateKey privateKey;

    // encoded public point, non-null between doPhase() & generateSecret() only

    private byte[] publicValue;

    // length of the secret to be derived

    private int secretLen;

    /**

     * Constructs a new ECDHKeyAgreement.

     *

     * @exception ProviderException if the native ECC library is unavailable.

     */

    public ECDHKeyAgreement() {

        if (!implementationPresent) {

            throw new ProviderException("ECDH implementation is not available");

        }

    }

    // see JCE spec

    protected void engineInit(Key key, SecureRandom random)

            throws InvalidKeyException {

        if (!(key instanceof PrivateKey)) {

            throw new InvalidKeyException

                        ("Key must be instance of PrivateKey");

        }

        privateKey = (ECPrivateKey) ECKeyFactory.toECKey(key);

        publicValue = null;

    }

    // see JCE spec

    protected void engineInit(Key key, AlgorithmParameterSpec params,

            SecureRandom random) throws InvalidKeyException,

            InvalidAlgorithmParameterException {

        if (params != null) {

            throw new InvalidAlgorithmParameterException

                        ("Parameters not supported");

        }

        engineInit(key, random);

    }

    // see JCE spec

    protected Key engineDoPhase(Key key, boolean lastPhase)

            throws InvalidKeyException, IllegalStateException {

        if (privateKey == null) {

            throw new IllegalStateException("Not initialized");

        }

        if (publicValue != null) {

            throw new IllegalStateException("Phase already executed");

        }

        if (!lastPhase) {

            throw new IllegalStateException

                ("Only two party agreement supported, lastPhase must be true");

        }

        if (!(key instanceof ECPublicKey)) {

            throw new InvalidKeyException

                ("Key must be a PublicKey with algorithm EC");

        }

        ECPublicKey ecKey = (ECPublicKey)key;

        ECParameterSpec params = ecKey.getParams();

        if (ecKey instanceof ECPublicKeyImpl) {

            publicValue = ((ECPublicKeyImpl)ecKey).getEncodedPublicValue();

        } else { // instanceof ECPublicKey

            publicValue =

                ECParameters.encodePoint(ecKey.getW(), params.getCurve());

        }

        int keyLenBits = params.getCurve().getField().getFieldSize();

        secretLen = (keyLenBits + 7) >> 3;

        return null;

    }

    // see JCE spec

    protected byte[] engineGenerateSecret() throws IllegalStateException {

        if ((privateKey == null) || (publicValue == null)) {

            throw new IllegalStateException("Not initialized correctly");

        }

        byte[] s = privateKey.getS().toByteArray();

        byte[] encodedParams =

            ECParameters.encodeParameters(privateKey.getParams()); // DER OID

        try {

            return deriveKey(s, publicValue, encodedParams);

        } catch (GeneralSecurityException e) {

            throw new ProviderException("Could not derive key", e);

        }

    }

    // see JCE spec

    protected int engineGenerateSecret(byte[] sharedSecret, int

            offset) throws IllegalStateException, ShortBufferException {

        if (offset + secretLen > sharedSecret.length) {

            throw new ShortBufferException("Need " + secretLen

                + " bytes, only " + (sharedSecret.length - offset) + " available");

        }

        byte[] secret = engineGenerateSecret();

        System.arraycopy(secret, 0, sharedSecret, offset, secret.length);

        return secret.length;

    }

    // see JCE spec

    protected SecretKey engineGenerateSecret(String algorithm)

            throws IllegalStateException, NoSuchAlgorithmException,

            InvalidKeyException {

        if (algorithm == null) {

            throw new NoSuchAlgorithmException("Algorithm must not be null");

        }

        if (!(algorithm.equals("TlsPremasterSecret"))) {

            throw new NoSuchAlgorithmException

                ("Only supported for algorithm TlsPremasterSecret");

        }

        return new SecretKeySpec(engineGenerateSecret(), "TlsPremasterSecret");

    }

    /**

     * Generates a secret key using the public and private keys.

     *

     * @param s the private key's S value.

     * @param w the public key's W point (in uncompressed form).

     * @param encodedParams the curve's DER encoded object identifier.

     *

     * @return byte[] the secret key.

     */

    private static native byte[] deriveKey(byte[] s, byte[] w,

        byte[] encodedParams) throws GeneralSecurityException;

}