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

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

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 * 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

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package sun.security.ec;

import java.math.*;

import java.security.*;

import java.security.interfaces.*;

import java.security.spec.*;

import java.util.Optional;

import javax.crypto.*;

import javax.crypto.spec.*;

import sun.security.util.ArrayUtil;

import sun.security.util.ECUtil;

import sun.security.util.math.*;

import sun.security.ec.point.*;

/**

 * KeyAgreement implementation for ECDH.

 *

 * @since   1.7

 */

public final class ECDHKeyAgreement extends KeyAgreementSpi {

    // private key, if initialized

    private ECPrivateKey privateKey;

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

    private ECPublicKey publicKey;

    // length of the secret to be derived

    private int secretLen;

    /**

     * Constructs a new ECDHKeyAgreement.

     */

    public ECDHKeyAgreement() {

    }

    // see JCE spec

    @Override

    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);

        publicKey = null;

    }

    // see JCE spec

    @Override

    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

    @Override

    protected Key engineDoPhase(Key key, boolean lastPhase)

            throws InvalidKeyException, IllegalStateException {

        if (privateKey == null) {

            throw new IllegalStateException("Not initialized");

        }

        if (publicKey != 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");

        }

        this.publicKey = (ECPublicKey) key;

        ECParameterSpec params = publicKey.getParams();

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

        secretLen = (keyLenBits + 7) >> 3;

        return null;

    }

    private static void validateCoordinate(BigInteger c, BigInteger mod) {

        if (c.compareTo(BigInteger.ZERO) < 0) {

            throw new ProviderException("invalid coordinate");

        }

        if (c.compareTo(mod) >= 0) {

            throw new ProviderException("invalid coordinate");

        }

    }

    /*

     * Check whether a public key is valid. Throw ProviderException

     * if it is not valid or could not be validated.

     */

    private static void validate(ECOperations ops, ECPublicKey key) {

        // ensure that integers are in proper range

        BigInteger x = key.getW().getAffineX();

        BigInteger y = key.getW().getAffineY();

        BigInteger p = ops.getField().getSize();

        validateCoordinate(x, p);

        validateCoordinate(y, p);

        // ensure the point is on the curve

        EllipticCurve curve = key.getParams().getCurve();

        BigInteger rhs = x.modPow(BigInteger.valueOf(3), p).add(curve.getA()

            .multiply(x)).add(curve.getB()).mod(p);

        BigInteger lhs = y.modPow(BigInteger.valueOf(2), p).mod(p);

        if (!rhs.equals(lhs)) {

            throw new ProviderException("point is not on curve");

        }

        // check the order of the point

        ImmutableIntegerModuloP xElem = ops.getField().getElement(x);

        ImmutableIntegerModuloP yElem = ops.getField().getElement(y);

        AffinePoint affP = new AffinePoint(xElem, yElem);

        byte[] order = key.getParams().getOrder().toByteArray();

        ArrayUtil.reverse(order);

        Point product = ops.multiply(affP, order);

        if (!ops.isNeutral(product)) {

            throw new ProviderException("point has incorrect order");

        }

    }

    // see JCE spec

    @Override

    protected byte[] engineGenerateSecret() throws IllegalStateException {

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

            throw new IllegalStateException("Not initialized correctly");

        }

        Optional<byte[]> resultOpt = deriveKeyImpl(privateKey, publicKey);

        return resultOpt.orElseGet(

            () -> deriveKeyNative(privateKey, publicKey)

        );

    }

    // see JCE spec

    @Override

    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

    @Override

    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");

    }

    private static

    Optional<byte[]> deriveKeyImpl(ECPrivateKey priv, ECPublicKey pubKey) {

        ECParameterSpec ecSpec = priv.getParams();

        EllipticCurve curve = ecSpec.getCurve();

        Optional<ECOperations> opsOpt = ECOperations.forParameters(ecSpec);

        if (!opsOpt.isPresent()) {

            return Optional.empty();

        }

        ECOperations ops = opsOpt.get();

        if (! (priv instanceof ECPrivateKeyImpl)) {

            return Optional.empty();

        }

        ECPrivateKeyImpl privImpl = (ECPrivateKeyImpl) priv;

        byte[] sArr = privImpl.getArrayS();

        // to match the native implementation, validate the public key here

        // and throw ProviderException if it is invalid

        validate(ops, pubKey);

        IntegerFieldModuloP field = ops.getField();

        // convert s array into field element and multiply by the cofactor

        MutableIntegerModuloP scalar = field.getElement(sArr).mutable();

        SmallValue cofactor =

            field.getSmallValue(priv.getParams().getCofactor());

        scalar.setProduct(cofactor);

        int keySize = (curve.getField().getFieldSize() + 7) / 8;

        byte[] privArr = scalar.asByteArray(keySize);

        ImmutableIntegerModuloP x =

            field.getElement(pubKey.getW().getAffineX());

        ImmutableIntegerModuloP y =

            field.getElement(pubKey.getW().getAffineY());

        AffinePoint affPub = new AffinePoint(x, y);

        Point product = ops.multiply(affPub, privArr);

        if (ops.isNeutral(product)) {

            throw new ProviderException("Product is zero");

        }

        AffinePoint affProduct = product.asAffine();

        byte[] result = affProduct.getX().asByteArray(keySize);

        ArrayUtil.reverse(result);

        return Optional.of(result);

    }

    private static

    byte[] deriveKeyNative(ECPrivateKey privateKey, ECPublicKey publicKey) {

        ECParameterSpec params = privateKey.getParams();

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

        byte[] encodedParams =                   // DER OID

            ECUtil.encodeECParameterSpec(null, params);

        byte[] publicValue;

        if (publicKey instanceof ECPublicKeyImpl) {

            ECPublicKeyImpl ecPub = (ECPublicKeyImpl) publicKey;

            publicValue = ecPub.getEncodedPublicValue();

        } else { // instanceof ECPublicKey

            publicValue =

                ECUtil.encodePoint(publicKey.getW(), params.getCurve());

        }

        try {

            return deriveKey(s, publicValue, encodedParams);

        } catch (GeneralSecurityException e) {

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

        }

    }

    /**

     * 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;

}