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 * 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.  Oracle designates this

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

 * by Oracle 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.

 *

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package sun.security.ec;

import java.math.BigInteger;

import java.security.InvalidKeyException;

import java.security.KeyRep;

import java.security.PublicKey;

import java.security.interfaces.XECPublicKey;

import java.security.spec.AlgorithmParameterSpec;

import java.security.spec.NamedParameterSpec;

import java.util.Arrays;

import sun.security.util.BitArray;

import sun.security.x509.AlgorithmId;

import sun.security.x509.X509Key;

public final class XDHPublicKeyImpl extends X509Key implements XECPublicKey {

    private static final long serialVersionUID = 1L;

    private final BigInteger u;

    private final NamedParameterSpec paramSpec;

    XDHPublicKeyImpl(XECParameters params, BigInteger u)

        throws InvalidKeyException {

        this.paramSpec = new NamedParameterSpec(params.getName());

        this.algid = new AlgorithmId(params.getOid());

        this.u = u.mod(params.getP());

        byte[] u_arr = this.u.toByteArray();

        reverse(u_arr);

        // u_arr may be too large or too small, depending on the value of u

        u_arr = Arrays.copyOf(u_arr, params.getBytes());

        setKey(new BitArray(u_arr.length * 8, u_arr));

        checkLength(params);

    }

    XDHPublicKeyImpl(byte[] encoded) throws InvalidKeyException {

        decode(encoded);

        XECParameters params =

            XECParameters.get(InvalidKeyException::new, algid);

        this.paramSpec = new NamedParameterSpec(params.getName());

        // construct the BigInteger representation

        byte[] u_arr = getKey().toByteArray();

        reverse(u_arr);

        // clear the extra bits

        int bitsMod8 = params.getBits() % 8;

        if (bitsMod8 != 0) {

            int mask = (1 << bitsMod8) - 1;

            u_arr[0] &= mask;

        }

        this.u = new BigInteger(1, u_arr);

        checkLength(params);

    }

    void checkLength(XECParameters params) throws InvalidKeyException {

        if (params.getBytes() * 8 != getKey().length()) {

            throw new InvalidKeyException(

                "key length must be " + params.getBytes());

        }

    }

    @Override

    public BigInteger getU() {

        return u;

    }

    @Override

    public AlgorithmParameterSpec getParams() {

        return paramSpec;

    }

    @Override

    public String getAlgorithm() {

        return "XDH";

    }

    protected Object writeReplace() throws java.io.ObjectStreamException {

        return new KeyRep(KeyRep.Type.PUBLIC,

            getAlgorithm(),

            getFormat(),

            getEncoded());

    }

    private static void swap(byte[] arr, int i, int j) {

        byte tmp = arr[i];

        arr[i] = arr[j];

        arr[j] = tmp;

    }

    private static void reverse(byte [] arr) {

        int i = 0;

        int j = arr.length - 1;

        while (i < j) {

            swap(arr, i, j);

            i++;

            j--;

        }

    }

}