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/*******************************************************************************
Copyright ArxanFintech Technology Ltd. 2018 All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

                 http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*******************************************************************************/

package com.arxanfintech.common.crypto;

import java.math.BigInteger;
import java.util.Arrays;

import com.arxanfintech.common.util.ByteUtils;

/**
 * An EC public Key suitable for verifying a signature created with the
 * corresponding EC PrivateKey
 *
 * @see PrivateKey
 */
public class PublicKey implements Key {
    private final Cryptography crypto;
    private final byte[] pub;

    /**
     * Create from uncompressed binary representation
     * 
     * @param pub
     *            pub
     * @param crypto
     *            crypto
     */
    public PublicKey(byte[] pub, Cryptography crypto) {
        this.pub = pub;
        this.crypto = crypto;
    }

    public static PublicKey fromCompressed(byte[] pub, Cryptography crypto) {
        return new PublicKey(crypto.uncompressPoint(pub), crypto);
    }

    @Override
    public byte[] toByteArray() {
        return pub.clone();
    }

    /**
     * verify a signature created with the private counterpart of this key
     *
     * @param hash
     *            arbitrary data
     * @param signature
     *            signature
     * @return true if valid
     */
    public boolean verify(byte[] hash, byte[] signature) {
        return crypto.verify(hash, signature, pub);
    }

    @Override
    public PublicKey offsetKey(BigInteger offset) {
        byte[] atOffset = crypto.getPublicKeyAtOffset(pub, offset.toByteArray());
        return fromCompressed(atOffset, crypto);
    }

    @Override
    public int hashCode() {
        return Arrays.hashCode(pub);
    }

    @Override
    public boolean equals(Object obj) {
        if (obj instanceof PublicKey) {
            PublicKey other = (PublicKey) obj;
            return Arrays.equals(this.pub, other.pub);
        }
        return false;
    }

    @Override
    public String toString() {
        return ByteUtils.toHex(pub);
    }

}