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/*
 * Copyright www.jingtum.com Inc. 
 * 
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.jingtum.core.crypto.ecdsa;

import org.bouncycastle.crypto.params.ECDomainParameters;
import org.bouncycastle.math.ec.ECConstants;
import org.bouncycastle.math.ec.ECCurve;
import org.bouncycastle.math.ec.ECPoint;
import org.bouncycastle.util.encoders.Hex;

import java.math.BigInteger;

public class SECP256K1 {
	
	private static final ECDomainParameters params;
	
    static {
        params = createParameters();
    }
	
    private static BigInteger fromHex(
    String hex)
    {
    	return new BigInteger(1, Hex.decode(hex));
    }

    public static BigInteger order() {    	
    	return params.getN();
    }

    public static ECPoint basePoint() {
    	return params.getG();
    }

    static byte[] basePointMultipliedBy(BigInteger secret) {
        return basePoint().multiply(secret).getEncoded(true);
    }
    
    private static ECDomainParameters createParameters()
    {
        // p = 2^256 - 2^32 - 2^9 - 2^8 - 2^7 - 2^6 - 2^4 - 1
        BigInteger p = fromHex("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F");
        BigInteger a = ECConstants.ZERO;
        BigInteger b = BigInteger.valueOf(7);
        byte[] S = null;
        BigInteger n = fromHex("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141");
        BigInteger h = BigInteger.valueOf(1);

        ECCurve curve = new ECCurve.Fp(p, a, b);
        ECPoint G = curve.decodePoint(Hex.decode("04"
            + "79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798"
            + "483ADA7726A3C4655DA4FBFC0E1108A8FD17B448A68554199C47D08FFB10D4B8"));

        return new ECDomainParameters(curve, G, n, h, S);
    }

	public static ECDomainParameters params() {
		return params;
	}
}