package repack.org.bouncycastle.crypto.generators;

import repack.org.bouncycastle.crypto.AsymmetricCipherKeyPair;
import repack.org.bouncycastle.crypto.AsymmetricCipherKeyPairGenerator;
import repack.org.bouncycastle.crypto.KeyGenerationParameters;
import repack.org.bouncycastle.crypto.params.GOST3410KeyGenerationParameters;
import repack.org.bouncycastle.crypto.params.GOST3410Parameters;
import repack.org.bouncycastle.crypto.params.GOST3410PrivateKeyParameters;
import repack.org.bouncycastle.crypto.params.GOST3410PublicKeyParameters;

import java.math.BigInteger;
import java.security.SecureRandom;

/**
 * a GOST3410 key pair generator.
 * This generates GOST3410 keys in line with the method described
 * in GOST R 34.10-94.
 */
public class GOST3410KeyPairGenerator
		implements AsymmetricCipherKeyPairGenerator
{
	private static final BigInteger ZERO = BigInteger.valueOf(0);

	private GOST3410KeyGenerationParameters param;

	public void init(
			KeyGenerationParameters param)
	{
		this.param = (GOST3410KeyGenerationParameters) param;
	}

	public AsymmetricCipherKeyPair generateKeyPair()
	{
		BigInteger p, q, a, x, y;
		GOST3410Parameters GOST3410Params = param.getParameters();
		SecureRandom random = param.getRandom();

		q = GOST3410Params.getQ();
		p = GOST3410Params.getP();
		a = GOST3410Params.getA();

		do
		{
			x = new BigInteger(256, random);
		}
		while(x.equals(ZERO) || x.compareTo(q) >= 0);

		//
		// calculate the public key.
		//
		y = a.modPow(x, p);

		return new AsymmetricCipherKeyPair(
				new GOST3410PublicKeyParameters(y, GOST3410Params),
				new GOST3410PrivateKeyParameters(x, GOST3410Params));
	}
}
