package org.bouncycastle.crypto.signers;import org.bouncycastle.math.ec.ECConstants;import org.bouncycastle.math.ec.ECPoint;import org.bouncycastle.crypto.params.ECKeyParameters;import org.bouncycastle.crypto.params.ParametersWithRandom;import org.bouncycastle.crypto.params.ECPrivateKeyParameters;import org.bouncycastle.crypto.params.ECPublicKeyParameters;import org.bouncycastle.crypto.CipherParameters;import org.bouncycastle.crypto.DSA;import java.security.SecureRandom;import java.math.BigInteger;/** * GOST R 34.10-2001 Signature Algorithm */public class ECGOST3410Signer    implements DSA{    ECKeyParameters key;    SecureRandom    random;    public void init(        boolean                 forSigning,        CipherParameters        param)    {        if (forSigning)        {            if (param instanceof ParametersWithRandom)            {                ParametersWithRandom    rParam = (ParametersWithRandom)param;                this.random = rParam.getRandom();                this.key = (ECPrivateKeyParameters)rParam.getParameters();            }            else            {                this.random = new SecureRandom();                this.key = (ECPrivateKeyParameters)param;            }        }        else        {            this.key = (ECPublicKeyParameters)param;        }    }    /**     * generate a signature for the given message using the key we were     * initialised with. For conventional GOST3410 the message should be a GOST3411     * hash of the message of interest.     *     * @param message the message that will be verified later.     */    public BigInteger[] generateSignature(        byte[] message)    {        byte[] mRev = new byte[message.length]; // conversion is little-endian        for (int i = 0; i != mRev.length; i++)        {            mRev[i] = message[mRev.length - 1 - i];        }                BigInteger e = new BigInteger(1, mRev);        BigInteger n = key.getParameters().getN();        BigInteger r = null;        BigInteger s = null;        do // generate s        {            BigInteger k = null;            do // generate r            {                do                {                    k = new BigInteger(n.bitLength(), random);                }                while (k.equals(ECConstants.ZERO));                ECPoint p = key.getParameters().getG().multiply(k);                BigInteger x = p.getX().toBigInteger();                r = x.mod(n);            }            while (r.equals(ECConstants.ZERO));            BigInteger d = ((ECPrivateKeyParameters)key).getD();            s = (k.multiply(e)).add(d.multiply(r)).mod(n);        }        while (s.equals(ECConstants.ZERO));        BigInteger[]  res = new BigInteger[2];        res[0] = r;        res[1] = s;        return res;    }    /**     * return true if the value r and s represent a GOST3410 signature for     * the passed in message (for standard GOST3410 the message should be     * a GOST3411 hash of the real message to be verified).     */    public boolean verifySignature(        byte[]      message,        BigInteger  r,        BigInteger  s)    {        byte[] mRev = new byte[message.length]; // conversion is little-endian        for (int i = 0; i != mRev.length; i++)        {            mRev[i] = message[mRev.length - 1 - i];        }                BigInteger e = new BigInteger(1, mRev);        BigInteger n = key.getParameters().getN();        // r in the range [1,n-1]        if (r.compareTo(ECConstants.ONE) < 0 || r.compareTo(n) >= 0)        {            return false;        }        // s in the range [1,n-1]        if (s.compareTo(ECConstants.ONE) < 0 || s.compareTo(n) >= 0)        {            return false;        }        BigInteger v = e.modInverse(n);        BigInteger z1 = s.multiply(v).mod(n);        BigInteger z2 = (n.subtract(r)).multiply(v).mod(n);        ECPoint G = key.getParameters().getG(); // P        ECPoint Q = ((ECPublicKeyParameters)key).getQ();        ECPoint point = G.multiply(z1).add(Q.multiply(z2));        BigInteger R = point.getX().toBigInteger().mod(n);        return R.equals(r);    }}