package org.bouncycastle.crypto.signers;import org.bouncycastle.crypto.CipherParameters;import org.bouncycastle.crypto.DSA;import org.bouncycastle.crypto.params.*;import java.security.SecureRandom;import java.math.BigInteger;/** * GOST R 34.10-94 Signature Algorithm */public class GOST3410Signer        implements DSA{        GOST3410KeyParameters 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 = (GOST3410PrivateKeyParameters)rParam.getParameters();                }                else                {                    this.random = new SecureRandom();                    this.key = (GOST3410PrivateKeyParameters)param;                }            }            else            {                this.key = (GOST3410PublicKeyParameters)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      m = new BigInteger(1, mRev);            GOST3410Parameters   params = key.getParameters();            BigInteger      k;            do            {                k = new BigInteger(params.getQ().bitLength(), random);            }            while (k.compareTo(params.getQ()) >= 0);            BigInteger  r = params.getA().modPow(k, params.getP()).mod(params.getQ());            BigInteger  s = k.multiply(m).                                add(((GOST3410PrivateKeyParameters)key).getX().multiply(r)).                                    mod(params.getQ());            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           m = new BigInteger(1, mRev);            GOST3410Parameters   params = key.getParameters();            BigInteger           zero = BigInteger.valueOf(0);            if (zero.compareTo(r) >= 0 || params.getQ().compareTo(r) <= 0)            {                return false;            }            if (zero.compareTo(s) >= 0 || params.getQ().compareTo(s) <= 0)            {                return false;            }            BigInteger  v = m.modPow(params.getQ().subtract(new BigInteger("2")),params.getQ());            BigInteger  z1 = s.multiply(v).mod(params.getQ());            BigInteger  z2 = (params.getQ().subtract(r)).multiply(v).mod(params.getQ());                        z1 = params.getA().modPow(z1, params.getP());            z2 = ((GOST3410PublicKeyParameters)key).getY().modPow(z2, params.getP());            BigInteger  u = z1.multiply(z2).mod(params.getP()).mod(params.getQ());            return u.equals(r);        }}