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The FIPS 140-2 Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms certified to FIPS 140-2 level 1. This jar contains the debug version JCE provider and low-level API for the BC-FJA version 1.0.2.3, FIPS Certificate #3514. Please note the debug jar is not certified.

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/***************************************************************/
/******    DO NOT EDIT THIS CLASS bc-java SOURCE FILE     ******/
/***************************************************************/
package org.bouncycastle.crypto.general;

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

import org.bouncycastle.crypto.internal.CipherParameters;
import org.bouncycastle.crypto.internal.DSA;
import org.bouncycastle.crypto.internal.params.ParametersWithRandom;

/**
 * GOST R 34.10-94 Signature Algorithm
 */
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
            {
                throw new IllegalArgumentException("No random provided where one required.");
            }
        }
        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);
    }
}