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package org.spongycastle.crypto.signers;
import org.spongycastle.crypto.CipherParameters;
import org.spongycastle.crypto.DSA;
import org.spongycastle.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);
}
}
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