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package org.spongycastle.crypto.signers;
import java.math.BigInteger;
import java.security.SecureRandom;
import org.spongycastle.crypto.CipherParameters;
import org.spongycastle.crypto.DSA;
import org.spongycastle.crypto.params.ECDomainParameters;
import org.spongycastle.crypto.params.ECKeyParameters;
import org.spongycastle.crypto.params.ECPrivateKeyParameters;
import org.spongycastle.crypto.params.ECPublicKeyParameters;
import org.spongycastle.crypto.params.ParametersWithRandom;
import org.spongycastle.math.ec.ECAlgorithms;
import org.spongycastle.math.ec.ECCurve;
import org.spongycastle.math.ec.ECFieldElement;
import org.spongycastle.math.ec.ECMultiplier;
import org.spongycastle.math.ec.ECPoint;
import org.spongycastle.math.ec.FixedPointCombMultiplier;
import org.spongycastle.util.Arrays;
/**
* DSTU 4145-2002
* <p>
* National Ukrainian standard of digital signature based on elliptic curves (DSTU 4145-2002).
* </p>
*/
public class DSTU4145Signer
implements DSA
{
private static final BigInteger ONE = BigInteger.valueOf(1);
private ECKeyParameters key;
private SecureRandom random;
public void init(boolean forSigning, CipherParameters param)
{
if (forSigning)
{
if (param instanceof ParametersWithRandom)
{
ParametersWithRandom rParam = (ParametersWithRandom)param;
this.random = rParam.getRandom();
param = rParam.getParameters();
}
else
{
this.random = new SecureRandom();
}
this.key = (ECPrivateKeyParameters)param;
}
else
{
this.key = (ECPublicKeyParameters)param;
}
}
public BigInteger[] generateSignature(byte[] message)
{
ECDomainParameters ec = key.getParameters();
ECCurve curve = ec.getCurve();
ECFieldElement h = hash2FieldElement(curve, message);
if (h.isZero())
{
h = curve.fromBigInteger(ONE);
}
BigInteger n = ec.getN();
BigInteger e, r, s;
ECFieldElement Fe, y;
BigInteger d = ((ECPrivateKeyParameters)key).getD();
ECMultiplier basePointMultiplier = createBasePointMultiplier();
do
{
do
{
do
{
e = generateRandomInteger(n, random);
Fe = basePointMultiplier.multiply(ec.getG(), e).normalize().getAffineXCoord();
}
while (Fe.isZero());
y = h.multiply(Fe);
r = fieldElement2Integer(n, y);
}
while (r.signum() == 0);
s = r.multiply(d).add(e).mod(n);
}
while (s.signum() == 0);
return new BigInteger[]{r, s};
}
public boolean verifySignature(byte[] message, BigInteger r, BigInteger s)
{
if (r.signum() <= 0 || s.signum() <= 0)
{
return false;
}
ECDomainParameters parameters = key.getParameters();
BigInteger n = parameters.getN();
if (r.compareTo(n) >= 0 || s.compareTo(n) >= 0)
{
return false;
}
ECCurve curve = parameters.getCurve();
ECFieldElement h = hash2FieldElement(curve, message);
if (h.isZero())
{
h = curve.fromBigInteger(ONE);
}
ECPoint R = ECAlgorithms.sumOfTwoMultiplies(parameters.getG(), s, ((ECPublicKeyParameters)key).getQ(), r).normalize();
// components must be bogus.
if (R.isInfinity())
{
return false;
}
ECFieldElement y = h.multiply(R.getAffineXCoord());
return fieldElement2Integer(n, y).compareTo(r) == 0;
}
protected ECMultiplier createBasePointMultiplier()
{
return new FixedPointCombMultiplier();
}
/**
* Generates random integer such, than its bit length is less than that of n
*/
private static BigInteger generateRandomInteger(BigInteger n, SecureRandom random)
{
return new BigInteger(n.bitLength() - 1, random);
}
private static ECFieldElement hash2FieldElement(ECCurve curve, byte[] hash)
{
byte[] data = Arrays.reverse(hash);
return curve.fromBigInteger(truncate(new BigInteger(1, data), curve.getFieldSize()));
}
private static BigInteger fieldElement2Integer(BigInteger n, ECFieldElement fe)
{
return truncate(fe.toBigInteger(), n.bitLength() - 1);
}
private static BigInteger truncate(BigInteger x, int bitLength)
{
if (x.bitLength() > bitLength)
{
x = x.mod(ONE.shiftLeft(bitLength));
}
return x;
}
}
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