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package org.spongycastle.crypto.signers;
import org.spongycastle.crypto.CipherParameters;
import org.spongycastle.crypto.DSA;
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.ECConstants;
import org.spongycastle.math.ec.ECPoint;
import java.math.BigInteger;
import java.security.SecureRandom;
/**
* 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).normalize();
BigInteger x = p.getAffineXCoord().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 = ECAlgorithms.sumOfTwoMultiplies(G, z1, Q, z2).normalize();
// components must be bogus.
if (point.isInfinity())
{
return false;
}
BigInteger R = point.getAffineXCoord().toBigInteger().mod(n);
return R.equals(r);
}
}
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