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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8. Note: this package includes the NTRU encryption algorithms.

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package org.bouncycastle.crypto.signers;

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

import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DSA;
import org.bouncycastle.crypto.params.ECDomainParameters;
import org.bouncycastle.crypto.params.ECKeyParameters;
import org.bouncycastle.crypto.params.ECPrivateKeyParameters;
import org.bouncycastle.crypto.params.ECPublicKeyParameters;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.math.ec.ECAlgorithms;
import org.bouncycastle.math.ec.ECCurve;
import org.bouncycastle.math.ec.ECFieldElement;
import org.bouncycastle.math.ec.ECMultiplier;
import org.bouncycastle.math.ec.ECPoint;
import org.bouncycastle.math.ec.FixedPointCombMultiplier;
import org.bouncycastle.util.Arrays;

/**
 * DSTU 4145-2002
 * 

* National Ukrainian standard of digital signature based on elliptic curves (DSTU 4145-2002). *

*/ 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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