org.bouncycastle.crypto.signers.DSASigner Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of bcprov-ext-debug-jdk18on Show documentation
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 Java 1.8 and later with debug enabled.
The newest version!
package org.bouncycastle.crypto.signers;

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

import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.CryptoServicesRegistrar;
import org.bouncycastle.crypto.DSAExt;
import org.bouncycastle.crypto.params.DSAKeyParameters;
import org.bouncycastle.crypto.params.DSAParameters;
import org.bouncycastle.crypto.params.DSAPrivateKeyParameters;
import org.bouncycastle.crypto.params.DSAPublicKeyParameters;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.util.BigIntegers;

/**
 * The Digital Signature Algorithm - as described in "Handbook of Applied
 * Cryptography", pages 452 - 453.
 */
public class DSASigner
    implements DSAExt
{
    private final DSAKCalculator kCalculator;

    private DSAKeyParameters key;
    private SecureRandom    random;

    /**
     * Default configuration, random K values.
     */
    public DSASigner()
    {
        this.kCalculator = new RandomDSAKCalculator();
    }

    /**
     * Configuration with an alternate, possibly deterministic calculator of K.
     *
     * @param kCalculator a K value calculator.
     */
    public DSASigner(DSAKCalculator kCalculator)
    {
        this.kCalculator = kCalculator;
    }

    public void init(
        boolean                 forSigning,
        CipherParameters        param)
    {
        SecureRandom providedRandom = null;

        if (forSigning)
        {
            if (param instanceof ParametersWithRandom)
            {
                ParametersWithRandom rParam = (ParametersWithRandom)param;

                this.key = (DSAPrivateKeyParameters)rParam.getParameters();
                providedRandom = rParam.getRandom();
            }
            else
            {
                this.key = (DSAPrivateKeyParameters)param;
            }
        }
        else
        {
            this.key = (DSAPublicKeyParameters)param;
        }

        CryptoServicesRegistrar.checkConstraints(Utils.getDefaultProperties("DSA", key, forSigning));

        this.random = initSecureRandom(forSigning && !kCalculator.isDeterministic(), providedRandom);
    }

    public BigInteger getOrder()
    {
        return key.getParameters().getQ();
    }

    /**
     * generate a signature for the given message using the key we were
     * initialised with. For conventional DSA the message should be a SHA-1
     * hash of the message of interest.
     *
     * @param message the message that will be verified later.
     */
    public BigInteger[] generateSignature(
        byte[] message)
    {
        DSAParameters   params = key.getParameters();
        BigInteger      q = params.getQ();
        BigInteger      m = calculateE(q, message);
        BigInteger      x = ((DSAPrivateKeyParameters)key).getX();

        if (kCalculator.isDeterministic())
        {
            kCalculator.init(q, x, message);
        }
        else
        {
            kCalculator.init(q, random);
        }

        BigInteger  k = kCalculator.nextK();

        // the randomizer is to conceal timing information related to k and x.
        BigInteger  r = params.getG().modPow(k.add(getRandomizer(q, random)), params.getP()).mod(q);

        k = BigIntegers.modOddInverse(q, k).multiply(m.add(x.multiply(r)));

        BigInteger  s = k.mod(q);

        return new BigInteger[]{ r, s };
    }

    /**
     * return true if the value r and s represent a DSA signature for
     * the passed in message for standard DSA the message should be a
     * SHA-1 hash of the real message to be verified.
     */
    public boolean verifySignature(
        byte[]      message,
        BigInteger  r,
        BigInteger  s)
    {
        DSAParameters   params = key.getParameters();
        BigInteger      q = params.getQ();
        BigInteger      m = calculateE(q, message);
        BigInteger      zero = BigInteger.valueOf(0);

        if (zero.compareTo(r) >= 0 || q.compareTo(r) <= 0)
        {
            return false;
        }

        if (zero.compareTo(s) >= 0 || q.compareTo(s) <= 0)
        {
            return false;
        }

        BigInteger w = BigIntegers.modOddInverseVar(q, s);

        BigInteger  u1 = m.multiply(w).mod(q);
        BigInteger  u2 = r.multiply(w).mod(q);

        BigInteger p = params.getP();
        u1 = params.getG().modPow(u1, p);
        u2 = ((DSAPublicKeyParameters)key).getY().modPow(u2, p);

        BigInteger  v = u1.multiply(u2).mod(p).mod(q);

        return v.equals(r);
    }

    private BigInteger calculateE(BigInteger n, byte[] message)
    {
        if (n.bitLength() >= message.length * 8)
        {
            return new BigInteger(1, message);
        }
        else
        {
            byte[] trunc = new byte[n.bitLength() / 8];

            System.arraycopy(message, 0, trunc, 0, trunc.length);

            return new BigInteger(1, trunc);
        }
    }

    protected SecureRandom initSecureRandom(boolean needed, SecureRandom provided)
    {
        return needed ? CryptoServicesRegistrar.getSecureRandom(provided) : null;
    }

    private BigInteger getRandomizer(BigInteger q, SecureRandom provided)
    {
        // Calculate a random multiple of q to add to k. Note that g^q = 1 (mod p), so adding multiple of q to k does not change r.
        int randomBits = 7;

        return BigIntegers.createRandomBigInteger(randomBits, CryptoServicesRegistrar.getSecureRandom(provided)).add(BigInteger.valueOf(128)).multiply(q);
    }
}