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.ECKeyParameters;import org.bouncycastle.crypto.params.ECPrivateKeyParameters;import org.bouncycastle.crypto.params.ECPublicKeyParameters;import org.bouncycastle.crypto.params.ParametersWithRandom;import org.bouncycastle.math.ec.ECConstants;import org.bouncycastle.math.ec.ECPoint;/** * EC-DSA as described in X9.62 */public class ECDSASigner    implements ECConstants, 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;        }    }    // 5.3 pg 28    /**     * 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)    {        BigInteger e = new BigInteger(1, message);        BigInteger n = key.getParameters().getN();        BigInteger r = null;        BigInteger s = null;        // 5.3.2        do // generate s        {            BigInteger k = null;            int            nBitLength = n.bitLength();            do // generate r            {                do                {                    k = new BigInteger(nBitLength, random);                }                while (k.equals(ZERO));                ECPoint p = key.getParameters().getG().multiply(k);                // 5.3.3                BigInteger x = p.getX().toBigInteger();                r = x.mod(n);            }            while (r.equals(ZERO));            BigInteger d = ((ECPrivateKeyParameters)key).getD();            s = k.modInverse(n).multiply(e.add(d.multiply(r))).mod(n);        }        while (s.equals(ZERO));        BigInteger[]  res = new BigInteger[2];        res[0] = r;        res[1] = s;        return res;    }    // 5.4 pg 29    /**     * 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)    {        BigInteger e = new BigInteger(1, message);        BigInteger n = key.getParameters().getN();        // r in the range [1,n-1]        if (r.compareTo(ONE) < 0 || r.compareTo(n) >= 0)        {            return false;        }        // s in the range [1,n-1]        if (s.compareTo(ONE) < 0 || s.compareTo(n) >= 0)        {            return false;        }        BigInteger c = s.modInverse(n);        BigInteger u1 = e.multiply(c).mod(n);        BigInteger u2 = r.multiply(c).mod(n);        ECPoint G = key.getParameters().getG();        ECPoint Q = ((ECPublicKeyParameters)key).getQ();        ECPoint point = G.multiply(u1).add(Q.multiply(u2));        BigInteger v = point.getX().toBigInteger().mod(n);        return v.equals(r);    }}