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Spongy Castle is a package-rename (org.bouncycastle.* to org.spongycastle.*) of Bouncy Castle intended for Android.
Android ships with a stripped-down version of Bouncy Castle - this causes classloader collisions if you try to add
an alternative (updated/complete) Bouncy Castle jar.
This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5.
package org.spongycastle.crypto.signers;
import org.spongycastle.crypto.AsymmetricCipherKeyPair;
import org.spongycastle.crypto.CipherParameters;
import org.spongycastle.crypto.DSA;
import org.spongycastle.crypto.DataLengthException;
import org.spongycastle.crypto.generators.ECKeyPairGenerator;
import org.spongycastle.crypto.params.ECKeyGenerationParameters;
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;
/**
* EC-NR as described in IEEE 1363-2000
*/
public class ECNRSigner
implements DSA
{
private boolean forSigning;
private ECKeyParameters key;
private SecureRandom random;
public void init(
boolean forSigning,
CipherParameters param)
{
this.forSigning = forSigning;
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;
}
}
// Section 7.2.5 ECSP-NR, pg 34
/**
* generate a signature for the given message using the key we were
* initialised with. Generally, the order of the curve should be at
* least as long as the hash of the message of interest, and with
* ECNR it *must* be at least as long.
*
* @param digest the digest to be signed.
* @exception DataLengthException if the digest is longer than the key allows
*/
public BigInteger[] generateSignature(
byte[] digest)
{
if (! this.forSigning)
{
throw new IllegalStateException("not initialised for signing");
}
BigInteger n = ((ECPrivateKeyParameters)this.key).getParameters().getN();
int nBitLength = n.bitLength();
BigInteger e = new BigInteger(1, digest);
int eBitLength = e.bitLength();
ECPrivateKeyParameters privKey = (ECPrivateKeyParameters)key;
if (eBitLength > nBitLength)
{
throw new DataLengthException("input too large for ECNR key.");
}
BigInteger r = null;
BigInteger s = null;
AsymmetricCipherKeyPair tempPair;
do // generate r
{
// generate another, but very temporary, key pair using
// the same EC parameters
ECKeyPairGenerator keyGen = new ECKeyPairGenerator();
keyGen.init(new ECKeyGenerationParameters(privKey.getParameters(), this.random));
tempPair = keyGen.generateKeyPair();
// BigInteger Vx = tempPair.getPublic().getW().getAffineX();
ECPublicKeyParameters V = (ECPublicKeyParameters)tempPair.getPublic(); // get temp's public key
BigInteger Vx = V.getQ().getX().toBigInteger(); // get the point's x coordinate
r = Vx.add(e).mod(n);
}
while (r.equals(ECConstants.ZERO));
// generate s
BigInteger x = privKey.getD(); // private key value
BigInteger u = ((ECPrivateKeyParameters)tempPair.getPrivate()).getD(); // temp's private key value
s = u.subtract(r.multiply(x)).mod(n);
BigInteger[] res = new BigInteger[2];
res[0] = r;
res[1] = s;
return res;
}
// Section 7.2.6 ECVP-NR, pg 35
/**
* return true if the value r and s represent a signature for the
* message passed in. Generally, the order of the curve should be at
* least as long as the hash of the message of interest, and with
* ECNR, it *must* be at least as long. But just in case the signer
* applied mod(n) to the longer digest, this implementation will
* apply mod(n) during verification.
*
* @param digest the digest to be verified.
* @param r the r value of the signature.
* @param s the s value of the signature.
* @exception DataLengthException if the digest is longer than the key allows
*/
public boolean verifySignature(
byte[] digest,
BigInteger r,
BigInteger s)
{
if (this.forSigning)
{
throw new IllegalStateException("not initialised for verifying");
}
ECPublicKeyParameters pubKey = (ECPublicKeyParameters)key;
BigInteger n = pubKey.getParameters().getN();
int nBitLength = n.bitLength();
BigInteger e = new BigInteger(1, digest);
int eBitLength = e.bitLength();
if (eBitLength > nBitLength)
{
throw new DataLengthException("input too large for ECNR key.");
}
// r in the range [1,n-1]
if (r.compareTo(ECConstants.ONE) < 0 || r.compareTo(n) >= 0)
{
return false;
}
// s in the range [0,n-1] NB: ECNR spec says 0
if (s.compareTo(ECConstants.ZERO) < 0 || s.compareTo(n) >= 0)
{
return false;
}
// compute P = sG + rW
ECPoint G = pubKey.getParameters().getG();
ECPoint W = pubKey.getQ();
// calculate P using Bouncy math
ECPoint P = ECAlgorithms.sumOfTwoMultiplies(G, s, W, r);
BigInteger x = P.getX().toBigInteger();
BigInteger t = r.subtract(x).mod(n);
return t.equals(e);
}
}