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package org.bouncycastle.crypto.generators;
import java.math.BigInteger;
import java.security.SecureRandom;
import org.bouncycastle.crypto.AsymmetricCipherKeyPair;
import org.bouncycastle.crypto.AsymmetricCipherKeyPairGenerator;
import org.bouncycastle.crypto.KeyGenerationParameters;
import org.bouncycastle.crypto.params.CramerShoupKeyGenerationParameters;
import org.bouncycastle.crypto.params.CramerShoupParameters;
import org.bouncycastle.crypto.params.CramerShoupPrivateKeyParameters;
import org.bouncycastle.crypto.params.CramerShoupPublicKeyParameters;
import org.bouncycastle.util.BigIntegers;
/**
* a Cramer Shoup key pair generator
*
*/
public class CramerShoupKeyPairGenerator implements AsymmetricCipherKeyPairGenerator {
private static final BigInteger ONE = BigInteger.valueOf(1);
private CramerShoupKeyGenerationParameters param;
public void init(KeyGenerationParameters param) {
this.param = (CramerShoupKeyGenerationParameters) param;
}
public AsymmetricCipherKeyPair generateKeyPair() {
CramerShoupParameters csParams = param.getParameters();
CramerShoupPrivateKeyParameters sk = generatePrivateKey(param.getRandom(), csParams);
CramerShoupPublicKeyParameters pk = calculatePublicKey(csParams, sk);
sk.setPk(pk);
return new AsymmetricCipherKeyPair(pk, sk);
}
private BigInteger generateRandomElement(BigInteger p, SecureRandom random) {
return BigIntegers.createRandomInRange(ONE, p.subtract(ONE), random);
}
private CramerShoupPrivateKeyParameters generatePrivateKey(SecureRandom random, CramerShoupParameters csParams){
BigInteger p = csParams.getP();
CramerShoupPrivateKeyParameters key = new CramerShoupPrivateKeyParameters(csParams,
generateRandomElement(p, random), generateRandomElement(p, random),
generateRandomElement(p, random), generateRandomElement(p, random),
generateRandomElement(p, random));
return key;
}
private CramerShoupPublicKeyParameters calculatePublicKey(CramerShoupParameters csParams, CramerShoupPrivateKeyParameters sk) {
BigInteger g1 = csParams.getG1();
BigInteger g2 = csParams.getG2();
BigInteger p = csParams.getP();
BigInteger c = g1.modPow(sk.getX1(), p).multiply(g2.modPow(sk.getX2(), p));
BigInteger d = g1.modPow(sk.getY1(), p).multiply(g2.modPow(sk.getY2(), p));
BigInteger h = g1.modPow(sk.getZ(), p);
return new CramerShoupPublicKeyParameters(csParams, c, d, h);
}
}
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