elgamalencryption.java

这是一个用Java实现ElGamal加密解密和签名验证的算法

/*
 * ElGamal Encryption Method
 *
 * @author Ge ZHANG (2937207)
 * @login name: gz847
 * @version 1.00 07/08/11*/

import java.math.BigInteger;
import java.security.*;

public class ElGamalEncryption{
	
	protected ElGamalKey mKey;
	
	protected static BigInteger kOne = BigInteger.valueOf(1);
	
	protected void engineInitEncrypt(PublicKey key) throws InvalidKeyException {
    if (!(key instanceof ElGamalPublicKey)) throw new InvalidKeyException("Invalid ElGamalPublicKey.");
    mKey = (ElGamalKey)key;
    }
	
	protected void engineInitDecrypt(PrivateKey key) throws InvalidKeyException {
    if (!(key instanceof ElGamalPrivateKey)) throw new InvalidKeyException("Invalid ElGamalPrivateKey.");
    mKey = (ElGamalKey)key;
    }
    
	protected BigInteger[] engineEncrypt(BigInteger M){
  	BigInteger y = ((ElGamalPublicKey)mKey).getY();
    BigInteger g = mKey.getG();
    BigInteger p = mKey.getP();

    BigInteger k;
    do {
      k = new BigInteger(p.bitLength() - 1, new SecureRandom());
    } while (k.gcd(p).equals(kOne) == false);
    
    BigInteger a = g.modPow(k, p);
    
    BigInteger temp = y.modPow(k, p);
    BigInteger C = (M.multiply(temp)).mod(p);
    BigInteger[] result = new BigInteger[2];
    result[0] = a;
    result[1] = C;
    
    return result;
  }
  
  protected BigInteger engineDecrypt(BigInteger[] result){
  	BigInteger k = ((ElGamalPrivateKey)mKey).getK();
    BigInteger p = mKey.getP();
    
    BigInteger a = result[0];
    BigInteger C = result[1];
  	BigInteger temp = a.modPow(k, p).modInverse(p);
  	
  	
  	return C.multiply(temp).mod(p);
  }
}