eccryptosystem.java

java写的椭圆曲线加密(ECC)算法源码

package ecc.elliptic;

import ecc.*;
import java.math.BigInteger;
import java.io.*;
import java.util.*;
import java.security.MessageDigest;

public class ECCryptoSystem implements CryptoSystem {
    MessageDigest hash;

    private EllipticCurve ec;    

    public ECCryptoSystem(EllipticCurve ec) {
	this.ec = ec;
	try {
	    hash = MessageDigest.getInstance("SHA-1");
	} catch (java.security.NoSuchAlgorithmException e) {
	    System.out.println("RSACryptoSystem: THIS CANNOT HAPPEN\n"+e);
	    System.exit(0);
	}
    }

    public int blockSize() {
	return 20;
    }

    public byte[] encrypt(byte[] input,int numbytes, Key key) {
	ECKey ek = (ECKey) key;
	byte[] res=new byte[ek.mother.getPCS()+numbytes];
	hash.reset();

	BigInteger rk = new BigInteger(ek.mother.getp().bitLength() + 17, Rand.om);
	if (ek.mother.getOrder() != null) {
	    rk = rk.mod(ek.mother.getOrder());
	}
	ECPoint gamma = ek.mother.getGenerator().multiply(rk);
	ECPoint sec = ek.beta.multiply(rk);
	System.arraycopy(gamma.compress(),0,res,0,ek.mother.getPCS());
	hash.update(sec.getx().toByteArray());
	hash.update(sec.gety().toByteArray());
	byte[] digest = hash.digest();
	for(int j = 0; j < numbytes; j++) {
	    res[j+ek.mother.getPCS()]=(byte) (input[j]^digest[j]);
	}
	return res;
    }

    public byte[] decrypt(byte[] input, Key key) {
	ECKey dk = (ECKey) key;
	byte[] res=new byte[input.length-dk.mother.getPCS()];
	byte[] gammacom=new byte[dk.mother.getPCS()];
	hash.reset();
	
	System.arraycopy(input,0,gammacom,0,dk.mother.getPCS());
	ECPoint gamma = new ECPoint(gammacom,dk.mother);
	ECPoint sec = gamma.multiply(dk.sk);
	if(sec.isZero()) {
	    hash.update(BigInteger.ZERO.toByteArray());
	    hash.update(BigInteger.ZERO.toByteArray());
	} else {
	    hash.update(sec.getx().toByteArray());
	    hash.update(sec.gety().toByteArray());
	}
	byte[] digest = hash.digest();
	for(int j = 0; j < input.length-dk.mother.getPCS(); j++) {
	    res[j]=(byte) (input[j+dk.mother.getPCS()]^digest[j]);
	}
	return res;
    }

    

    /** This method generates a new key for the cryptosystem.
     *@return the new key generated*/
    public Key generateKey() {
	return new ECKey(ec);
    }

    public String toString(){
	return "ECC - " + ec.toString();
    }

}