Quadcap Embeddable Database

com/quadcap/crypto/RSAPrivateKey.java

Go to the documentation of this file.

package com.quadcap.crypto;

/* Copyright 2002 - 2003 Quadcap Software.  All rights reserved.
 *
 * This software is distributed under the Quadcap Free Software License.
 * This software may be used or modified for any purpose, personal or
 * commercial.  Open Source redistributions are permitted.  Commercial
 * redistribution of larger works derived from, or works which bundle
 * this software requires a "Commercial Redistribution License"; see
 * http://www.quadcap.com/purchase.
 *
 * Redistributions qualify as "Open Source" under  one of the following terms:
 *   
 *    Redistributions are made at no charge beyond the reasonable cost of
 *    materials and delivery.
 *
 *    Redistributions are accompanied by a copy of the Source Code or by an
 *    irrevocable offer to provide a copy of the Source Code for up to three
 *    years at the cost of materials and delivery.  Such redistributions
 *    must allow further use, modification, and redistribution of the Source
 *    Code under substantially the same terms as this license.
 *
 * Redistributions of source code must retain the copyright notices as they
 * appear in each source code file, these license terms, and the
 * disclaimer/limitation of liability set forth as paragraph 6 below.
 *
 * Redistributions in binary form must reproduce this Copyright Notice,
 * these license terms, and the disclaimer/limitation of liability set
 * forth as paragraph 6 below, in the documentation and/or other materials
 * provided with the distribution.
 *
 * The Software is provided on an "AS IS" basis.  No warranty is
 * provided that the Software is free of defects, or fit for a
 * particular purpose.  
 *
 * Limitation of Liability. Quadcap Software shall not be liable
 * for any damages suffered by the Licensee or any third party resulting
 * from use of the Software.
 */

import java.util.Random;
import java.math.BigInteger;
import java.nio.ByteBuffer;

import com.quadcap.util.text.Text;

/**
 * RSA Private Key implementation
 *
 * @author Stan Bailes
 */
public class RSAPrivateKey extends RSAKey implements PrivateKey {
    private final BigInteger ZERO       = BigInteger.ZERO;
    private final BigInteger ONE        = BigInteger.ONE;
    private final BigInteger TWO        = new BigInteger("2");
    private final BigInteger THREE      = new BigInteger("3");

    private BigInteger p;       // first prime
    private BigInteger q;       // second prime
    
    private BigInteger d;       // decryption exponent
    private BigInteger dP;      // d % (p-1)
    private BigInteger dQ;      // d % (q-1)
    private BigInteger qInv;    // p.modInverse(q)

    /**
     * Default constructor
     */
    public RSAPrivateKey() {}

    /**
     * Initialize from string representation
     */
    public void init(String s) {
        String[] v = Text.extractN(s, "*:*:*:*:*:*:*:*");
        this.p = new BigInteger(v[2]);
        this.q = new BigInteger(v[3]);
        super.init(v[4], Integer.parseInt(v[1]), p.multiply(q));
        init();
    }

    /**
     * Return the string representation
     */
    public String toString() {
        return "RSAPriv:" + size + ":" + p + ":" + q + ":" +
            dP + ":" + dQ + ":" + qInv + ":" + text;
    }

    /**
     * Create a new keypair
     */
    public void init(String text, int siz, Random random) {
        int s2 = (siz / 2);
        int offset = (int)(random.nextDouble() * 10) - 5;
        offset += (offset < 0) ? -5.0 : 5.0;

        do {
            this.p = makePrime(s2 + offset, random);
            this.q = makePrime(s2 - offset, random);
            this.n = p.multiply(q);
        } while (n.bitLength() != siz);

        super.init(text, siz, n);
        init();
    }

    /**
     * Decrypt a buffer (in chunks)
     */
    public void f(ByteBuffer cipher, ByteBuffer plain) {
        engine(cipher, plain);
    }

    /**
     * Return the public portion of the key
     */
    public PublicKey getPublicKey() {
        RSAPublicKey pub = new RSAPublicKey();
        pub.init(text, size, n);
        return pub;
    }
    
    private final void init() {
        BigInteger p1  = p.subtract(BigInteger.ONE);
        BigInteger q1  = q.subtract(BigInteger.ONE);
        BigInteger m = p1.multiply(q1); // M = (p-1)*(q-1)

        this.d = e.modInverse(m);

        dP = d.remainder(p1);
        dQ = d.remainder(q1);
        qInv = p.modInverse(q);
    }

    final private BigInteger makePrime(int size, Random random) {
        BigInteger bn = new BigInteger(size, 100, random);
        while (bn.subtract(ONE).remainder(THREE).equals(ZERO)) {
            bn = new BigInteger(size, 100, random);
        }
        return bn;
    }

    final protected BigInteger engine(BigInteger c) {
        if (false) {
            return c.modPow(d, n);
        } else {
            BigInteger m1 = c.modPow(dP, p);
            BigInteger m2 = c.modPow(dQ, q);
            BigInteger h = ((m2.subtract(m1)).multiply(qInv)).remainder(q);
            if (h.compareTo(BigInteger.ZERO) < 0) {
                h = h.add(q);
            }
            return m1.add(h.multiply(p));
        }
    }

}