keypairgenerator.java

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/*
 * @(#)KeyPairGenerator.java	1.56 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, as published by the Free Software Foundation.   
 *   
 * This program is distributed in the hope that it will be useful, but  
 * WITHOUT ANY WARRANTY; without even the implied warranty of  
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */
 
package java.security;

import java.security.spec.AlgorithmParameterSpec;

/**
 * The KeyPairGenerator class is used to generate pairs of
 * public and private keys. Key pair generators are constructed using the
 * <code>getInstance</code> factory methods (static methods that
 * return instances of a given class).
 *
 * <p>A Key pair generator for a particular algorithm creates a public/private
 * key pair that can be used with this algorithm. It also associates
 * algorithm-specific parameters with each of the generated keys.
 * 
 * <p>There are two ways to generate a key pair: in an algorithm-independent
 * manner, and in an algorithm-specific manner.
 * The only difference between the two is the initialization of the object:
 * 
 * <ul>
 * <li><b>Algorithm-Independent Initialization</b>
 * <p>All key pair generators share the concepts of a keysize and a
 * source of randomness. The keysize is interpreted differently for different
 * algorithms (e.g., in the case of the <i>DSA</i> algorithm, the keysize 
 * corresponds to the length of the modulus).
 * There is an 
 * {@link #initialize(int, java.security.SecureRandom) initialize}
 * method in this KeyPairGenerator class that takes these two universally
 * shared types of arguments. There is also one that takes just a
 * <code>keysize</code> argument, and uses the <code>SecureRandom</code>
 * implementation of the highest-priority installed provider as the source
 * of randomness. (If none of the installed providers supply an implementation
 * of <code>SecureRandom</code>, a system-provided source of randomness is
 * used.)
 * 
 * <p>Since no other parameters are specified when you call the above
 * algorithm-independent <code>initialize</code> methods, it is up to the
 * provider what to do about the algorithm-specific parameters (if any) to be
 * associated with each of the keys.
 * 
 * <p>If the algorithm is the <i>DSA</i> algorithm, and the keysize (modulus
 * size) is 512, 768, or 1024, then the <i>Sun</i> provider uses a set of
 * precomputed values for the <code>p</code>, <code>q</code>, and
 * <code>g</code> parameters. If the modulus size is not one of the above
 * values, the <i>Sun</i> provider creates a new set of parameters. Other
 * providers might have precomputed parameter sets for more than just the
 * three modulus sizes mentioned above. Still others might not have a list of
 * precomputed parameters at all and instead always create new parameter sets.
 * <p>
 *
 * <li><b>Algorithm-Specific Initialization</b>
 * <p>For situations where a set of algorithm-specific parameters already
 * exists (e.g., so-called <i>community parameters</i> in DSA), there are two
 * {@link #initialize(java.security.spec.AlgorithmParameterSpec)
 * initialize} methods that have an <code>AlgorithmParameterSpec</code>
 * argument. One also has a <code>SecureRandom</code> argument, while the
 * the other uses the <code>SecureRandom</code>
 * implementation of the highest-priority installed provider as the source
 * of randomness. (If none of the installed providers supply an implementation
 * of <code>SecureRandom</code>, a system-provided source of randomness is
 * used.)
 * </ul>
 *
 * <p>In case the client does not explicitly initialize the KeyPairGenerator
 * (via a call to an <code>initialize</code> method), each provider must
 * supply (and document) a default initialization.
 * For example, the <i>Sun</i> provider uses a default modulus size (keysize)
 * of 1024 bits.
 *
 * <p>Note that this class is abstract and extends from
 * <code>KeyPairGeneratorSpi</code> for historical reasons.
 * Application developers should only take notice of the methods defined in
 * this <code>KeyPairGenerator</code> class; all the methods in
 * the superclass are intended for cryptographic service providers who wish to
 * supply their own implementations of key pair generators.
 *
 * @author Benjamin Renaud
 *
 * @version 1.49, 02/02/00
 *
 * @see java.security.spec.AlgorithmParameterSpec
 */

public abstract class KeyPairGenerator extends KeyPairGeneratorSpi {

    private String algorithm;

    // The provider
    private Provider provider;

    /**
     * Creates a KeyPairGenerator object for the specified algorithm.
     *
     * @param algorithm the standard string name of the algorithm. 
     * See Appendix A in the <a href=
     * "../../../guide/security/CryptoSpec.html#AppA">
     * Java Cryptography Architecture API Specification &amp; Reference </a> 
     * for information about standard algorithm names.
     */
    protected KeyPairGenerator(String algorithm) {
	this.algorithm = algorithm;
    }
    
    /**
     * Returns the standard name of the algorithm for this key pair generator.
     * See Appendix A in the <a href=
     * "../../../guide/security/CryptoSpec.html#AppA">
     * Java Cryptography Architecture API Specification &amp; Reference </a> 
     * for information about standard algorithm names.
     * 
     * @return the standard string name of the algorithm. 
     */
    public String getAlgorithm() {
	return this.algorithm;
    }

    /**
     * Generates a KeyPairGenerator object that implements the specified digest
     * algorithm. If the default provider package
     * provides an implementation of the requested digest algorithm,
     * an instance of KeyPairGenerator containing that implementation is
     * returned.
     * If the algorithm is not available in the default 
     * package, other packages are searched.
     *
     * @param algorithm the standard string name of the algorithm. 
     * See Appendix A in the <a href=
     * "../../../guide/security/CryptoSpec.html#AppA">
     * Java Cryptography Architecture API Specification &amp; Reference </a> 
     * for information about standard algorithm names.
     *
     * @return the new KeyPairGenerator object.
     *
     * @exception NoSuchAlgorithmException if the algorithm is
     * not available in the environment.  
     */
    public static KeyPairGenerator getInstance(String algorithm)
    throws NoSuchAlgorithmException {
	try {
	    Object[] objs = Security.getImpl(algorithm, "KeyPairGenerator",
					     (String)null);
	    if (objs[0] instanceof KeyPairGenerator) {
		KeyPairGenerator keyPairGen = (KeyPairGenerator)objs[0];
		keyPairGen.provider = (Provider)objs[1];
		return keyPairGen;
	    } else {
		KeyPairGenerator delegate =
		    new Delegate((KeyPairGeneratorSpi)objs[0], algorithm);
		delegate.provider = (Provider)objs[1];
		return delegate;
	    }
	} catch(NoSuchProviderException e) {
	    throw new NoSuchAlgorithmException(algorithm + " not found");
	}
    }

    /** 
     * Generates a KeyPairGenerator object implementing the specified
     * algorithm, as supplied from the specified provider, 
     * if such an algorithm is available from the provider.
     *
     * @param algorithm the standard string name of the algorithm.
     * See Appendix A in the <a href=
     * "../../../guide/security/CryptoSpec.html#AppA">
     * Java Cryptography Architecture API Specification &amp; Reference </a> 
     * for information about standard algorithm names.
     *
     * @param provider the string name of the provider.
     *
     * @return the new KeyPairGenerator object.
     *
     * @exception NoSuchAlgorithmException if the algorithm is
     * not available from the provider.
     *
     * @exception NoSuchProviderException if the provider is not
     * available in the environment.
     *
     * @exception IllegalArgumentException if the provider name is null
     * or empty.
     * 
     * @see Provider 
     */
    public static KeyPairGenerator getInstance(String algorithm,
					       String provider) 
	throws NoSuchAlgorithmException, NoSuchProviderException
    {
	if (provider == null || provider.length() == 0)
	    throw new IllegalArgumentException("missing provider");
	Object[] objs = Security.getImpl(algorithm, "KeyPairGenerator",
					 provider);
	if (objs[0] instanceof KeyPairGenerator) {
	    KeyPairGenerator keyPairGen = (KeyPairGenerator)objs[0];
	    keyPairGen.provider = (Provider)objs[1];
	    return keyPairGen;
	} else {
	    KeyPairGenerator delegate =
		new Delegate((KeyPairGeneratorSpi)objs[0], algorithm);
	    delegate.provider = (Provider)objs[1];
	    return delegate;
	}
    }

    /** 
     * Generates a KeyPairGenerator object implementing the specified
     * algorithm, as supplied from the specified provider, 
     * if such an algorithm is available from the provider.
     * Note: the <code>provider</code> doesn't have to be registered.
     *
     * @param algorithm the standard string name of the algorithm.
     * See Appendix A in the <a href=
     * "../../../guide/security/CryptoSpec.html#AppA">
     * Java Cryptography Architecture API Specification &amp; Reference </a> 
     * for information about standard algorithm names.
     *
     * @param provider the provider.
     *
     * @return the new KeyPairGenerator object.
     *
     * @exception NoSuchAlgorithmException if the algorithm is
     * not available from the provider.
     *
     * @exception IllegalArgumentException if the <code>provider</code> is
     * null.
     *