Java tutorial
/* * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code 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. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code 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 in the LICENSE file that * accompanied this code). * * 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.security; import java.security.spec.AlgorithmParameterSpec; import java.util.Objects; /** * The {@code AlgorithmParameterGenerator} class is used to generate a * set of * parameters to be used with a certain algorithm. Parameter generators * are constructed using the {@code getInstance} factory methods * (static methods that return instances of a given class). * * <P>The object that will generate the parameters can be initialized * in two different ways: in an algorithm-independent manner, or in an * algorithm-specific manner: * * <ul> * <li>The algorithm-independent approach uses the fact that all parameter * generators share the concept of a "size" and a * source of randomness. The measure of size is universally shared * by all algorithm parameters, though it is interpreted differently * for different algorithms. For example, in the case of parameters for * the <i>DSA</i> algorithm, "size" corresponds to the size * of the prime modulus (in bits). * When using this approach, algorithm-specific parameter generation * values - if any - default to some standard values, unless they can be * derived from the specified size. * * <li>The other approach initializes a parameter generator object * using algorithm-specific semantics, which are represented by a set of * algorithm-specific parameter generation values. To generate * Diffie-Hellman system parameters, for example, the parameter generation * values usually * consist of the size of the prime modulus and the size of the * random exponent, both specified in number of bits. * </ul> * * <P>In case the client does not explicitly initialize the * AlgorithmParameterGenerator (via a call to an {@code init} method), * each provider must supply (and document) a default initialization. * See the Keysize Restriction sections of the * {@extLink security_guide_jdk_providers JDK Providers} * document for information on the AlgorithmParameterGenerator defaults * used by JDK providers. * However, note that defaults may vary across different providers. * Additionally, the default value for a provider may change in a future * version. Therefore, it is recommended to explicitly initialize the * AlgorithmParameterGenerator instead of relying on provider-specific defaults. * * <p> Every implementation of the Java platform is required to support the * following standard {@code AlgorithmParameterGenerator} algorithms and * keysizes in parentheses: * <ul> * <li>{@code DiffieHellman} (1024, 2048)</li> * <li>{@code DSA} (1024, 2048)</li> * </ul> * These algorithms are described in the <a href= * "{@docRoot}/../specs/security/standard-names.html#algorithmparametergenerator-algorithms"> * AlgorithmParameterGenerator section</a> of the * Java Security Standard Algorithm Names Specification. * Consult the release documentation for your implementation to see if any * other algorithms are supported. * * @author Jan Luehe * * * @see AlgorithmParameters * @see java.security.spec.AlgorithmParameterSpec * * @since 1.2 */ public class AlgorithmParameterGenerator { // The provider private Provider provider; // The provider implementation (delegate) private AlgorithmParameterGeneratorSpi paramGenSpi; // The algorithm private String algorithm; /** * Creates an AlgorithmParameterGenerator object. * * @param paramGenSpi the delegate * @param provider the provider * @param algorithm the algorithm */ protected AlgorithmParameterGenerator(AlgorithmParameterGeneratorSpi paramGenSpi, Provider provider, String algorithm) { this.paramGenSpi = paramGenSpi; this.provider = provider; this.algorithm = algorithm; } /** * Returns the standard name of the algorithm this parameter * generator is associated with. * * @return the string name of the algorithm. */ public final String getAlgorithm() { return this.algorithm; } /** * Returns an AlgorithmParameterGenerator object for generating * a set of parameters to be used with the specified algorithm. * * <p> This method traverses the list of registered security Providers, * starting with the most preferred Provider. * A new AlgorithmParameterGenerator object encapsulating the * AlgorithmParameterGeneratorSpi implementation from the first * Provider that supports the specified algorithm is returned. * * <p> Note that the list of registered providers may be retrieved via * the {@link Security#getProviders() Security.getProviders()} method. * * @implNote * The JDK Reference Implementation additionally uses the * {@code jdk.security.provider.preferred} * {@link Security#getProperty(String) Security} property to determine * the preferred provider order for the specified algorithm. This * may be different than the order of providers returned by * {@link Security#getProviders() Security.getProviders()}. * * @param algorithm the name of the algorithm this * parameter generator is associated with. * See the AlgorithmParameterGenerator section in the <a href= * "{@docRoot}/../specs/security/standard-names.html#algorithmparametergenerator-algorithms"> * Java Security Standard Algorithm Names Specification</a> * for information about standard algorithm names. * * @return the new {@code AlgorithmParameterGenerator} object * * @throws NoSuchAlgorithmException if no {@code Provider} supports an * {@code AlgorithmParameterGeneratorSpi} implementation for the * specified algorithm * * @throws NullPointerException if {@code algorithm} is {@code null} * * @see Provider */ public static AlgorithmParameterGenerator getInstance(String algorithm) throws NoSuchAlgorithmException { Objects.requireNonNull(algorithm, "null algorithm name"); try { Object[] objs = Security.getImpl(algorithm, "AlgorithmParameterGenerator", (String) null); return new AlgorithmParameterGenerator((AlgorithmParameterGeneratorSpi) objs[0], (Provider) objs[1], algorithm); } catch (NoSuchProviderException e) { throw new NoSuchAlgorithmException(algorithm + " not found"); } } /** * Returns an AlgorithmParameterGenerator object for generating * a set of parameters to be used with the specified algorithm. * * <p> A new AlgorithmParameterGenerator object encapsulating the * AlgorithmParameterGeneratorSpi implementation from the specified provider * is returned. The specified provider must be registered * in the security provider list. * * <p> Note that the list of registered providers may be retrieved via * the {@link Security#getProviders() Security.getProviders()} method. * * @param algorithm the name of the algorithm this * parameter generator is associated with. * See the AlgorithmParameterGenerator section in the <a href= * "{@docRoot}/../specs/security/standard-names.html#algorithmparametergenerator-algorithms"> * Java Security Standard Algorithm Names Specification</a> * for information about standard algorithm names. * * @param provider the string name of the Provider. * * @return the new {@code AlgorithmParameterGenerator} object * * @throws IllegalArgumentException if the provider name is {@code null} * or empty * * @throws NoSuchAlgorithmException if an * {@code AlgorithmParameterGeneratorSpi} * implementation for the specified algorithm is not * available from the specified provider * * @throws NoSuchProviderException if the specified provider is not * registered in the security provider list * * @throws NullPointerException if {@code algorithm} is {@code null} * * @see Provider */ public static AlgorithmParameterGenerator getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException { Objects.requireNonNull(algorithm, "null algorithm name"); if (provider == null || provider.isEmpty()) throw new IllegalArgumentException("missing provider"); Object[] objs = Security.getImpl(algorithm, "AlgorithmParameterGenerator", provider); return new AlgorithmParameterGenerator((AlgorithmParameterGeneratorSpi) objs[0], (Provider) objs[1], algorithm); } /** * Returns an AlgorithmParameterGenerator object for generating * a set of parameters to be used with the specified algorithm. * * <p> A new AlgorithmParameterGenerator object encapsulating the * AlgorithmParameterGeneratorSpi implementation from the specified Provider * object is returned. Note that the specified Provider object * does not have to be registered in the provider list. * * @param algorithm the string name of the algorithm this * parameter generator is associated with. * See the AlgorithmParameterGenerator section in the <a href= * "{@docRoot}/../specs/security/standard-names.html#algorithmparametergenerator-algorithms"> * Java Security Standard Algorithm Names Specification</a> * for information about standard algorithm names. * * @param provider the {@code Provider} object. * * @return the new {@code AlgorithmParameterGenerator} object * * @throws IllegalArgumentException if the specified provider is * {@code null} * * @throws NoSuchAlgorithmException if an * {@code AlgorithmParameterGeneratorSpi} * implementation for the specified algorithm is not available * from the specified {@code Provider} object * * @throws NullPointerException if {@code algorithm} is {@code null} * * @see Provider * * @since 1.4 */ public static AlgorithmParameterGenerator getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException { Objects.requireNonNull(algorithm, "null algorithm name"); if (provider == null) throw new IllegalArgumentException("missing provider"); Object[] objs = Security.getImpl(algorithm, "AlgorithmParameterGenerator", provider); return new AlgorithmParameterGenerator((AlgorithmParameterGeneratorSpi) objs[0], (Provider) objs[1], algorithm); } /** * Returns the provider of this algorithm parameter generator object. * * @return the provider of this algorithm parameter generator object */ public final Provider getProvider() { return this.provider; } /** * Initializes this parameter generator for a certain size. * To create the parameters, the {@code SecureRandom} * implementation of the highest-priority installed provider is used as * the source of randomness. * (If none of the installed providers supply an implementation of * {@code SecureRandom}, a system-provided source of randomness is * used.) * * @param size the size (number of bits). */ public final void init(int size) { paramGenSpi.engineInit(size, new SecureRandom()); } /** * Initializes this parameter generator for a certain size and source * of randomness. * * @param size the size (number of bits). * @param random the source of randomness. */ public final void init(int size, SecureRandom random) { paramGenSpi.engineInit(size, random); } /** * Initializes this parameter generator with a set of algorithm-specific * parameter generation values. * To generate the parameters, the {@code SecureRandom} * implementation of the highest-priority installed provider is used as * the source of randomness. * (If none of the installed providers supply an implementation of * {@code SecureRandom}, a system-provided source of randomness is * used.) * * @param genParamSpec the set of algorithm-specific parameter generation values. * * @exception InvalidAlgorithmParameterException if the given parameter * generation values are inappropriate for this parameter generator. */ public final void init(AlgorithmParameterSpec genParamSpec) throws InvalidAlgorithmParameterException { paramGenSpi.engineInit(genParamSpec, new SecureRandom()); } /** * Initializes this parameter generator with a set of algorithm-specific * parameter generation values. * * @param genParamSpec the set of algorithm-specific parameter generation values. * @param random the source of randomness. * * @exception InvalidAlgorithmParameterException if the given parameter * generation values are inappropriate for this parameter generator. */ public final void init(AlgorithmParameterSpec genParamSpec, SecureRandom random) throws InvalidAlgorithmParameterException { paramGenSpi.engineInit(genParamSpec, random); } /** * Generates the parameters. * * @return the new AlgorithmParameters object. */ public final AlgorithmParameters generateParameters() { return paramGenSpi.engineGenerateParameters(); } }