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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.length() == 0)

            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();

    }

}