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package java.security;

import java.security.spec.AlgorithmParameterSpec;
import java.util.Objects;


The AlgorithmParameterGenerator class is used to generate a set of parameters to be used with a certain algorithm. Parameter generators are constructed using the getInstance factory methods (static methods that return instances of a given class). 
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:

    

  • 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 DSA 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.

  • 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.



In case the client does not explicitly initialize the AlgorithmParameterGenerator (via a call to an 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. 
 Every implementation of the Java platform is required to support the following standard AlgorithmParameterGenerator algorithms and keysizes in parentheses: 
    

  • DiffieHellman (1024, 2048)
    • 

  • DSA (1024, 2048)
    • 


These algorithms are described in the 
AlgorithmParameterGenerator section 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 Also:
Since:1.2
/**
 * 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.

Params:
  • paramGenSpi – the delegate
  • provider – the provider
  • algorithm – the 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.

Returns:the string name of the 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.

 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.

 Note that the list of registered providers may be retrieved via the Security.getProviders() method. 
Params:
Throws:
See Also:
Implementation Note: The JDK Reference Implementation additionally uses the jdk.security.provider.preferred Security property to determine the preferred provider order for the specified algorithm. This may be different than the order of providers returned by Security.getProviders().
Returns:the new AlgorithmParameterGenerator object
/**
     * 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.

 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.

 Note that the list of registered providers may be retrieved via the Security.getProviders() method. 
Params:
  • algorithm – the name of the algorithm this
parameter generator is associated with.
See the AlgorithmParameterGenerator section in the 
Java Security Standard Algorithm Names Specification
for information about standard algorithm names.
  • provider – the string name of the Provider.
Throws:
See Also:
Returns:the new AlgorithmParameterGenerator object
/**
     * 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.

 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.

Params:
  • algorithm – the string name of the algorithm this
parameter generator is associated with.
See the AlgorithmParameterGenerator section in the 
Java Security Standard Algorithm Names Specification
for information about standard algorithm names.
  • provider – the Provider object.
Throws:
See Also:
Returns:the new AlgorithmParameterGenerator object
Since:1.4
/**
     * 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.

Returns:the provider of this algorithm parameter generator object
/**
     * 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 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 SecureRandom, a system-provided source of randomness is used.) 
Params:
  • size – the size (number of bits).
/**
     * 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.

Params:
  • size – the size (number of bits).
  • random – the source of randomness.
/**
     * 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 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 SecureRandom, a system-provided source of randomness is used.) 
Params:
  • genParamSpec – the set of algorithm-specific parameter generation values.
Throws:
/**
     * 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.

Params:
  • genParamSpec – the set of algorithm-specific parameter generation values.
  • random – the source of randomness.
Throws:
/**
     * 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.

Returns:the new AlgorithmParameters object.
/**
     * Generates the parameters.
     *
     * @return the new AlgorithmParameters object.
     */
    public final AlgorithmParameters generateParameters() {
        return paramGenSpi.engineGenerateParameters();
    }
}