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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.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();
}
}