Class AlgorithmParameterGenerator
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
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)
- Since:
- 1.2
- See Also:
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Constructor Summary
ConstructorsModifierConstructorDescriptionprotectedAlgorithmParameterGenerator(AlgorithmParameterGeneratorSpi paramGenSpi, Provider provider, String algorithm) Creates anAlgorithmParameterGeneratorobject. -
Method Summary
Modifier and TypeMethodDescriptionfinal AlgorithmParametersGenerates the parameters.final StringReturns the standard name of the algorithm this parameter generator is associated with.static AlgorithmParameterGeneratorgetInstance(String algorithm) Returns anAlgorithmParameterGeneratorobject for generating a set of parameters to be used with the specified algorithm.static AlgorithmParameterGeneratorgetInstance(String algorithm, String provider) Returns anAlgorithmParameterGeneratorobject for generating a set of parameters to be used with the specified algorithm.static AlgorithmParameterGeneratorgetInstance(String algorithm, Provider provider) Returns anAlgorithmParameterGeneratorobject for generating a set of parameters to be used with the specified algorithm.final ProviderReturns the provider of this algorithm parameter generator object.final voidinit(int size) Initializes this parameter generator for a certain size.final voidinit(int size, SecureRandom random) Initializes this parameter generator for a certain size and source of randomness.final voidinit(AlgorithmParameterSpec genParamSpec) Initializes this parameter generator with a set of algorithm-specific parameter generation values.final voidinit(AlgorithmParameterSpec genParamSpec, SecureRandom random) Initializes this parameter generator with a set of algorithm-specific parameter generation values.
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Constructor Details
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AlgorithmParameterGenerator
protected AlgorithmParameterGenerator(AlgorithmParameterGeneratorSpi paramGenSpi, Provider provider, String algorithm) Creates anAlgorithmParameterGeneratorobject.- Parameters:
paramGenSpi- the delegateprovider- the provideralgorithm- the algorithm
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Method Details
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getAlgorithm
Returns the standard name of the algorithm this parameter generator is associated with.- Returns:
- the string name of the algorithm.
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getInstance
public static AlgorithmParameterGenerator getInstance(String algorithm) throws NoSuchAlgorithmException Returns anAlgorithmParameterGeneratorobject 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
AlgorithmParameterGeneratorobject encapsulating theAlgorithmParameterGeneratorSpiimplementation 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.- Implementation Note:
- The JDK Reference Implementation additionally uses the
jdk.security.provider.preferredSecurityproperty to determine the preferred provider order for the specified algorithm. This may be different from the order of providers returned bySecurity.getProviders(). - Parameters:
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.- Returns:
- the new
AlgorithmParameterGeneratorobject - Throws:
NoSuchAlgorithmException- if noProvidersupports anAlgorithmParameterGeneratorSpiimplementation for the specified algorithmNullPointerException- ifalgorithmisnull- See Also:
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getInstance
public static AlgorithmParameterGenerator getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException Returns anAlgorithmParameterGeneratorobject for generating a set of parameters to be used with the specified algorithm.A new
AlgorithmParameterGeneratorobject encapsulating theAlgorithmParameterGeneratorSpiimplementation 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.- Parameters:
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 theProvider.- Returns:
- the new
AlgorithmParameterGeneratorobject - Throws:
IllegalArgumentException- if the provider name isnullor emptyNoSuchAlgorithmException- if anAlgorithmParameterGeneratorSpiimplementation for the specified algorithm is not available from the specified providerNoSuchProviderException- if the specified provider is not registered in the security provider listNullPointerException- ifalgorithmisnull- See Also:
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getInstance
public static AlgorithmParameterGenerator getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException Returns anAlgorithmParameterGeneratorobject for generating a set of parameters to be used with the specified algorithm.A new
AlgorithmParameterGeneratorobject encapsulating theAlgorithmParameterGeneratorSpiimplementation from the specified provider is returned. Note that the specified provider does not have to be registered in the provider list.- Parameters:
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- theProviderobject.- Returns:
- the new
AlgorithmParameterGeneratorobject - Throws:
IllegalArgumentException- if the specified provider isnullNoSuchAlgorithmException- if anAlgorithmParameterGeneratorSpiimplementation for the specified algorithm is not available from the specifiedProviderobjectNullPointerException- ifalgorithmisnull- Since:
- 1.4
- See Also:
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getProvider
Returns the provider of this algorithm parameter generator object.- Returns:
- the provider of this algorithm parameter generator object
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init
public final void init(int size) Initializes this parameter generator for a certain size. To create the parameters, theSecureRandomimplementation of the highest-priority installed provider is used as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom, a system-provided source of randomness is used.)- Parameters:
size- the size (number of bits).
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init
Initializes this parameter generator for a certain size and source of randomness.- Parameters:
size- the size (number of bits).random- the source of randomness.
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init
public final void init(AlgorithmParameterSpec genParamSpec) throws InvalidAlgorithmParameterException Initializes this parameter generator with a set of algorithm-specific parameter generation values. To generate the parameters, theSecureRandomimplementation of the highest-priority installed provider is used as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom, a system-provided source of randomness is used.)- Parameters:
genParamSpec- the set of algorithm-specific parameter generation values.- Throws:
InvalidAlgorithmParameterException- if the given parameter generation values are inappropriate for this parameter generator.
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init
public final void init(AlgorithmParameterSpec genParamSpec, SecureRandom random) throws InvalidAlgorithmParameterException Initializes this parameter generator with a set of algorithm-specific parameter generation values.- Parameters:
genParamSpec- the set of algorithm-specific parameter generation values.random- the source of randomness.- Throws:
InvalidAlgorithmParameterException- if the given parameter generation values are inappropriate for this parameter generator.
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generateParameters
Generates the parameters.- Returns:
- the new
AlgorithmParametersobject.
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