Class KeyPairGenerator
KeyPairGenerator class is used to generate pairs of
 public and private keys. Key pair generators are constructed using the
 getInstance factory methods (static methods that
 return instances of a given class).
 A Key pair generator for a particular algorithm creates a public/private key pair that can be used with this algorithm. It also associates algorithm-specific parameters with each of the generated keys.
There are two ways to generate a key pair: in an algorithm-independent manner, and in an algorithm-specific manner. The only difference between the two is the initialization of the object:
- Algorithm-Independent Initialization
 All key pair generators share the concepts of a keysize and a source of randomness. The keysize is interpreted differently for different algorithms (e.g., in the case of the DSA algorithm, the keysize corresponds to the length of the modulus). There is an initializemethod in thisKeyPairGeneratorclass that takes these two universally shared types of arguments. There is also one that takes just akeysizeargument, and uses theSecureRandomimplementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom, a system-provided source of randomness is used.)Since no other parameters are specified when you call the above algorithm-independent initializemethods, it is up to the provider what to do about the algorithm-specific parameters (if any) to be associated with each of the keys.If the algorithm is the DSA algorithm, and the keysize (modulus size) is 512, 768, 1024, or 2048, then the Sun provider uses a set of precomputed values for the p,q, andgparameters. If the modulus size is not one of the above values, the Sun provider creates a new set of parameters. Other providers might have precomputed parameter sets for more than just the modulus sizes mentioned above. Still others might not have a list of precomputed parameters at all and instead always create new parameter sets.
- Algorithm-Specific Initialization
 For situations where a set of algorithm-specific parameters already exists (e.g., so-called community parameters in DSA), there are two initializemethods that have anAlgorithmParameterSpecargument. One also has aSecureRandomargument, while the other uses theSecureRandomimplementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom, a system-provided source of randomness is used.)
In case the client does not explicitly initialize the
 KeyPairGenerator
 (via a call to an initialize method), each provider must
 supply (and document) a default initialization.
 See the Keysize Restriction sections of the
 JDK Providers
 document for information on the KeyPairGenerator 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
 KeyPairGenerator instead of relying on provider-specific defaults.
 
Note that this class is abstract and extends from
 KeyPairGeneratorSpi for historical reasons.
 Application developers should only take notice of the methods defined in
 this KeyPairGenerator class; all the methods in
 the superclass are intended for cryptographic service providers who wish to
 supply their own implementations of key pair generators.
 
 Every implementation of the Java platform is required to support the
 following standard KeyPairGenerator algorithms and keysizes in
 parentheses:
 
- DiffieHellman(1024, 2048, 4096)
- DSA(1024, 2048)
- RSA(1024, 2048, 4096)
- Since:
- 1.1
- See Also:
- 
Constructor SummaryConstructorsModifierConstructorDescriptionprotectedKeyPairGenerator(String algorithm) Creates aKeyPairGeneratorobject for the specified algorithm.
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Method SummaryModifier and TypeMethodDescriptionGenerates a key pair.final KeyPairGenerates a key pair.Returns the standard name of the algorithm for this key pair generator.static KeyPairGeneratorgetInstance(String algorithm) Returns aKeyPairGeneratorobject that generates public/private key pairs for the specified algorithm.static KeyPairGeneratorgetInstance(String algorithm, String provider) Returns aKeyPairGeneratorobject that generates public/private key pairs for the specified algorithm.static KeyPairGeneratorgetInstance(String algorithm, Provider provider) Returns aKeyPairGeneratorobject that generates public/private key pairs for the specified algorithm.final ProviderReturns the provider of this key pair generator object.voidinitialize(int keysize) Initializes the key pair generator for a certain keysize using a default parameter set and theSecureRandomimplementation of the highest-priority installed provider as the source of randomness.voidinitialize(int keysize, SecureRandom random) Initializes the key pair generator for a certain keysize with the given source of randomness (and a default parameter set).voidinitialize(AlgorithmParameterSpec params) Initializes the key pair generator using the specified parameter set and theSecureRandomimplementation of the highest-priority installed provider as the source of randomness.voidinitialize(AlgorithmParameterSpec params, SecureRandom random) Initializes the key pair generator with the given parameter set and source of randomness.
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Constructor Details- 
KeyPairGeneratorCreates aKeyPairGeneratorobject for the specified algorithm.- Parameters:
- algorithm- the standard string name of the algorithm. See the KeyPairGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
 
 
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Method Details- 
getAlgorithmReturns the standard name of the algorithm for this key pair generator. See the KeyPairGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.- Returns:
- the standard string name of the algorithm.
 
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getInstanceReturns aKeyPairGeneratorobject that generates public/private key pairs for the specified algorithm.This method traverses the list of registered security Providers, starting with the most preferred Provider. A new KeyPairGeneratorobject encapsulating theKeyPairGeneratorSpiimplementation 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 standard string name of the algorithm. See the KeyPairGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
- Returns:
- the new KeyPairGeneratorobject
- Throws:
- NoSuchAlgorithmException- if no- Providersupports a- KeyPairGeneratorSpiimplementation for the specified algorithm
- NullPointerException- if- algorithmis- null
- See Also:
 
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getInstancepublic static KeyPairGenerator getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException Returns aKeyPairGeneratorobject that generates public/private key pairs for the specified algorithm.A new KeyPairGeneratorobject encapsulating theKeyPairGeneratorSpiimplementation 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 standard string name of the algorithm. See the KeyPairGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
- provider- the string name of the provider.
- Returns:
- the new KeyPairGeneratorobject
- Throws:
- IllegalArgumentException- if the provider name is- nullor empty
- NoSuchAlgorithmException- if a- KeyPairGeneratorSpiimplementation for the specified algorithm is not available from the specified provider
- NoSuchProviderException- if the specified provider is not registered in the security provider list
- NullPointerException- if- algorithmis- null
- See Also:
 
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getInstancepublic static KeyPairGenerator getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException Returns aKeyPairGeneratorobject that generates public/private key pairs for the specified algorithm.A new KeyPairGeneratorobject encapsulating theKeyPairGeneratorSpiimplementation from the specified provider is returned. Note that the specified provider does not have to be registered in the provider list.- Parameters:
- algorithm- the standard string name of the algorithm. See the KeyPairGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
- provider- the provider.
- Returns:
- the new KeyPairGeneratorobject
- Throws:
- IllegalArgumentException- if the specified provider is- null
- NoSuchAlgorithmException- if a- KeyPairGeneratorSpiimplementation for the specified algorithm is not available from the specified- Providerobject
- NullPointerException- if- algorithmis- null
- Since:
- 1.4
- See Also:
 
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getProviderReturns the provider of this key pair generator object.- Returns:
- the provider of this key pair generator object
 
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initializepublic void initialize(int keysize) Initializes the key pair generator for a certain keysize using a default parameter set and theSecureRandomimplementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom, a system-provided source of randomness is used.)- Parameters:
- keysize- the keysize. This is an algorithm-specific metric, such as modulus length, specified in number of bits.
- Throws:
- InvalidParameterException- if the- keysizeis not supported by this- KeyPairGeneratorobject.
 
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initializeInitializes the key pair generator for a certain keysize with the given source of randomness (and a default parameter set).- Specified by:
- initializein class- KeyPairGeneratorSpi
- Parameters:
- keysize- the keysize. This is an algorithm-specific metric, such as modulus length, specified in number of bits.
- random- the source of randomness.
- Throws:
- InvalidParameterException- if the- keysizeis not supported by this- KeyPairGeneratorobject.
- Since:
- 1.2
 
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initializeInitializes the key pair generator using the specified parameter set and theSecureRandomimplementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom, a system-provided source of randomness is used.)This concrete method has been added to this previously-defined abstract class. This method calls the KeyPairGeneratorSpi initializemethod, passing itparamsand a source of randomness (obtained from the highest-priority installed provider or system-provided if none of the installed providers supply one). Thatinitializemethod always throws anUnsupportedOperationExceptionif it is not overridden by the provider.- Parameters:
- params- the parameter set used to generate the keys.
- Throws:
- InvalidAlgorithmParameterException- if the given parameters are inappropriate for this key pair generator.
- Since:
- 1.2
 
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initializepublic void initialize(AlgorithmParameterSpec params, SecureRandom random) throws InvalidAlgorithmParameterException Initializes the key pair generator with the given parameter set and source of randomness.This concrete method has been added to this previously-defined abstract class. This method calls the KeyPairGeneratorSpi initializemethod, passing itparamsandrandom. Thatinitializemethod always throws anUnsupportedOperationExceptionif it is not overridden by the provider.- Overrides:
- initializein class- KeyPairGeneratorSpi
- Parameters:
- params- the parameter set used to generate the keys.
- random- the source of randomness.
- Throws:
- InvalidAlgorithmParameterException- if the given parameters are inappropriate for this key pair generator.
- Since:
- 1.2
 
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genKeyPairGenerates a key pair.If this KeyPairGeneratorhas not been initialized explicitly, provider-specific defaults will be used for the size and other (algorithm-specific) values of the generated keys.This will generate a new key pair every time it is called. This method is functionally equivalent to generateKeyPair.- Returns:
- the generated key pair
- Since:
- 1.2
 
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generateKeyPairGenerates a key pair.If this KeyPairGeneratorhas not been initialized explicitly, provider-specific defaults will be used for the size and other (algorithm-specific) values of the generated keys.This will generate a new key pair every time it is called. This method is functionally equivalent to genKeyPair.- Specified by:
- generateKeyPairin class- KeyPairGeneratorSpi
- Returns:
- the generated key pair
 
 
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