Class KeyGenerator
Key generators are constructed using one of the getInstance
 class methods of this class.
 
KeyGenerator objects are reusable, i.e., after a key has been
 generated, the same KeyGenerator object can be re-used
 to generate further keys.
 
There are two ways to generate a key: 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 generators share the concepts of a keysize and a source of randomness. There is an initmethod in thisKeyGeneratorclass 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 (or a system-provided source of randomness if none of the installed providers supply a SecureRandom implementation), and one that takes just a source of randomness.Since no other parameters are specified when you call the above algorithm-independent initmethods, it is up to the provider what to do about the algorithm-specific parameters (if any) to be associated with each of the keys.
- Algorithm-Specific Initialization
 For situations where a set of algorithm-specific parameters already exists, there are two initmethods that have anAlgorithmParameterSpecargument. One also has aSecureRandomargument, while the other uses the SecureRandom implementation of the highest-priority installed provider as the source of randomness (or a system-provided source of randomness if none of the installed providers supply a SecureRandom implementation).
In case the client does not explicitly initialize the KeyGenerator
 (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 KeyGenerator 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
 KeyGenerator instead of relying on provider-specific defaults.
 
 Every implementation of the Java platform is required to support the
 following standard KeyGenerator algorithms with the keysizes in
 parentheses:
 
- AES(128)
- DESede(168)
- HmacSHA1
- HmacSHA256
- Since:
- 1.4
- See Also:
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Constructor SummaryConstructorsModifierConstructorDescriptionprotectedKeyGenerator(KeyGeneratorSpi keyGenSpi, Provider provider, String algorithm) Creates aKeyGeneratorobject.
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Method SummaryModifier and TypeMethodDescriptionfinal SecretKeyGenerates a secret key.final StringReturns the algorithm name of thisKeyGeneratorobject.static final KeyGeneratorgetInstance(String algorithm) Returns aKeyGeneratorobject that generates secret keys for the specified algorithm.static final KeyGeneratorgetInstance(String algorithm, String provider) Returns aKeyGeneratorobject that generates secret keys for the specified algorithm.static final KeyGeneratorgetInstance(String algorithm, Provider provider) Returns aKeyGeneratorobject that generates secret keys for the specified algorithm.final ProviderReturns the provider of thisKeyGeneratorobject.final voidinit(int keysize) Initializes this key generator for a certain keysize.final voidinit(int keysize, SecureRandom random) Initializes this key generator for a certain keysize, using a user-provided source of randomness.final voidinit(SecureRandom random) Initializes this key generator.final voidinit(AlgorithmParameterSpec params) Initializes this key generator with the specified parameter set.final voidinit(AlgorithmParameterSpec params, SecureRandom random) Initializes this key generator with the specified parameter set and a user-provided source of randomness.
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Constructor Details- 
KeyGeneratorCreates aKeyGeneratorobject.- Parameters:
- keyGenSpi- the delegate
- provider- the provider
- algorithm- the algorithm
 
 
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Method Details- 
getAlgorithmReturns the algorithm name of thisKeyGeneratorobject.This is the same name that was specified in one of the getInstancecalls that created thisKeyGeneratorobject.- Returns:
- the algorithm name of this KeyGeneratorobject.
 
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getInstanceReturns aKeyGeneratorobject that generates secret keys for the specified algorithm.This method traverses the list of registered security providers, starting with the most preferred provider. A new KeyGeneratorobject encapsulating theKeyGeneratorSpiimplementation 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 name of the requested key algorithm. See the KeyGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
- Returns:
- the new KeyGeneratorobject
- Throws:
- NoSuchAlgorithmException- if no- Providersupports a- KeyGeneratorSpiimplementation for the specified algorithm
- NullPointerException- if- algorithmis- null
- See Also:
 
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getInstancepublic static final KeyGenerator getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException Returns aKeyGeneratorobject that generates secret keys for the specified algorithm.A new KeyGeneratorobject encapsulating theKeyGeneratorSpiimplementation 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 name of the requested key algorithm. See the KeyGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
- provider- the name of the provider.
- Returns:
- the new KeyGeneratorobject
- Throws:
- IllegalArgumentException- if the- provideris- nullor empty
- NoSuchAlgorithmException- if a- KeyGeneratorSpiimplementation 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 final KeyGenerator getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException Returns aKeyGeneratorobject that generates secret keys for the specified algorithm.A new KeyGeneratorobject encapsulating theKeyGeneratorSpiimplementation from the specified provider object is returned. Note that the specified provider object does not have to be registered in the provider list.- Parameters:
- algorithm- the standard name of the requested key algorithm. See the KeyGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
- provider- the provider.
- Returns:
- the new KeyGeneratorobject
- Throws:
- IllegalArgumentException- if the- provideris- null
- NoSuchAlgorithmException- if a- KeyGeneratorSpiimplementation for the specified algorithm is not available from the specified- Providerobject
- NullPointerException- if- algorithmis- null
- See Also:
 
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getProviderReturns the provider of thisKeyGeneratorobject.- Returns:
- the provider of this KeyGeneratorobject
 
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initInitializes this key generator.- Parameters:
- random- the source of randomness for this generator
 
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initInitializes this key generator with the specified parameter set.If this key generator requires any random bytes, it will get them using the SecureRandomimplementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation of SecureRandom, a system-provided source of randomness will be used.)- Parameters:
- params- the key generation parameters
- Throws:
- InvalidAlgorithmParameterException- if the given parameters are inappropriate for this key generator
 
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initpublic final void init(AlgorithmParameterSpec params, SecureRandom random) throws InvalidAlgorithmParameterException Initializes this key generator with the specified parameter set and a user-provided source of randomness.- Parameters:
- params- the key generation parameters
- random- the source of randomness for this key generator
- Throws:
- InvalidAlgorithmParameterException- if- paramsis inappropriate for this key generator
 
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initpublic final void init(int keysize) Initializes this key generator for a certain keysize.If this key generator requires any random bytes, it will get them using the SecureRandomimplementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation of SecureRandom, a system-provided source of randomness will be used.)- Parameters:
- keysize- the keysize. This is an algorithm-specific metric, specified in number of bits.
- Throws:
- InvalidParameterException- if the keysize is wrong or not supported.
 
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initInitializes this key generator for a certain keysize, using a user-provided source of randomness.- Parameters:
- keysize- the keysize. This is an algorithm-specific metric, specified in number of bits.
- random- the source of randomness for this key generator
- Throws:
- InvalidParameterException- if the keysize is wrong or not supported.
 
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generateKey
 
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