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)HmacSHA1HmacSHA256
- Since:
- 1.4
- See Also:
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Constructor Summary
ConstructorsModifierConstructorDescriptionprotectedKeyGenerator(KeyGeneratorSpi keyGenSpi, Provider provider, String algorithm) Creates aKeyGeneratorobject. -
Method Summary
Modifier 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
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KeyGenerator
Creates aKeyGeneratorobject.- Parameters:
keyGenSpi- the delegateprovider- the provideralgorithm- the algorithm
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Method Details
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getAlgorithm
Returns 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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getInstance
Returns 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 noProvidersupports aKeyGeneratorSpiimplementation for the specified algorithmNullPointerException- ifalgorithmisnull- See Also:
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getInstance
public 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 theproviderisnullor emptyNoSuchAlgorithmException- if aKeyGeneratorSpiimplementation 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 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 theproviderisnullNoSuchAlgorithmException- if aKeyGeneratorSpiimplementation for the specified algorithm is not available from the specifiedProviderobjectNullPointerException- ifalgorithmisnull- See Also:
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getProvider
Returns the provider of thisKeyGeneratorobject.- Returns:
- the provider of this
KeyGeneratorobject
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init
Initializes this key generator.- Parameters:
random- the source of randomness for this generator
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init
Initializes 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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init
public 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 parametersrandom- the source of randomness for this key generator- Throws:
InvalidAlgorithmParameterException- ifparamsis inappropriate for this key generator
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init
public 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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init
Initializes 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
Generates a secret key.- Returns:
- the new key
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