- java.lang.Object
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- javax.crypto.KeyGenerator
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public class KeyGenerator extends Object
This class provides the functionality of a secret (symmetric) key generator.Key generators are constructed using one of the
getInstanceclass 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 this KeyGenerator class that takes these two universally shared types of arguments. There is also one that takes just akeysizeargument, and 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), 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
initmethod), 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
KeyGeneratoralgorithms with the keysizes in parentheses:AES(128)DES(56)DESede(168)HmacSHA1HmacSHA256
- Since:
- 1.4
- See Also:
SecretKey
- Algorithm-Independent Initialization
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Constructor Summary
Constructors Modifier Constructor Description protectedKeyGenerator(KeyGeneratorSpi keyGenSpi, Provider provider, String algorithm)Creates a KeyGenerator object.
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description SecretKeygenerateKey()Generates a secret key.StringgetAlgorithm()Returns the algorithm name of thisKeyGeneratorobject.static KeyGeneratorgetInstance(String algorithm)Returns aKeyGeneratorobject that generates secret keys for the specified algorithm.static KeyGeneratorgetInstance(String algorithm, String provider)Returns aKeyGeneratorobject that generates secret keys for the specified algorithm.static KeyGeneratorgetInstance(String algorithm, Provider provider)Returns aKeyGeneratorobject that generates secret keys for the specified algorithm.ProvidergetProvider()Returns the provider of thisKeyGeneratorobject.voidinit(int keysize)Initializes this key generator for a certain keysize.voidinit(int keysize, SecureRandom random)Initializes this key generator for a certain keysize, using a user-provided source of randomness.voidinit(SecureRandom random)Initializes this key generator.voidinit(AlgorithmParameterSpec params)Initializes this key generator with the specified parameter set.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 Detail
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KeyGenerator
protected KeyGenerator(KeyGeneratorSpi keyGenSpi, Provider provider, String algorithm)
Creates a KeyGenerator object.- Parameters:
keyGenSpi- the delegateprovider- the provideralgorithm- the algorithm
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Method Detail
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getAlgorithm
public final String 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
public static final KeyGenerator getInstance(String algorithm) throws NoSuchAlgorithmException
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 KeyGenerator object encapsulating the KeyGeneratorSpi implementation 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 than 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:
Provider
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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 KeyGenerator object encapsulating the KeyGeneratorSpi implementation 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:
Provider
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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 KeyGenerator object encapsulating the KeyGeneratorSpi implementation 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:
Provider
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getProvider
public final Provider getProvider()
Returns the provider of thisKeyGeneratorobject.- Returns:
- the provider of this
KeyGeneratorobject
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init
public final void init(SecureRandom random)
Initializes this key generator.- Parameters:
random- the source of randomness for this generator
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init
public final void init(AlgorithmParameterSpec params) throws InvalidAlgorithmParameterException
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
public final void init(int keysize, SecureRandom random)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
public final SecretKey generateKey()
Generates a secret key.- Returns:
- the new key
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