public class KeyGenerator extends Object
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:
All key generators share the concepts of a keysize and a source of randomness. There is an init
method in this KeyGenerator
class that takes these two universally shared types of arguments. There is also one that takes just a keysize
argument, 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 init
methods, it is up to the provider what to do about the algorithm-specific parameters (if any) to be associated with each of the keys.
For situations where a set of algorithm-specific parameters already exists, there are two init
methods that have an AlgorithmParameterSpec
argument. One also has a SecureRandom
argument, 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
Modifier | Constructor | Description |
---|---|---|
protected |
Creates a KeyGenerator object. |
Modifier and Type | Method | Description |
---|---|---|
final SecretKey |
generateKey() |
Generates a secret key. |
final String |
getAlgorithm() |
Returns the algorithm name of this KeyGenerator object. |
static final KeyGenerator |
getInstance |
Returns a KeyGenerator object that generates secret keys for the specified algorithm. |
static final KeyGenerator |
getInstance |
Returns a KeyGenerator object that generates secret keys for the specified algorithm. |
static final KeyGenerator |
getInstance |
Returns a KeyGenerator object that generates secret keys for the specified algorithm. |
final Provider |
getProvider() |
Returns the provider of this KeyGenerator object. |
final void |
init |
Initializes this key generator for a certain keysize. |
final void |
init |
Initializes this key generator for a certain keysize, using a user-provided source of randomness. |
final void |
init |
Initializes this key generator. |
final void |
init |
Initializes this key generator with the specified parameter set. |
final void |
init |
Initializes this key generator with the specified parameter set and a user-provided source of randomness. |
protected KeyGenerator(KeyGeneratorSpi keyGenSpi, Provider provider, String algorithm)
KeyGenerator
object.keyGenSpi
- the delegateprovider
- the provideralgorithm
- the algorithmpublic final String getAlgorithm()
KeyGenerator
object. This is the same name that was specified in one of the getInstance
calls that created this KeyGenerator
object.
KeyGenerator
object.public static final KeyGenerator getInstance(String algorithm) throws NoSuchAlgorithmException
KeyGenerator
object 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.
jdk.security.provider.preferred
Security
property to determine the preferred provider order for the specified algorithm. This may be different from the order of providers returned by Security.getProviders()
.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.KeyGenerator
objectNoSuchAlgorithmException
- if no Provider
supports a KeyGeneratorSpi
implementation for the specified algorithmNullPointerException
- if algorithm
is null
public static final KeyGenerator getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
KeyGenerator
object 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.
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.KeyGenerator
objectIllegalArgumentException
- if the provider
is null
or emptyNoSuchAlgorithmException
- if a KeyGeneratorSpi
implementation for the specified algorithm is not available from the specified providerNoSuchProviderException
- if the specified provider is not registered in the security provider listNullPointerException
- if algorithm
is null
public static final KeyGenerator getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
KeyGenerator
object 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.
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.KeyGenerator
objectIllegalArgumentException
- if the provider
is null
NoSuchAlgorithmException
- if a KeyGeneratorSpi
implementation for the specified algorithm is not available from the specified Provider
objectNullPointerException
- if algorithm
is null
public final Provider getProvider()
KeyGenerator
object.KeyGenerator
objectpublic final void init(SecureRandom random)
random
- the source of randomness for this generatorpublic final void init(AlgorithmParameterSpec params) throws InvalidAlgorithmParameterException
If this key generator requires any random bytes, it will get them using the SecureRandom
implementation 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.)
params
- the key generation parametersInvalidAlgorithmParameterException
- if the given parameters are inappropriate for this key generatorpublic final void init(AlgorithmParameterSpec params, SecureRandom random) throws InvalidAlgorithmParameterException
params
- the key generation parametersrandom
- the source of randomness for this key generatorInvalidAlgorithmParameterException
- if params
is inappropriate for this key generatorpublic final void init(int keysize)
If this key generator requires any random bytes, it will get them using the SecureRandom
implementation 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.)
keysize
- the keysize. This is an algorithm-specific metric, specified in number of bits.InvalidParameterException
- if the keysize is wrong or not supported.public final void init(int keysize, SecureRandom random)
keysize
- the keysize. This is an algorithm-specific metric, specified in number of bits.random
- the source of randomness for this key generatorInvalidParameterException
- if the keysize is wrong or not supported.public final SecretKey generateKey()
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/javax/crypto/KeyGenerator.html