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java.lang.Objectjavax.crypto.KeyGenerator
public class KeyGenerator
This class provides the functionality of a (symmetric) key generator.
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.
SecretKey
Constructor Summary | |
---|---|
protected |
KeyGenerator(KeyGeneratorSpi keyGenSpi,
Provider provider,
String algorithm)
Creates a KeyGenerator object. |
Method Summary | |
---|---|
SecretKey |
generateKey()
Generates a secret key. |
String |
getAlgorithm()
Returns the algorithm name of this KeyGenerator
object. |
static KeyGenerator |
getInstance(String algorithm)
Generates a KeyGenerator object for the specified
algorithm. |
static KeyGenerator |
getInstance(String algorithm,
Provider provider)
Generates a KeyGenerator object for the specified key
algorithm from the specified provider. |
static KeyGenerator |
getInstance(String algorithm,
String provider)
Generates a KeyGenerator object for the specified key
algorithm from the specified provider. |
Provider |
getProvider()
Returns the provider of this KeyGenerator object. |
void |
init(AlgorithmParameterSpec params)
Initializes this key generator with the specified parameter set. |
void |
init(AlgorithmParameterSpec params,
SecureRandom random)
Initializes this key generator with the specified parameter set and a user-provided source of randomness. |
void |
init(int keysize)
Initializes this key generator for a certain keysize. |
void |
init(int keysize,
SecureRandom random)
Initializes this key generator for a certain keysize, using a user-provided source of randomness. |
void |
init(SecureRandom random)
Initializes this key generator. |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll,
toString, wait, wait, wait |
Constructor Detail |
---|
protected KeyGenerator(KeyGeneratorSpi keyGenSpi,
Provider provider,
String algorithm)
keyGenSpi
- the delegateprovider
- the provideralgorithm
- the algorithmMethod Detail |
---|
public 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
for the specified algorithm. If the default provider package provides
an implementation of the requested key generator, an instance of KeyGenerator
containing that implementation is returned. If the requested key
generator is not available in the default provider package, other
provider packages are searched.
algorithm
- the standard name
of the requested key algorithm. See Appendix A in the
Java Cryptography Extension Reference Guide for information
about standard algorithm names.
KeyGenerator
object
NullPointerException
- if the specified algorithm is null.
NoSuchAlgorithmException
- if a key generator for the specified algorithm is not available in
the default provider package or any of the other provider packages that
were searched.public static final KeyGenerator getInstance(String algorithm,
String provider)
throws NoSuchAlgorithmException,
NoSuchProviderException
KeyGenerator
object
for the specified key algorithm from the specified provider.
algorithm
- the standard name
of the requested key algorithm. See Appendix A in the
Java Cryptography Extension Reference Guide for information
about standard algorithm names.provider
- the name of the
provider
KeyGenerator
object
NullPointerException
- if the specified algorithm is null.
NoSuchAlgorithmException
- if a key generator for the specified algorithm is not available from
the specified provider.
NoSuchProviderException
- if the specified provider has not been configured.
IllegalArgumentException
- if the provider
is null.public static final KeyGenerator getInstance(String algorithm,
Provider provider)
throws NoSuchAlgorithmException
KeyGenerator
object
for the specified key algorithm from the specified provider. Note: the provider
doesn't have to be registered.
algorithm
- the standard name
of the requested key algorithm. See Appendix A in the
Java Cryptography Extension Reference Guide for information
about standard algorithm names.provider
- the provider
KeyGenerator
object
NullPointerException
- if the specified algorithm is null.
NoSuchAlgorithmException
- if a key generator for the specified algorithm is not available from
the specified provider.
IllegalArgumentException
- if the provider
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
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.)
SecureRandom
params
- the key generation
parameters
InvalidAlgorithmParameterException
- 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 generator
InvalidAlgorithmParameterException
- 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
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.)
SecureRandom
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 generator
InvalidParameterException
- if the keysize is wrong or not supported.public final SecretKey generateKey()
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