public abstract class KeyPairGenerator extends KeyPairGeneratorSpi
getInstance factory methods (static methods that
return instances of a given class).
A Key pair generator for a particular algorithm creates a public/private key pair that can be used with this algorithm. It also associates algorithm-specific parameters with each of the generated keys.
There are two ways to generate a key pair: 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 pair generators share the concepts of a keysize and a
source of randomness. The keysize is interpreted differently for different
algorithms (e.g., in the case of the DSA algorithm, the keysize
corresponds to the length of the modulus).
There is an
initialize
method in this KeyPairGenerator 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. (If none of the installed providers supply an implementation
of SecureRandom, a system-provided source of randomness is
used.)
Since no other parameters are specified when you call the above
algorithm-independent initialize 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.
If the algorithm is the DSA algorithm, and the keysize (modulus
size) is 512, 768, or 1024, then the Sun provider uses a set of
precomputed values for the p, q, and
g parameters. If the modulus size is not one of the above
values, the Sun provider creates a new set of parameters. Other
providers might have precomputed parameter sets for more than just the
three modulus sizes mentioned above. Still others might not have a list of
precomputed parameters at all and instead always create new parameter sets.
For situations where a set of algorithm-specific parameters already
exists (e.g., so-called community parameters in DSA), there are two
initialize methods that have an AlgorithmParameterSpec
argument. One also has a SecureRandom argument, while the
the other uses 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 is
used.)
In case the client does not explicitly initialize the KeyPairGenerator
(via a call to an initialize method), each provider must
supply (and document) a default initialization.
For example, the Sun provider uses a default modulus size (keysize)
of 1024 bits.
Note that this class is abstract and extends from
KeyPairGeneratorSpi for historical reasons.
Application developers should only take notice of the methods defined in
this KeyPairGenerator class; all the methods in
the superclass are intended for cryptographic service providers who wish to
supply their own implementations of key pair generators.
Every implementation of the Java platform is required to support the
following standard KeyPairGenerator algorithms and keysizes in
parentheses:
AlgorithmParameterSpec| Modifier | Constructor and Description |
|---|---|
protected |
KeyPairGenerator(String algorithm)
Creates a KeyPairGenerator object for the specified algorithm.
|
| Modifier and Type | Method and Description |
|---|---|
KeyPair |
generateKeyPair()
Generates a key pair.
|
KeyPair |
genKeyPair()
Generates a key pair.
|
String |
getAlgorithm()
Returns the standard name of the algorithm for this key pair generator.
|
static KeyPairGenerator |
getInstance(String algorithm)
Returns a KeyPairGenerator object that generates public/private
key pairs for the specified algorithm.
|
static KeyPairGenerator |
getInstance(String algorithm,
Provider provider)
Returns a KeyPairGenerator object that generates public/private
key pairs for the specified algorithm.
|
static KeyPairGenerator |
getInstance(String algorithm,
String provider)
Returns a KeyPairGenerator object that generates public/private
key pairs for the specified algorithm.
|
Provider |
getProvider()
Returns the provider of this key pair generator object.
|
void |
initialize(AlgorithmParameterSpec params)
Initializes the key pair generator using the specified parameter
set and the
SecureRandom
implementation of the highest-priority installed provider as the source
of randomness. |
void |
initialize(AlgorithmParameterSpec params,
SecureRandom random)
Initializes the key pair generator with the given parameter
set and source of randomness.
|
void |
initialize(int keysize)
Initializes the key pair generator for a certain keysize using
a default parameter set and the
SecureRandom
implementation of the highest-priority installed provider as the source
of randomness. |
void |
initialize(int keysize,
SecureRandom random)
Initializes the key pair generator for a certain keysize with
the given source of randomness (and a default parameter set).
|
protected KeyPairGenerator(String algorithm)
algorithm - the standard string name of the algorithm.
See the KeyPairGenerator section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names.public String getAlgorithm()
public static KeyPairGenerator getInstance(String algorithm) throws NoSuchAlgorithmException
This method traverses the list of registered security Providers, starting with the most preferred Provider. A new KeyPairGenerator object encapsulating the KeyPairGeneratorSpi 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.
algorithm - the standard string name of the algorithm.
See the KeyPairGenerator section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names.NoSuchAlgorithmException - if no Provider supports a
KeyPairGeneratorSpi implementation for the
specified algorithm.Providerpublic static KeyPairGenerator getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
A new KeyPairGenerator object encapsulating the KeyPairGeneratorSpi 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 string name of the algorithm.
See the KeyPairGenerator section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names.provider - the string name of the provider.NoSuchAlgorithmException - if a KeyPairGeneratorSpi
implementation for the specified algorithm is not
available from the specified provider.NoSuchProviderException - if the specified provider is not
registered in the security provider list.IllegalArgumentException - if the provider name is null
or empty.Providerpublic static KeyPairGenerator getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
A new KeyPairGenerator object encapsulating the KeyPairGeneratorSpi 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 string name of the algorithm.
See the KeyPairGenerator section in the
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard algorithm names.provider - the provider.NoSuchAlgorithmException - if a KeyPairGeneratorSpi
implementation for the specified algorithm is not available
from the specified Provider object.IllegalArgumentException - if the specified provider is null.Providerpublic final Provider getProvider()
public void initialize(int keysize)
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 is
used.)keysize - the keysize. This is an
algorithm-specific metric, such as modulus length, specified in
number of bits.InvalidParameterException - if the keysize is not
supported by this KeyPairGenerator object.public void initialize(int keysize,
SecureRandom random)
initialize in class KeyPairGeneratorSpikeysize - the keysize. This is an
algorithm-specific metric, such as modulus length, specified in
number of bits.random - the source of randomness.InvalidParameterException - if the keysize is not
supported by this KeyPairGenerator object.public void initialize(AlgorithmParameterSpec params) throws InvalidAlgorithmParameterException
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 is
used.).
This concrete method has been added to this previously-defined
abstract class.
This method calls the KeyPairGeneratorSpi
initialize method,
passing it params and a source of randomness (obtained
from the highest-priority installed provider or system-provided if none
of the installed providers supply one).
That initialize method always throws an
UnsupportedOperationException if it is not overridden by the provider.
params - the parameter set used to generate the keys.InvalidAlgorithmParameterException - if the given parameters
are inappropriate for this key pair generator.public void initialize(AlgorithmParameterSpec params, SecureRandom random) throws InvalidAlgorithmParameterException
This concrete method has been added to this previously-defined
abstract class.
This method calls the KeyPairGeneratorSpi initialize method,
passing it params and random.
That initialize
method always throws an
UnsupportedOperationException if it is not overridden by the provider.
initialize in class KeyPairGeneratorSpiparams - the parameter set used to generate the keys.random - the source of randomness.InvalidAlgorithmParameterException - if the given parameters
are inappropriate for this key pair generator.public final KeyPair genKeyPair()
If this KeyPairGenerator has not been initialized explicitly, provider-specific defaults will be used for the size and other (algorithm-specific) values of the generated keys.
This will generate a new key pair every time it is called.
This method is functionally equivalent to
generateKeyPair.
public KeyPair generateKeyPair()
If this KeyPairGenerator has not been initialized explicitly, provider-specific defaults will be used for the size and other (algorithm-specific) values of the generated keys.
This will generate a new key pair every time it is called.
This method is functionally equivalent to
genKeyPair.
generateKeyPair in class KeyPairGeneratorSpi