KeyPairGeneratorpublic abstract class KeyPairGenerator extends KeyPairGeneratorSpi The KeyPairGenerator class is used to generate pairs of
public and private keys. Key pair generators are constructed using the
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:
- Algorithm-Independent Initialization
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
{@link #initialize(int, java.security.SecureRandom) 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.
- Algorithm-Specific Initialization
For situations where a set of algorithm-specific parameters already
exists (e.g., so-called community parameters in DSA), there are two
{@link #initialize(java.security.spec.AlgorithmParameterSpec)
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. |
| Fields Summary |
|---|
| private final String | algorithm | | Provider | provider |
| Constructors Summary |
|---|
protected KeyPairGenerator(String algorithm)Creates a KeyPairGenerator object for the specified algorithm.
this.algorithm = algorithm;
|
| Methods Summary |
|---|
| void | disableFailover()
// empty, overridden in Delegate
| | public final java.security.KeyPair | genKeyPair()Generates a key pair.
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
{@link #generateKeyPair() generateKeyPair}.
return generateKeyPair();
| | public java.security.KeyPair | generateKeyPair()Generates a key pair.
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
{@link #genKeyPair() genKeyPair}.
// This does nothing (except returning null), because either:
//
// 1. the implementation object returned by getInstance() is an
// instance of KeyPairGenerator which has its own implementation
// of generateKeyPair (overriding this one), so the application
// would be calling that method directly, or
//
// 2. the implementation returned by getInstance() is an instance
// of Delegate, in which case generateKeyPair is
// overridden to invoke the corresponding SPI method.
//
// (This is a special case, because in JDK 1.1.x the generateKeyPair
// method was used both as an API and a SPI method.)
return null;
| | public java.lang.String | getAlgorithm()Returns the standard name of the algorithm for this key pair generator.
See Appendix A in the
Java Cryptography Architecture API Specification & Reference
for information about standard algorithm names.
return this.algorithm;
| | private static java.security.KeyPairGenerator | getInstance(sun.security.jca.GetInstance.Instance instance, java.lang.String algorithm)
KeyPairGenerator kpg;
if (instance.impl instanceof KeyPairGenerator) {
kpg = (KeyPairGenerator)instance.impl;
} else {
KeyPairGeneratorSpi spi = (KeyPairGeneratorSpi)instance.impl;
kpg = new Delegate(spi, algorithm);
}
kpg.provider = instance.provider;
return kpg;
| | public static java.security.KeyPairGenerator | getInstance(java.lang.String algorithm)Generates a KeyPairGenerator object that implements the specified digest
algorithm. If the default provider package
provides an implementation of the requested digest algorithm,
an instance of KeyPairGenerator containing that implementation is
returned.
If the algorithm is not available in the default
package, other packages are searched.
List<Service> list =
GetInstance.getServices("KeyPairGenerator", algorithm);
Iterator<Service> t = list.iterator();
if (t.hasNext() == false) {
throw new NoSuchAlgorithmException
(algorithm + " KeyPairGenerator not available");
}
// find a working Spi or KeyPairGenerator subclass
NoSuchAlgorithmException failure = null;
do {
Service s = t.next();
try {
Instance instance =
GetInstance.getInstance(s, KeyPairGeneratorSpi.class);
if (instance.impl instanceof KeyPairGenerator) {
return getInstance(instance, algorithm);
} else {
return new Delegate(instance, t, algorithm);
}
} catch (NoSuchAlgorithmException e) {
if (failure == null) {
failure = e;
}
}
} while (t.hasNext());
throw failure;
| | public static java.security.KeyPairGenerator | getInstance(java.lang.String algorithm, java.lang.String provider)Generates a KeyPairGenerator object implementing the specified
algorithm, as supplied from the specified provider,
if such an algorithm is available from the provider.
Instance instance = GetInstance.getInstance("KeyPairGenerator",
KeyPairGeneratorSpi.class, algorithm, provider);
return getInstance(instance, algorithm);
| | public static java.security.KeyPairGenerator | getInstance(java.lang.String algorithm, java.security.Provider provider)Generates a KeyPairGenerator object implementing the specified
algorithm, as supplied from the specified provider,
if such an algorithm is available from the provider.
Note: the provider doesn't have to be registered.
Instance instance = GetInstance.getInstance("KeyPairGenerator",
KeyPairGeneratorSpi.class, algorithm, provider);
return getInstance(instance, algorithm);
| | public final java.security.Provider | getProvider()Returns the provider of this key pair generator object.
disableFailover();
return this.provider;
| | public void | initialize(int keysize, java.security.SecureRandom random)Initializes the key pair generator for a certain keysize with
the given source of randomness (and a default parameter set).
// This does nothing, because either
// 1. the implementation object returned by getInstance() is an
// instance of KeyPairGenerator which has its own
// initialize(keysize, random) method, so the application would
// be calling that method directly, or
// 2. the implementation returned by getInstance() is an instance
// of Delegate, in which case initialize(keysize, random) is
// overridden to call the corresponding SPI method.
// (This is a special case, because the API and SPI method have the
// same name.)
| | public void | initialize(java.security.spec.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.
(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
{@link KeyPairGeneratorSpi#initialize(
java.security.spec.AlgorithmParameterSpec,
java.security.SecureRandom) 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.
initialize(params, JCAUtil.getSecureRandom());
| | public void | initialize(java.security.spec.AlgorithmParameterSpec params, java.security.SecureRandom random)Initializes the key pair generator with the given parameter
set and source of randomness.
This concrete method has been added to this previously-defined
abstract class.
This method calls the KeyPairGeneratorSpi {@link
KeyPairGeneratorSpi#initialize(
java.security.spec.AlgorithmParameterSpec,
java.security.SecureRandom) initialize} method,
passing it params and random.
That initialize
method always throws an
UnsupportedOperationException if it is not overridden by the provider.
// This does nothing, because either
// 1. the implementation object returned by getInstance() is an
// instance of KeyPairGenerator which has its own
// initialize(params, random) method, so the application would
// be calling that method directly, or
// 2. the implementation returned by getInstance() is an instance
// of Delegate, in which case initialize(params, random) is
// overridden to call the corresponding SPI method.
// (This is a special case, because the API and SPI method have the
// same name.)
| | public 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.
(If none of the installed providers supply an implementation of
SecureRandom, a system-provided source of randomness is
used.)
initialize(keysize, JCAUtil.getSecureRandom());
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