public abstract class KeyPairGenerator extends KeyPairGeneratorSpi
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:
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, 1024, or 2048, 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 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 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. See the Keysize Restriction sections of the JDK Providers document for information on the KeyPairGenerator
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 KeyPairGenerator
instead of relying on provider-specific defaults.
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:
DiffieHellman
(1024, 2048, 4096)DSA
(1024, 2048)RSA
(1024, 2048, 4096)Modifier | Constructor | Description |
---|---|---|
protected |
Creates a KeyPairGenerator object for the specified algorithm. |
Modifier and Type | Method | Description |
---|---|---|
KeyPair |
generateKeyPair() |
Generates a key pair. |
final KeyPair |
genKeyPair() |
Generates a key pair. |
String |
getAlgorithm() |
Returns the standard name of the algorithm for this key pair generator. |
static KeyPairGenerator |
getInstance |
Returns a KeyPairGenerator object that generates public/private key pairs for the specified algorithm. |
static KeyPairGenerator |
getInstance |
Returns a KeyPairGenerator object that generates public/private key pairs for the specified algorithm. |
static KeyPairGenerator |
getInstance |
Returns a KeyPairGenerator object that generates public/private key pairs for the specified algorithm. |
final Provider |
getProvider() |
Returns the provider of this key pair generator object. |
void |
initialize |
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 |
Initializes the key pair generator for a certain keysize with the given source of randomness (and a default parameter set). |
void |
initialize |
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 |
Initializes the key pair generator with the given parameter set and source of randomness. |
protected KeyPairGenerator(String algorithm)
KeyPairGenerator
object for the specified algorithm.algorithm
- the standard string name of the algorithm. See the KeyPairGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.public String getAlgorithm()
public static KeyPairGenerator getInstance(String algorithm) throws NoSuchAlgorithmException
KeyPairGenerator
object that generates public/private key pairs for the specified algorithm. 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.
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 string name of the algorithm. See the KeyPairGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.KeyPairGenerator
objectNoSuchAlgorithmException
- if no Provider
supports a KeyPairGeneratorSpi
implementation for the specified algorithmNullPointerException
- if algorithm
is null
public static KeyPairGenerator getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
KeyPairGenerator
object that generates public/private key pairs for the specified algorithm. 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 Security Standard Algorithm Names Specification for information about standard algorithm names.provider
- the string name of the provider.KeyPairGenerator
objectIllegalArgumentException
- if the provider name is null
or emptyNoSuchAlgorithmException
- if a KeyPairGeneratorSpi
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 KeyPairGenerator getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
KeyPairGenerator
object that generates public/private key pairs for the specified algorithm. A new KeyPairGenerator
object encapsulating the KeyPairGeneratorSpi
implementation from the specified provider is returned. Note that the specified provider 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 Security Standard Algorithm Names Specification for information about standard algorithm names.provider
- the provider.KeyPairGenerator
objectIllegalArgumentException
- if the specified provider is null
NoSuchAlgorithmException
- if a KeyPairGeneratorSpi
implementation for the specified algorithm is not available from the specified Provider
objectNullPointerException
- if algorithm
is null
public 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 KeyPairGeneratorSpi
keysize
- 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 KeyPairGeneratorSpi
params
- 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
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