Class KeyPairGenerator
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
initialize
method in thisKeyPairGenerator
class that takes these two universally shared types of arguments. There is also one that takes just akeysize
argument, and uses theSecureRandom
implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom
, 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
, andg
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. - 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
initialize
methods that have anAlgorithmParameterSpec
argument. One also has aSecureRandom
argument, while the other uses theSecureRandom
implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom
, 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)
- Since:
- 1.1
- See Also:
-
Constructor Summary
ModifierConstructorDescriptionprotected
KeyPairGenerator
(String algorithm) Creates aKeyPairGenerator
object for the specified algorithm. -
Method Summary
Modifier and TypeMethodDescriptionGenerates a key pair.final KeyPair
Generates a key pair.Returns the standard name of the algorithm for this key pair generator.static KeyPairGenerator
getInstance
(String algorithm) Returns aKeyPairGenerator
object that generates public/private key pairs for the specified algorithm.static KeyPairGenerator
getInstance
(String algorithm, String provider) Returns aKeyPairGenerator
object that generates public/private key pairs for the specified algorithm.static KeyPairGenerator
getInstance
(String algorithm, Provider provider) Returns aKeyPairGenerator
object that generates public/private key pairs for the specified algorithm.final Provider
Returns the provider of this key pair generator object.void
initialize
(int keysize) Initializes the key pair generator for a certain keysize using a default parameter set and theSecureRandom
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).void
initialize
(AlgorithmParameterSpec params) Initializes the key pair generator using the specified parameter set and theSecureRandom
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.
-
Constructor Details
-
KeyPairGenerator
Creates aKeyPairGenerator
object for the specified algorithm.- Parameters:
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.
-
-
Method Details
-
getAlgorithm
Returns the standard name of the algorithm for this key pair generator. See the KeyPairGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.- Returns:
- the standard string name of the algorithm.
-
getInstance
Returns aKeyPairGenerator
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 theKeyPairGeneratorSpi
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.- Implementation Note:
- The JDK Reference Implementation additionally uses the
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 bySecurity.getProviders()
. - Parameters:
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.- Returns:
- the new
KeyPairGenerator
object - Throws:
NoSuchAlgorithmException
- if noProvider
supports aKeyPairGeneratorSpi
implementation for the specified algorithmNullPointerException
- ifalgorithm
isnull
- See Also:
-
getInstance
public static KeyPairGenerator getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException Returns aKeyPairGenerator
object that generates public/private key pairs for the specified algorithm.A new
KeyPairGenerator
object encapsulating theKeyPairGeneratorSpi
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.- Parameters:
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.- Returns:
- the new
KeyPairGenerator
object - Throws:
IllegalArgumentException
- if the provider name isnull
or emptyNoSuchAlgorithmException
- if aKeyPairGeneratorSpi
implementation for the specified algorithm is not available from the specified providerNoSuchProviderException
- if the specified provider is not registered in the security provider listNullPointerException
- ifalgorithm
isnull
- See Also:
-
getInstance
public static KeyPairGenerator getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException Returns aKeyPairGenerator
object that generates public/private key pairs for the specified algorithm.A new
KeyPairGenerator
object encapsulating theKeyPairGeneratorSpi
implementation from the specified provider is returned. Note that the specified provider does not have to be registered in the provider list.- Parameters:
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.- Returns:
- the new
KeyPairGenerator
object - Throws:
IllegalArgumentException
- if the specified provider isnull
NoSuchAlgorithmException
- if aKeyPairGeneratorSpi
implementation for the specified algorithm is not available from the specifiedProvider
objectNullPointerException
- ifalgorithm
isnull
- Since:
- 1.4
- See Also:
-
getProvider
Returns the provider of this key pair generator object.- Returns:
- the provider of this key pair generator object
-
initialize
public void initialize(int keysize) Initializes the key pair generator for a certain keysize using a default parameter set and theSecureRandom
implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom
, a system-provided source of randomness is used.)- Parameters:
keysize
- the keysize. This is an algorithm-specific metric, such as modulus length, specified in number of bits.- Throws:
InvalidParameterException
- if thekeysize
is not supported by thisKeyPairGenerator
object.
-
initialize
Initializes the key pair generator for a certain keysize with the given source of randomness (and a default parameter set).- Specified by:
initialize
in classKeyPairGeneratorSpi
- Parameters:
keysize
- the keysize. This is an algorithm-specific metric, such as modulus length, specified in number of bits.random
- the source of randomness.- Throws:
InvalidParameterException
- if thekeysize
is not supported by thisKeyPairGenerator
object.- Since:
- 1.2
-
initialize
Initializes the key pair generator using the specified parameter set and theSecureRandom
implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom
, 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 itparams
and a source of randomness (obtained from the highest-priority installed provider or system-provided if none of the installed providers supply one). Thatinitialize
method always throws anUnsupportedOperationException
if it is not overridden by the provider.- Parameters:
params
- the parameter set used to generate the keys.- Throws:
InvalidAlgorithmParameterException
- if the given parameters are inappropriate for this key pair generator.- Since:
- 1.2
-
initialize
public void initialize(AlgorithmParameterSpec params, SecureRandom random) throws InvalidAlgorithmParameterException 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
initialize
method, passing itparams
andrandom
. Thatinitialize
method always throws anUnsupportedOperationException
if it is not overridden by the provider.- Overrides:
initialize
in classKeyPairGeneratorSpi
- Parameters:
params
- the parameter set used to generate the keys.random
- the source of randomness.- Throws:
InvalidAlgorithmParameterException
- if the given parameters are inappropriate for this key pair generator.- Since:
- 1.2
-
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
generateKeyPair
.- Returns:
- the generated key pair
- Since:
- 1.2
-
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
genKeyPair
.- Specified by:
generateKeyPair
in classKeyPairGeneratorSpi
- Returns:
- the generated key pair
-