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KeyPairGenerator

public abstract class KeyPairGenerator
extends KeyPairGeneratorSpi

java.lang.Object
   ↳ java.security.KeyPairGeneratorSpi
     ↳ java.security.KeyPairGenerator


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 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 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.

Android provides the following KeyPairGenerator algorithms:

Name Supported (API Levels)
DH 1+
DSA 1+
EC 11+
RSA 1+
These algorithms are described in the KeyPairGenerator section of the Java Cryptography Architecture Standard Algorithm Name Documentation.

See also:

Summary

Protected constructors

KeyPairGenerator(String algorithm)

Creates a KeyPairGenerator object for the specified algorithm.

Public methods

final KeyPair genKeyPair()

Generates a key pair.

KeyPair generateKeyPair()

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, String provider)

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.

final Provider getProvider()

Returns the provider of this key pair generator object.

void initialize(AlgorithmParameterSpec params, SecureRandom random)

Initializes the key pair generator with the given parameter set and source of randomness.

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(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(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.

Inherited methods

From class java.security.KeyPairGeneratorSpi
From class java.lang.Object

Protected constructors

KeyPairGenerator

Added in API level 1
KeyPairGenerator (String algorithm)

Creates a KeyPairGenerator object for the specified algorithm.

Parameters
algorithm String: 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 methods

genKeyPair

Added in API level 1
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 generateKeyPair.

Returns
KeyPair the generated key pair

generateKeyPair

Added in API level 1
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 genKeyPair.

Returns
KeyPair the generated key pair

getAlgorithm

Added in API level 1
String getAlgorithm ()

Returns the standard name of the algorithm for this key pair generator. See the KeyPairGenerator section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.

Returns
String the standard string name of the algorithm.

getInstance

Added in API level 1
KeyPairGenerator getInstance (String algorithm)

Returns a 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.

Parameters
algorithm String: 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.
Returns
KeyPairGenerator the new KeyPairGenerator object.
Throws
NoSuchAlgorithmException if no Provider supports a KeyPairGeneratorSpi implementation for the specified algorithm.

See also:

getInstance

Added in API level 1
KeyPairGenerator getInstance (String algorithm, 
                String provider)

Returns a 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.

Parameters
algorithm String: 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 String: the string name of the provider.
Returns
KeyPairGenerator the new KeyPairGenerator object.
Throws
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.

See also:

getInstance

Added in API level 1
KeyPairGenerator getInstance (String algorithm, 
                Provider provider)

Returns a KeyPairGenerator object that generates public/private key pairs for the specified algorithm.

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.

Parameters
algorithm String: 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 Provider: the provider.
Returns
KeyPairGenerator the new KeyPairGenerator object.
Throws
NoSuchAlgorithmException if a KeyPairGeneratorSpi implementation for the specified algorithm is not available from the specified Provider object.
IllegalArgumentException if the specified provider is null.

See also:

getProvider

Added in API level 1
Provider getProvider ()

Returns the provider of this key pair generator object.

Returns
Provider the provider of this key pair generator object

initialize

Added in API level 1
void initialize (AlgorithmParameterSpec params, 
                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 initialize method, passing it params and random. That initialize method always throws an UnsupportedOperationException if it is not overridden by the provider.

Parameters
params AlgorithmParameterSpec: the parameter set used to generate the keys.
random SecureRandom: the source of randomness.
Throws
InvalidAlgorithmParameterException if the given parameters are inappropriate for this key pair generator.

initialize

Added in API level 1
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. (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.

Parameters
params AlgorithmParameterSpec: the parameter set used to generate the keys.
Throws
InvalidAlgorithmParameterException if the given parameters are inappropriate for this key pair generator.

initialize

Added in API level 1
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).

Parameters
keysize int: the keysize. This is an algorithm-specific metric, such as modulus length, specified in number of bits.
random SecureRandom: the source of randomness.
Throws
InvalidParameterException if the keysize is not supported by this KeyPairGenerator object.

initialize

Added in API level 1
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.)

Parameters
keysize int: the keysize. This is an algorithm-specific metric, such as modulus length, specified in number of bits.
Throws
InvalidParameterException if the keysize is not supported by this KeyPairGenerator object.
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