Added in API level 1

Summary: Protected Ctors | Methods | Inherited Methods

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, 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.

• 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 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:

Algorithm	Supported API Levels
DH	1+
DSA	1+
EC	11+
RSA	1+
XDH	33+

These algorithms are described in the KeyPairGenerator section of the Java Cryptography Architecture Standard Algorithm Name Documentation.

See also:

• AlgorithmParameterSpec

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 abstract KeyPair generateKeyPair() Generates a key pair. void initialize(AlgorithmParameterSpec params, SecureRandom random) Initializes the key pair generator using the specified parameter set and user-provided source of randomness. abstract void initialize(int keysize, SecureRandom random) Initializes the key pair generator for a certain keysize, using the default parameter set.
From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long timeoutMillis, int nanos) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait(long timeoutMillis) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait() Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Protected constructors

KeyPairGenerator

Added in API level 1

protected 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 Security Standard Algorithm Names Specification for information about standard algorithm names.

Public methods

genKeyPair

Added in API level 1

public final 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

public 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

public String 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
String	the standard string name of the algorithm.

getInstance

Added in API level 1

public static 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.

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 than the order of providers returned by Security.getProviders().

Parameters
algorithm	String: 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
KeyPairGenerator	the new KeyPairGenerator object

Throws
NoSuchAlgorithmException	if no Provider supports a KeyPairGeneratorSpi implementation for the specified algorithm
NullPointerException	if algorithm is null

See also:

• Provider

getInstance

Added in API level 1

public static 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 Security Standard Algorithm Names Specification for information about standard algorithm names.
provider	String: the string name of the provider.

Returns
KeyPairGenerator	the new KeyPairGenerator object

Throws
IllegalArgumentException	if the provider name is null or empty
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
NullPointerException	if algorithm is null

See also:

• Provider

getInstance

Added in API level 1

public static 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 Security Standard Algorithm Names Specification for information about standard algorithm names.
provider	Provider: the provider.

Returns
KeyPairGenerator	the new KeyPairGenerator object

Throws
IllegalArgumentException	if the specified provider is null
NoSuchAlgorithmException	if a KeyPairGeneratorSpi implementation for the specified algorithm is not available from the specified Provider object
NullPointerException	if algorithm is null

See also:

• Provider

getProvider

Added in API level 1

public final 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

public 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

public 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

public 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

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.)

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.