KeyPairGenerator

public 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 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.

Protected Constructor Summary

KeyPairGenerator(String algorithm)
Creates a KeyPairGenerator object for the specified algorithm.

Public Method Summary

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 Method Summary

Protected Constructors

protected KeyPairGenerator (String algorithm)

Creates a KeyPairGenerator object for the specified algorithm.

Parameters
algorithm 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

public final KeyPair genKeyPair ()

Generates a key pair.

If this KeyPairGenerator has not been initialized explicitly, provider-specific defa