Class 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.

Every implementation of the Java platform is required to support the following standard KeyPairGenerator algorithms and keysizes in parentheses:

• DiffieHellman (1024)
• DSA (1024)
• RSA (1024, 2048)

These algorithms are described in the KeyPairGenerator section of the Java Cryptography Architecture Standard Algorithm Name Documentation. Consult the release documentation for your implementation to see if any other algorithms are supported.

Constructors

KeyPairGenerator

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.

Methods

getAlgorithm

public 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:

the standard string name of the algorithm.

getInstance

public static KeyPairGenerator getInstance(String algorithm)
                                    throws NoSuchAlgorithmException

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.

Returns:

the new KeyPairGenerator object.

Throws:

NoSuchAlgorithmException - if no Provider supports a KeyPairGeneratorSpi implementation for the specified algorithm.

See Also:

Provider

getInstance

public static KeyPairGenerator getInstance(String algorithm,
                                           String provider)
                                    throws NoSuchAlgorithmException,
                                           NoSuchProviderException

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.

provider - the string name of the provider.

Returns:

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:

Provider

getInstance

public static KeyPairGenerator getInstance(String algorithm,
                                           Provider provider)
                                    throws NoSuchAlgorithmException

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.

provider - the provider.

Returns:

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.

Since:

1.4

See Also:

Provider

getProvider

public final Provider 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 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 - 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.

initialize

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).

Specified by:

initialize in class KeyPairGeneratorSpi

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 the keysize is not supported by this KeyPairGenerator object.

Since:

1.2

initialize

public void initialize(AlgorithmParameterSpec params)
                throws InvalidAlgorithmParameterException

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

Overrides:

initialize in class KeyPairGeneratorSpi

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

public final KeyPair genKeyPair()

Returns:

the generated key pair

Since:

1.2

generateKeyPair

public KeyPair generateKeyPair()

Specified by:

generateKeyPair in class KeyPairGeneratorSpi

Returns:

the generated key pair