Module java.base
Package java.security

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, 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. 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)
    These algorithms are described in the KeyPairGenerator section of the Java Security Standard Algorithm Names Specification. Consult the release documentation for your implementation to see if any other algorithms are supported.
    Since:
    1.1
    See Also:
    AlgorithmParameterSpec

    • Constructor Detail

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

    • Method Detail

      • getAlgorithm

        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:
        the standard string name of the algorithm.

      • getInstance

        public static KeyPairGenerator getInstance​(String algorithm)
                                    throws NoSuchAlgorithmException
        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 - 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 no Provider supports a KeyPairGeneratorSpi implementation for the specified algorithm
        NullPointerException - if algorithm is null
        See Also:
        Provider

      • getInstance

        public static KeyPairGenerator getInstance​(String algorithm,
                                           Provider provider)
                                    throws NoSuchAlgorithmException
        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 - 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 is null
        NoSuchAlgorithmException - if a KeyPairGeneratorSpi implementation for the specified algorithm is not available from the specified Provider object
        NullPointerException - if algorithm 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
        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 - 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 it params and random. That initialize method always throws an UnsupportedOperationException if it is not overridden by the provider.

        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()
        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

        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.

        Specified by:
        generateKeyPair in class KeyPairGeneratorSpi
        Returns:
        the generated key pair