Module java.base
Package javax.crypto

Class KeyGenerator

  • public class KeyGenerator
extends Object
    This class provides the functionality of a secret (symmetric) key generator.

    Key generators are constructed using one of the getInstance class methods of this class.

    KeyGenerator objects are reusable, i.e., after a key has been generated, the same KeyGenerator object can be re-used to generate further keys.

    There are two ways to generate a key: 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 generators share the concepts of a keysize and a source of randomness. There is an init method in this KeyGenerator 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 (or a system-provided source of randomness if none of the installed providers supply a SecureRandom implementation), and one that takes just a source of randomness.

      Since no other parameters are specified when you call the above algorithm-independent init 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.

    • Algorithm-Specific Initialization

      For situations where a set of algorithm-specific parameters already exists, there are two init 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 (or a system-provided source of randomness if none of the installed providers supply a SecureRandom implementation).

    In case the client does not explicitly initialize the KeyGenerator (via a call to an init method), each provider must supply (and document) a default initialization. See the Keysize Restriction sections of the JDK Providers document for information on the KeyGenerator 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 KeyGenerator instead of relying on provider-specific defaults.

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

    • AES (128)
    • DES (56)
    • DESede (168)
    • HmacSHA1
    • HmacSHA256
    These algorithms are described in the KeyGenerator 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:
    1.4
    See Also:
    SecretKey

    • Constructor Detail

      • KeyGenerator

        protected KeyGenerator​(KeyGeneratorSpi keyGenSpi,
                       Provider provider,
                       String algorithm)
        Creates a KeyGenerator object.
        Parameters:
        keyGenSpi - the delegate
        provider - the provider
        algorithm - the algorithm

    • Method Detail

      • getAlgorithm

        public final String getAlgorithm()
        Returns the algorithm name of this KeyGenerator object.

        This is the same name that was specified in one of the getInstance calls that created this KeyGenerator object.

        Returns:
        the algorithm name of this KeyGenerator object.

      • getInstance

        public static final KeyGenerator getInstance​(String algorithm)
                                      throws NoSuchAlgorithmException
        Returns a KeyGenerator object that generates secret keys for the specified algorithm.

        This method traverses the list of registered security Providers, starting with the most preferred Provider. A new KeyGenerator object encapsulating the KeyGeneratorSpi 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 name of the requested key algorithm. See the KeyGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
        Returns:
        the new KeyGenerator object
        Throws:
        NoSuchAlgorithmException - if no Provider supports a KeyGeneratorSpi implementation for the specified algorithm
        NullPointerException - if algorithm is null
        See Also:
        Provider

      • getInstance

        public static final KeyGenerator getInstance​(String algorithm,
                                             Provider provider)
                                      throws NoSuchAlgorithmException
        Returns a KeyGenerator object that generates secret keys for the specified algorithm.

        A new KeyGenerator object encapsulating the KeyGeneratorSpi 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 name of the requested key algorithm. See the KeyGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
        provider - the provider.
        Returns:
        the new KeyGenerator object
        Throws:
        IllegalArgumentException - if the provider is null
        NoSuchAlgorithmException - if a KeyGeneratorSpi implementation for the specified algorithm is not available from the specified Provider object
        NullPointerException - if algorithm is null
        See Also:
        Provider

      • getProvider

        public final Provider getProvider()
        Returns the provider of this KeyGenerator object.
        Returns:
        the provider of this KeyGenerator object

      • init

        public final void init​(SecureRandom random)
        Initializes this key generator.
        Parameters:
        random - the source of randomness for this generator

      • init

        public final void init​(AlgorithmParameterSpec params)
                throws InvalidAlgorithmParameterException
        Initializes this key generator with the specified parameter set.

        If this key generator requires any random bytes, it will get them using 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 will be used.)

        Parameters:
        params - the key generation parameters
        Throws:
        InvalidAlgorithmParameterException - if the given parameters are inappropriate for this key generator

      • init

        public final void init​(int keysize)
        Initializes this key generator for a certain keysize.

        If this key generator requires any random bytes, it will get them using 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 will be used.)

        Parameters:
        keysize - the keysize. This is an algorithm-specific metric, specified in number of bits.
        Throws:
        InvalidParameterException - if the keysize is wrong or not supported.

      • init

        public final void init​(int keysize,
                       SecureRandom random)
        Initializes this key generator for a certain keysize, using a user-provided source of randomness.
        Parameters:
        keysize - the keysize. This is an algorithm-specific metric, specified in number of bits.
        random - the source of randomness for this key generator
        Throws:
        InvalidParameterException - if the keysize is wrong or not supported.

      • generateKey

        public final SecretKey generateKey()
        Generates a secret key.
        Returns:
        the new key