Module java.base
Package javax.crypto

Class KeyGenerator


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

    Key generators are constructed using one of thegetInstance 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 akeysize and asource of randomness. There is aninit method in this KeyGenerator class that takes these two universally shared types of arguments. There is also one that takes just akeysize 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-independentinit 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 twoinit methods that have anAlgorithmParameterSpec argument. One also has aSecureRandom 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 aninit method), each provider must supply (and document) a default initialization.

    Every implementation of the Java platform is required to support the following standardKeyGenerator 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 Cryptography Architecture Standard Algorithm Name Documentation. 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 thisKeyGenerator object.

        This is the same name that was specified in one of thegetInstance calls that created thisKeyGenerator object.

        Returns:
        the algorithm name of thisKeyGenerator object.

      • getInstance

        public static final KeyGenerator getInstance(String algorithm)                                      throwsNoSuchAlgorithmException
        Returns aKeyGenerator 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 theSecurity.getProviders() method.

        Implementation Note:
        The JDK Reference Implementation additionally uses thejdk.security.provider.preferredSecurity property to determine the preferred provider order for the specified algorithm. This may be different than the order of providers returned bySecurity.getProviders().
        Parameters:
        algorithm - the standard name of the requested key algorithm. See the KeyGenerator section in the Java Cryptography Architecture Standard Algorithm Name Documentation for information about standard algorithm names.
        Returns:
        the newKeyGenerator object
        Throws:
        NoSuchAlgorithmException - if noProvider supports aKeyGeneratorSpi implementation for the specified algorithm
        NullPointerException - ifalgorithm isnull
        See Also:
        Provider

      • getProvider

        public final Provider getProvider()
        Returns the provider of thisKeyGenerator object.
        Returns:
        the provider of thisKeyGenerator 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)                throwsInvalidAlgorithmParameterException
        Initializes this key generator with the specified parameter set.

        If this key generator requires any random bytes, it will get them using theSecureRandom 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 theSecureRandom 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