Package javax.crypto

Class KeyGenerator

  • public class KeyGenerator
extends java.lang.Object
    This class provides the functionality of a (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 Also:
    SecretKey

    • Constructor Summary

      Constructors 
      Modifier Constructor Description
      protected KeyGenerator​(KeyGeneratorSpi keyGenSpi, java.lang.String algorithm)
      Creates a KeyGenerator object.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      SecretKey generateKey()
      Generates a secret key.
      java.lang.String getAlgorithm()
      Returns the algorithm name of this KeyGenerator object.
      static KeyGenerator getInstance​(java.lang.String algorithm)
      Generates a KeyGenerator object for the specified algorithm.
      void init​(int keysize)
      Initializes this key generator for a certain keysize.
      void init​(int keysize, SecureRandom random)
      Initializes this key generator for a certain keysize, using a user-provided source of randomness.
      void init​(SecureRandom random)
      Initializes this key generator.
      void init​(AlgorithmParameterSpec params)
      Initializes this key generator with the specified parameter set.
      void init​(AlgorithmParameterSpec params, SecureRandom random)
      Initializes this key generator with the specified parameter set and a user-provided source of randomness.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • KeyGenerator

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

    • Method Detail

      • getAlgorithm

        public final java.lang.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​(java.lang.String algorithm)
                                      throws NoSuchAlgorithmException
        Generates a KeyGenerator object for the specified algorithm. If the default provider package provides an implementation of the requested key generator, an instance of KeyGenerator containing that implementation is returned. If the requested key generator is not available in the default provider package, other provider packages are searched.
        Parameters:
        algorithm - the standard name of the requested key algorithm. See Appendix A in the Java Cryptography Extension API Specification & Reference for information about standard algorithm names.
        Returns:
        the new KeyGenerator object
        Throws:
        NoSuchAlgorithmException - if a key generator for the specified algorithm is not available in the default provider package or any of the other provider packages that were searched.

      • 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