Class KeyPairGenerator

java.lang.Object
java.security.KeyPairGeneratorSpi
java.security.KeyPairGenerator
public abstract classKeyPairGeneratorextendsKeyPairGeneratorSpi
TheKeyPairGenerator class is used to generate pairs of public and private keys. Key pair generators are constructed using thegetInstance 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 theDSA algorithm, the keysize corresponds to the length of the modulus). There is aninitialize method in thisKeyPairGenerator class that takes these two universally shared types of arguments. There is also one that takes just akeysize argument, and uses theSecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom, a system-provided source of randomness is used.)

    Since no other parameters are specified when you call the above algorithm-independentinitialize 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 theDSA algorithm, and the keysize (modulus size) is 512, 768, 1024, or 2048, then theSun provider uses a set of precomputed values for thep,q, andg parameters. If the modulus size is not one of the above values, theSun 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-calledcommunity parameters in DSA), there are twoinitialize methods that have anAlgorithmParameterSpec argument. One also has aSecureRandom argument, while the other uses theSecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom, a system-provided source of randomness is used.)

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

Note that this class is abstract and extends fromKeyPairGeneratorSpi for historical reasons. Application developers should only take notice of the methods defined in thisKeyPairGenerator 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 standardKeyPairGenerator 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:

  • Constructor Details

    • KeyPairGenerator

      protected KeyPairGenerator(String algorithm)
      Creates aKeyPairGenerator 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 Details

    • 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) throwsNoSuchAlgorithmException
      Returns aKeyPairGenerator 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 newKeyPairGenerator object encapsulating theKeyPairGeneratorSpi 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 from the order of providers returned bySecurity.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 newKeyPairGenerator object
      Throws:
      NoSuchAlgorithmException - if noProvider supports aKeyPairGeneratorSpi implementation for the specified algorithm
      NullPointerException - ifalgorithm isnull
      See Also:

    • getInstance

      public static KeyPairGenerator getInstance(String algorithm,String provider) throwsNoSuchAlgorithmException,NoSuchProviderException
      Returns aKeyPairGenerator object that generates public/private key pairs for the specified algorithm.

      A newKeyPairGenerator object encapsulating theKeyPairGeneratorSpi implementation from the specified provider is returned. The specified provider must be registered in the security provider list.

      Note that the list of registered providers may be retrieved via theSecurity.getProviders() method.

      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 string name of the provider.
      Returns:
      the newKeyPairGenerator object
      Throws:
      IllegalArgumentException - if the provider name isnull or empty
      NoSuchAlgorithmException - if aKeyPairGeneratorSpi 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
      NullPointerException - ifalgorithm isnull
      See Also:

    • getInstance

      public static KeyPairGenerator getInstance(String algorithm,Provider provider) throwsNoSuchAlgorithmException
      Returns aKeyPairGenerator object that generates public/private key pairs for the specified algorithm.

      A newKeyPairGenerator object encapsulating theKeyPairGeneratorSpi implementation from the specified provider is returned. Note that the specified provider 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 newKeyPairGenerator object
      Throws:
      IllegalArgumentException - if the specified provider isnull
      NoSuchAlgorithmException - if aKeyPairGeneratorSpi implementation for the specified algorithm is not available from the specifiedProvider object
      NullPointerException - ifalgorithm isnull
      Since:
      1.4
      See Also:

    • 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 theSecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom, 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 thekeysize is not supported by thisKeyPairGenerator 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 thekeysize is not supported by thisKeyPairGenerator object.
      Since:
      1.2

    • initialize

      public void initialize(AlgorithmParameterSpec params) throwsInvalidAlgorithmParameterException
      Initializes the key pair generator using the specified parameter set and theSecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation ofSecureRandom, a system-provided source of randomness is used.)

      This concrete method has been added to this previously-defined abstract class. This method calls the KeyPairGeneratorSpiinitialize method, passing itparams and a source of randomness (obtained from the highest-priority installed provider or system-provided if none of the installed providers supply one). Thatinitialize method always throws anUnsupportedOperationException 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) throwsInvalidAlgorithmParameterException
      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 KeyPairGeneratorSpiinitialize method, passing itparams andrandom. Thatinitialize method always throws anUnsupportedOperationException 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 thisKeyPairGenerator 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 togenerateKeyPair.

      Returns:
      the generated key pair
      Since:
      1.2

    • generateKeyPair

      public KeyPair generateKeyPair()
      Generates a key pair.

      If thisKeyPairGenerator 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 togenKeyPair.

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