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:
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, or 1024, 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
three modulus sizes mentioned above. Still others might not have a list of
precomputed parameters at all and instead always create new parameter sets.
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
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.
For example, the Sun provider uses a default modulus size (keysize)
of 1024 bits.
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.
The equals method implements an equivalence relation
on non-null object references:
x, x.equals(x) should return
true.
x and y, x.equals(y)
should return true if and only if
y.equals(x) returns true.
x, y, and z, if
x.equals(y) returns true and
y.equals(z) returns true, then
x.equals(z) should return true.
x and y, multiple invocations of
x.equals(y) consistently return true
or consistently return false, provided no
information used in equals comparisons on the
objects is modified.
x,
x.equals(null) should return false.
The equals method for class Object implements
the most discriminating possible equivalence relation on objects;
that is, for any non-null reference values x and
y, this method returns true if and only
if x and y refer to the same object
(x == y has the value true).
Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.
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 .
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 .
provider doesn't have to be registered.java.util.Hashtable.
The general contract of hashCode is:
hashCode method on each of
the two objects must produce the same integer result.
As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)
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.
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.
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.)wait methods.
The awakened thread will not be able to proceed until the current thread relinquishes the lock on this object. The awakened thread will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; for example, the awakened thread enjoys no reliable privilege or disadvantage in being the next thread to lock this object.
This method should only be called by a thread that is the owner of this object's monitor. A thread becomes the owner of the object's monitor in one of three ways:
synchronized statement
that synchronizes on the object.
Class, by executing a
synchronized static method of that class.
Only one thread at a time can own an object's monitor.
wait methods.
The awakened threads will not be able to proceed until the current thread relinquishes the lock on this object. The awakened threads will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; for example, the awakened threads enjoy no reliable privilege or disadvantage in being the next thread to lock this object.
This method should only be called by a thread that is the owner
of this object's monitor. See the notify method for a
description of the ways in which a thread can become the owner of
a monitor.
toString method returns a string that
"textually represents" this object. The result should
be a concise but informative representation that is easy for a
person to read.
It is recommended that all subclasses override this method.
The toString method for class Object
returns a string consisting of the name of the class of which the
object is an instance, the at-sign character `@', and
the unsigned hexadecimal representation of the hash code of the
object. In other words, this method returns a string equal to the
value of:
getClass().getName() + '@' + Integer.toHexString(hashCode())
The current thread must own this object's monitor. The thread
releases ownership of this monitor and waits until another thread
notifies threads waiting on this object's monitor to wake up
either through a call to the notify method or the
notifyAll method. The thread then waits until it can
re-obtain ownership of the monitor and resumes execution.
As in the one argument version, interrupts and spurious wakeups are possible, and this method should always be used in a loop:
synchronized (obj) {
while (<condition does not hold>)
obj.wait();
... // Perform action appropriate to condition
}
This method should only be called by a thread that is the owner
of this object's monitor. See the notify method for a
description of the ways in which a thread can become the owner of
a monitor.The current thread must own this object's monitor.
This method causes the current thread (call it T) to place itself in the wait set for this object and then to relinquish any and all synchronization claims on this object. Thread T becomes disabled for thread scheduling purposes and lies dormant until one of four things happens:
A thread can also wake up without being notified, interrupted, or timing out, a so-called spurious wakeup. While this will rarely occur in practice, applications must guard against it by testing for the condition that should have caused the thread to be awakened, and continuing to wait if the condition is not satisfied. In other words, waits should always occur in loops, like this one:
synchronized (obj) {
while (<condition does not hold>)
obj.wait(timeout);
... // Perform action appropriate to condition
}
(For more information on this topic, see Section 3.2.3 in Doug Lea's
"Concurrent Programming in Java (Second Edition)" (Addison-Wesley,
2000), or Item 50 in Joshua Bloch's "Effective Java Programming
Language Guide" (Addison-Wesley, 2001).
If the current thread is interrupted by another thread while it is waiting, then an InterruptedException is thrown. This exception is not thrown until the lock status of this object has been restored as described above.
Note that the wait method, as it places the current thread into the wait set for this object, unlocks only this object; any other objects on which the current thread may be synchronized remain locked while the thread waits.
This method should only be called by a thread that is the owner
of this object's monitor. See the notify method for a
description of the ways in which a thread can become the owner of
a monitor.
This method is similar to the wait method of one
argument, but it allows finer control over the amount of time to
wait for a notification before giving up. The amount of real time,
measured in nanoseconds, is given by:
1000000*timeout+nanos
In all other respects, this method does the same thing as the method of one argument. In particular, wait(0, 0) means the same thing as wait(0).
The current thread must own this object's monitor. The thread releases ownership of this monitor and waits until either of the following two conditions has occurred:
notify method
or the notifyAll method.
timeout
milliseconds plus nanos nanoseconds arguments, has
elapsed.
The thread then waits until it can re-obtain ownership of the monitor and resumes execution.
As in the one argument version, interrupts and spurious wakeups are possible, and this method should always be used in a loop:
synchronized (obj) {
while (<condition does not hold>)
obj.wait(timeout, nanos);
... // Perform action appropriate to condition
}
This method should only be called by a thread that is the owner
of this object's monitor. See the notify method for a
description of the ways in which a thread can become the owner of
a monitor.