The signature algorithm can be, among others, the NIST standard DSA, using DSA and SHA-1. The DSA algorithm using the SHA-1 message digest algorithm can be specified as SHA1withDSA. In the case of RSA, there are multiple choices for the message digest algorithm, so the signing algorithm could be specified as, for example, MD2withRSA, MD5withRSA, or SHA1withRSA. The algorithm name must be specified, as there is no default.
Like other algorithm-based classes in Java Security, Signature
provides implementation-independent algorithms, whereby a caller
(application code) requests a particular signature algorithm
and is handed back a properly initialized Signature object. It is
also possible, if desired, to request a particular algorithm from a
particular provider. See the getInstance methods.
Thus, there are two ways to request a Signature algorithm object: by specifying either just an algorithm name, or both an algorithm name and a package provider.
A Signature object can be used to generate and verify digital signatures.
There are three phases to the use of a Signature object for either signing data or verifying a signature:
Depending on the type of initialization, this will update the bytes to be signed or verified. See the update methods.
Note that this class is abstract and extends from
SignatureSpi for historical reasons.
Application developers should only take notice of the methods defined in
this Signature class; all the methods in
the superclass are intended for cryptographic service providers who wish to
supply their own implementations of digital signature algorithms.
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.
provider doesn't have to be registered.The returned parameters may be the same that were used to initialize this signature, or may contain a combination of default and randomly generated parameter values used by the underlying signature implementation if this signature requires algorithm parameters but was not initialized with any.
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.)
If the certificate is of type X.509 and has a key usage
extension field marked as critical, and the value of the key usage
extension field implies that the public key in
the certificate and its corresponding private key are not
supposed to be used for digital signatures, an
InvalidKeyException is thrown.
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.
A call to this method resets this signature object to the state
it was in when previously initialized for signing via a
call to initSign(PrivateKey). That is, the object is
reset and available to generate another signature from the same
signer, if desired, via new calls to update and
sign.
outbuf, starting at
offset.
The format of the signature depends on the underlying
signature scheme.
This signature object is reset to its initial state (the state it
was in after a call to one of the initSign methods) and
can be reused to generate further signatures with the same private key.
data.remaining() bytes
starting at at data.position().
Upon return, the buffer's position will be equal to its limit;
its limit will not have changed.A call to this method resets this signature object to the state
it was in when previously initialized for verification via a
call to initVerify(PublicKey). That is, the object is
reset and available to verify another signature from the identity
whose public key was specified in the call to initVerify.
A call to this method resets this signature object to the state
it was in when previously initialized for verification via a
call to initVerify(PublicKey). That is, the object is
reset and available to verify another signature from the identity
whose public key was specified in the call to initVerify.
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.