MessageDigestSpi

public abstract class MessageDigestSpi extends Object

Known Direct Subclasses MessageDigest MessageDigest This MessageDigest class provides applications the functionality of a message digest algorithm, such as SHA-1 or SHA-256.

This class defines the Service Provider Interface (SPI) for the MessageDigest class, which provides the functionality of a message digest algorithm, such as MD5 or SHA. Message digests are secure one-way hash functions that take arbitrary-sized data and output a fixed-length hash value.

All the abstract methods in this class must be implemented by a cryptographic service provider who wishes to supply the implementation of a particular message digest algorithm.

Implementations are free to implement the Cloneable interface.

See Also

• MessageDigest

Public Constructor Summary

MessageDigestSpi()

Public Method Summary

Object

clone() Returns a clone if the implementation is cloneable.

Protected Method Summary

int	engineDigest(byte[] buf, int offset, int len) Completes the hash computation by performing final operations such as padding.
abstract byte[]	engineDigest() Completes the hash computation by performing final operations such as padding.
int	engineGetDigestLength() Returns the digest length in bytes.
abstract void	engineReset() Resets the digest for further use.
void	engineUpdate(ByteBuffer input) Update the digest using the specified ByteBuffer.
abstract void	engineUpdate(byte input) Updates the digest using the specified byte.
abstract void	engineUpdate(byte[] input, int offset, int len) Updates the digest using the specified array of bytes, starting at the specified offset.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Constructors

public MessageDigestSpi ()

Public Methods

public Object clone ()

Returns a clone if the implementation is cloneable.

Returns

• a clone if the implementation is cloneable.

Throws

CloneNotSupportedException	if this is called on an implementation that does not support Cloneable.

Protected Methods

protected int engineDigest (byte[] buf, int offset, int len)

Completes the hash computation by performing final operations such as padding. Once engineDigest has been called, the engine should be reset (see engineReset). Resetting is the responsibility of the engine implementor. This method should be abstract, but we leave it concrete for binary compatibility. Knowledgeable providers should override this method.

Parameters

buf	the output buffer in which to store the digest
offset	offset to start from in the output buffer
len	number of bytes within buf allotted for the digest. Both this default implementation and the SUN provider do not return partial digests. The presence of this parameter is solely for consistency in our API's. If the value of this parameter is less than the actual digest length, the method will throw a DigestException. This parameter is ignored if its value is greater than or equal to the actual digest length.

Returns

• the length of the digest stored in the output buffer.

Throws

DigestException	if an error occurs.

protected abstract byte[] engineDigest ()

Completes the hash computation by performing final operations such as padding. Once engineDigest has been called, the engine should be reset (see engineReset). Resetting is the responsibility of the engine implementor.

Returns

• the array of bytes for the resulting hash value.

protected int engineGetDigestLength ()

Returns the digest length in bytes.

This concrete method has been added to this previously-defined abstract class. (For backwards compatibility, it cannot be abstract.)

The default behavior is to return 0.

This method may be overridden by a provider to return the digest length.

Returns

• the digest length in bytes.

protected abstract void engineReset ()

Resets the digest for further use.

protected void engineUpdate (ByteBuffer input)

Update the digest using the specified ByteBuffer. The digest is updated using the input.remaining() bytes starting at input.position(). Upon return, the buffer's position will be equal to its limit; its limit will not have changed.

Parameters

input	the ByteBuffer

protected abstract void engineUpdate (byte input)

Updates the digest using the specified byte.

Parameters

input	the byte to use for the update.

protected abstract void engineUpdate (byte[] input, int offset, int len)

Updates the digest using the specified array of bytes, starting at the specified offset.

Parameters

input	the array of bytes to use for the update.
offset	the offset to start from in the array of bytes.
len	the number of bytes to use, starting at offset.