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MessageDigestSpi.javaAPI DocJava SE 6 API6010Tue Jun 10 00:25:46 BST 2008java.security

MessageDigestSpi

public abstract class MessageDigestSpi extends Object
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.

author
Benjamin Renaud
version
1.17, 03/10/06
see
MessageDigest

Fields Summary
private byte[]
tempArray
Constructors Summary
Methods Summary
public java.lang.Objectclone()
Returns a clone if the implementation is cloneable.

return
a clone if the implementation is cloneable.
exception
CloneNotSupportedException if this is called on an implementation that does not support Cloneable.

	if (this instanceof Cloneable) {
	    return super.clone();
	} else {
	    throw new CloneNotSupportedException();
	}
    
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 {@link #engineReset() engineReset}). Resetting is the responsibility of the engine implementor.

return
the array of bytes for the resulting hash value.

protected intengineDigest(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 {@link #engineReset() 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.

param
buf the output buffer in which to store the digest
param
offset offset to start from in the output buffer
param
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.
return
the length of the digest stored in the output buffer.
exception
DigestException if an error occurs.
since
1.2


	byte[] digest = engineDigest();
	if (len < digest.length)
		throw new DigestException("partial digests not returned");
	if (buf.length - offset < digest.length)
		throw new DigestException("insufficient space in the output "
					  + "buffer to store the digest");
	System.arraycopy(digest, 0, buf, offset, digest.length);
	return digest.length;
    
protected intengineGetDigestLength()
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.

return
the digest length in bytes.
since
1.2

	return 0;
    
protected abstract voidengineReset()
Resets the digest for further use.

protected abstract voidengineUpdate(byte input)
Updates the digest using the specified byte.

param
input the byte to use for the update.

protected abstract voidengineUpdate(byte[] input, int offset, int len)
Updates the digest using the specified array of bytes, starting at the specified offset.

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

protected voidengineUpdate(java.nio.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.

param
input the ByteBuffer
since
1.5

	if (input.hasRemaining() == false) {
	    return;
	}
	if (input.hasArray()) {
	    byte[] b = input.array();
	    int ofs = input.arrayOffset();
	    int pos = input.position();
	    int lim = input.limit();
	    engineUpdate(b, ofs + pos, lim - pos);
	    input.position(lim);
	} else {
	    int len = input.remaining();
	    int n = JCAUtil.getTempArraySize(len);
	    if ((tempArray == null) || (n > tempArray.length)) {
		tempArray = new byte[n];
	    }
	    while (len > 0) {
		int chunk = Math.min(len, tempArray.length);
		input.get(tempArray, 0, chunk);
		engineUpdate(tempArray, 0, chunk);
		len -= chunk;
	    }
	}