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 * * * @see MessageDigest */ public abstract class MessageDigestSpi { // for re-use in engineUpdate(ByteBuffer input) private byte[] tempArray; /** * 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
*/
protected int engineGetDigestLength() {
return 0;
}
/**
* Updates the digest using the specified byte.
*
* @param input the byte to use for the update.
*/
protected abstract void engineUpdate(byte input);
/**
* 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 abstract void engineUpdate(byte[] input, int offset, int len);
/**
* 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
*/
protected void engineUpdate(ByteBuffer input) {
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;
}
}
}
/**
* 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 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.
*
* 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
*/
protected int engineDigest(byte[] buf, int offset, int len)
throws DigestException {
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;
}
/**
* Resets the digest for further use.
*/
protected abstract void engineReset();
/**
* 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.
*/
public Object clone() throws CloneNotSupportedException {
if (this instanceof Cloneable) {
return super.clone();
} else {
throw new CloneNotSupportedException();
}
}
}