Java tutorial
/* * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.security; import java.nio.ByteBuffer; import sun.security.jca.JCAUtil; /** * This class defines the <i>Service Provider Interface</i> (<b>SPI</b>) * for the {@code 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. * * <p> 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. * * <p> Implementations are free to implement the Cloneable interface. * * @author Benjamin Renaud * @since 1.2 * * * @see MessageDigest */ public abstract class MessageDigestSpi { // for re-use in engineUpdate(ByteBuffer input) private byte[] tempArray; /** * Returns the digest length in bytes. * * <p>This concrete method has been added to this previously-defined * abstract class. (For backwards compatibility, it cannot be abstract.) * * <p>The default behavior is to return 0. * * <p>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 * {@code offset}. */ protected abstract void engineUpdate(byte[] input, int offset, int len); /** * Update the digest using the specified ByteBuffer. The digest is * updated using the {@code input.remaining()} bytes starting * at {@code 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 {@code 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 {@code 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 {@code Cloneable}. */ public Object clone() throws CloneNotSupportedException { if (this instanceof Cloneable) { return super.clone(); } else { throw new CloneNotSupportedException(); } } }