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	/*
	* Copyright (c) 2002, 2017, 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 com.sun.crypto.provider;

	import java.security.InvalidKeyException;
	import java.util.Objects;

	import jdk.internal.HotSpotIntrinsicCandidate;

	/**
	* This class represents ciphers in counter (CTR) mode.
	*
	* <p>This mode is implemented independently of a particular cipher.
	* Ciphers to which this mode should apply (e.g., DES) must be
	* <i>plugged-in</i> using the constructor.
	*
	* <p>NOTE: This class does not deal with buffering or padding.
	*
	* @author Andreas Sterbenz
	* @since 1.4.2
	*/
	class CounterMode extends FeedbackCipher {

	// current counter value
	final byte[] counter;

	// encrypted bytes of the previous counter value
	private final byte[] encryptedCounter;

	// number of bytes in encryptedCounter already used up
	private int used;

	// variables for save/restore calls
	private byte[] counterSave = null;
	private byte[] encryptedCounterSave = null;
	private int usedSave = 0;

	CounterMode(SymmetricCipher embeddedCipher) {
	super(embeddedCipher);
	counter = new byte[blockSize];
	encryptedCounter = new byte[blockSize];
	}

	/**
	* Gets the name of the feedback mechanism
	*
	* @return the name of the feedback mechanism
	*/
	String getFeedback() {
	return "CTR";
	}

	/**
	* Resets the iv to its original value.
	* This is used when doFinal is called in the Cipher class, so that the
	* cipher can be reused (with its original iv).
	*/
	void reset() {
	System.arraycopy(iv, 0, counter, 0, blockSize);
	used = blockSize;
	}

	/**
	* Save the current content of this cipher.
	*/
	void save() {
	if (counterSave == null) {
	counterSave = new byte[blockSize];
	encryptedCounterSave = new byte[blockSize];
	}
	System.arraycopy(counter, 0, counterSave, 0, blockSize);
	System.arraycopy(encryptedCounter, 0, encryptedCounterSave, 0,
	blockSize);
	usedSave = used;
	}

	/**
	* Restores the content of this cipher to the previous saved one.
	*/
	void restore() {
	System.arraycopy(counterSave, 0, counter, 0, blockSize);
	System.arraycopy(encryptedCounterSave, 0, encryptedCounter, 0,
	blockSize);
	used = usedSave;
	}

	/**
	* Initializes the cipher in the specified mode with the given key
	* and iv.
	*
	* @param decrypting flag indicating encryption or decryption
	* @param algorithm the algorithm name
	* @param key the key
	* @param iv the iv
	*
	* @exception InvalidKeyException if the given key is inappropriate for
	* initializing this cipher
	*/
	void init(boolean decrypting, String algorithm, byte[] key, byte[] iv)
	throws InvalidKeyException {
	if ((key == null) \|\| (iv == null) \|\| (iv.length != blockSize)) {
	throw new InvalidKeyException("Internal error");
	}
	this.iv = iv;
	reset();
	// always encrypt mode for embedded cipher
	embeddedCipher.init(false, algorithm, key);
	}

	/**
	* Performs encryption operation.
	*
	* <p>The input plain text <code>plain</code>, starting at
	* <code>plainOffset</code> and ending at
	* <code>(plainOffset + len - 1)</code>, is encrypted.
	* The result is stored in <code>cipher</code>, starting at
	* <code>cipherOffset</code>.
	*
	* @param in the buffer with the input data to be encrypted
	* @param inOff the offset in <code>plain</code>
	* @param len the length of the input data
	* @param out the buffer for the result
	* @param outOff the offset in <code>cipher</code>
	* @return the length of the encrypted data
	*/
	int encrypt(byte[] in, int inOff, int len, byte[] out, int outOff) {
	return crypt(in, inOff, len, out, outOff);
	}

	// CTR encrypt and decrypt are identical
	int decrypt(byte[] in, int inOff, int len, byte[] out, int outOff) {
	return crypt(in, inOff, len, out, outOff);
	}

	/**
	* Increment the counter value.
	*/
	private static void increment(byte[] b) {
	int n = b.length - 1;
	while ((n >= 0) && (++b[n] == 0)) {
	n--;
	}
	}

	/**
	* Do the actual encryption/decryption operation.
	* Essentially we XOR the input plaintext/ciphertext stream with a
	* keystream generated by encrypting the counter values. Counter values
	* are encrypted on demand.
	*/
	private int crypt(byte[] in, int inOff, int len, byte[] out, int outOff) {
	if (len == 0) {
	return 0;
	}
	Objects.checkFromIndexSize(inOff, len, in.length);
	Objects.checkFromIndexSize(outOff, len, out.length);
	return implCrypt(in, inOff, len, out, outOff);
	}

	// Implementation of crpyt() method. Possibly replaced with a compiler intrinsic.
	@HotSpotIntrinsicCandidate
	private int implCrypt(byte[] in, int inOff, int len, byte[] out, int outOff) {
	int result = len;
	while (len-- > 0) {
	if (used >= blockSize) {
	embeddedCipher.encryptBlock(counter, 0, encryptedCounter, 0);
	increment(counter);
	used = 0;
	}
	out[outOff++] = (byte)(in[inOff++] ^ encryptedCounter[used++]);
	}
	return result;
	}

	}

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