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/*
* Copyright (c) 2002, 2018, 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;
/**
* 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
*/
final class CounterMode extends FeedbackCipher {
// current counter value
private 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 inOffset 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;
}
RangeUtil.nullAndBoundsCheck(in, inOff, len);
RangeUtil.nullAndBoundsCheck(out, outOff, len);
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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