1 /*
2 * Copyright (c) 2002, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package com.sun.crypto.provider;
27
28 import java.security.InvalidKeyException;
29
30 import jdk.internal.HotSpotIntrinsicCandidate;
31
32 /**
33 * This class represents ciphers in counter (CTR) mode.
34 *
35 * <p>This mode is implemented independently of a particular cipher.
36 * Ciphers to which this mode should apply (e.g., DES) must be
37 * <i>plugged-in</i> using the constructor.
38 *
39 * <p>NOTE: This class does not deal with buffering or padding.
40 *
41 * @author Andreas Sterbenz
42 * @since 1.4.2
43 */
44 final class CounterMode extends FeedbackCipher {
45
46 // current counter value
47 private final byte[] counter;
48
49 // encrypted bytes of the previous counter value
50 private final byte[] encryptedCounter;
51
52 // number of bytes in encryptedCounter already used up
53 private int used;
54
55 // variables for save/restore calls
56 private byte[] counterSave = null;
57 private byte[] encryptedCounterSave = null;
58 private int usedSave = 0;
59
60 CounterMode(SymmetricCipher embeddedCipher) {
61 super(embeddedCipher);
62 counter = new byte[blockSize];
63 encryptedCounter = new byte[blockSize];
64 }
65
66 /**
67 * Gets the name of the feedback mechanism
68 *
69 * @return the name of the feedback mechanism
70 */
71 String getFeedback() {
72 return "CTR";
73 }
74
75 /**
76 * Resets the iv to its original value.
77 * This is used when doFinal is called in the Cipher class, so that the
78 * cipher can be reused (with its original iv).
79 */
80 void reset() {
81 System.arraycopy(iv, 0, counter, 0, blockSize);
82 used = blockSize;
83 }
84
85 /**
86 * Save the current content of this cipher.
87 */
88 void save() {
89 if (counterSave == null) {
90 counterSave = new byte[blockSize];
91 encryptedCounterSave = new byte[blockSize];
92 }
93 System.arraycopy(counter, 0, counterSave, 0, blockSize);
94 System.arraycopy(encryptedCounter, 0, encryptedCounterSave, 0,
95 blockSize);
96 usedSave = used;
97 }
98
99 /**
100 * Restores the content of this cipher to the previous saved one.
101 */
102 void restore() {
103 System.arraycopy(counterSave, 0, counter, 0, blockSize);
104 System.arraycopy(encryptedCounterSave, 0, encryptedCounter, 0,
105 blockSize);
106 used = usedSave;
107 }
108
109 /**
110 * Initializes the cipher in the specified mode with the given key
111 * and iv.
112 *
113 * @param decrypting flag indicating encryption or decryption
114 * @param algorithm the algorithm name
115 * @param key the key
116 * @param iv the iv
117 *
118 * @exception InvalidKeyException if the given key is inappropriate for
119 * initializing this cipher
120 */
121 void init(boolean decrypting, String algorithm, byte[] key, byte[] iv)
122 throws InvalidKeyException {
123 if ((key == null) || (iv == null) || (iv.length != blockSize)) {
124 throw new InvalidKeyException("Internal error");
125 }
126 this.iv = iv;
127 reset();
128 // always encrypt mode for embedded cipher
129 embeddedCipher.init(false, algorithm, key);
130 }
131
132 /**
133 * Performs encryption operation.
134 *
135 * <p>The input plain text <code>plain</code>, starting at
136 * <code>plainOffset</code> and ending at
137 * <code>(plainOffset + len - 1)</code>, is encrypted.
138 * The result is stored in <code>cipher</code>, starting at
139 * <code>cipherOffset</code>.
140 *
141 * @param in the buffer with the input data to be encrypted
142 * @param inOffset the offset in <code>plain</code>
143 * @param len the length of the input data
144 * @param out the buffer for the result
145 * @param outOff the offset in <code>cipher</code>
146 * @return the length of the encrypted data
147 */
148 int encrypt(byte[] in, int inOff, int len, byte[] out, int outOff) {
149 return crypt(in, inOff, len, out, outOff);
150 }
151
152 // CTR encrypt and decrypt are identical
153 int decrypt(byte[] in, int inOff, int len, byte[] out, int outOff) {
154 return crypt(in, inOff, len, out, outOff);
155 }
156
157 /**
158 * Increment the counter value.
159 */
160 private static void increment(byte[] b) {
161 int n = b.length - 1;
162 while ((n >= 0) && (++b[n] == 0)) {
163 n--;
164 }
165 }
166
167 /**
168 * Do the actual encryption/decryption operation.
169 * Essentially we XOR the input plaintext/ciphertext stream with a
170 * keystream generated by encrypting the counter values. Counter values
171 * are encrypted on demand.
172 */
173 @HotSpotIntrinsicCandidate
174 private int crypt(byte[] in, int inOff, int len, byte[] out, int outOff) {
175 int result = len;
176 while (len-- > 0) {
177 if (used >= blockSize) {
178 embeddedCipher.encryptBlock(counter, 0, encryptedCounter, 0);
179 increment(counter);
180 used = 0;
181 }
182 out[outOff++] = (byte)(in[inOff++] ^ encryptedCounter[used++]);
183 }
184 return result;
185 }
186 }