1 /*
2 * Copyright (c) 2013, 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 * (C) Copyright IBM Corp. 2013
27 */
28
29 package com.sun.crypto.provider;
30
31 import java.security.ProviderException;
32
33 /**
34 * This class represents the GHASH function defined in NIST 800-38D
35 * under section 6.4. It needs to be constructed w/ a hash subkey, i.e.
36 * block H. Given input of 128-bit blocks, it will process and output
37 * a 128-bit block.
38 *
39 * <p>This function is used in the implementation of GCM mode.
40 *
41 * @since 1.8
42 */
43 final class GHASH {
44
45 private static long getLong(byte[] buffer, int offset) {
46 long result = 0;
47 int end = offset + 8;
48 for (int i = offset; i < end; ++i) {
49 result = (result << 8) + (buffer[i] & 0xFF);
50 }
51 return result;
52 }
53
54 private static void putLong(byte[] buffer, int offset, long value) {
55 int end = offset + 8;
56 for (int i = end - 1; i >= offset; --i) {
57 buffer[i] = (byte) value;
58 value >>= 8;
59 }
60 }
61
62 private static final int AES_BLOCK_SIZE = 16;
63
64 // Multiplies state0, state1 by V0, V1.
65 private void blockMult(long V0, long V1) {
66 long Z0 = 0;
67 long Z1 = 0;
68 long X;
69
70 // Separate loops for processing state0 and state1.
71 X = state0;
72 for (int i = 0; i < 64; i++) {
73 // Zi+1 = Zi if bit i of x is 0
74 long mask = X >> 63;
75 Z0 ^= V0 & mask;
76 Z1 ^= V1 & mask;
77
78 // Save mask for conditional reduction below.
79 mask = (V1 << 63) >> 63;
80
81 // V = rightshift(V)
82 long carry = V0 & 1;
83 V0 = V0 >>> 1;
84 V1 = (V1 >>> 1) | (carry << 63);
85
86 // Conditional reduction modulo P128.
87 V0 ^= 0xe100000000000000L & mask;
88 X <<= 1;
89 }
90
91 X = state1;
92 for (int i = 64; i < 127; i++) {
93 // Zi+1 = Zi if bit i of x is 0
94 long mask = X >> 63;
95 Z0 ^= V0 & mask;
96 Z1 ^= V1 & mask;
97
98 // Save mask for conditional reduction below.
99 mask = (V1 << 63) >> 63;
100
101 // V = rightshift(V)
102 long carry = V0 & 1;
103 V0 = V0 >>> 1;
104 V1 = (V1 >>> 1) | (carry << 63);
105
106 // Conditional reduction.
107 V0 ^= 0xe100000000000000L & mask;
108 X <<= 1;
109 }
110
111 // calculate Z128
112 long mask = X >> 63;
113 Z0 ^= V0 & mask;
114 Z1 ^= V1 & mask;
115
116 // Save result.
117 state0 = Z0;
118 state1 = Z1;
119 }
120
121 // hash subkey H; should not change after the object has been constructed
122 private final long subkeyH0, subkeyH1;
123
124 // buffer for storing hash
125 private long state0, state1;
126
127 // variables for save/restore calls
128 private long stateSave0, stateSave1;
129
130 /**
131 * Initializes the cipher in the specified mode with the given key
132 * and iv.
133 *
134 * @param subkeyH the hash subkey
135 *
136 * @exception ProviderException if the given key is inappropriate for
137 * initializing this digest
138 */
139 GHASH(byte[] subkeyH) throws ProviderException {
140 if ((subkeyH == null) || subkeyH.length != AES_BLOCK_SIZE) {
141 throw new ProviderException("Internal error");
142 }
143 this.subkeyH0 = getLong(subkeyH, 0);
144 this.subkeyH1 = getLong(subkeyH, 8);
145 }
146
147 /**
148 * Resets the GHASH object to its original state, i.e. blank w/
149 * the same subkey H. Used after digest() is called and to re-use
150 * this object for different data w/ the same H.
151 */
152 void reset() {
153 state0 = 0;
154 state1 = 0;
155 }
156
157 /**
158 * Save the current snapshot of this GHASH object.
159 */
160 void save() {
161 stateSave0 = state0;
162 stateSave1 = state1;
163 }
164
165 /**
166 * Restores this object using the saved snapshot.
167 */
168 void restore() {
169 state0 = stateSave0;
170 state1 = stateSave1;
171 }
172
173 private void processBlock(byte[] data, int ofs) {
174 if (data.length - ofs < AES_BLOCK_SIZE) {
175 throw new RuntimeException("need complete block");
176 }
177 state0 ^= getLong(data, ofs);
178 state1 ^= getLong(data, ofs + 8);
179 blockMult(subkeyH0, subkeyH1);
180 }
181
182 void update(byte[] in) {
183 update(in, 0, in.length);
184 }
185
186 void update(byte[] in, int inOfs, int inLen) {
187 if (inLen - inOfs > in.length) {
188 throw new RuntimeException("input length out of bound");
189 }
190 if (inLen % AES_BLOCK_SIZE != 0) {
191 throw new RuntimeException("input length unsupported");
192 }
193
194 for (int i = inOfs; i < (inOfs + inLen); i += AES_BLOCK_SIZE) {
195 processBlock(in, i);
196 }
197 }
198
199 byte[] digest() {
200 byte[] result = new byte[AES_BLOCK_SIZE];
201 putLong(result, 0, state0);
202 putLong(result, 8, state1);
203 reset();
204 return result;
205 }
206 }