1 |
769 |
jeremybenn |
/* ICM.java --
|
2 |
|
|
Copyright (C) 2001, 2002, 2003, 2006 Free Software Foundation, Inc.
|
3 |
|
|
|
4 |
|
|
This file is a part of GNU Classpath.
|
5 |
|
|
|
6 |
|
|
GNU Classpath is free software; you can redistribute it and/or modify
|
7 |
|
|
it under the terms of the GNU General Public License as published by
|
8 |
|
|
the Free Software Foundation; either version 2 of the License, or (at
|
9 |
|
|
your option) any later version.
|
10 |
|
|
|
11 |
|
|
GNU Classpath is distributed in the hope that it will be useful, but
|
12 |
|
|
WITHOUT ANY WARRANTY; without even the implied warranty of
|
13 |
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
14 |
|
|
General Public License for more details.
|
15 |
|
|
|
16 |
|
|
You should have received a copy of the GNU General Public License
|
17 |
|
|
along with GNU Classpath; if not, write to the Free Software
|
18 |
|
|
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
|
19 |
|
|
USA
|
20 |
|
|
|
21 |
|
|
Linking this library statically or dynamically with other modules is
|
22 |
|
|
making a combined work based on this library. Thus, the terms and
|
23 |
|
|
conditions of the GNU General Public License cover the whole
|
24 |
|
|
combination.
|
25 |
|
|
|
26 |
|
|
As a special exception, the copyright holders of this library give you
|
27 |
|
|
permission to link this library with independent modules to produce an
|
28 |
|
|
executable, regardless of the license terms of these independent
|
29 |
|
|
modules, and to copy and distribute the resulting executable under
|
30 |
|
|
terms of your choice, provided that you also meet, for each linked
|
31 |
|
|
independent module, the terms and conditions of the license of that
|
32 |
|
|
module. An independent module is a module which is not derived from
|
33 |
|
|
or based on this library. If you modify this library, you may extend
|
34 |
|
|
this exception to your version of the library, but you are not
|
35 |
|
|
obligated to do so. If you do not wish to do so, delete this
|
36 |
|
|
exception statement from your version. */
|
37 |
|
|
|
38 |
|
|
|
39 |
|
|
package gnu.javax.crypto.mode;
|
40 |
|
|
|
41 |
|
|
import gnu.java.security.Registry;
|
42 |
|
|
import gnu.javax.crypto.cipher.IBlockCipher;
|
43 |
|
|
|
44 |
|
|
import java.math.BigInteger;
|
45 |
|
|
|
46 |
|
|
/**
|
47 |
|
|
* An implementation of <i>David McGrew</i> Integer Counter Mode (ICM) as an
|
48 |
|
|
* {@link IMode}.
|
49 |
|
|
* <p>
|
50 |
|
|
* ICM is a way to define a pseudorandom keystream generator using a block
|
51 |
|
|
* cipher. The keystream can be used for additive encryption, key derivation, or
|
52 |
|
|
* any other application requiring pseudorandom data. In the case of this class,
|
53 |
|
|
* it is used as additive encryption, XOR-ing the keystream with the input text
|
54 |
|
|
* --for both encryption and decryption.
|
55 |
|
|
* <p>
|
56 |
|
|
* In ICM, the keystream is logically broken into segments. Each segment is
|
57 |
|
|
* identified with a segment index, and the segments have equal lengths. This
|
58 |
|
|
* segmentation makes ICM especially appropriate for securing packet-based
|
59 |
|
|
* protocols. ICM also allows a variety of configurations based, among other
|
60 |
|
|
* things, on two parameters: the <i>block index length</i> and the <i>segment
|
61 |
|
|
* index length</i>. A constraint on those two values exists: The sum of
|
62 |
|
|
* <i>segment index length</i> and <i>block index length</i> <b>must not</b>
|
63 |
|
|
* half the <i>block size</i> of the underlying cipher. This requirement
|
64 |
|
|
* protects the ICM keystream generator from potentially failing to be
|
65 |
|
|
* pseudorandom.
|
66 |
|
|
* <p>
|
67 |
|
|
* For simplicity, this implementation, fixes these two values to the following:
|
68 |
|
|
* <ul>
|
69 |
|
|
* <li>block index length: is half the underlying cipher block size, and</li>
|
70 |
|
|
* <li>segment index length: is zero.</li>
|
71 |
|
|
* </ul>
|
72 |
|
|
* <p>
|
73 |
|
|
* For a 128-bit block cipher, the above values imply a maximum keystream length
|
74 |
|
|
* of 295,147,905,179,352,825,856 octets, since in ICM, each segment must not
|
75 |
|
|
* exceed the value
|
76 |
|
|
* <code>(256 ^ <i>block index length</i>) * <i>block length</i></code>
|
77 |
|
|
* octets.
|
78 |
|
|
* <p>
|
79 |
|
|
* Finally, for this implementation of the ICM, the IV placeholder will be used
|
80 |
|
|
* to pass the value of the <i>Offset</i> in the keystream segment.
|
81 |
|
|
* <p>
|
82 |
|
|
* References:
|
83 |
|
|
* <ol>
|
84 |
|
|
* <li><a
|
85 |
|
|
* href="http://www.ietf.org/internet-drafts/draft-mcgrew-saag-icm-00.txt">
|
86 |
|
|
* Integer Counter Mode</a>, David A. McGrew.</li>
|
87 |
|
|
* </ol>
|
88 |
|
|
*/
|
89 |
|
|
public class ICM
|
90 |
|
|
extends BaseMode
|
91 |
|
|
implements Cloneable
|
92 |
|
|
{
|
93 |
|
|
/** The integer value 256 as a BigInteger. */
|
94 |
|
|
private static final BigInteger TWO_FIFTY_SIX = new BigInteger("256");
|
95 |
|
|
/** Maximum number of blocks per segment. */
|
96 |
|
|
private BigInteger maxBlocksPerSegment;
|
97 |
|
|
/** A work constant. */
|
98 |
|
|
private BigInteger counterRange;
|
99 |
|
|
/** The initial counter for a given keystream segment. */
|
100 |
|
|
private BigInteger C0;
|
101 |
|
|
/** The index of the next block for a given keystream segment. */
|
102 |
|
|
private BigInteger blockNdx;
|
103 |
|
|
|
104 |
|
|
/**
|
105 |
|
|
* Trivial package-private constructor for use by the Factory class.
|
106 |
|
|
*
|
107 |
|
|
* @param underlyingCipher the underlying cipher implementation.
|
108 |
|
|
* @param cipherBlockSize the underlying cipher block size to use.
|
109 |
|
|
*/
|
110 |
|
|
ICM(IBlockCipher underlyingCipher, int cipherBlockSize)
|
111 |
|
|
{
|
112 |
|
|
super(Registry.ICM_MODE, underlyingCipher, cipherBlockSize);
|
113 |
|
|
}
|
114 |
|
|
|
115 |
|
|
/**
|
116 |
|
|
* Private constructor for cloning purposes.
|
117 |
|
|
*
|
118 |
|
|
* @param that the instance to clone.
|
119 |
|
|
*/
|
120 |
|
|
private ICM(ICM that)
|
121 |
|
|
{
|
122 |
|
|
this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize);
|
123 |
|
|
}
|
124 |
|
|
|
125 |
|
|
public Object clone()
|
126 |
|
|
{
|
127 |
|
|
return new ICM(this);
|
128 |
|
|
}
|
129 |
|
|
|
130 |
|
|
public void setup()
|
131 |
|
|
{
|
132 |
|
|
if (modeBlockSize != cipherBlockSize)
|
133 |
|
|
throw new IllegalArgumentException();
|
134 |
|
|
counterRange = TWO_FIFTY_SIX.pow(cipherBlockSize);
|
135 |
|
|
maxBlocksPerSegment = TWO_FIFTY_SIX.pow(cipherBlockSize / 2);
|
136 |
|
|
BigInteger r = new BigInteger(1, iv);
|
137 |
|
|
C0 = maxBlocksPerSegment.add(r).modPow(BigInteger.ONE, counterRange);
|
138 |
|
|
blockNdx = BigInteger.ZERO;
|
139 |
|
|
}
|
140 |
|
|
|
141 |
|
|
public void teardown()
|
142 |
|
|
{
|
143 |
|
|
counterRange = null;
|
144 |
|
|
maxBlocksPerSegment = null;
|
145 |
|
|
C0 = null;
|
146 |
|
|
blockNdx = null;
|
147 |
|
|
}
|
148 |
|
|
|
149 |
|
|
public void encryptBlock(byte[] in, int i, byte[] out, int o)
|
150 |
|
|
{
|
151 |
|
|
icm(in, i, out, o);
|
152 |
|
|
}
|
153 |
|
|
|
154 |
|
|
public void decryptBlock(byte[] in, int i, byte[] out, int o)
|
155 |
|
|
{
|
156 |
|
|
icm(in, i, out, o);
|
157 |
|
|
}
|
158 |
|
|
|
159 |
|
|
private void icm(byte[] in, int inOffset, byte[] out, int outOffset)
|
160 |
|
|
{
|
161 |
|
|
if (blockNdx.compareTo(maxBlocksPerSegment) >= 0)
|
162 |
|
|
throw new RuntimeException("Maximum blocks for segment reached");
|
163 |
|
|
BigInteger Ci = C0.add(blockNdx).modPow(BigInteger.ONE, counterRange);
|
164 |
|
|
byte[] result = Ci.toByteArray();
|
165 |
|
|
int limit = result.length;
|
166 |
|
|
int ndx = 0;
|
167 |
|
|
if (limit < cipherBlockSize)
|
168 |
|
|
{
|
169 |
|
|
byte[] data = new byte[cipherBlockSize];
|
170 |
|
|
System.arraycopy(result, 0, data, cipherBlockSize - limit, limit);
|
171 |
|
|
result = data;
|
172 |
|
|
}
|
173 |
|
|
else if (limit > cipherBlockSize)
|
174 |
|
|
ndx = limit - cipherBlockSize;
|
175 |
|
|
|
176 |
|
|
cipher.encryptBlock(result, ndx, result, ndx);
|
177 |
|
|
blockNdx = blockNdx.add(BigInteger.ONE); // increment blockNdx
|
178 |
|
|
for (int i = 0; i < modeBlockSize; i++) // xor result with input block
|
179 |
|
|
out[outOffset++] = (byte)(in[inOffset++] ^ result[ndx++]);
|
180 |
|
|
}
|
181 |
|
|
}
|