| /* ICM.java -- |
| Copyright (C) 2001, 2002, 2003, 2006 Free Software Foundation, Inc. |
| |
| This file is a part of GNU Classpath. |
| |
| GNU Classpath is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2 of the License, or (at |
| your option) any later version. |
| |
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| WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| General Public License for more details. |
| |
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| along with GNU Classpath; if not, write to the Free Software |
| Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 |
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| |
| Linking this library statically or dynamically with other modules is |
| making a combined work based on this library. Thus, the terms and |
| conditions of the GNU General Public License cover the whole |
| combination. |
| |
| As a special exception, the copyright holders of this library give you |
| permission to link this library with independent modules to produce an |
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| modules, and to copy and distribute the resulting executable under |
| terms of your choice, provided that you also meet, for each linked |
| independent module, the terms and conditions of the license of that |
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| exception statement from your version. */ |
| |
| |
| package gnu.javax.crypto.mode; |
| |
| import gnu.java.security.Registry; |
| import gnu.javax.crypto.cipher.IBlockCipher; |
| |
| import java.math.BigInteger; |
| |
| /** |
| * An implementation of <i>David McGrew</i> Integer Counter Mode (ICM) as an |
| * {@link IMode}. |
| * <p> |
| * ICM is a way to define a pseudorandom keystream generator using a block |
| * cipher. The keystream can be used for additive encryption, key derivation, or |
| * any other application requiring pseudorandom data. In the case of this class, |
| * it is used as additive encryption, XOR-ing the keystream with the input text |
| * --for both encryption and decryption. |
| * <p> |
| * In ICM, the keystream is logically broken into segments. Each segment is |
| * identified with a segment index, and the segments have equal lengths. This |
| * segmentation makes ICM especially appropriate for securing packet-based |
| * protocols. ICM also allows a variety of configurations based, among other |
| * things, on two parameters: the <i>block index length</i> and the <i>segment |
| * index length</i>. A constraint on those two values exists: The sum of |
| * <i>segment index length</i> and <i>block index length</i> <b>must not</b> |
| * half the <i>block size</i> of the underlying cipher. This requirement |
| * protects the ICM keystream generator from potentially failing to be |
| * pseudorandom. |
| * <p> |
| * For simplicity, this implementation, fixes these two values to the following: |
| * <ul> |
| * <li>block index length: is half the underlying cipher block size, and</li> |
| * <li>segment index length: is zero.</li> |
| * </ul> |
| * <p> |
| * For a 128-bit block cipher, the above values imply a maximum keystream length |
| * of 295,147,905,179,352,825,856 octets, since in ICM, each segment must not |
| * exceed the value |
| * <code>(256 ^ <i>block index length</i>) * <i>block length</i></code> |
| * octets. |
| * <p> |
| * Finally, for this implementation of the ICM, the IV placeholder will be used |
| * to pass the value of the <i>Offset</i> in the keystream segment. |
| * <p> |
| * References: |
| * <ol> |
| * <li><a |
| * href="http://www.ietf.org/internet-drafts/draft-mcgrew-saag-icm-00.txt"> |
| * Integer Counter Mode</a>, David A. McGrew.</li> |
| * </ol> |
| */ |
| public class ICM |
| extends BaseMode |
| implements Cloneable |
| { |
| /** The integer value 256 as a BigInteger. */ |
| private static final BigInteger TWO_FIFTY_SIX = new BigInteger("256"); |
| /** Maximum number of blocks per segment. */ |
| private BigInteger maxBlocksPerSegment; |
| /** A work constant. */ |
| private BigInteger counterRange; |
| /** The initial counter for a given keystream segment. */ |
| private BigInteger C0; |
| /** The index of the next block for a given keystream segment. */ |
| private BigInteger blockNdx; |
| |
| /** |
| * Trivial package-private constructor for use by the Factory class. |
| * |
| * @param underlyingCipher the underlying cipher implementation. |
| * @param cipherBlockSize the underlying cipher block size to use. |
| */ |
| ICM(IBlockCipher underlyingCipher, int cipherBlockSize) |
| { |
| super(Registry.ICM_MODE, underlyingCipher, cipherBlockSize); |
| } |
| |
| /** |
| * Private constructor for cloning purposes. |
| * |
| * @param that the instance to clone. |
| */ |
| private ICM(ICM that) |
| { |
| this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize); |
| } |
| |
| public Object clone() |
| { |
| return new ICM(this); |
| } |
| |
| public void setup() |
| { |
| if (modeBlockSize != cipherBlockSize) |
| throw new IllegalArgumentException(); |
| counterRange = TWO_FIFTY_SIX.pow(cipherBlockSize); |
| maxBlocksPerSegment = TWO_FIFTY_SIX.pow(cipherBlockSize / 2); |
| BigInteger r = new BigInteger(1, iv); |
| C0 = maxBlocksPerSegment.add(r).modPow(BigInteger.ONE, counterRange); |
| blockNdx = BigInteger.ZERO; |
| } |
| |
| public void teardown() |
| { |
| counterRange = null; |
| maxBlocksPerSegment = null; |
| C0 = null; |
| blockNdx = null; |
| } |
| |
| public void encryptBlock(byte[] in, int i, byte[] out, int o) |
| { |
| icm(in, i, out, o); |
| } |
| |
| public void decryptBlock(byte[] in, int i, byte[] out, int o) |
| { |
| icm(in, i, out, o); |
| } |
| |
| private void icm(byte[] in, int inOffset, byte[] out, int outOffset) |
| { |
| if (blockNdx.compareTo(maxBlocksPerSegment) >= 0) |
| throw new RuntimeException("Maximum blocks for segment reached"); |
| BigInteger Ci = C0.add(blockNdx).modPow(BigInteger.ONE, counterRange); |
| byte[] result = Ci.toByteArray(); |
| int limit = result.length; |
| int ndx = 0; |
| if (limit < cipherBlockSize) |
| { |
| byte[] data = new byte[cipherBlockSize]; |
| System.arraycopy(result, 0, data, cipherBlockSize - limit, limit); |
| result = data; |
| } |
| else if (limit > cipherBlockSize) |
| ndx = limit - cipherBlockSize; |
| |
| cipher.encryptBlock(result, ndx, result, ndx); |
| blockNdx = blockNdx.add(BigInteger.ONE); // increment blockNdx |
| for (int i = 0; i < modeBlockSize; i++) // xor result with input block |
| out[outOffset++] = (byte)(in[inOffset++] ^ result[ndx++]); |
| } |
| } |