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Diffstat (limited to 'libjava/classpath/gnu/javax/crypto/mode/ICM.java')
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diff --git a/libjava/classpath/gnu/javax/crypto/mode/ICM.java b/libjava/classpath/gnu/javax/crypto/mode/ICM.java new file mode 100644 index 00000000000..d37908b5dfd --- /dev/null +++ b/libjava/classpath/gnu/javax/crypto/mode/ICM.java @@ -0,0 +1,228 @@ +/* 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. + +GNU Classpath 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 for more details. + +You should have received a copy of the GNU General Public License +along with GNU Classpath; if not, write to the Free Software +Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 +USA + +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 +executable, regardless of the license terms of these independent +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 +module. An independent module is a module which is not derived from +or based on this library. If you modify this library, you may extend +this exception to your version of the library, but you are not +obligated to do so. If you do not wish to do so, delete this +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; + +/** + * <p>An implementation of <i>David McGrew</i> Integer Counter Mode (ICM) as an + * {@link IMode}.</p> + * + * <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> + * + * <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> + * + * <p>For simplicity, this implementation, fixes these two values to the + * following:</p> + * + * <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> + * + * <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> + * + * <p>References:</p> + * + * <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 +{ + + // Constants and variables + // ------------------------------------------------------------------------- + + /** 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; + + // Constructor(s) + // ------------------------------------------------------------------------- + + /** + * <p>Trivial package-private constructor for use by the Factory class.</p> + * + * @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); + } + + /** + * <p>Private constructor for cloning purposes.<p> + * + * @param that the instance to clone. + */ + private ICM(ICM that) + { + this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize); + } + + // Class methods + // ------------------------------------------------------------------------- + + // Cloneable interface implementation + // ------------------------------------------------------------------------- + + public Object clone() + { + return new ICM(this); + } + + // Implementation of abstract methods in BaseMode + // ------------------------------------------------------------------------- + + 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); + } + + // Instance methods + // ------------------------------------------------------------------------- + + private void icm(byte[] in, int inOffset, byte[] out, int outOffset) + { + if (blockNdx.compareTo(maxBlocksPerSegment) >= 0) + throw new RuntimeException("Maximum blocks for segment reached"); + + // encrypt the counter for the current blockNdx + // C[i] = (C[0] + i) modulo (256^BLOCK_LENGTH). + + BigInteger Ci = C0.add(blockNdx).modPow(BigInteger.ONE, counterRange); + byte[] result = Ci.toByteArray(); + int limit = result.length; + // if (limit < cipherBlockSize) { + // byte[] data = new byte[cipherBlockSize]; + // System.arraycopy(result, 0, data, cipherBlockSize-limit, limit); + // result = data; + // } else if (limit > cipherBlockSize) { + // byte[] data = new byte[cipherBlockSize]; + // System.arraycopy(result, limit-cipherBlockSize, data, 0, cipherBlockSize); + // result = data; + // } + // + // cipher.encryptBlock(result, 0, result, 0); + // blockNdx = blockNdx.add(BigInteger.ONE); // increment blockNdx + // for (int i = 0; i < modeBlockSize; ) { // xor result with input block + // out[outOffset++] = (byte)(in[inOffset++] ^ result[i++]); + // } + 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++]); + } + } +}
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