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Diffstat (limited to 'libjava/classpath/gnu/javax/crypto/mode/CFB.java')
| -rw-r--r-- | libjava/classpath/gnu/javax/crypto/mode/CFB.java | 175 |
1 files changed, 175 insertions, 0 deletions
diff --git a/libjava/classpath/gnu/javax/crypto/mode/CFB.java b/libjava/classpath/gnu/javax/crypto/mode/CFB.java new file mode 100644 index 00000000000..fef2b634cf2 --- /dev/null +++ b/libjava/classpath/gnu/javax/crypto/mode/CFB.java @@ -0,0 +1,175 @@ +/* CFB.java -- + Copyright (C) 2002, 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; + +/** + * The cipher feedback mode. CFB mode is a stream mode that operates on + * <i>s</i> bit blocks, where 1 <= <i>s</i> <= <i>b</i>, if + * <i>b</i> is the underlying cipher's block size. Encryption is: + * + <pre> + I[1] = IV + I[j] = LSB(b-s, I[j-1]) | C[j-1] for j = 2...n + O[j] = CIPH(K, I[j]) for j = 1,2...n + C[j] = P[j] ^ MSB(s, O[j]) for j = 1,2...n + </pre> + * + * <p>And decryption is:</p> + * + <pre> + I[1] = IV + I[j] = LSB(b-s, I[j-1]) | C[j-1] for j = 2...n + O[j] = CIPH(K, I[j]) for j = 1,2...n + P[j] = C[j] ^ MSB(s, O[j]) for j = 1,2...n + </pre> + * + * <p>CFB mode requires an initialization vector, which need not be kept + * secret.</p> + * + * <p>References:</p> + * <ol> + * <li>Bruce Schneier, <i>Applied Cryptography: Protocols, Algorithms, + * and Source Code in C, Second Edition</i>. (1996 John Wiley and Sons) + * ISBN 0-471-11709-9.</li> + * + * <li><a href="http://csrc.nist.gov/encryption/modes/Recommendation/Modes01.pdf"> + * Recommendation for Block Cipher Modes of Operation Methods and Techniques</a>, + * Morris Dworkin.</li> + * </ol> + */ +public class CFB extends BaseMode +{ + + // Constants and variables. + // ----------------------------------------------------------------------- + + /** The shift register, the input block to the block cipher. */ + private byte[] shiftRegister; + + /** The output block from the block cipher. */ + private byte[] scratch; + + // Constructors. + // ----------------------------------------------------------------------- + + /** + * Package-private constructor for the factory class. + * + * @param underlyingCipher The cipher implementation. + * @param cipherBlockSize The cipher's block size. + */ + CFB(IBlockCipher underlyingCipher, int cipherBlockSize) + { + super(Registry.CFB_MODE, underlyingCipher, cipherBlockSize); + } + + /** + * Cloneing constructor. + * + * @param that The instance being cloned. + */ + private CFB(CFB that) + { + this((IBlockCipher) that.cipher.clone(), that.cipherBlockSize); + } + + // Instance methods implementing BaseMode. + // ----------------------------------------------------------------------- + + public Object clone() + { + return new CFB(this); + } + + public void setup() + { + if (modeBlockSize > cipherBlockSize) + { + throw new IllegalArgumentException( + "CFB block size cannot be larger than the cipher block size"); + } + shiftRegister = new byte[cipherBlockSize]; + scratch = new byte[cipherBlockSize]; + System.arraycopy(iv, 0, shiftRegister, 0, Math.min(iv.length, + cipherBlockSize)); + } + + public void teardown() + { + if (shiftRegister != null) + { + for (int i = 0; i < shiftRegister.length; i++) + { + shiftRegister[i] = 0; + } + } + shiftRegister = null; + } + + public void encryptBlock(byte[] in, int inOffset, byte[] out, int outOffset) + { + cipher.encryptBlock(shiftRegister, 0, scratch, 0); + for (int i = 0; i < modeBlockSize; i++) + { + out[outOffset + i] = (byte) (in[inOffset + i] ^ scratch[i]); + } + System.arraycopy(shiftRegister, modeBlockSize, shiftRegister, 0, + cipherBlockSize - modeBlockSize); + System.arraycopy(out, outOffset, shiftRegister, cipherBlockSize + - modeBlockSize, + modeBlockSize); + } + + public void decryptBlock(byte[] in, int inOffset, byte[] out, int outOffset) + { + cipher.encryptBlock(shiftRegister, 0, scratch, 0); + for (int i = 0; i < modeBlockSize; i++) + { + out[outOffset + i] = (byte) (in[inOffset + i] ^ scratch[i]); + } + System.arraycopy(shiftRegister, modeBlockSize, shiftRegister, 0, + cipherBlockSize - modeBlockSize); + System.arraycopy(in, inOffset, shiftRegister, cipherBlockSize + - modeBlockSize, + modeBlockSize); + } +}
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