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package org.bouncycastle.crypto.modes;
import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.params.ParametersWithIV;
import org.bouncycastle.util.Arrays;
/**
* implements Cipher-Block-Chaining (CBC) mode on top of a simple cipher.
*/
public class CBCBlockCipher
implements BlockCipher
{
private byte[] IV;
private byte[] cbcV;
private byte[] cbcNextV;
private int blockSize;
private BlockCipher cipher = null;
private boolean encrypting;
/**
* Basic constructor.
*
* @param cipher the block cipher to be used as the basis of chaining.
*/
public CBCBlockCipher(
BlockCipher cipher)
{
this.cipher = cipher;
this.blockSize = cipher.getBlockSize();
this.IV = new byte[blockSize];
this.cbcV = new byte[blockSize];
this.cbcNextV = new byte[blockSize];
}
/**
* return the underlying block cipher that we are wrapping.
*
* @return the underlying block cipher that we are wrapping.
*/
public BlockCipher getUnderlyingCipher()
{
return cipher;
}
/**
* Initialise the cipher and, possibly, the initialisation vector (IV).
* If an IV isn't passed as part of the parameter, the IV will be all zeros.
*
* @param encrypting if true the cipher is initialised for
* encryption, if false for decryption.
* @param params the key and other data required by the cipher.
* @exception IllegalArgumentException if the params argument is
* inappropriate.
*/
public void init(
boolean encrypting,
CipherParameters params)
throws IllegalArgumentException
{
boolean oldEncrypting = this.encrypting;
this.encrypting = encrypting;
if (params instanceof ParametersWithIV)
{
ParametersWithIV ivParam = (ParametersWithIV)params;
byte[] iv = ivParam.getIV();
if (iv.length != blockSize)
{
throw new IllegalArgumentException("initialisation vector must be the same length as block size");
}
System.arraycopy(iv, 0, IV, 0, iv.length);
reset();
// if null it's an IV changed only.
if (ivParam.getParameters() != null)
{
cipher.init(encrypting, ivParam.getParameters());
}
else if (oldEncrypting != encrypting)
{
throw new IllegalArgumentException("cannot change encrypting state without providing key.");
}
}
else
{
reset();
// if it's null, key is to be reused.
if (params != null)
{
cipher.init(encrypting, params);
}
else if (oldEncrypting != encrypting)
{
throw new IllegalArgumentException("cannot change encrypting state without providing key.");
}
}
}
/**
* return the algorithm name and mode.
*
* @return the name of the underlying algorithm followed by "/CBC".
*/
public String getAlgorithmName()
{
return cipher.getAlgorithmName() + "/CBC";
}
/**
* return the block size of the underlying cipher.
*
* @return the block size of the underlying cipher.
*/
public int getBlockSize()
{
return cipher.getBlockSize();
}
/**
* Process one block of input from the array in and write it to
* the out array.
*
* @param in the array containing the input data.
* @param inOff offset into the in array the data starts at.
* @param out the array the output data will be copied into.
* @param outOff the offset into the out array the output will start at.
* @exception DataLengthException if there isn't enough data in in, or
* space in out.
* @exception IllegalStateException if the cipher isn't initialised.
* @return the number of bytes processed and produced.
*/
public int processBlock(
byte[] in,
int inOff,
byte[] out,
int outOff)
throws DataLengthException, IllegalStateException
{
return (encrypting) ? encryptBlock(in, inOff, out, outOff) : decryptBlock(in, inOff, out, outOff);
}
/**
* reset the chaining vector back to the IV and reset the underlying
* cipher.
*/
public void reset()
{
System.arraycopy(IV, 0, cbcV, 0, IV.length);
Arrays.fill(cbcNextV, (byte)0);
cipher.reset();
}
/**
* Do the appropriate chaining step for CBC mode encryption.
*
* @param in the array containing the data to be encrypted.
* @param inOff offset into the in array the data starts at.
* @param out the array the encrypted data will be copied into.
* @param outOff the offset into the out array the output will start at.
* @exception DataLengthException if there isn't enough data in in, or
* space in out.
* @exception IllegalStateException if the cipher isn't initialised.
* @return the number of bytes processed and produced.
*/
private int encryptBlock(
byte[] in,
int inOff,
byte[] out,
int outOff)
throws DataLengthException, IllegalStateException
{
if ((inOff + blockSize) > in.length)
{
throw new DataLengthException("input buffer too short");
}
/*
* XOR the cbcV and the input,
* then encrypt the cbcV
*/
for (int i = 0; i < blockSize; i++)
{
cbcV[i] ^= in[inOff + i];
}
int length = cipher.processBlock(cbcV, 0, out, outOff);
/*
* copy ciphertext to cbcV
*/
System.arraycopy(out, outOff, cbcV, 0, cbcV.length);
return length;
}
/**
* Do the appropriate chaining step for CBC mode decryption.
*
* @param in the array containing the data to be decrypted.
* @param inOff offset into the in array the data starts at.
* @param out the array the decrypted data will be copied into.
* @param outOff the offset into the out array the output will start at.
* @exception DataLengthException if there isn't enough data in in, or
* space in out.
* @exception IllegalStateException if the cipher isn't initialised.
* @return the number of bytes processed and produced.
*/
private int decryptBlock(
byte[] in,
int inOff,
byte[] out,
int outOff)
throws DataLengthException, IllegalStateException
{
if ((inOff + blockSize) > in.length)
{
throw new DataLengthException("input buffer too short");
}
System.arraycopy(in, inOff, cbcNextV, 0, blockSize);
int length = cipher.processBlock(in, inOff, out, outOff);
/*
* XOR the cbcV and the output
*/
for (int i = 0; i < blockSize; i++)
{
out[outOff + i] ^= cbcV[i];
}
/*
* swap the back up buffer into next position
*/
byte[] tmp;
tmp = cbcV;
cbcV = cbcNextV;
cbcNextV = tmp;
return length;
}
}
