package org.bouncycastle.crypto.macs;
import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.Mac;
import org.bouncycastle.crypto.paddings.BlockCipherPadding;
import org.bouncycastle.crypto.params.ParametersWithIV;
/**
* implements a Cipher-FeedBack (CFB) mode on top of a simple cipher.
*/
class MacCFBBlockCipher
{
private byte[] IV;
private byte[] cfbV;
private byte[] cfbOutV;
private int blockSize;
private BlockCipher cipher = null;
/**
* Basic constructor.
*
* @param cipher the block cipher to be used as the basis of the
* feedback mode.
* @param blockSize the block size in bits (note: a multiple of 8)
*/
public MacCFBBlockCipher(
BlockCipher cipher,
int bitBlockSize)
{
this.cipher = cipher;
this.blockSize = bitBlockSize / 8;
this.IV = new byte[cipher.getBlockSize()];
this.cfbV = new byte[cipher.getBlockSize()];
this.cfbOutV = new byte[cipher.getBlockSize()];
}
/**
* 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.
* An IV which is too short is handled in FIPS compliant fashion.
*
* @param param the key and other data required by the cipher.
* @exception IllegalArgumentException if the params argument is
* inappropriate.
*/
public void init(
CipherParameters params)
throws IllegalArgumentException
{
if (params instanceof ParametersWithIV)
{
ParametersWithIV ivParam = (ParametersWithIV)params;
byte[] iv = ivParam.getIV();
if (iv.length < IV.length)
{
System.arraycopy(iv, 0, IV, IV.length - iv.length, iv.length);
}
else
{
System.arraycopy(iv, 0, IV, 0, IV.length);
}
reset();
cipher.init(true, ivParam.getParameters());
}
else
{
reset();
cipher.init(true, params);
}
}
/**
* return the algorithm name and mode.
*
* @return the name of the underlying algorithm followed by "/CFB"
* and the block size in bits.
*/
public String getAlgorithmName()
{
return cipher.getAlgorithmName() + "/CFB" + (blockSize * 8);
}
/**
* return the block size we are operating at.
*
* @return the block size we are operating at (in bytes).
*/
public int getBlockSize()
{
return blockSize;
}
/**
* 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
{
if ((inOff + blockSize) > in.length)
{
throw new DataLengthException("input buffer too short");
}
if ((outOff + blockSize) > out.length)
{
throw new DataLengthException("output buffer too short");
}
cipher.processBlock(cfbV, 0, cfbOutV, 0);
//
// XOR the cfbV with the plaintext producing the cipher text
//
for (int i = 0; i < blockSize; i++)
{
out[outOff + i] = (byte)(cfbOutV[i] ^ in[inOff + i]);
}
//
// change over the input block.
//
System.arraycopy(cfbV, blockSize, cfbV, 0, cfbV.length - blockSize);
System.arraycopy(out, outOff, cfbV, cfbV.length - blockSize, blockSize);
return blockSize;
}
/**
* reset the chaining vector back to the IV and reset the underlying
* cipher.
*/
public void reset()
{
System.arraycopy(IV, 0, cfbV, 0, IV.length);
cipher.reset();
}
void getMacBlock(
byte[] mac)
{
cipher.processBlock(cfbV, 0, mac, 0);
}
}
public class CFBBlockCipherMac
implements Mac
{
private byte[] mac;
private byte[] buf;
private int bufOff;
private MacCFBBlockCipher cipher;
private BlockCipherPadding padding = null;
private int macSize;
/**
* create a standard MAC based on a CFB block cipher. This will produce an
* authentication code half the length of the block size of the cipher, with
* the CFB mode set to 8 bits.
*
* @param cipher the cipher to be used as the basis of the MAC generation.
*/
public CFBBlockCipherMac(
BlockCipher cipher)
{
this(cipher, 8, (cipher.getBlockSize() * 8) / 2, null);
}
/**
* create a standard MAC based on a CFB block cipher. This will produce an
* authentication code half the length of the block size of the cipher, with
* the CFB mode set to 8 bits.
*
* @param cipher the cipher to be used as the basis of the MAC generation.
* @param padding the padding to be used.
*/
public CFBBlockCipherMac(
BlockCipher cipher,
BlockCipherPadding padding)
{
this(cipher, 8, (cipher.getBlockSize() * 8) / 2, padding);
}
/**
* create a standard MAC based on a block cipher with the size of the
* MAC been given in bits. This class uses CFB mode as the basis for the
* MAC generation.
* <p>
* Note: the size of the MAC must be at least 24 bits (FIPS Publication 81),
* or 16 bits if being used as a data authenticator (FIPS Publication 113),
* and in general should be less than the size of the block cipher as it reduces
* the chance of an exhaustive attack (see Handbook of Applied Cryptography).
*
* @param cipher the cipher to be used as the basis of the MAC generation.
* @param cfbBitSize the size of an output block produced by the CFB mode.
* @param macSizeInBits the size of the MAC in bits, must be a multiple of 8.
*/
public CFBBlockCipherMac(
BlockCipher cipher,
int cfbBitSize,
int macSizeInBits)
{
this(cipher, cfbBitSize, macSizeInBits, null);
}
/**
* create a standard MAC based on a block cipher with the size of the
* MAC been given in bits. This class uses CFB mode as the basis for the
* MAC generation.
* <p>
* Note: the size of the MAC must be at least 24 bits (FIPS Publication 81),
* or 16 bits if being used as a data authenticator (FIPS Publication 113),
* and in general should be less than the size of the block cipher as it reduces
* the chance of an exhaustive attack (see Handbook of Applied Cryptography).
*
* @param cipher the cipher to be used as the basis of the MAC generation.
* @param cfbBitSize the size of an output block produced by the CFB mode.
* @param macSizeInBits the size of the MAC in bits, must be a multiple of 8.
* @param padding a padding to be used.
*/
public CFBBlockCipherMac(
BlockCipher cipher,
int cfbBitSize,
int macSizeInBits,
BlockCipherPadding padding)
{
if ((macSizeInBits % 8) != 0)
{
throw new IllegalArgumentException("MAC size must be multiple of 8");
}
mac = new byte[cipher.getBlockSize()];
this.cipher = new MacCFBBlockCipher(cipher, cfbBitSize);
this.padding = padding;
this.macSize = macSizeInBits / 8;
buf = new byte[this.cipher.getBlockSize()];
bufOff = 0;
}
public String getAlgorithmName()
{
return cipher.getAlgorithmName();
}
public void init(
CipherParameters params)
{
reset();
cipher.init(params);
}
public int getMacSize()
{
return macSize;
}
public void update(
byte in)
{
int resultLen = 0;
if (bufOff == buf.length)
{
resultLen = cipher.processBlock(buf, 0, mac, 0);
bufOff = 0;
}
buf[bufOff++] = in;
}
public void update(
byte[] in,
int inOff,
int len)
{
if (len < 0)
{
throw new IllegalArgumentException("Can't have a negative input length!");
}
int blockSize = cipher.getBlockSize();
int resultLen = 0;
int gapLen = blockSize - bufOff;
if (len > gapLen)
{
System.arraycopy(in, inOff, buf, bufOff, gapLen);
resultLen += cipher.processBlock(buf, 0, mac, 0);
bufOff = 0;
len -= gapLen;
inOff += gapLen;
while (len > blockSize)
{
resultLen += cipher.processBlock(in, inOff, mac, 0);
len -= blockSize;
inOff += blockSize;
}
}
System.arraycopy(in, inOff, buf, bufOff, len);
bufOff += len;
}
public int doFinal(
byte[] out,
int outOff)
{
int blockSize = cipher.getBlockSize();
//
// pad with zeroes
//
if (this.padding == null)
{
while (bufOff < blockSize)
{
buf[bufOff] = 0;
bufOff++;
}
}
else
{
padding.addPadding(buf, bufOff);
}
cipher.processBlock(buf, 0, mac, 0);
cipher.getMacBlock(mac);
System.arraycopy(mac, 0, out, outOff, macSize);
reset();
return macSize;
}
/**
* Reset the mac generator.
*/
public void reset()
{
/*
* clean the buffer.
*/
for (int i = 0; i < buf.length; i++)
{
buf[i] = 0;
}
bufOff = 0;
/*
* reset the underlying cipher.
*/
cipher.reset();
}
}
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