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package org.bouncycastle.crypto.macs;
import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.Mac;
import org.bouncycastle.crypto.modes.CBCBlockCipher;
import org.bouncycastle.crypto.paddings.BlockCipherPadding;
/**
* standard CBC Block Cipher MAC - if no padding is specified the default of
* pad of zeroes is used.
*/
public class CBCBlockCipherMac
implements Mac
{
private byte[] mac;
private byte[] buf;
private int bufOff;
private BlockCipher cipher;
private BlockCipherPadding padding;
private int macSize;
/**
* create a standard MAC based on a CBC block cipher. This will produce an
* authentication code half the length of the block size of the cipher.
*
* @param cipher the cipher to be used as the basis of the MAC generation.
*/
public CBCBlockCipherMac(
BlockCipher cipher)
{
this(cipher, (cipher.getBlockSize() * 8) / 2, null);
}
/**
* create a standard MAC based on a CBC block cipher. This will produce an
* authentication code half the length of the block size of the cipher.
*
* @param cipher the cipher to be used as the basis of the MAC generation.
* @param padding the padding to be used to complete the last block.
*/
public CBCBlockCipherMac(
BlockCipher cipher,
BlockCipherPadding padding)
{
this(cipher, (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 CBC 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 macSizeInBits the size of the MAC in bits, must be a multiple of 8.
*/
public CBCBlockCipherMac(
BlockCipher cipher,
int macSizeInBits)
{
this(cipher, macSizeInBits, null);
}
/**
* create a standard MAC based on a block cipher with the size of the
* MAC been given in bits. This class uses CBC 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 macSizeInBits the size of the MAC in bits, must be a multiple of 8.
* @param padding the padding to be used to complete the last block.
*/
public CBCBlockCipherMac(
BlockCipher cipher,
int macSizeInBits,
BlockCipherPadding padding)
{
if ((macSizeInBits % 8) != 0)
{
throw new IllegalArgumentException("MAC size must be multiple of 8");
}
this.cipher = new CBCBlockCipher(cipher);
this.padding = padding;
this.macSize = macSizeInBits / 8;
mac = new byte[cipher.getBlockSize()];
buf = new byte[cipher.getBlockSize()];
bufOff = 0;
}
public String getAlgorithmName()
{
return cipher.getAlgorithmName();
}
public void init(
CipherParameters params)
{
reset();
cipher.init(true, params);
}
public int getMacSize()
{
return macSize;
}
public void update(
byte in)
{
if (bufOff == buf.length)
{
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 gapLen = blockSize - bufOff;
if (len > gapLen)
{
System.arraycopy(in, inOff, buf, bufOff, gapLen);
cipher.processBlock(buf, 0, mac, 0);
bufOff = 0;
len -= gapLen;
inOff += gapLen;
while (len > blockSize)
{
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();
if (padding == null)
{
//
// pad with zeroes
//
while (bufOff < blockSize)
{
buf[bufOff] = 0;
bufOff++;
}
}
else
{
if (bufOff == blockSize)
{
cipher.processBlock(buf, 0, mac, 0);
bufOff = 0;
}
padding.addPadding(buf, bufOff);
}
cipher.processBlock(buf, 0, mac, 0);
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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