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.ISO7816d4Padding;
/**
* CMAC - as specified at www.nuee.nagoya-u.ac.jp/labs/tiwata/omac/omac.html
* <p>
* CMAC is analogous to OMAC1 - see also en.wikipedia.org/wiki/CMAC
* </p><p>
* CMAC is a NIST recomendation - see
* csrc.nist.gov/CryptoToolkit/modes/800-38_Series_Publications/SP800-38B.pdf
* </p><p>
* CMAC/OMAC1 is a blockcipher-based message authentication code designed and
* analyzed by Tetsu Iwata and Kaoru Kurosawa.
* </p><p>
* CMAC/OMAC1 is a simple variant of the CBC MAC (Cipher Block Chaining Message
* Authentication Code). OMAC stands for One-Key CBC MAC.
* </p><p>
* It supports 128- or 64-bits block ciphers, with any key size, and returns
* a MAC with dimension less or equal to the block size of the underlying
* cipher.
* </p>
*/
public class CMac implements Mac
{
private static final byte CONSTANT_128 = (byte)0x87;
private static final byte CONSTANT_64 = (byte)0x1b;
private byte[] ZEROES;
private byte[] mac;
private byte[] buf;
private int bufOff;
private BlockCipher cipher;
private int macSize;
private byte[] L, Lu, Lu2;
/**
* create a standard MAC based on a CBC block cipher (64 or 128 bit block).
* This will produce an authentication code the length of the block size
* of the cipher.
*
* @param cipher the cipher to be used as the basis of the MAC generation.
*/
public CMac(BlockCipher cipher)
{
this(cipher, cipher.getBlockSize() * 8);
}
/**
* create a standard MAC based on a block cipher with the size of the
* MAC been given in bits.
* <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 and <= 128.
*/
public CMac(BlockCipher cipher, int macSizeInBits)
{
if ((macSizeInBits % 8) != 0)
{
throw new IllegalArgumentException("MAC size must be multiple of 8");
}
if (macSizeInBits > (cipher.getBlockSize() * 8))
{
throw new IllegalArgumentException(
"MAC size must be less or equal to "
+ (cipher.getBlockSize() * 8));
}
if (cipher.getBlockSize() != 8 && cipher.getBlockSize() != 16)
{
throw new IllegalArgumentException(
"Block size must be either 64 or 128 bits");
}
this.cipher = new CBCBlockCipher(cipher);
this.macSize = macSizeInBits / 8;
mac = new byte[cipher.getBlockSize()];
buf = new byte[cipher.getBlockSize()];
ZEROES = new byte[cipher.getBlockSize()];
bufOff = 0;
}
public String getAlgorithmName()
{
return cipher.getAlgorithmName();
}
private static byte[] doubleLu(byte[] in)
{
int FirstBit = (in[0] & 0xFF) >> 7;
byte[] ret = new byte[in.length];
for (int i = 0; i < in.length - 1; i++)
{
ret[i] = (byte)((in[i] << 1) + ((in[i + 1] & 0xFF) >> 7));
}
ret[in.length - 1] = (byte)(in[in.length - 1] << 1);
if (FirstBit == 1)
{
ret[in.length - 1] ^= in.length == 16 ? CONSTANT_128 : CONSTANT_64;
}
return ret;
}
public void init(CipherParameters params)
{
if (params != null)
{
cipher.init(true, params);
//initializes the L, Lu, Lu2 numbers
L = new byte[ZEROES.length];
cipher.processBlock(ZEROES, 0, L, 0);
Lu = doubleLu(L);
Lu2 = doubleLu(Lu);
}
reset();
}
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();
byte[] lu;
if (bufOff == blockSize)
{
lu = Lu;
}
else
{
new ISO7816d4Padding().addPadding(buf, bufOff);
lu = Lu2;
}
for (int i = 0; i < mac.length; i++)
{
buf[i] ^= lu[i];
}
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();
}
}