org.bouncycastle.crypto.macs.CMac Maven / Gradle / Ivy
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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.ISO7816d4Padding;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.util.Pack;
/**
* CMAC - as specified at www.nuee.nagoya-u.ac.jp/labs/tiwata/omac/omac.html
*
* CMAC is analogous to OMAC1 - see also en.wikipedia.org/wiki/CMAC
*
* CMAC is a NIST recomendation - see
* csrc.nist.gov/CryptoToolkit/modes/800-38_Series_Publications/SP800-38B.pdf
*
* CMAC/OMAC1 is a blockcipher-based message authentication code designed and
* analyzed by Tetsu Iwata and Kaoru Kurosawa.
*
* CMAC/OMAC1 is a simple variant of the CBC MAC (Cipher Block Chaining Message
* Authentication Code). OMAC stands for One-Key CBC MAC.
*
* 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.
*
*/
public class CMac implements Mac
{
private byte[] poly;
private byte[] ZEROES;
private byte[] mac;
private byte[] buf;
private int bufOff;
private BlockCipher cipher;
private int macSize;
private byte[] 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.
*
* 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));
}
this.cipher = CBCBlockCipher.newInstance(cipher);
this.macSize = macSizeInBits / 8;
this.poly = lookupPoly(cipher.getBlockSize());
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 int shiftLeft(byte[] block, byte[] output)
{
int i = block.length;
int bit = 0;
while (--i >= 0)
{
int b = block[i] & 0xff;
output[i] = (byte)((b << 1) | bit);
bit = (b >>> 7) & 1;
}
return bit;
}
private byte[] doubleLu(byte[] in)
{
byte[] ret = new byte[in.length];
int carry = shiftLeft(in, ret);
/*
* NOTE: This construction is an attempt at a constant-time implementation.
*/
int mask = (-carry) & 0xff;
ret[in.length - 3] ^= poly[1] & mask;
ret[in.length - 2] ^= poly[2] & mask;
ret[in.length - 1] ^= poly[3] & mask;
return ret;
}
private static byte[] lookupPoly(int blockSizeLength)
{
int xor;
switch (blockSizeLength * 8)
{
case 64:
xor = 0x1B;
break;
case 128:
xor = 0x87;
break;
case 160:
xor = 0x2D;
break;
case 192:
xor = 0x87;
break;
case 224:
xor = 0x309;
break;
case 256:
xor = 0x425;
break;
case 320:
xor = 0x1B;
break;
case 384:
xor = 0x100D;
break;
case 448:
xor = 0x851;
break;
case 512:
xor = 0x125;
break;
case 768:
xor = 0xA0011;
break;
case 1024:
xor = 0x80043;
break;
case 2048:
xor = 0x86001;
break;
default:
throw new IllegalArgumentException("Unknown block size for CMAC: " + (blockSizeLength * 8));
}
return Pack.intToBigEndian(xor);
}
public void init(CipherParameters params)
{
validate(params);
cipher.init(true, params);
//initializes the L, Lu, Lu2 numbers
byte[] L = new byte[ZEROES.length];
cipher.processBlock(ZEROES, 0, L, 0);
Lu = doubleLu(L);
Lu2 = doubleLu(Lu);
reset();
}
void validate(CipherParameters params)
{
if (params != null)
{
if (!(params instanceof KeyParameter))
{
// CMAC mode does not permit IV to underlying CBC mode
throw new IllegalArgumentException("CMac mode only permits key to be set.");
}
}
}
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();
}
}