/**
* Constructor that accepts an instance of a block cipher engine.
*
* @param cipher the engine to use
*/
public EaxBlockCipher(
IBlockCipher cipher)
{
blockSize = cipher.GetBlockSize();
mac = new CMac(cipher);
macBlock = new byte[blockSize];
associatedTextMac = new byte[mac.GetMacSize()];
nonceMac = new byte[mac.GetMacSize()];
this.cipher = new SicBlockCipher(cipher);
}
/**
* Process a packet of data for either CCM decryption or encryption.
*
* @param in data for processing.
* @param inOff offset at which data starts in the input array.
* @param inLen length of the data in the input array.
* @param output output array.
* @param outOff offset into output array to start putting processed bytes.
* @return the number of bytes added to output.
* @throws IllegalStateException if the cipher is not appropriately set up.
* @throws InvalidCipherTextException if the input data is truncated or the mac check fails.
* @throws DataLengthException if output buffer too short.
*/
public virtual int ProcessPacket(byte[] input, int inOff, int inLen, byte[] output, int outOff)
{
// TODO: handle null keyParam (e.g. via RepeatedKeySpec)
// Need to keep the CTR and CBC Mac parts around and reset
if (keyParam == null)
{
throw new InvalidOperationException("CCM cipher unitialized.");
}
int n = nonce.Length;
int q = 15 - n;
if (q < 4)
{
int limitLen = 1 << (8 * q);
if (inLen >= limitLen)
{
throw new InvalidOperationException("CCM packet too large for choice of q.");
}
}
byte[] iv = new byte[BlockSize];
iv[0] = (byte)((q - 1) & 0x7);
nonce.CopyTo(iv, 1);
IBlockCipher ctrCipher = new SicBlockCipher(cipher);
ctrCipher.Init(forEncryption, new ParametersWithIV(keyParam, iv));
int outputLen;
int inIndex = inOff;
int outIndex = outOff;
if (forEncryption)
{
outputLen = inLen + macSize;
Check.OutputLength(output, outOff, outputLen, "Output buffer too short.");
CalculateMac(input, inOff, inLen, macBlock);
byte[] encMac = new byte[BlockSize];
ctrCipher.ProcessBlock(macBlock, 0, encMac, 0); // S0
while (inIndex < (inOff + inLen - BlockSize)) // S1...
{
ctrCipher.ProcessBlock(input, inIndex, output, outIndex);
outIndex += BlockSize;
inIndex += BlockSize;
}
byte[] block = new byte[BlockSize];
Array.Copy(input, inIndex, block, 0, inLen + inOff - inIndex);
ctrCipher.ProcessBlock(block, 0, block, 0);
Array.Copy(block, 0, output, outIndex, inLen + inOff - inIndex);
Array.Copy(encMac, 0, output, outOff + inLen, macSize);
}
else
{
if (inLen < macSize)
{
throw new InvalidCipherTextException("data too short");
}
outputLen = inLen - macSize;
Check.OutputLength(output, outOff, outputLen, "Output buffer too short.");
Array.Copy(input, inOff + outputLen, macBlock, 0, macSize);
ctrCipher.ProcessBlock(macBlock, 0, macBlock, 0);
for (int i = macSize; i != macBlock.Length; i++)
{
macBlock[i] = 0;
}
while (inIndex < (inOff + outputLen - BlockSize))
{
ctrCipher.ProcessBlock(input, inIndex, output, outIndex);
outIndex += BlockSize;
inIndex += BlockSize;
}
byte[] block = new byte[BlockSize];
Array.Copy(input, inIndex, block, 0, outputLen - (inIndex - inOff));
ctrCipher.ProcessBlock(block, 0, block, 0);
Array.Copy(block, 0, output, outIndex, outputLen - (inIndex - inOff));
byte[] calculatedMacBlock = new byte[BlockSize];
CalculateMac(output, outOff, outputLen, calculatedMacBlock);
if (!Arrays.ConstantTimeAreEqual(macBlock, calculatedMacBlock))
{
throw new InvalidCipherTextException("mac check in CCM failed");
}
}
return(outputLen);
}
