/**
* 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];
bufBlock = new byte[blockSize * 2];
associatedTextMac = new byte[mac.GetMacSize()];
nonceMac = new byte[mac.GetMacSize()];
this.cipher = new SicBlockCipher(cipher);
}
public byte[] ProcessPacket(
byte[] input,
int inOff,
int inLen)
{
if (keyParam == null)
{
throw new InvalidOperationException("CCM cipher unitialized.");
}
IBlockCipher ctrCipher = new SicBlockCipher(cipher);
byte[] iv = new byte[BlockSize];
byte[] output;
iv[0] = (byte)(((15 - nonce.Length) - 1) & 0x7);
Array.Copy(nonce, 0, iv, 1, nonce.Length);
ctrCipher.Init(forEncryption, new ParametersWithIV(keyParam, iv));
if (forEncryption)
{
int index = inOff;
int outOff = 0;
output = new byte[inLen + macSize];
calculateMac(input, inOff, inLen, macBlock);
ctrCipher.ProcessBlock(macBlock, 0, macBlock, 0); // S0
while (index < inLen - BlockSize) // S1...
{
ctrCipher.ProcessBlock(input, index, output, outOff);
outOff += BlockSize;
index += BlockSize;
}
byte[] block = new byte[BlockSize];
Array.Copy(input, index, block, 0, inLen - index);
ctrCipher.ProcessBlock(block, 0, block, 0);
Array.Copy(block, 0, output, outOff, inLen - index);
outOff += inLen - index;
Array.Copy(macBlock, 0, output, outOff, output.Length - outOff);
}
else
{
int index = inOff;
int outOff = 0;
output = new byte[inLen - macSize];
Array.Copy(input, inOff + inLen - macSize, macBlock, 0, macSize);
ctrCipher.ProcessBlock(macBlock, 0, macBlock, 0);
for (int i = macSize; i != macBlock.Length; i++)
{
macBlock[i] = 0;
}
while (outOff < output.Length - BlockSize)
{
ctrCipher.ProcessBlock(input, index, output, outOff);
outOff += BlockSize;
index += BlockSize;
}
byte[] block = new byte[BlockSize];
Array.Copy(input, index, block, 0, output.Length - outOff);
ctrCipher.ProcessBlock(block, 0, block, 0);
Array.Copy(block, 0, output, outOff, output.Length - outOff);
byte[] calculatedMacBlock = new byte[BlockSize];
calculateMac(output, 0, output.Length, calculatedMacBlock);
if (!Arrays.ConstantTimeAreEqual(macBlock, calculatedMacBlock))
{
throw new InvalidCipherTextException("mac check in CCM failed");
}
}
return(output);
}
