| public TransformFinalBlock ( byte inputBuffer, int inputOffset, int inputCount ) : byte[] | ||
| inputBuffer | byte | |
| inputOffset | int | |
| inputCount | int | |
| return | byte[] | |
/// <summary>
/// Reads a sequence of bytes from the current CryptoStream into buffer,
/// and advances the position within the stream by the number of bytes read.
/// </summary>
public override int Read(byte[] outBuffer, int offset, int count)
{
int nBytes = 0;
while (nBytes < count)
{
// Calculate buffer quantities vs read-ahead size, and check for sufficient free space
int byteCount = _slideBufFreePos - _slideBufStartPos;
// Need to handle final block and Auth Code specially, but don't know total data length.
// Maintain a read-ahead equal to the length of (crypto block + Auth Code).
// When that runs out we can detect these final sections.
int lengthToRead = _blockAndAuth - byteCount;
if (_slideBuffer.Length - _slideBufFreePos < lengthToRead)
{
// Shift the data to the beginning of the buffer
int iTo = 0;
for (int iFrom = _slideBufStartPos; iFrom < _slideBufFreePos; iFrom++, iTo++)
{
_slideBuffer[iTo] = _slideBuffer[iFrom];
}
_slideBufFreePos -= _slideBufStartPos; // Note the -=
_slideBufStartPos = 0;
}
int obtained = _stream.Read(_slideBuffer, _slideBufFreePos, lengthToRead);
_slideBufFreePos += obtained;
// Recalculate how much data we now have
byteCount = _slideBufFreePos - _slideBufStartPos;
if (byteCount >= _blockAndAuth)
{
// At least a 16 byte block and an auth code remains.
_transform.TransformBlock(_slideBuffer,
_slideBufStartPos,
CRYPTO_BLOCK_SIZE,
outBuffer,
offset);
nBytes += CRYPTO_BLOCK_SIZE;
offset += CRYPTO_BLOCK_SIZE;
_slideBufStartPos += CRYPTO_BLOCK_SIZE;
}
else
{
// Last round.
if (byteCount > AUTH_CODE_LENGTH)
{
// At least one byte of data plus auth code
int finalBlock = byteCount - AUTH_CODE_LENGTH;
byte[] fb = _transform.TransformFinalBlock(_slideBuffer,
_slideBufStartPos,
finalBlock);
Array.Copy(fb, 0, outBuffer, offset, fb.Length);
nBytes += finalBlock;
_slideBufStartPos += finalBlock;
}
else if (byteCount < AUTH_CODE_LENGTH)
{
throw new Exception("Internal error missed auth code"); // Coding bug
}
// Final block done. Check Auth code.
byte[] calcAuthCode = _transform.GetAuthCode();
for (int i = 0; i < AUTH_CODE_LENGTH; i++)
{
if (calcAuthCode[i] != _slideBuffer[_slideBufStartPos + i])
{
throw new Exception("AES Authentication Code does not match. This is a super-CRC check on the data in the file after compression and encryption. \r\n"
+ "The file may be damaged.");
}
}
break; // Reached the auth code
}
}
return(nBytes);
}
