protected override int UncheckedTransformBlock(ReadOnlySpan <byte> inputBuffer, Span <byte> outputBuffer)
{
//
// If we're decrypting, it's possible to be called with the last blocks of the data, and then
// have TransformFinalBlock called with an empty array. Since we don't know if this is the case,
// we won't decrypt the last block of the input until either TransformBlock or
// TransformFinalBlock is next called.
//
// We don't need to do this for PaddingMode.None because there is no padding to strip, and
// we also don't do this for PaddingMode.Zeros since there is no way for us to tell if the
// zeros at the end of a block are part of the plaintext or the padding.
//
int decryptedBytes = 0;
if (SymmetricPadding.DepaddingRequired(PaddingMode))
{
// If we have data saved from a previous call, decrypt that into the output first
if (_heldoverCipher != null)
{
int depadDecryptLength = BasicSymmetricCipher.Transform(_heldoverCipher, outputBuffer);
outputBuffer = outputBuffer.Slice(depadDecryptLength);
decryptedBytes += depadDecryptLength;
}
else
{
_heldoverCipher = new byte[InputBlockSize];
}
// Postpone the last block to the next round.
Debug.Assert(inputBuffer.Length >= _heldoverCipher.Length, "inputBuffer.Length >= _heldoverCipher.Length");
inputBuffer.Slice(inputBuffer.Length - _heldoverCipher.Length).CopyTo(_heldoverCipher);
inputBuffer = inputBuffer.Slice(0, inputBuffer.Length - _heldoverCipher.Length);
Debug.Assert(inputBuffer.Length % InputBlockSize == 0, "Did not remove whole blocks for depadding");
}
if (inputBuffer.Length > 0)
{
decryptedBytes += BasicSymmetricCipher.Transform(inputBuffer, outputBuffer);
}
return(decryptedBytes);
}
protected override int UncheckedTransformBlock(ReadOnlySpan <byte> inputBuffer, Span <byte> outputBuffer)
{
return(BasicSymmetricCipher.Transform(inputBuffer, outputBuffer));
}