protected override int UncheckedTransformFinalBlock(ReadOnlySpan <byte> inputBuffer, Span <byte> outputBuffer)
{
// The only caller of this method is the array-allocating overload, outputBuffer is
// always new memory, not a user-provided buffer.
Debug.Assert(!inputBuffer.Overlaps(outputBuffer));
int padWritten = SymmetricPadding.PadBlock(inputBuffer, outputBuffer, PaddingSizeBytes, PaddingMode);
int transformWritten = BasicSymmetricCipher.TransformFinal(outputBuffer.Slice(0, padWritten), outputBuffer);
// After padding, we should have an even number of blocks, and the same applies
// to the transform.
Debug.Assert(padWritten == transformWritten);
return(transformWritten);
}
protected override unsafe int UncheckedTransformFinalBlock(ReadOnlySpan <byte> inputBuffer, Span <byte> outputBuffer)
{
// We can't complete decryption on a partial block
if (inputBuffer.Length % PaddingSizeBytes != 0)
{
throw new CryptographicException(SR.Cryptography_PartialBlock);
}
//
// If we have postponed cipher bits from the prior round, copy that into the decryption buffer followed by the input data.
// Otherwise the decryption buffer is just the input data.
//
ReadOnlySpan <byte> inputCiphertext;
Span <byte> ciphertext;
byte[]? rentedCiphertext = null;
int rentedCiphertextSize = 0;
try
{
if (_heldoverCipher == null)
{
rentedCiphertextSize = inputBuffer.Length;
rentedCiphertext = CryptoPool.Rent(inputBuffer.Length);
ciphertext = rentedCiphertext.AsSpan(0, inputBuffer.Length);
inputCiphertext = inputBuffer;
}
else
{
rentedCiphertextSize = _heldoverCipher.Length + inputBuffer.Length;
rentedCiphertext = CryptoPool.Rent(rentedCiphertextSize);
ciphertext = rentedCiphertext.AsSpan(0, rentedCiphertextSize);
_heldoverCipher.AsSpan().CopyTo(ciphertext);
inputBuffer.CopyTo(ciphertext.Slice(_heldoverCipher.Length));
// Decrypt in-place
inputCiphertext = ciphertext;
}
int unpaddedLength = 0;
fixed(byte *pCiphertext = ciphertext)
{
// Decrypt the data, then strip the padding to get the final decrypted data. Note that even if the cipherText length is 0, we must
// invoke TransformFinal() so that the cipher object knows to reset for the next cipher operation.
int decryptWritten = BasicSymmetricCipher.TransformFinal(inputCiphertext, ciphertext);
Span <byte> decryptedBytes = ciphertext.Slice(0, decryptWritten);
if (decryptedBytes.Length > 0)
{
unpaddedLength = SymmetricPadding.GetPaddingLength(decryptedBytes, PaddingMode, InputBlockSize);
decryptedBytes.Slice(0, unpaddedLength).CopyTo(outputBuffer);
}
}
Reset();
return(unpaddedLength);
}
finally
{
if (rentedCiphertext != null)
{
CryptoPool.Return(rentedCiphertext, clearSize: rentedCiphertextSize);
}
}
}