internal Deserializer(CryptoDtoChannel channel, ReadOnlySpan <byte> bytes, bool ignoreSequence)
{
sequenceValid = false;
headerLength = Unsafe.ReadUnaligned <ushort>(ref MemoryMarshal.GetReference(bytes)); //.NET Standard 2.0 doesn't have BitConverter.ToUInt16(Span<T>)
if (bytes.Length < (2 + headerLength))
{
throw new CryptographicException("Not enough bytes to process packet.");
}
ReadOnlySpan <byte> headerBuffer = bytes.Slice(2, headerLength);
header = MessagePackSerializer.Deserialize <CryptoDtoHeaderDto>(headerBuffer.ToArray());
if (header.ChannelTag != channel.ChannelTag)
{
throw new CryptographicException("Channel Tag doesn't match provided Channel");
}
switch (header.Mode)
{
case CryptoDtoMode.ChaCha20Poly1305:
{
int aeLength = bytes.Length - (2 + headerLength);
ReadOnlySpan <byte> aePayloadBuffer = bytes.Slice(2 + headerLength, aeLength);
ReadOnlySpan <byte> adBuffer = bytes.Slice(0, 2 + headerLength);
Span <byte> nonceBuffer = stackalloc byte[Aead.NonceSize];
BinaryPrimitives.WriteUInt64LittleEndian(nonceBuffer.Slice(4), header.Sequence);
ReadOnlySpan <byte> receiveKey = channel.GetReceiveKey(header.Mode);
var aead = new ChaCha20Poly1305(receiveKey.ToArray());
ReadOnlySpan <byte> decryptedPayload = aead.Decrypt(aePayloadBuffer.ToArray(), adBuffer.ToArray(), nonceBuffer);
if (ignoreSequence)
{
sequenceValid = channel.IsReceivedSequenceAllowed(header.Sequence);
}
else
{
channel.CheckReceivedSequence(header.Sequence); //The packet has passed MAC, so now check if it's being duplicated or replayed
sequenceValid = true;
}
dtoNameLength = Unsafe.ReadUnaligned <ushort>(ref MemoryMarshal.GetReference(decryptedPayload)); //.NET Standard 2.0 doesn't have BitConverter.ToUInt16(Span<T>)
if (decryptedPayload.Length < (2 + dtoNameLength))
{
throw new CryptographicException("Not enough bytes to process packet. (2) " + dtoNameLength + " " + decryptedPayload.Length);
}
dtoNameBuffer = decryptedPayload.Slice(2, dtoNameLength);
dataLength = Unsafe.ReadUnaligned <ushort>(ref MemoryMarshal.GetReference(decryptedPayload.Slice(2 + dtoNameLength, 2))); //.NET Standard 2.0 doesn't have BitConverter.ToUInt16(Span<T>)
if (decryptedPayload.Length < (2 + dtoNameLength + 2 + dataLength))
{
throw new CryptographicException("Not enough bytes to process packet. (3) " + dataLength + " " + decryptedPayload.Length);
}
dataBuffer = decryptedPayload.Slice(2 + dtoNameLength + 2, dataLength);
break;
}
default:
throw new CryptographicException("Mode not recognised");
}
}
