/// <summary>
/// Reads and decrypts auxiliary channel chunk.
/// </summary>
/// <returns>Decrypted chunk.</returns>
/// <param name="stream">Stream.</param>
private byte[] ReadAndDecryptChunk(Stream stream)
{
var reader = new EndianReader(stream);
// 0xde, 0xad
reader.ReadBytes(2);
var length = reader.ReadUInt16BE();
var encryptedPayloadLength = length + Padding.CalculatePaddingSize(length, 16);
var encryptedPayloadBytes = new byte[encryptedPayloadLength];
var encryptedPayloadPosition = 0;
while (encryptedPayloadPosition < encryptedPayloadLength - 1)
{
var received = reader.ReadBytes(encryptedPayloadLength - encryptedPayloadPosition);
received.CopyTo(encryptedPayloadBytes, encryptedPayloadPosition);
encryptedPayloadPosition += received.Length;
}
var signature = reader.ReadBytes(32);
var bodyWriter = new EndianWriter();
bodyWriter.Write(new byte[] { 0xde, 0xad });
bodyWriter.WriteBE(length);
bodyWriter.Write(encryptedPayloadBytes);
var messageSignature = _cryptoContext.CalculateMessageSignature(bodyWriter.ToBytes());
if (!signature.SequenceEqual(messageSignature))
{
throw new InvalidDataException("Invalid message signature.");
}
var decryptedPayload = _cryptoContext.Decrypt(encryptedPayloadBytes);
return(decryptedPayload.Take(length).ToArray());
}
