public Message(Stream input, RSAPrivateKey key, Converter <Guid, Salt> sessionSecret)
{
(_protected = new MemoryStream(0)).Dispose();
_hash = new HashStream(new SHA256Managed(), input);
_payload = input;
ReadHeader(_hash, out _version, out _state, out _transferId, out _salt);
Salt secret;
if (!UsesSessionKey)
{
// Begin private key decryption
_payload = key.Decrypt(input);
_hash.ChangeStream(_payload);
// Decrypt the aes key used in this package
byte[] keybits = IOStream.Read(_hash, 32);
secret = Salt.FromBytes(keybits);
}
else
{
secret = sessionSecret(_transferId);
Check.IsEqual(32, Check.NotNull(secret).Length);
}
AESCryptoKey sessionKey = new AESCryptoKey(
// Prefix the key with the message's salt and compute a SHA256 hash to be used as the key
Hash.SHA256(_salt.GetData(secret.ToArray()).ToStream()).ToArray(),
// Compute an IV for this aes key and salt combination
IV(secret, _salt)
);
_payload = sessionKey.Decrypt(_payload);
_hash.ChangeStream(_payload);
}
private static Salt SessionSecret(Salt clientKeyBits, byte[] serverKeyBits)
{
Salt sessionSecret = Salt.FromBytes(
Hash.SHA256(
new CombinedStream(
clientKeyBits.ToStream(),
new MemoryStream(serverKeyBits, false)
)
).ToArray()
);
return(sessionSecret);
}
private static void ReadHeader(Stream input, out int ver, out TransferState state, out Guid txid, out Salt salt)
{
ver = PrimitiveSerializer.Int32.ReadFrom(input);
Check.Assert <InvalidDataException>(ver == VersionHeader);
int istate = PrimitiveSerializer.Int32.ReadFrom(input);
Check.Assert <InvalidDataException>(Enum.IsDefined(typeof(TransferState), istate));
state = (TransferState)istate;
byte[] bytes = new byte[16];
Check.Assert <InvalidDataException>(bytes.Length == input.Read(bytes, 0, bytes.Length));
txid = new Guid(bytes);
bytes = new byte[32];
Check.Assert <InvalidDataException>(bytes.Length == input.Read(bytes, 0, bytes.Length));
salt = Salt.FromBytes(bytes);
}