In computer networking, TCP Stealth is a proposed modification of the Transmission Control Protocol (TCP) to hide open ports of some TCP services from the public, in order to impede port scans.
[3] The proposal modifies the TCP three-way handshake by only accepting connections from clients that transmit a proof of knowledge of a shared secret.
If the connection attempt does not use TCP Stealth, or if authentication fails, the server acts as if no service was listening on the port number.
[4] The project and initial Internet Draft specification was announced on 15 August 2014,[3] following the revelations about the GCHQ project HACIENDA, which uses port scanning to find vulnerable systems for Five Eyes intelligence agencies.
[1][5] The draft was written by researchers from the Technische Universität München, Jacob Appelbaum of the Tor Project and Holger Kenn from Microsoft.