UDP Speedy Secure Shell (USSH)
draft-x1co-ussh-00

Independent Submission                                           X. x1co
Internet-Draft                                                 x1colegal
Intended status: Experimental                                7 June 2026
Expires: 9 December 2026

                     UDP Speedy Secure Shell (USSH)
                           draft-x1co-ussh-00

Abstract

   This document describes UDP Speedy Secure Shell (USSH), an
   experimental remote shell protocol built on top of USTPS.  USSH
   provides an interactive shell session over a secure UDP-based
   transport while preserving USTPS transport semantics.  USSH
   reconstructs application-level terminal streams where necessary,
   while relying on USTPS for secure unreliable-underneath, selective-
   recovery transport behavior.

Status of This Memo

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   This Internet-Draft will expire on 9 December 2026.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Relationship to USTPS . . . . . . . . . . . . . . . . . . . .   2
   4.  Message Identification  . . . . . . . . . . . . . . . . . . .   3
   5.  Protocol Model  . . . . . . . . . . . . . . . . . . . . . . .   3
   6.  Interactive Stream Handling . . . . . . . . . . . . . . . . .   3
   7.  Head-of-Line Considerations . . . . . . . . . . . . . . . . .   4
   8.  Security Model  . . . . . . . . . . . . . . . . . . . . . . .   4
   9.  Operational Status  . . . . . . . . . . . . . . . . . . . . .   4
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   11. Security Considerations . . . . . . . . . . . . . . . . . . .   4
   12. Normative References  . . . . . . . . . . . . . . . . . . . .   5
   13. Informative References  . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   USSH is an experimental secure shell protocol built directly on top
   of USTPS rather than on TCP.  Its goal is to provide interactive
   remote shell access while preserving the properties of the underlying
   USTPS transport, including packet-level authenticated encryption,
   per-client session keys, selective retransmission, and lack of
   transport-level Head-of-Line blocking.

   USSH is not intended to be wire-compatible with SSH.  It is a
   distinct protocol with its own packetization and control semantics.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Relationship to USTPS

   USSH uses USTPS as its secure transport substrate.  The outer secure
   envelope and inner transport packet format are provided by USTPS.
   USSH then defines its own application messages for shell
   authentication, PTY setup, standard input delivery, standard output
   delivery, resize events, and session termination.

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   USTPS remains unordered at the transport layer.  USSH therefore
   performs additional application-layer handling where terminal
   behavior requires ordered reconstruction of logical streams such as
   standard output.

4.  Message Identification

   USSH application messages begin with the magic value USS1, meaning
   "UDP Speedy Secure Shell, version 1" in the USSH application context.

   In deployed implementations, the USTPS secure envelope also uses the
   identifier USS1 at the encrypted outer framing layer.  The inner
   USTPS transport packet uses UST1.  Implementers should therefore
   distinguish between the secure envelope, the USTPS transport packet,
   and the USSH application payload when analyzing packet captures or
   decrypted data.

5.  Protocol Model

   A USSH client first establishes a USTPS session with the server.
   Once that secure transport session exists, the client performs USSH
   authentication and requests an interactive shell or PTY-backed
   session.  Current implementations support password-based entry and
   derive per-client session state over the already-established USTPS
   channel.

   USSH messages currently cover at least the following categories:

   *  Authentication and session setup

   *  Standard input delivery

   *  Standard output delivery

   *  Terminal resize events

   *  Keepalive and liveness signaling

   *  Session close and exit signaling

6.  Interactive Stream Handling

   Interactive shells are highly sensitive to stream corruption and
   terminal redraw behavior.  Although USTPS is unordered at the
   transport layer, a shell's logical input and output streams often
   require application-level ordering.  USSH therefore reconstructs
   ordered logical output where needed before presenting terminal bytes
   to the local client terminal.

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   This reconstruction is an application-layer behavior of USSH.  It
   does not convert USTPS itself into an ordered transport.

7.  Head-of-Line Considerations

   USSH inherits the lack of transport-level Head-of-Line blocking from
   USTPS.  However, because terminal streams and PTY behavior often
   require coherent ordered interpretation, USSH may temporarily delay
   terminal-visible output while reconstructing the correct logical
   order of shell output fragments.

   That delay occurs at the application layer and is distinct from
   transport-level Head-of-Line blocking.

8.  Security Model

   USSH relies on USTPS for mandatory AEAD and per-client key
   establishment.  Current public implementations additionally support
   persistent server host keys, TOFU-based server identity continuity,
   and application-level authentication before granting shell access.

   Implementations SHOULD carefully protect shell spawn logic, PTY
   handling, session teardown, and terminal state restoration.  Clients
   SHOULD restore local terminal settings even when the session closes
   unexpectedly.

9.  Operational Status

   USSH has been implemented and exercised as a Beta-grade experimental
   protocol.  Public development has focused on stability over the USTPS
   substrate, interactive shell usability, session liveness, and
   terminal negotiation.

10.  IANA Considerations

   This document has no IANA actions.

11.  Security Considerations

   Remote shell protocols expose high-impact capabilities.  In addition
   to the security requirements inherited from USTPS, USSH
   implementations MUST authenticate clients before granting shell
   access, MUST avoid leaking shell access to unauthenticated peers, and
   SHOULD defend against terminal-state corruption, stale-session reuse,
   and unauthorized session migration.

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   Applications and operators should understand that USSH is
   experimental and not interchangeable with SSH security review,
   ecosystem hardening, or deployment maturity.

12.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, May 2017,
              <https://www.rfc-editor.org/info/rfc8174>.

13.  Informative References

   [USTPS-DRAFT]
              x1co, X., "UDP Speedy Transmission Protocol Secure
              (USTPS)", Work in Progress, Internet-Draft, draft-x1co-
              ustps-00, June 2026,
              <https://example.invalid/draft-x1co-ustps-00>.

Author's Address

   x1co
   x1colegal
   Email: x1colegal@outlook.com.br

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