Internet-Draft SSH3 February 2024
Michel & Bonaventure Expires 31 August 2024 [Page]
Security Dispatch
Intended Status:
F. Michel
O. Bonaventure
UCLouvain and WELRI

Secure shell over HTTP/3 connections


The secure shell (SSH) traditionally offers its secure services over an insecure network using the TCP transport protocol. This document defines mechanisms to run the SSH protocol over HTTP/3 using Extended CONNECT. Running SSH over HTTP/3 enables additional benefits such as the scalability offered by HTTP multiplexing, relying on TLS for secure channel establishment leveraging X.509 certificates, HTTP Authentication schemes for client and server authentication, UDP port forwarding and stronger resilience against packet injection attacks and middlebox interference.

About This Document

This note is to be removed before publishing as an RFC.

The latest revision of this draft can be found at Status information for this document may be found at

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Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on 31 August 2024.

Table of Contents

1. Introduction

The SSH protocol [SSH-ARCH] provides a secure way to access computers remotely over an untrusted network. SSH is currently the most popular way to access Unix hosts and network equipments remotely. Built atop the unencrypted TCP protocol [TCP], SSH proposes its own mechanisms to establish a secure channel [SSH-TRANSPORT] and perform user authentication [SSH-AUTH]. Once the secure session is established and the user is authenticated and authorized, SSH uses the Connection protocol to run and manage remote processes and functionalities executed on the remote host [SSH-CONNECT]. Among others, SSH provides different services such as remote program execution, shell access and TCP port forwarding. Figure 1 provides a graphical representation of the SSHv2 protocol stack.

     |                           SSHv2                            |
     | +---------------+   +---------------+   +----------------+ |
     | | SSH Transport |   |   SSH Auth.   |   | SSH Connection | |
     | |   (RFC4253)   |   |   (RFC4252)   |   |   (RFC4254)    | |
     | +---------------+   +---------------+   +----------------+ |
     |  secure channel            user            SSH services    |
     |   establishment       authentication                       |
                                   |  - reliable transport
               |                  TCP                   |
Figure 1: The SSHv2 architecture protocol stack.

This document defines mechanisms to run the SSH Connection protocol [SSH-CONNECT] over HTTP/3 and uses the name "SSH3" to refer to this solution. The secure channel establishment uses TLS included in QUIC [QUIC] [QUIC-TLS] while user authentication is performed using existing HTTP authentication schemes, focusing the design of SSH on the Connection protocol itself. Figure 2 provides a graphical representation of the architecture proposed in this document. One benefit of the approach is that the HTTP3 and QUIC layers can evolve independently of SSH. For instance, new encryption and MAC algorithms can be added to TLS and used in SSH3 without impacting the specification or adding new code points in SSH3 for these new algorithms.

                 |              SSH3               |
                 |   +-------------------------+   |
                 |   |     SSH Connection      |   |
                 |   |       (~RFC4254)        |   |
                 |   +-------------------------+   |
                 |          SSH services           |
                   | - user authentication   | - reliable transport
                   | - URL multiplexing      | - secure channel
                   v                         |    establishment
             +-----------------------+       | - streams multiplexing
             |        HTTP/3         |       |            & datagrams
             +-----------------------+       v
             |                 QUIC / TLS                   |

Figure 2: The proposed SSH3 architecture.

The mechanisms used for establishing an SSH3 conversation are similar to the WebTransport session establishment [WEBTRANSPORT-H3]. WebTransport is also a good transport layer candidate for SSH3. The current SSH3 prototype [SSH3-PROTOTYPE] is built directly over HTTP/3 since there is no public WebTransport implementation meeting all our requirements as of now. The semantics of HTTP/2 being comparable to HTTP/3, the mechanisms defined in this document could be implemented using HTTP/2 if a fallback to TCP is required. There is an ongoing effort to be able to run HTTP/3 over QUIC on TCP Streams [QUIC-ON-STREAMS]. This document is a first introductory document. We limit its current scope to HTTP/3 using the classical QUIC.

1.1. How SSH benefits from HTTP/3

Using HTTP/3 and QUIC as a substrate for SSH brings several different benefits that are highlighted in this section.

1.1.1. QUIC: datagrams support, streams multiplexing and connection migration

Using QUIC, SSH3 can send data through both reliable streams and unreliable datagrams. This makes SSH3 able to support port forwarding for both UDP [UDP] and TCP-based protocols. Being based exclusively on TCP, SSHv2 does not offer UDP port forwarding and therefore provides no support to UDP-based protocols such as RTP or QUIC. This lack of UDP support in SSHv2 may become problematic as the use of QUIC-based applications (HTTP/3, MOQT [MOQT], DOQ [DOQ]) grows. Support for UDP port forwarding with SSH3 also allows accessing real-time media content such as low-latency live video available on the server. The stream multiplexing capabilities of QUIC allow reducing the head-of-line blocking that SSHv2 encounters when multiplexing several SSH channels over the same TCP connection.

QUIC also supports connection migration (Section 9 of [QUIC]). Using connection migration, a mobile host roaming between networks can maintain established connections alive across different networks by migrating them on their newly acquired IP address. This avoids disrupting the SSH conversation upon network changes. Finally, QUIC also offers a significantly reduced connection establishment time compared to the SSHv2 session establishment.

1.1.2. Protecting transport-layer control fields

Since QUIC integrates authentication and encryption as part of its transport features, it makes SSH3 robust to transport-layer attacks that were possible with TCP, such as packet injections or reset attacks [RFC5961]. For instance, the recent Terrapin attack [TERRAPIN] manipulates the TCP sequence number to alter the SSH extension negotiation mechanism [RFC8308] and downgrade the client authentication algorithms. QUIC control information such as packet numbers and frame formats are all authenticated and encrypted starting from the Handshake encryption level. Furthermore, QUIC prevents middlebox interference.

1.1.3. Leveraging the X.509 ecosystem

By using TLS for their secure channel establishment, HTTPS and QUIC leverage the X.509 certificates ecosystem with low implementation effort. TLS and QUIC libraries already implement support for generating, parsing and verifying X.509 certificates. Similarly to classical OpenSSH certificates, this avoids encouraging SSH users to rely on the Trust On First Use pattern when connecting to their remote hosts. Relying on the X.509 certificates ecosystem additionally enables SSH3 servers to use ACME [ACME] to automatically (with no additional user action) generate X.509 certificates for their domain names using well-known certificate authorities such as Let's Encrypt. These certificates are publicly valid and can be verified like classical HTTPS certificates. Client certificates can also be issued and used as an authentication method for the client.

1.1.4. HTTP authentication: compatibility with existing authentication systems

Using HTTP authentication schemes for user authentication allows implementing diverse authentication mechanisms such as the classical password-based and public key authentication, but also popular web authentication mechanisms such as OpenID Connect [OpenID.Core], SAML2 [OASIS.saml-core-2.0-os] or the recent Passkeys/WebAuthn standard [WebAuthn]. All these authentication schemes are already deployed for managing access to critical resources in different organizations. Sharing computing resources using SSHv2 through these mechanisms generally requires the deployment of a middleware managing the mapping between identities and SSH keys or certificates. Adding HTTP authentication to SSH allows welcoming these authentication methods directly and interfaces SSH3 more naturally with existing architectures. As a proof-of-concept, OpenID Connect support has been added to our SSH3 prototype [SSH3-PROTOTYPE]. Other web authentication standards such as Passkeys/WebAuthn [WebAuthn] allow administrators to restrict remote access to specific client devices in addition to users.

1.1.5. URL multiplexing and undiscoverability

Relying on HTTP allows easily placing SSH endpoints as resources accessible through specific URLs. First, this makes it easier to integrate SSH endpoints on web servers that already perform user authentication and authorization. Second, it allows placing several SSH server instances on the same physical machine on the same port. These instances can run in different virtual machines, containers or simply different users with user's priviledges and be multiplexed on a URL-basis. Finally, SSH3 endpoints can be placed behind secret URLs, reducing the exposure of SSH3 hosts to scanning and brute force attacks. This goes in line with the will of having undiscoverable resources also tackled by other IETF working groups [HTTP-SIGNATURE]. This property is not provided by SSHv2 since the SSHv2 server announces its SSH version string to any connected TCP client. If wanted, SSH3 hosts can be made indistinguishable from any HTTP server. This is however only complementary to and MUST NOT replace user authentication.

2. Conventions and Definitions

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. Establishing an SSH3 conversation

We choose the term "conversation" to avoid ambiguities with the existing concepts of SSH shell session and QUIC connection. An SSH3 conversation can be started using the HTTP/3 Extended CONNECT method [EXTENDED-CONNECT]. The :protocol pseudo-header MUST be set to ssh3 and the :scheme pseudo-header MUST be set to https. If an SSH3 client or server supports the UDP forwarding feature, it MUST indicate support for HTTP/3 datagrams by sending a SETTINGS_H3_DATAGRAM value set to 1 in their SETTINGS frame (Section 2.1.1 of [HTTP-DATAGRAM]).

An SSH3 server listens for CONNECT requests with the ssh3 protocol on URI templates having the username variable. Example URIs can be found below.{username}{?username}

[[Note: In the current prototype [SSH3-PROTOTYPE], percent-encoding is used for characters outside the allowed set of [URI]. An alternative can be to perform base64url encoding of the username instead.]]

Figure 3 illustrates a successful SSH3 conversation establishment.

          |                QUIC HANDSHAKE                 |
          |                                               |
          | HTTP/3, Stream x CONNECT /<path>?user=<user>  |
          |         :protocol="ssh3"                      |
          |         Authorization=<auth_material>         |
          |                                               |
          |               HTTP/3, Stream x 200 OK         |
          |                                               |
          |           Conversation established            |
          |                                               |
          |    (endpoints now run the SSH Connection)     |
          |    (protocol over QUIC streams          )     |
          |                                               |
Figure 3: SSH3 successful conversation establishment.

Authentication material is placed inside the Authorization header of the Extended CONNECT request. The format and value of <auth_material> depends on the HTTP authentication scheme used (Section 3.1 explores several examples of authentication mechanisms). If an SSH3 endpoint is available to the HTTP/3 server and if the user is successfully authenticated and authorized, the server responds with a 2xx HTTP status code and the conversation is established.

The stream ID used for the Extended CONNECT request is then remembered by each endpoint as the SSH conversation ID, uniquely identifying this SSH conversation.

3.1. Authenticating the client

Authorization of the CONNECT request is done using HTTP Authorization as defined in [HTTP-SEMANTICS], with no restriction on the authentication scheme used. If no Authorization header is present in the request or if the authentication scheme is not supported by the server, the server SHOULD respond with a 401 (Unauthorized) response message. Once the user authentication is successful, the SSH3 server can process the request and start the conversation. This section only provides example user authentication mechanisms. Other mechanisms may be proposed in the future in separate documents. The two first examples are implemented by our current prototype [SSH3-PROTOTYPE]. The third example leverages the Signature authentication scheme [HTTP-SIGNATURE] and will be preferred for public key authentication in future versions of our prototype.

3.1.1. Password authentication using HTTP Basic Authentication

Password-based authentication is performed using the HTTP Basic authentication scheme [HTTP-BASIC]. The user-id part of the <credentials> in the Authorization header defined in [HTTP-BASIC] MUST be equal to the username variable in the request URI defined in Section 3.

     |                QUIC HANDSHAKE                 |
     |                                               |
     | HTTP/3, Stream x CONNECT /<path>?user=<user>  |
     |         :protocol="ssh3"                      |
     |         Authorization="Basic <credentials>"   |
     |                                               |
     |               HTTP/3, Stream x 200 OK         |
     |                                               |
     |           Conversation established            |
     |                                               |

3.1.2. Public key authentication using OAUTH2 and JWTs

Classical public key authentication can be performed using the OAUTH2 framework [OAUTH2]: the HTTP Bearer authentication scheme is used to carry an OAUTH access token encoded in the JWT [JWT] format [OAUTH2-JWT].

     |                QUIC HANDSHAKE                 |
     |                                               |
     | HTTP/3, Stream x CONNECT /<path>?user=<user>  |
     |         :protocol="ssh3"                      |
     |         Authorization="Bearer <JWT token>"    |
     |                                               |
     |               HTTP/3, Stream x 200 OK         |
     |                                               |
     |           Conversation established            |
     |                                               |

For classical client-server public key authentication with no third-party involved, only the following claims are required (see [JWT] for their definition):

  • sub: set to ssh3-<user>

  • iat: set to the date of issuance of the JWT

  • exp: set to a short expiration value to limit the token replay window

The jti claim may also be used to prevent the token from being replayed.

3.1.3. Public key authentication using HTTP Signature authentication

Public key authentication can also be performed using the HTTP Signature Authentication scheme [HTTP-SIGNATURE]. The <k> parameter designates the key ID of the public key used by the authentication process. Classical SSH implementations usually do not assign IDs to public keys. The value <k> can therefore be set to the cryptographic hash of the public key instead.

     |                QUIC HANDSHAKE                 |
     |                                               |
     | HTTP/3, Stream x CONNECT /<path>?user=<user>  |
     |    :protocol="ssh3"                           |
     |    Signature k=<k>, a=<a>,s=<s>,v=<v>,p=<p>   |
     |                                               |
     |               HTTP/3, Stream x 200 OK         |
     |                                               |
     |           Conversation established            |
     |                                               |

4. Mapping the SSH Connection protocol

This document reuses the SSH Connection protocol defined in [SSH-CONNECT]. SSH Channels are run over their dedicated HTTP streams and carry SSH messages. The boolean and string data types defined in [SSH-ARCH] are reused. The byte, uint32 and uint64 data types are replaced by variable-length integers as defined in Section 16 of [QUIC].

4.1. Channels

Similarly to [SSH-TRANSPORT], SSH3 defines bidirectional channels over which the endpoints exchange SSH messages. Each channel runs over a bidirectional HTTP/3 stream and is attached to a single SSH conversation. In this document, channels are therefore not assigned a channel number conversely to SSHv2.

4.1.1. Opening a channel

SSH channels can be opened on HTTP/3 client-initiated bidirectional streams. By default, HTTP/3 considers every client-initiated bidirectional stream as a request stream. Similarly to WebTransport, SSH3 extends HTTP/3 using a specific signal value. An SSH3 client can open a stream with this signal value to indicate that it is not a request stream and that the remaining stream bytes will be used arbitrarily by the SSH3 protocol to carry the content of a channel. For experimental purpose, the signal value is chosen at random and will change over time. The current signal value is 0xaf3627e6. The content of an HTTP/3 stream carrying an SSH3 channel is illustrated below.

Channel {
    Signal Value (i) = 0xaf3627e6,
    Conversation ID (i),
    Channel Type Length (i)
    Channel Type (..)
    Maximum Message Size (i)
    SSH messages (..)

The first value sent on the HTTP/3 stream is the Signal Value. The Channel Type is a UTF-8-encoded string whose length is defined by the Channel Type Length field.

[[Note: SSHv2 uses text-based channel types. Should we keep that or use something else instead ? If we change, we loose a 1-1 mapping with SSHv2.]]

The Maximum Message Size field defines the maximum size in bytes of SSH messages.

The remaining bytes of the stream are interpreted as a sequence of SSH messages. Their format and length can vary depending on the message type (see Section 4.1.4).

4.1.2. Channel types

This document defines the following channel types, the four first being also defined in [SSH-CONNECT]:

  • session

  • x11

  • direct-tcp

  • reverse-tcp

  • direct-udp

  • reverse-udp

The direct-tcp and direct-udp channels offer TCP and UDP port forwarding from a local port on the client towards a remote address accessible from the remote host. The reverse-tcp and reverse-udp channels offer the forwarding of UDP packets and TCP connections arriving on a specific port on the remote host to the client.

4.1.3. Port forwarding

The HTTP bidirectional stream attached to the direct-tcp or reverse-tcp channel directly carries the TCP payload to forward.

For UDP forwarding, UDP packets are carried through HTTP Datagrams (Section 2 of [HTTP-DATAGRAM]) whose Quarter Stream IDs refer directly to the HTTP Stream ID of the corresponding direct-udp or reverse-udp channel.

Forwarding of other layers (e.g. IP) is left for future versions of the document.

4.1.4. Messages

Messages are exchanged over channels similarly to SSHv2. The same message format as the one defined in [SSH-CONNECT] applies, with channel numbers removed from the messages headers as channel run over dedicated HTTP streams. Hereunder is an example showing the wire format of the exit-status SSH message for SSH3. Its SSHv2 variant is described in Section 6.10 of [SSH-CONNECT].

ExitStatusMessage {
    Message Type (string) = "exit-status",
    Want Reply (bool) = false,
    Exit Status (i)

5. SSH3 and MASQUE

SSH3 shares common objectives with the MASQUE proxy [MASQUE] and while it is currently out of scope of this introductory document, interactions between the two protocols may exist in the future. For instance, a MASQUE endpoint can be integrated with SSH3 to provide diverse forwarding services. Another possible outcome is the integration of SSH3 in the MASQUE family of proxies in the form of a "CONNECT-SHELL" endpoint.

6. Version Negotiation

For SSH3 implementations to be able to follow the versions of this draft while being interoperable with a large amount of peers, we define the "ssh-version" header to list the supported draft versions. The value of this field sent by the client is a comma-separated list of strings representing the filenames of the supported drafts without the "draft-" prefix. For instance, SSH3 clients implementing this draft in versions 00 and 01 send the "ssh-version: michel-ssh3-00,michel-ssh3-01" HTTP header in the CONNECT request. Upon receiving this header, the server chooses a version from the ones supported by the client. It then sets this single version as the value of the "ssh-version" header.

7. Compatibility with SSHv2 and TCP-only networks

While the protocol described in this document is not directly compatible with SSHv2, mechanisms can be defined in the future to announce the availability of SSH3 and upgrade to SSH3 from SSHv2 sessions. SSH3 can also be made available on networks supporting only TCP using either HTTP/2 [HTTP2] or HTTP/3 [HTTP3] with QUIC on Streams [QUIC-ON-STREAMS] as a substrate for SSH3.

8. Security Considerations

Running an SSH3 endpoint with weak or no authentication methods exposes the host to non-negligible risks allowing attackers to gain full control of the server. SSH3 servers should not be run without authentication and user authentication material should be verified thoroughly. Public key authentication should be preferred to passwords.

It is recommended to deploy public TLS certificates on SSH3 servers similarly to classical HTTPS servers. Using valid public TLS certificates on the server allows their automatic verification on the client with no explicit user action required. Connecting an SSH3 client to a server with a certificate that cannot be validated using the client's trusted Certificate Authorities exposes the user to the same risk incurred by SSHv2 endpoints relying on Host keys: the user needs to manually validate the certificate before connecting. Ignoring this verification may allow an attacker to impersonate the server and access the keystrokes typed by the user during the conversation.

9. IANA Considerations

9.1. HTTP Upgrade Token

This document will request IANA to register "ssh3" in the "HTTP Upgrade Tokens" registry maintained at

[[Note: This may be removed if we decide to run SSH3 atop WebTransport instead of HTTP/3 only.]]

10. References

10.1. Normative References

Huitema, C., Dickinson, S., and A. Mankin, "DNS over Dedicated QUIC Connections", RFC 9250, DOI 10.17487/RFC9250, , <>.
McManus, P., "Bootstrapping WebSockets with HTTP/2", RFC 8441, DOI 10.17487/RFC8441, , <>.
Reschke, J., "The 'Basic' HTTP Authentication Scheme", RFC 7617, DOI 10.17487/RFC7617, , <>.
Schinazi, D. and L. Pardue, "HTTP Datagrams and the Capsule Protocol", RFC 9297, DOI 10.17487/RFC9297, , <>.
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, , <>.
Schinazi, D., Oliver, D., and J. Hoyland, "The Signature HTTP Authentication Scheme", Work in Progress, Internet-Draft, draft-ietf-httpbis-unprompted-auth-06, , <>.
Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113, DOI 10.17487/RFC9113, , <>.
Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114, , <>.
Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, , <>.
Bertocci, V., "JSON Web Token (JWT) Profile for OAuth 2.0 Access Tokens", RFC 9068, DOI 10.17487/RFC9068, , <>.
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, , <>.
Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection and Congestion Control", RFC 9002, DOI 10.17487/RFC9002, , <>.
Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure QUIC", RFC 9001, DOI 10.17487/RFC9001, , <>.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, , <>.
Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252, , <>.
Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Connection Protocol", RFC 4254, DOI 10.17487/RFC4254, , <>.
Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253, , <>.
Eddy, W., Ed., "Transmission Control Protocol (TCP)", STD 7, RFC 9293, DOI 10.17487/RFC9293, , <>.
Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI 10.17487/RFC0768, , <>.
Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, , <>.
Frindell, A., Kinnear, E., and V. Vasiliev, "WebTransport over HTTP/3", Work in Progress, Internet-Draft, draft-ietf-webtrans-http3-08, , <>.

10.2. Informative References

Barnes, R., Hoffman-Andrews, J., McCarney, D., and J. Kasten, "Automatic Certificate Management Environment (ACME)", RFC 8555, DOI 10.17487/RFC8555, , <>.
Schinazi, D., "The MASQUE Proxy", Work in Progress, Internet-Draft, draft-schinazi-masque-proxy-01, , <>.
Curley, L., Pugin, K., Nandakumar, S., Vasiliev, V., and I. Swett, "Media over QUIC Transport", Work in Progress, Internet-Draft, draft-ietf-moq-transport-02, , <>.
Cantor, S., Kemp, J., Philpott, R., and E. Maler, "Assertions and Protocols for the OASIS Security Assertion Markup Language (SAML) V2.0", Web, n.d..
Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, , <>.
Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and C. Mortimore, "OpenID Connect Core 1.0", Web, n.d..
"OpenSSH release 5.4", Web
"PuTTY Certificates", Web
Oku, K. and L. Pardue, "QUIC on Streams", Work in Progress, Internet-Draft, draft-kazuho-quic-quic-on-streams-00, , <>.
Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's Robustness to Blind In-Window Attacks", RFC 5961, DOI 10.17487/RFC5961, , <>.
Bider, D., "Extension Negotiation in the Secure Shell (SSH) Protocol", RFC 8308, DOI 10.17487/RFC8308, , <>.
Michel, F., "SSH3: faster and rich secure shell using HTTP/3", Web, n.d..
"Tectia Certificates", Web
Bäumer, F., Brinkmann, M., and J. Schwenk, "Terrapin Attack: Breaking SSH Channel Integrity By Sequence Number Manipulation", DOI 10.48550/arXiv.2312.12422, , <>.
"Web Authentication: An API for accessing Public Key Credentials Level 3", Web, n.d..


We warmly thank Maxime Piraux, Lucas Pardue and David Schinazi for their precious comments on the document before the submission. We also thank Ryan Hurst for all the motivating discussions around the protocol.

Authors' Addresses

François Michel
Olivier Bonaventure
UCLouvain and WELRI