Extension Negotiation in the Secure Shell (SSH) Protocol
RFC 8308
Document | Type | RFC - Proposed Standard (March 2018; No errata) | |
---|---|---|---|
Author | denis bider | ||
Last updated | 2018-03-19 | ||
Replaces | draft-ssh-ext-info | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Reviews | |||
Stream | WG state | Submitted to IESG for Publication | |
Document shepherd | Daniel Migault | ||
Shepherd write-up | Show (last changed 2017-06-01) | ||
IESG | IESG state | RFC 8308 (Proposed Standard) | |
Action Holders |
(None)
|
||
Consensus Boilerplate | Yes | ||
Telechat date | |||
Responsible AD | Eric Rescorla | ||
Send notices to | Daniel Migault <daniel.migault@ericsson.com> | ||
IANA | IANA review state | Version Changed - Review Needed | |
IANA action state | RFC-Ed-Ack |
Internet Engineering Task Force (IETF) D. Bider Request for Comments: 8308 Bitvise Limited Updates: 4251, 4252, 4253, 4254 March 2018 Category: Standards Track ISSN: 2070-1721 Extension Negotiation in the Secure Shell (SSH) Protocol Abstract This memo updates RFCs 4251, 4252, 4253, and 4254 by defining a mechanism for Secure Shell (SSH) clients and servers to exchange information about supported protocol extensions confidentially after SSH key exchange. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8308. Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Bider Standards Track [Page 1] RFC 8308 Extension Negotiation in SSH March 2018 Table of Contents 1. Overview and Rationale ..........................................3 1.1. Requirements Terminology ...................................3 1.2. Wire Encoding Terminology ..................................3 2. Extension Negotiation Mechanism .................................3 2.1. Signaling of Extension Negotiation in SSH_MSG_KEXINIT ......3 2.2. Enabling Criteria ..........................................4 2.3. SSH_MSG_EXT_INFO Message ...................................4 2.4. Message Order ..............................................5 2.5. Interpretation of Extension Names and Values ...............6 3. Initially Defined Extensions ....................................6 3.1. "server-sig-algs" ..........................................6 3.2. "delay-compression" ........................................7 3.2.1. Awkwardly Timed Key Re-Exchange .....................9 3.2.2. Subsequent Re-Exchange ..............................9 3.2.3. Compatibility Note: OpenSSH up to Version 7.5 .......9 3.3. "no-flow-control" .........................................10 3.3.1. Prior "No Flow Control" Practice ...................10 3.4. "elevation" ...............................................11 4. IANA Considerations ............................................12 4.1. Additions to Existing Registries ..........................12 4.2. New Registry: Extension Names .............................12 4.2.1. Future Assignments to Extension Names Registry .....12 5. Security Considerations ........................................12 6. References .....................................................13 6.1. Normative References ......................................13 6.2. Informative References ....................................13 Acknowledgments ...................................................14 Author's Address ..................................................14 Bider Standards Track [Page 2] RFC 8308 Extension Negotiation in SSH March 2018 1. Overview and Rationale Secure Shell (SSH) is a common protocol for secure communication on the Internet. The original design of the SSH transport layer [RFC4253] lacks proper extension negotiation. Meanwhile, diverse implementations take steps to ensure that known message types contain no unrecognized information. This makes it difficult for implementations to signal capabilities and negotiate extensions without risking disconnection. This obstacle has been recognized in the process of updating SSH to support RSA signatures using SHA-256 and SHA-512 [RFC8332]. To avoid trial and error as well as authentication penalties, a client must be able to discover public key algorithms a server accepts. This extension mechanism permitsShow full document text