The Secure Shell (SSH) Transport Layer Protocol
RFC 4253
Document | Type | RFC - Proposed Standard (January 2006; Errata) | |
---|---|---|---|
Authors | Chris Lonvick , Tatu Ylonen | ||
Last updated | 2020-01-21 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized with errata bibtex | ||
Stream | WG state | WG Document | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 4253 (Proposed Standard) | |
Action Holders |
(None)
|
||
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Russ Housley | ||
Send notices to | (None) |
Network Working Group T. Ylonen Request for Comments: 4253 SSH Communications Security Corp Category: Standards Track C. Lonvick, Ed. Cisco Systems, Inc. January 2006 The Secure Shell (SSH) Transport Layer Protocol Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2006). Abstract The Secure Shell (SSH) is a protocol for secure remote login and other secure network services over an insecure network. This document describes the SSH transport layer protocol, which typically runs on top of TCP/IP. The protocol can be used as a basis for a number of secure network services. It provides strong encryption, server authentication, and integrity protection. It may also provide compression. Key exchange method, public key algorithm, symmetric encryption algorithm, message authentication algorithm, and hash algorithm are all negotiated. This document also describes the Diffie-Hellman key exchange method and the minimal set of algorithms that are needed to implement the SSH transport layer protocol. Ylonen & Lonvick Standards Track [Page 1] RFC 4253 SSH Transport Layer Protocol January 2006 Table of Contents 1. Introduction ....................................................3 2. Contributors ....................................................3 3. Conventions Used in This Document ...............................3 4. Connection Setup ................................................4 4.1. Use over TCP/IP ............................................4 4.2. Protocol Version Exchange ..................................4 5. Compatibility With Old SSH Versions .............................5 5.1. Old Client, New Server .....................................6 5.2. New Client, Old Server .....................................6 5.3. Packet Size and Overhead ...................................6 6. Binary Packet Protocol ..........................................7 6.1. Maximum Packet Length ......................................8 6.2. Compression ................................................8 6.3. Encryption .................................................9 6.4. Data Integrity ............................................12 6.5. Key Exchange Methods ......................................13 6.6. Public Key Algorithms .....................................13 7. Key Exchange ...................................................15 7.1. Algorithm Negotiation .....................................17 7.2. Output from Key Exchange ..................................20 7.3. Taking Keys Into Use ......................................21 8. Diffie-Hellman Key Exchange ....................................21 8.1. diffie-hellman-group1-sha1 ................................23 8.2. diffie-hellman-group14-sha1 ...............................23 9. Key Re-Exchange ................................................23 10. Service Request ...............................................24 11. Additional Messages ...........................................25 11.1. Disconnection Message ....................................25 11.2. Ignored Data Message .....................................26 11.3. Debug Message ............................................26 11.4. Reserved Messages ........................................27 12. Summary of Message Numbers ....................................27 13. IANA Considerations ...........................................27 14. Security Considerations .......................................28 15. References ....................................................29 15.1. Normative References .....................................29 15.2. Informative References ...................................30 Authors' Addresses ................................................31 Trademark Notice ..................................................31 Ylonen & Lonvick Standards Track [Page 2] RFC 4253 SSH Transport Layer Protocol January 2006 1. Introduction The SSH transport layer is a secure, low level transport protocol. It provides strong encryption, cryptographic host authentication, and integrity protection.Show full document text