RFC 4251

The Secure Shell (SSH) Protocol Architecture, January 2006

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Updated by:
RFC 8308, RFC 9141
T. Ylonen
C. Lonvick, Ed.
secsh (sec)

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DOI:  https://doi.org/10.17487/RFC4251

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The Secure Shell (SSH) Protocol is a protocol for secure remote login and other secure network services over an insecure network. This document describes the architecture of the SSH protocol, as well as the notation and terminology used in SSH protocol documents. It also discusses the SSH algorithm naming system that allows local extensions. The SSH protocol consists of three major components: The Transport Layer Protocol provides server authentication, confidentiality, and integrity with perfect forward secrecy. The User Authentication Protocol authenticates the client to the server. The Connection Protocol multiplexes the encrypted tunnel into several logical channels. Details of these protocols are described in separate documents. [STANDARDS-TRACK]

For the definition of Status, see RFC 2026.

For the definition of Stream, see RFC 8729.

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