SSH1

SSH1, short for Secure Shell version 1, is the original version of the Secure Shell protocol designed to provide encrypted remote login and secure network services over insecure networks. It was developed in the mid-1990s by Tatu Ylönen and became widely used as a replacement for Telnet, rlogin, and other unencrypted protocols.

SSH1 offers confidentiality, authentication, and data integrity for remote sessions. It relies on public-key cryptography for host authentication and supports user authentication methods, including passwords and public-key credentials. The protocol negotiates a set of symmetric ciphers and message authentication codes to protect data in transit, with various implementations offering different algorithm options.

However, SSH1 contains design weaknesses in its authentication and integrity mechanisms. It is vulnerable to certain man-in-the-middle attacks and several flaws that hinder robust security in practice. Over time, cryptographers and practitioners determined that SSH1 could not meet modern security requirements, particularly regarding strong key exchange, forward secrecy, and strong integrity protection.

Because of these problems, SSH-2, a more secure and extensible revision of the protocol, was developed and widely adopted. By the early 2000s, SSH-2 largely supplanted SSH1, and major servers and clients discontinued SSH1 support. Today, SSH1 is considered obsolete and is generally disabled in contemporary systems, except in environments that require compatibility with legacy equipment.