SSH, The Secure Shell: The Definitive Guide, 2nd Edition

The SSH Protocol

SSH is a protocol, not a product. It is a specification of how to conduct secure communication over a network.^[3]

The SSH protocol covers authentication, encryption, and the integrity of data transmitted over a network, as shown in Figure 1-2. Let’s define these terms:

Authentication

Reliably determines someone’s identity. If you try to log into an account on a remote computer, SSH asks for digital proof of your identity. If you pass the test, you may log in; otherwise, SSH rejects the connection.

Encryption

Scrambles data so that it is unintelligible except to the intended recipients. This protects your data as it passes over the network.

Integrity

Guarantees the data traveling over the network arrives unaltered. If a third party captures and modifies your data in transit, SSH detects this fact.

Figure 1-2. Authentication, encryption, and integrity

In short, SSH makes network connections between computers, with strong guarantees that the parties on both ends of the connection are genuine. It also ensures that any data passing over these connections arrives unmodified and unread by eavesdroppers.

1.3.1 Protocols, Products, Clients, and Confusion

The first SSH product, created by Tatu Ylönen for Unix, was simply called “SSH.” This caused confusion because SSH was also the name of the protocol. In this book, we use more precise terminology to refer to protocols, products, and ...