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

Overview of Features

The major features and guarantees of the SSH protocol are:

• Privacy of your data, via strong encryption

• Integrity of communications, guaranteeing they haven’t been altered

• Authentication, i.e., proof of identity of senders and receivers

• Authorization, i.e., access control to accounts

• Forwarding or tunneling to encrypt other TCP/IP-based sessions

3.1.1 Privacy (Encryption)

Privacy means protecting data from disclosure. Typical computer networks don’t guarantee privacy ; anyone with access to the network hardware, or to hosts connected to the network, may be able to read (or sniff) all data passing over the network. Although modern switched networks have reduced this problem in local area networks, it is still a serious issue; passwords are easily stolen by such sniffing attacks.

SSH provides privacy by encrypting data that passes over the network. This end-to-end encryption is based on random keys that are securely negotiated for that session and then destroyed when the session is over. SSH supports a variety of encryption algorithms for session data, including such standard ciphers as AES, ARCFOUR, Blowfish, Twofish, IDEA, DES, and triple-DES (3DES).

3.1.2 Integrity

Integrity means assuring that data transmitted from one end of a network connection arrives unaltered on the other end. The underlying transport of SSH, TCP/IP, does have integrity checking to detect alteration due to network problems (electrical noise, lost packets due to excessive traffic, etc.). Nevertheless, ...