Installing and Configuring OpenSSH

Matt Lesko

Thanks to the proliferation of packet sniffers and the escalating reasons for data security and integrity, it should no longer be acceptable to allow network logins to be sent in plain text. By discovering passwords sent over the wire or hijacking a connection via man-in-the-middle attacks, a malicious cracker could quickly commandeer your network for her own nefarious purposes. Luckily, a solution has been created, Secure Shell, which replaces plain-text communication protocols, such as telnet, rsh, and rlogin. Many other features are included besides encryption, such as X11 forwarding (which allows secure use of X applications across a network), port forwarding (allowing standard TCP ports to be securely accessed), strong authentication, authentication forwarding (allowing a single resource to hold authorization information), Kerberos and AFS ticket forwarding, and data compression.

Secure Shell, or SSH, was originally a free implementation written by Tatu Ylonen. After restrictive licenses were placed upon the code, Bjorn Gronvall decided to write a more open version of the software, called OSSH. This caught the attention of the developers of OpenBSD, already well known for their extensive attention to security. Within a few months, OpenSSH 1.2.2 had been released (and incorporated into OpenBSD 2.6). Many additions and improvements were made to the previous version, including: all patent-encumbered algorithms removed and replaced, support of ssh 1.5 protocol, support for Kerberos IV authentication, and far leaner, cleaner, more secure code. The license is extremely liberal, and may be used without charge for commercial and non-commercial applications alike.