Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 683 — #709
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26
Security in the Network
In the seventies, it was argued that this method would be more secure than
others due to the relative slowness of the algorithm used, which took a
few seconds to encrypt just one password. In the meantime, however, PCs
have become powerful enough to do several hundred thousand or even
millions of encryptions per second. Because of this, encrypted passwords
should not be visible to regular users (/etc/shadow cannot be read by
normal users). It is even more important that passwords are not easy to
guess, in case the password file becomes visible due to some error. Conse-
quently, it is not really useful to “translate” a password like “tantalise” into
“t@nt@1ls3”.
Replacing some letters of a word with similar looking numbers is not safe
enough. Password cracking programs that use dictionaries to guess words
also play with substitutions like that. A better way is to make up a word
with no common meaning, something that only makes sense to you per-
sonally, like the first letters of the words of a sentence or the title of a book,
such as “The Name of the Rose” by Umberto Eco. This would give the fol-
lowing safe password: “TNotRbUE9”. In contrast, passwords like “beer-
buddy” or “jasmine76” are easily guessed even by someone who has only
some casual knowledge about you.
The Boot Procedure
Configure your system so it cannot be booted from a floppy or from CD,
either by removing the drives entirely or by setting a BIOS password and
configuring the BIOS to allow booting from a hard disk only. Normally, a
Linux system is started by a boot loader, allowing you to pass additional
options to the booted kernel. Prevent others from using such parameters
during boot by setting an additional password in /boot/grub/menu.lst
(see Chapter 8 on page 203). This is crucial to your system’s security. Not
only does the kernel itself run with root permissions, but it is also the first
authority to grant root permissions at system start-up.
File Permissions
As a general rule, always work with the most restrictive privileges possi-
ble for a given task. For example, it is definitely not necessary to be root
to read or write e-mail. If the mail program has a bug, this bug could be ex-
ploited for an attack that acts with exactly the permissions of the program
when it was started. By following the above rule, minimize the possible
damage.
683SUSE LINUX Enterprise Server