By Kurt Seifried [email protected]
Encrypting data files and email
Several encryption programs are also available to encrypt your data, some at
the file level (PGP, GnuPG, etc.) and some at the drive level (Cryptographic
File System for example). These systems are very appropriate for the storage of
secure data, and to some degree for the transmission of secure data. However
both ends will require the correct software, compatible versions, and an
exchange of public keys will somehow have to take place, which is unfortunately,
an onerous task for most people. In addition to this you have no easy way of
trusting someone's public key unless you receive it directly from them (such as
at a key signing party), or unless it is signed by someone else you trust (but
how do you get the trusted signer's key securely?). Systems for drive encryption
such as CFS (Cryptographic FileSystem) are typically easy to implement, and only
require the user to provide a password or key of some form to access their
files. There is a really good article on choosing key sizes at https://www.cryptosavvy.com/
which raises some issues you probably hadn't considered. I would recomend
reading it.
GnuPG (Gnu Privacy Guard)
GnuPG is covered in the filesystem section at Linux
File System and File Security
pgp4pine
pgp4pine is a PGP shell for pine that allows easy usage of PGP/GnuPG from
within pine. Signing / encrypting and so on is made easier. You can get it from:
https://pgp4pine.flatline.de/
Netscape Messenger
Netscape Messenger supports X.509 certificates, as do most Windows mailer
programs.
Sources of random data
In order for encryption to be effective, especially on a large scale such as
IPSec across many hosts, good sources of random, cryptographically secure data
are needed. In Linux we have /dev/random and /dev/urandom which are good but not
always great. Part of the equation is measuring 'random' events, manipulating
that data and then making it available (via (u)random). These random events
include: keyboard and mouse input, interrupts, drive reads, etc.
However, as many servers have no keyboard/mouse, and new "blackbox" products
often contain no harddrive, sources of random data become harder to find. Some
sources, like network activity, are not entirely appropriate because the attacks
may be able to measure it as well (granted this would be a very exotic attack,
but enough to worry people nonetheless). There are several sources of random
data that can be used (or at least they appear random), radioactive decay and
radio frequency manipulations are two popular ones. Unfortunately the idea of
sticking a radioactive device in a computer makes most people nervous. And using
manipulated radio frequencies is prone to error, and the possibility of outside
manipulation. For most of us, this isn't a real concern, however for IPSec
gateway servers handling many connections it can be a problem. One potential
solution is the PIII, which has a built in random number generator that measures
thermal variance in the CPU, I think as we progress, solutions like this will
become more common.
