Stored Data Cryptographic Applications
An Article for Cybertek Electric, by Kathleen Ellis

The current debate surrounding the issue of cryptography is by far the
most heated in its history.  While agencies of law enforcement, federal
bureaucrats, and many politicians contend that criminals could use
powerful encryption technology to conceal their actions and evade law
enforcement, most in the private sector recognize the importance of
keeping one's private affairs concealed or unreadable to prying eyes,
particularly in the networked environment.  The Attorney General, the FBI,
and the NSA have deliberately done everything possible to thwart the
widespread implementation of crypto technology; doing everything from
disseminating misleading information about cryptography to harassing
anyone who gets too good at opposing them.  At the same time, a grassroots
campaign comprised mostly of cryptographers, network professionals, and
civil libertarians are doing everything they can to make encryption
technology ubiquitous.  They are devoted to creating more user-friendly
applications available for a wider range of platforms and to educating the
public about these opportunities.  This article was written to serve the
latter purpose; within it I will discuss some of the current technology 
available regarding the encryption of data files. 

 The Old Standby

Pretty Good Privacy, written by Phil Zimmerman, really deserves its own
article, and for the purpose of this article I will have to assume at
least a general familiarity with its background.  From a certain
perspective, Pretty Good Privacy (PGP) may be the best way for the
beginner to go about encrypting specific files, for several reasons.  From
a crypto advocate's point of view, it's best to get any beginner familiar
with PGP from the start, since it has become a de facto standard in
encryption.  In addition, PGP is probably the most well-tested and
carefully scrutinized encryption program available today. The source code
is freely available for review by anyone both online and in hardcopy from
most bookstores. PGP is best known for its use in encrypting
communications channels, using a cryptosystem known as public-key
cryptography, but it also works well as a means to encrypt files using a
symmetric-key algorithms.  Older versions are equipped with IDEA; 5.0
allows a choice between IDEA (the author's favorite, for a variety of
reasons), Triple-DES, and CAST.  A few things to keep in mind when using
PGP for conventional encryption:

1.  Be sure you are using a version obtained directly from an official
distribution site (the international site can be found at
http://www.ifi.uio.no/~staalesc/PGP/). If you aren't able to look at the
source yourself in order to detect any possible trapdoors or trojan
horses, it's the best way to ensure that you're getting an untampered
product.  This applies to all software you may use which is downloaded
from a network, but is of particular importance when dealing with security
and encryption tools.  Keep in mind that if you are outside the US and
Canada, you will have to obtain PGP from a non-American site, or else you
or the administrator of the site could be in violation of US law.

2.  When you use PGP to encrypt a file using one of the symmetric-key
algorithms, the program asks for a pass phrase to use to encrypt the file.
Do not use the same pass phrase you use for your secret key for
communications, or for anything else, for that matter.  It is extremely
important to choose your pass phrases wisely.  All the algorithms that
come with the PGP 5.0 package are as any that exist today; any
cryptanalytic attack will likely be on the user's pass phrase, rather than
the algorithm itself.

PGP is a wonderful tool to use when you need to encrypt only a few files,
but when you have more than just a few that need to be secured, keeping
all those passphrases in mind can be tedious.  PGP is secure and as easy
to use as anything for file encryption, but as a program it was clearly
designed as a communications tool.  With this in mind, several file
systems have been developed which use cryptography to encipher the files
contained within.  All PGP versions (including the new one, as long as you
are upgrading from a previous version) are freeware, and are capable of
running on a variety of operating systems and have trivial hardware
requirements.

  Secure File System (SFS)

Although SFS has been developed only for DOS and Windows 3.1 (16- and
32-bits), it works surprisingly well with a variety of low-tech hardware
and is compatible with a wide range of software utilities within the
DOS/Windows element. SFS was clearly designed with compatiblilty in mind;
it is perfect for the old 27 Mb DOS box sitting in the corner of your
bedroom as well as for the 2 gigabyte DOS partition of your pentium 200.
It is documented to encrypt up to 160 KB/s on a 386/40 and requires only
7.5 KB of memory.  SFS will work for hard drives and floppies
of any size, and is directly compatible with most popular DOS disk
utilities (and a few obscure ones).  Furthermore, it works directly with
IDE and EIDE drives, as well as almost all known SCSI host adaptors.

For the encryption of data, SFS uses the encryption code in cryptlib, a
programming interface designed to facilitate the production of
cryptographic applications by doing most of the gruntwork for the
developer. Cryptlib includes DES, triple DES, IDEA, Blowfish, and others,
and is distributed from New Zealand so that domestic restrictions on don't
apply.

SFS works by encrypting data in volumes, which are interpreted as normal
drives.  The user can access up to five of these volumes at once.  Some of
the finer features of SFS include a user-defined hotkey feature which
allows the user to unmount the volume instantly, and a file wiping feature
which allows the user to destroy the contents of the volume without the
possiblity of retrieval.


  Crypto File System (CFS)

Crypto File System is a program similar to SFS, designed for unix.  Rather
than encrypting volumes, however, it creates encrypted partitions of your
hard drive.  CFS is a good program, incredibly secure and compatible with
all the best algorithms (Blowfish seems to be the favorite when using CFS,
although 3DES and IDEA are also frequently used) although development has
been slow since it was first released three years ago.  Thus, as
technically elegant as CFS is, as with most free Unix software, the
user will have to do some tweaking to customize it to meet their needs.

 A Word on Commercial Applications

There are tons of commercial applications out there that look good, if you
insist on paying for your software.  Norton Secret Stuff, which runs
exclusively on Windows 3.1, NT, and 95, is actually free, and can be
downloaded from Symantec's web site.  Don't necessarily believe everything
you read on their site, however; Symantec seems determined to market NSS
as "information superhighway" software, designed for the transport of
files and email.  Don't believe it; NSS exclusively uses symmetric-key
algorithms, and the problem of getting the passphrase to the recipient of
the message/file without being intercepted is a significant one, from a
security standpoint.  On the other hand, if the recipient can get the
passphrase without it being intercepted, it is not necessary for them to
have a copy of NSS in order to decrypt the message, which is a nice
feature.  Unfortunately, NSS is designed to encrypt only one file per
passphrase, and as with PGP, this system is not always ideal for
encrypting more than a few files.  Furthermore, NSS uses Blowfish, a good
algorithm, but at a measly 32-bit key length, which will keep your little
brother from reading your files, but it certainly won't keep out anyone
with a budget.  It's not a great program; serious users will want to look
elsewhere.

RSA is a company who has been making great encryption software for a long
time, and they employ probably the best mathematicians and cryptographers
in the world.  They also have a product out, called SecurePC, which is
designed to encrypt multiple files all over your hard drive; they don't
even have to be in the same directory.  Developed for Macintosh and
Windows, Secure PC encrypts at a rather sluggish rate -- 25 MB/minute on a
Pentium 75, but it uses 128-bit RC4, a widely-used stream cipher.

 Snake Oil -- What Not To Use

Perhaps more important than knowing what to look for in good crypto is
how to recognize unreliable or insecure cryptographic applications.
This author is particularly wary of two common problems with some
applications; the first of which is the "Approved for Export" label
flashed by some products.  The product has been approved for export by the
US Federal government because it has made special concessions to comply
with the Department of Justice; specifically it is written to use
ridiculously short (and thus insecure) encryption keys, and it likely has
some 'key recovery' mechanism built in (meaning that there is another way
to decrypt your files besides entering the passphrase).  Just stay away
from the stuff -- real crypto is still legal in the US, no matter what the
DOJ would have you believe.  Most products from Trusted Information
Systems, Inc. proudly brandish a "Now Approved for Export!" label. Another
thing you want to watch out for is any application which generates the key
based solely on the passphrase entered by the user.  AT&T's SecretAgent
uses this method to generate keys, and it's dangerous.  An attack could be
launched on your encrypted files without even obtaining a key from your
machine; the key can be spontaneously generated at any location by
figuring out your passphrase.

Furthermore, watch out for any encryption product described by its
manufacturer as being a 'revolutionary breakthrough', 'unbreakable', or is
described using only new or trademarked terms.  If it sounds like
bullshit, it probably is, and there's a lot of it out there.  Also, don't
trust any encryption algorithm which relies on secrecy about how it works.
Algorithms are proven over time with widespread scrutiny, and if a company
won't tell you how an algorithm works because it is 'proprietary', it's
both bogus _and_ largely untested.

 Conclusion

With proposed import and domestic use restrictions, it is important that
cryptography be demystified for the common user as quickly as possible;
people need to recognize that personal privacy is not just an inalienable
right, but is also easily attainable.