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Snake Oil FAQ 0.4 [comments appreciated]
The Snake Oil FAQ version 0.4 is waiting for you to look at it and
comment on
http://research.megasoft.com/people/cmcurtin/snake-oil/snake-oil-faq.html
The text version follows...
-matt
--------------------------- snake-oil-faq ----------------------------
Snake-Oil Warning Signs
Encryption Software to Avoid
$Id: snake-oil-faq.html,v 0.4 1996/09/16 13:52:26 cmcurtin Exp $
Distribution
Please do not distribute this beyond the circles of cryptographic competence
yet. This is an incomplete work-in-progress. Feedback is greatly
appreciated.
The Snake Oil FAQ is (to be) posted monthly to cypherpunks, sci.crypt,
alt.security, comp.security, and comp.infosystems. We're targeting those who
have influence over or direct involvement in the purchasing decisions of
computer security software and equipment in the corporate and academic
worlds, as well as individual users who wish to assert their privacy through
the use of good cryptography.
Disclaimer
All contributors' employers will no doubt disown any statements herein.
We're not speaking for anyone but ourselves, based on our own experiences,
etc., etc., etc. This is a general guideline, and as such, cannot be the
sole metric by which a security product is rated, since there can be
exceptions to any of these rules. (But if you're looking at something that
sounds familiar on several of the 'things to watch out for,' you're probably
dealing with snake oil. From time to time, a reputable and decent vendor
will produce something that is actually quite good, but will use some
braindead marketing technique, so be aware of exceptions.)
Every effort has been made to produce an accurate and useful document, but
the information contained herein is completely without warranty. If you find
any errors, or wish to otherwise contribute, please contact the document
keeper, C Matthew Curtin <[email protected]>
Introduction
Good cryptography is an excellent and necessary tool for almost anyone.
However, there is a multitude of products around. Many good cryptographic
products are available, both commercial (including shareware) and free.
However, there are also some extremely bad cryptographic products (known in
the field as "Snake Oil"), which not only fail do their job of providing
security, but are based on, and add to, the many misconceptions and
misunderstandings surrounding cryptography and security.
Superficially, it is difficult for someone to distinguish the output of a
secure encryption utility from snake oil: both look garbled. The purpose of
this document is present some obvious "red flags" so that people unfamiliar
with the nuts and bolts of cryptography can use as a guideline for
determining whether they're dealing with snake oil or the Real Thing.
For a variety of reasons, this document is general in scope and does not
mention specific products or algorithms as being "good" or "Snake Oil".
When evaluating any product, be sure to understand what your needs are. For
data security products, what do you need protected? Do you want an archiver
that supports strong encryption? An E-mail client? Something that will
encrypt on-line communications? Do you want to encrypt an entire disk or
partition, or selectively some files? Do you need on-the-fly (automatic)
encryption and decryption, or are you willing to select when and which files
you want encrypted? How secure is "secure enough?" Does the data need to be
unreadable by third parties for 5 minutes? One year? 50 years? 100 years?
Different products will serve different needs, and it's rare that a product
will serve every need. (Sometimes a product won't be needed: it may be
better to use a utility to encrypt files, transmit them over a network using
standard file transfer tools, and decrypt them at the other end than to use
a separate encrypted utility in some cases.)
Some basics
The cryptography-faq (found at
ftp://rtfm.mit.edu/pub/usenet/cryptography-faq/) is a more general tutorial
of cryptography, and should also be consulted. In an effort to make this FAQ
more complete, some very basic topics are included below.
Conventional vs. Public Key Cryptography
There are two basic types of cryptosystems: symmetric (also known as
"conventional," sometimes also called "private key") and asymmetric (public
key). Symmetric ciphers require both the sender and the recipient to have
the same key. That key is applied to encrypt the data by the sender, and
again by the recipient to decrypt the data. Asymmetric ciphers are much more
flexible, from a key management perspective. Each user has a pair of keys: a
public key and a private key. The public key is shared widely, given to
everyone, while the private key is kept secret. If Alice wishes to mail Bob
some secrets, she simply gets Bob's public key, encrypts her message with
it, and sends it off to Bob. When Bob gets the message, he uses is private
key to decrypt the message.
Asymmetric cryptosystems are much slower than their symmetric counterparts.
Also, key sizes must be much larger. See the cryptography FAQ for a more
detailed discussion of the topic.
Key Sizes
Some ciphers, while currently secure against most attacks, are not
considered viable in the next few years because of relatively small keysizes
and increasing processor speeds (making a brute-force attacks feasible). The
tables below should give some general guidelines for making intelligent
decisions about the key length you need. If the key is too short, the system
will be easily broken, even if the cipher is a good one.
In [1] and [2], we're presented with some guidelines for deciding
appropriate key length. (It is important to note that this is based on the
ability to predict computing power 40, 65, and 100 years from now. Major
breakthroughs in computing power 30 years from now might render everything
on this chart kiddieplay.)
Security Requirements for Different Information
Type of Traffic Lifetime Minimum [Symmetric]
Key Length
Tactical military information minutes/hours 56-64 bits
Product announcements, mergers, interest
rates days/weeks 64 bits
Long-term business plans years 64 bits
Trade secrets (e.g., recipe for
Coca-Cola) decades 112 bits
H-bomb secrets >40 years 128 bits
Identities of spies >50 years 128 bits
Personal affairs >50 years 128 bits
Diplomatic embarrassments >65 years at least 128 bits
U.S. Census data 100 years at least 128 bits
As mentioned earlier, asymmetric ciphers require significantly longer keys
to provide the same level of security as their symmetric cipher
counterparts. Here is a comparison table, again, from Applied Cryptography,
second edition.
Symmetric and Public-Key Lengths With
Similar Resistance to Brute-Force Attacks
Symmetric Key Length Public-key Key Length
56 bits 384 bits
64 bits 512 bits
80 bits 768 bits
112 bits 1792 bits
128 bits 2304 bits
Some Common Snake-Oil Warning Signs
The following are some of the "red flags" one should watch for when
examining an encryption product
* Technobabble
The vendor's description of the product may contain a lot of
hard-to-follow use of technical terms to describe how the product
works. If this appears to be confusing nonsense, it may very well be
(even to someone familiar with the terminology). Technobabble is a good
means of confusing a potential user and masking the fact that the
vendor doesn't understand anything either.
A sign of technobabble is a descrption which drops a lot of technical
terms for how the system works without actually explaining how it
works. Often specifically coined terms are used to describe the scheme
which are not found in the literature.
* New Type of Cryptography?
Beware of any vendor who claims to have invented a "new type of
cryptography" or a "revolutionary breakthrough". Truly "new
break-throughs" are likely to show up in the literature, and many in
the field are unlikely to trust them until after years of analysis, by
which time they are not so new anymore.
Avoid software which claims to use 'new paradigms' of computing such as
cellular automata, neural nets, genetic algorithms, chaos theory, etc.
Just because software uses to different method of computation doesn't
make it more secure.
Anything that claims to have invented a new public key cryptosystem
without publishing the details or underlying mathematical principles is
highly suspect. Modern cryptography, especially public key systems, is
grounded in mathematical theory. The security is based on problems that
are believed, if not known to be hard to solve.
The strength of any encryption scheme is only proven by the test of
time. New crypto is like new pharmaceuticals, not new cars.
* Proprietary Algorithms
Avoid software which uses "proprietary" or "secret" algorithms.
Security through obscurity is not considered a safe means of protecting
your data. If the vendor does not feel confident that the method used
can withstand years of scrutiny by the academic community, then you
should be wary of trusting it. (Note that a vendor who specializes in
the cryptography may have a proprietary algorithm which they'll show to
others if they sign a non-disclosure agreement. If the vendor is
well-reputed in the field, this can be an exception.)
Beware of specially modified versions of well-known algorithms. This
may intentionally or unintentionally weaken the cipher.
The use of a trusted algorithm, if not with technical notes explaining
the implementation (if not availability of the source code for the
product) are a sign of good faith on the part of the vendor that you
can take apart and test the implementation yourself.
A common excuse for not disclosing how a program works is that "hackers
might try to crack the program's security." While this may be a valid
concern, it should be noted that such 'hackers' can reverse engineer
the program to see how it works anyway. If the program is implemented
properly and the algorithm is secure, this is not a problem. (If a
hypothetical 'hacker' was able to get access you your system, access to
encrypted data might be the least of your problems.)
* Experienced Security Experts and Rave Reviews
Beware of any product claiming that "experienced security experts" have
analyzed it, but it won't say who (especially if the scheme has not
been published in a reputable journal).
Don't rely on reviews in newspapers, magazines or television shows,
since they generally don't have cryptologists (celebrity hackers who
know about telephone systems don't count) take the software apart for
them.
Just because the vendor is a well known company or the algorithm is
patented doesn't make it secure either.
* Unbreakability
Some vendors will claim their software is "unbreakable". This is
marketing hype, and a common sign of snake-oil. Avoid any vendor that
makes unrealistic claims.
No algorithm is unbreakable. Even the best algorithms are breakable
using "brute force" (trying every possible key), but if the key size is
large enough, this is impractical even with vast amounts of computing
power.
One-time pads are unbreakable, but they must be implemented perfectly,
which is, at best, very difficult. See the next section for a more
detailed discussion.
* One-Time-Pads
A vendor might claim the system uses a one-time-pad (OTP), which is
theoretically unbreakable. That is, snake-oil sellers will try to
capitalize on the known strength of a OTP. It is important to
understand that any variation in the implementation means that it is
not an OTP, and has nowhere near the security of an OTP.
A OTP system is not an algorithm. It works by having a "pad" of random
bits in the possession of both the sender and recipient. The message is
encrypted using the next n bits in the pad as they key, where n is the
number of bits in the message. After the bits are used from the pad,
they're destroyed, and can never again be used. The bits in the pad
must be truly random, generated using a real random source, such as
specialized hardware, radioactive decay timings, etc., and not from an
algorithm or cipher. Anything else is not a one-time-pad.
The vendor may confuse random session keys or initialization vectors
with OTPs.
* Algorithm or product XXX is insecure
Be wary of anything that makes claims that particular algorithms or
other products are insecure without backing up those claims (or at
least citing references to them).
Sometimes attacks are theoretical or impractical (requiring special
circumstances or massive computing power running for many years), and
it's easy to confuse a layman by mentioning these.
* Keys and Passwords
The "key" and the "password" are often not the same thing. The "key"
generally refers to the actual data used by the cipher, while the
"password" refers to the word or phrase the user types in, which the
software converts into the key (usually through a process called
"hashing" or "key initialization").
The reason this is done is because the characters a user is likely to
type in do not cover the full range of possible characters. (Such keys
would be more redundant and easier for an attacker to guess.) By
hashing a key can be made from an arbitrary password that covers the
full range of possible keys. It also allows one to use longer words, or
phrases and whole sentences as a "passphrase", which is more secure.
Anything that restricts users' passwords to something like 10 or 16 or
even 32 characters is foolish. If the actual "password" is the cipher's
key (rather than hashing it into a key, as explained above), avoid it.
If the vendor confuses the distinctions between bits, bytes and
characters when discussing the key, avoid this product.
Convenience is nice, but be wary of anything that sounds too easy to
use. Avoid anything that lets anyone with your copy of the software to
access files, data, etc. without having to use some sort of key or
passphrase.
Avoid anything that doesn't let you generate your own keys (ie, the
vendor sends you a key in the mail, or it's embedded in the copy of the
software you buy).
Avoid anything by a vendor who does not seem to understand the
difference between public-key (asymmetric) cryptography and private-key
(symmetric) cryptography.
* Lost keys and passwords
If there's a third-party utility that can crack the software, avoid it.
If the vendor claims it can recover lost passwords (without using a
key-backup or escrow feature), avoid it.
If there is a key-backup or escrow feature, are you in control of the
backup, or does the vendor or someone else hold a copy of the key?
* Exportable from the USA
If the software is made in North America, can it be exported? If the
answer is yes, chances are it's not very strong. Strong cryptography is
considered munitions in terms of export from the United States, and
requires approval from the State Department. Chances are if the
software is exportable, the algorithm is weak or it is crackable (hence
it was approved for export).
If the vendor is unaware of export restrictions, avoid the software:
the vendor is not familiar with the state of the art.
Because of export restrictions, some legitimate (not-Snake Oil)
products may have a freely exportable version for outside of the USA,
which is different from a separate US/Canada-only distribution. Also
note that just because software has made it outside of North America
does not mean that it is exportable: sometimes a utility will be
illegally exported and posted on an overseas site.
Other Considerations
Interface isn't everything: user-friendliness is an important factor, but if
the product isn't secure then you're better off with something that is
secure (if not as easy to use).
No product is secure if it's not used properly. You can be the weakest link
in the chain if you use a product carelessly. Do not trust any product to be
foolproof, and be wary any product that claims it is.
Contributors
The following folks have contributed to this FAQ.
Jeremey Barrett <[email protected]>
<[email protected]>
Jim Ray <[email protected]>
Robert Rothenburg Walking-Owl <[email protected]>
References
1. B. Schneier, Applied Cryptography, second edition, John Wiley & Sons,
1996
2. M. Blaze, W. Diffie, R. L. Rivest, B. Schneier, T. Shimomura, E.
Thompson, M. Wiener, "Minimal Key Lengths for Symmetric Ciphers to
Provide Adequate Commercial Security," available via
ftp://ftp.research.att.com/dist/mab/keylength.ps
----------------------------------------------------------------------------
C Matthew Curtin
Last modified: Mon Sep 16 09:51:41 EDT
----------------------------------------------------------------------
--
C Matthew Curtin MEGASOFT, INC Chief Scientist
I speak only for myself. Don't whine to anyone but me about anything I say.
Hacker Security Firewall Crypto PGP Privacy Unix Perl Java Internet Intranet
[email protected] http://research.megasoft.com/people/cmcurtin/