Cryptography and the Open Source Security Debate

Tue Jul 20 12:46:03 EDT 2004

<http://www.osopinion.com/print.php?sid=1792>

osViews | osOpinion

Cryptography and the Open Source Security Debate

Articles / Security
Date: Jul 20, 2004 - 01:03 AM

Contributed by: Daniel R. Miessler
 :: Open Content

If you follow technology trends, you're probably aware of the two schools
of thought with regard to security and/or cryptography. Does cryptography
and security solutions become more secure as the number of eyes pouring
over its source code increases or is a private solution which leverages
security through obscurity provide a more secure environment?

 Daniel R. Miessler submitted the following editorial to osOpinion/osViews,
which offers some compelling arguments for both scenarios. In the end, his
well thought out opinion, comes to a universal conclusion.
 --

 I've been reading Bruce Schneier's Book on cryptography for the last
couple of days, and one of the main concepts in the text struck me as
interesting.

 One of the points of discussion when looking at the security of a given
algorithm is its exposure to scrutiny. Bruce explicitly states that no one
should ever trust a proprietary algorithm. He states that with few
exceptions, the only relatively secure algorithms are those that have stood
the test of time while being poured over by thousands of cryptanalysts.

Similar Situations

 What struck me is the similarity between this mode of thought and that of
the open source community on the topic of security. In that debate there is
much disagreement about which is better - open or closed -, while in the
crypto world it's considered common knowledge that open is better.
According to the crypto paradigm, having any measure of an algorithm's
security based on the fact that it's a secret is generally a bad thing.
There, keys are what makes the system secure - not the algorithm being a
secret.

 I realize there are some differences in these two models, but they are
small enough, in my opinion, to say that those participating in the
open/closed source debate could learn something by tapping into the body of
knowledge held by this related field.

 Can we, for example, take the analogy at face value and compare "Joe's
Nifty Algorithm" and DES, with the source code for the Windows kernel + IIS
and the Linux kernel + Apache?  Windows to Linux isn't quite fair since
Linux is a kernel alone...If we can, you realize, then it's fairly easy to
see which is more secure - Linux. Why? Well, to put it simply, because
there are all those people looking for ways to attack it while having full
access to the source code/(algorithm). For Windows and IIS, it's a
relatively paltry number in comparison.

 In the cryto world, an experienced analyst would never even consider
encrypting sensitive data with "Sally's Uber-Secure Algorithm" simply
because of one concept:  "Who the hell is Sally? Why is she qualified to
create algorithms that are secure? Why should I trust her?"

Take This Code... Please

 Well, to take the analogy to its conclusion, Sally's algorithm is very
much like Windows, Sun, or any other proprietary company's source code.
What you have is something like this:

 Proprietary Company: "Trust us, this stuff is pretty solid."
 Analyst/Skeptic: "Show me."
 Proprietary Company: "I can't...it's secret. But trust me, it's secure."

 If that were an algorithm up for review, the conversation would look more
like this:

 Algorithm Designer: "This is secure."
 Cryptanalyst: "Show me all the source code, let the world attack it for
years, and if it holds up, I'll believe you - a little bit."

Who Can you Trust?

 Call me crazy, but the second paradigm is the only system that I can place
any significant amount of trust in.

 Now, there is a trump card up the sleeve when it comes to secrets and
algorithms. When the organization or person creating the secret is trusted
to do a good job simply because of who they are, i.e. the NSA or Bruce
Schneier himself,  then, and only then, can a secret possibly be an asset.
The NSA doesn't, for example, give out its algorithms so that they can be
scrutinized even though they know this could potentially lead to the
discovery of weaknesses.

 To them, it's more important that it's secret. I would be relatively
confident that their algorithms were stout, despite the fact that it hasn't
been torn apart by the world's best. Why? Because they have many of the
world's best working for them, while Bruce...well, he's just the man.

 I would also place a fair amount of trust in the security of a closed
source web server package if that package was known to come from Weitse
Venema, for example. Realize though that Weitse himself would most likely
demand that the project was open source precisely so that the world could
verify its relative security. He's not likely to even trust himself to
produce code that's as secure as the world could make it, and that should
say something right there.

Final Thoughts

 So, now the question becomes very simple:

"Do you trust both the talent and moral integrity of the company you are
getting your closed source software from so much that you think the
products they are supplying you are superior (from a security standpoint)
to those that can be created via peer review and attack by tens of
thousands?"

 For me, in the case of Microsoft, Sun, and countless others, the answer is no.

 Go Linux; go BSD. ::

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R. A. Hettinga <mailto: rah at ibuc.com>
The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'

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