Is strong crypto worse than weaker crypto? Lessons from Skype
Submitted by brad on Tue, 2005-08-23 23:51A mantra in the security community, at least among some, has been that crypto that isn't really strong is worse than having no crypto at all. The feeling is that a false sense of security can be worse than having no security as long as you know you have none. The bad examples include of course truly weak systems (like 40 bit SSL and even DES), systems that appear strong but have not been independently verified, and perhaps the greatest villian, "security through obscurity" where the details of the security are kept secret -- and thus unverified by 3rd parties -- in a hope that might make them safer from attack.
On the surface, all of these arguments are valid. From a cryptographer's standpoint, since we know how to design good cryptography, why would we use anything less?
However, the problem is more complex than that, for it is not simply a problem of cryptography, but of business models, user interface and deployment. I fear that the attitude of "do it perfectly or not at all" has left the public with "not at all" far more than it should have.
An interesting illustration of the conflict is Skype. Skype encrypts all its calls as a matter of course. The user is unaware it's even happening, and does nothing to turn it on. It just works. However, Skype is proprietary. They have not allowed independent parties to study the quality of their encryption. They advertise they use AES-256, which is a well trusted cypher, but they haven't let people see if they've made mistakes in how they set it up.
This has caused criticism from the security community. And again, there is nothing wrong with the criticism in an academic sense. It certainly would be better if Skype laid bare their protocol and let people verify it. You could trust it more. Read on...




