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Re: entropicdata.com ?

From: Nate Lawson <nate () root org>
Date: Wed, 27 May 2009 09:00:14 -0700
Dave Aitel wrote:

Sure so one perspective is that anything cryptographic has to get done
on the server. Which seems perfectly valid, but in some cases people
don't want to do it that way.

Maybe they want to sign something, without having to upload it to the
server, say. Or maybe they just don't want to burden the server with
tons of crypto. There's lots of good reasons to do crypto without
reinventing SSL.


Could you finish your example? They are signing something, which is
verified by ... ?

Any scenario I come up with to complete your example has problems. Where
does the private key come from to sign it? How did the web browser get
this key and code. Where does the recipient of this data get the cert to
validate the signature?


And, of course, the cross ___domain stuff coming out makes this more
likely, I assume.


I'm interested in your proposal here. How would Javascript signatures help?

-Nate


Hold on here. You're running Javascript RSA in your browser. Where did
that Javascript come from? Right, you have to load it over SSL to be
sure the Javascript is unmodified. But if you're already using SSL, any
crypto you implement browser-side can only be less reviewed and more
likely to explode, in addition to requiring SSL anyway.

Loading your random data over HTTP is a bad idea too. DSA reveals your
private key to an attacker if even a few bits of the random nonce are
predictable:
http://rdist.root.org/2009/05/17/the-debian-pgp-disaster-that-almost-was/
http://rdist.root.org/2009/05/20/amazon-web-services-signature-vulnerability/

Please stop Web 2.0 from reimplementing crypto, badly. Help computer!

--
Nate

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