Very interesting paper, I shall have to give it the time for a thorough
read.
If my understanding of the paper is correct, then that attack would
apply to just about any cipher that makes heavy use of S-boxes. That
includes RC4, AES, blowfish, and [3-]DES, so you don't have much
possibility of choosing unaffected algorithms in SSH, unless some
obscure implementation build around Helix instead of block ciphers and
HMAC should arise...
Cheers
Mark
-----Original Message-----
From: Bryan McAninch [mailto:bryan@mcaninch.org]
Sent: May 17, 2005 14:34
To: secureshell@securityfocus.com
Subject: RE: Security Practices
The AES attack described by Dan Bernstein is impractical, as
it requires an enormous amount of known plaintext and is very
timing sensitive.
Furthermore, the issue does not lie within the algorithm
itself, but rather how it is implemented. The paper
specifically states that OpenSSL is vulnerable, which makes
OpenSSH vulnerable to the attack as well.
Stick with AES.
Cheers,
Bryan
-----Original Message-----
From: Nigel Stepp [mailto:stepp@atistar.net]
Sent: Tuesday, May 17, 2005 12:14 PM
To: David Busby
Cc: secureshell@securityfocus.com
Subject: Re: Security Practices
David Busby wrote:
List,
I'm trying to get my a sshd setup as secure as possible,
some folks
I know what to send financial data over this.
...
aes256-cbc cipher (only)
http://cr.yp.to/antiforgery/cachetiming-20050414.pdf
You may want to be aware of this paper. I believe the
results are still preliminary, but it's something to follow.
I'm thinking that
I'll make my key 4096bits to add some security.
Heh, is your name Avi? (cryptonomicon reference, couldn't
resist) That's probably overkill, but that assumes no
codebreaking paradigm shifts or what have you.
> Assume best means most secure even at
the sacrifice of performance. Thanks!
If you're going to use 4096 bit keys, you may want to move
away from md5 as a hashing algorithm, since it has been shown
to have some measure of weakness. You might look at SHA256,
SHA512, or something like whirlpool.
I'm not an expert, however, and I'm not sure how proven
whirlpool really is (or about the measure of support of these
hashes in ssh).
/djb
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