[tor-dev] Improved circuit-setup protocol [was: Re: Designing and implementing improved circuit-setup protocol [was: GSoC 2011]]

[Steven J. Murdoch]

On Thu, Apr 07, 2011 at 06:13:45PM -0400, Nick Mathewson wrote:
> Oh!  Also, for a bit of redundancy, I'm thinking that the symmetric
> crypto parts of the improved onion handshakes ought to be with a less
> malleable mode of operation than the counter-mode stuff we do now.
> Perhaps we could make use of an all-or-nothing mode of operation like
> LIONESS or biIGE.  (They're both slower than counter mode, but for
> purposes of CREATE cells, I don't think the hit will matter in
> comparison with the cost of the public-key operations.)

This is another thing that triggers my crypto-spidey-sense. The
particular problem that I'm thinking of is that for MAC-then-encrypt,
only some modes of operation are secure (CTR is, CBC is not). In some
ways, the malleability of CTR is a strength, and I'd be concerned that
something else might be able to be leveraged in an attack.

Steven.

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