[Security] Trivial preimage attack against the entity capabilities protocol
hildjj at gmail.com
Tue Aug 18 07:15:46 CDT 2009
On Jul 31, 2009, at 8:59 PM, Peter Saint-Andre wrote:
> I haven't yet had time (at least since the XMPP Summit last week) to
> think more about this problem. We did a lot of work in the more recent
> versions of XEP-0115 to maintain backward compatibility, and it
> would be
> a shame to lose all that work now. But sometimes sunk costs are a fact
> of life...
Backward-compatibility is very important to me. There is a LOT of
XEP-115 deployed out there. My preferences are:
1) characterize exactly the sorts of strings that lead to attack. Put
wording in the XEP that allows detecting those attacks by disallowing
certain combinations. I'm not sure if that's possible, but, for
example, forbidding empty type attributes in identities might mitigate
attacks 2 and 3.
2) add a new feature that sorts at the end, or a new extension that
sorts at the front to signal the shift between features and extensions
3) move extensions to deprecated, and have everyone who sends
extensions be viewed with suspicion. This is a distant last for me,
since there were valid compromises that went into the inclusion of
extensions in the first place. The last thing I want is for clients to
go back to sending iq:version to everyone on the roster every time
they receive presence.
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