[Standards] Security implications of entity capabilities

Olivier Goffart ogoffart at kde.org
Fri Mar 16 20:31:22 UTC 2007

Le vendredi 16 mars 2007, Greg Hudson a écrit :
> I am a bit concerned by the ability of one malicious client to poison
> the entity capability caches of other people's clients.  XEP-115
> considers this possibility:
> I suspect most implementations will simply cache the first response
> they get. 

Indeed, that's what I do :-)

> If, for instance, e2e encryption is advertised by a 
> capability, it will be relatively straightforward to induce two nodes
> to avoid e2e encryption when they would otherwise use it, by
> advertising that a particular node/ver or node/ext combination does
> not support that feature.
> Perhaps the right answer is simply "don't use caps for
> security-sensitive features like e2e encryption."  But it can be hard
> to determine in advance what's security-sensitive sometimes.

That would also make the use of "caps" completely useless.

Also, we have a bootstrap problem, because if the disco#info message is not 
signed, the server may also modify it.

Note that since the client need to visually show if message are encrypted or 
not, this make the use of such attack easily detectable.

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