[Standards-JIG] UPDATED: JEP-0027 (Current Jabber OpenPGP Usa ge)

Matthias Wimmer m at tthias.net
Thu Mar 18 08:52:36 UTC 2004


Hi Justin!

Justin Karneges schrieb am 2004-03-17 15:19:34:
> Unfortunately this would require the receiver to be available at the time of 
> send, in order to negotiate this value.  Maybe the receiver could leave some 
> values on the server for use while offline.  I discussed this matter with one 
> of my friends, and he devised a system that could work this way, but it 
> requires server modification.  It is somewhat complicated, maybe I'll write 
> it up and share it here.
> 
> Of course, this doesn't let the receiver off the hook about storing IDs 
> somewhere (ie, to disk).  Instead of storing sender IDs, now it must store 
> receiver IDs (the IDs it generated).

First thought: I think its better to store receiver IDs on the server.
As long as the server can not create the receiver IDs itself, the only
thing it could do is deleting the IDs which only results that senders
can not submit messages (DoS - which is possible by just not letting
the user come back online anyway) - but in this case the server has no
possibility to delete already used IDs to allow the same message again.

> > Storing on the server does not satisfy me as the client has to trust the
> > server that no message IDs have been removed from the storage on the
> > server.
> We must surrender to the fact that the server may DoS a user at any time, by 
> not delivering messages, eating offline messages, eating any stored values 
> (as mentioned above), etc.  As long as these actions do not cause security 
> violations, then we should not worry about them.

Sure the server can DoS - but if we care about replay attacks at all,
than we should not allow the server to make replay attacks possible
(maybe even unintentionally by restoring a backup of the user's
account).


Tot kijk
    Matthias

-- 
Fon: +49-(0)70 0770 07770       http://matthias.wimmer.name/
HAM: DB1MW                      xmpp:mawis at charente.de
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