Re: [xmpp] XMPP stanza encryption + EXI compression

I think you'll find that if you try to compress after encrypting, you're
going to have a bad time.  Exi1(Encrypt(Xml)) is not going to buy you
anything besides some wasted cycles.
--Richard

On Thu, Mar 14, 2013 at 11:25 AM, Peter Waher <Peter.Waher@clayster.com>wrote:

> Dear Matt
>
> I just became aware of your  IETF draft for XMPP end-to-end encryption. It
> looks very promising.
> http://tools.ietf.org/html/draft-miller-xmpp-e2e-05
>
> We work with sensor network architecture over XMPP, and some (but not all)
> applications require end-to-end encryption, so we want to look at this
> extension.
>
> At the same time, compression is a vital issue, since many sensors have
> limited memory. Therefore, we are working with an effort to include the use
> of EXI in XMPP. (See attached documents.) One important aspect to know,
> when including EXI into XMPP, is that packets cannot be binary copied when
> the server relays the information. The packets have to be decompressed, and
> re-compressed if both peers have EXI-compressed channels. This requires EXI
> to be applied after any message encryption transformation:
> Exi1(Encrypt(Xml)). Server then relays Exi2(DeExi1(Exi1(Encrypt(Xml)))) =
> Exi2(Encrypt(Xml)) to the second peer.
>
> The problem with this is that EXI does not do very well with
> base64-encoded binary data. Size(Exi(Base64(Bin))) would approximately be
> equal to Size(Bin). EXI would be able to cut the added length imposed by
> the base64 encoding, due to its limited character set.
>
> It would be nice with an end-to-end encryption method over XMPP that would
> also be able to take into account EXI compression of XML stanzas.
>
> If you have time, any comments would be appreciated,
>
> Sincerely,
> Peter Waher
>
>
> -----Original Message-----
> From: Peter Saint-Andre [mailto:stpeter@stpeter.im]
> Sent: den 14 mars 2013 11:57
> To: Peter Waher
> Cc: Joachim Lindborg (joachim.lindborg@sust.se); Matt Miller
> Subject: Re: XMPP stanza encryption
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 3/14/13 10:53 AM, Peter Waher wrote:
> > Hello Peter
> >
> > Do you participate in this work?
> > http://tools.ietf.org/html/draft-miller-xmpp-e2e-05
>
> Only indirectly, by chatting once in a while with Matt Miller (cc'd).
>
> Peter
>
> - --
> Peter Saint-Andre
> https://stpeter.im/
>
>
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