[Standards] On 'private' and 'no-copy'

Kurt Zeilenga kurt.zeilenga at isode.com
Sun Oct 11 15:00:03 UTC 2015

> On Oct 10, 2015, at 2:58 PM, Matthew Wild <mwild1 at gmail.com> wrote:
> After various discussions, including here at the summit, I'm seeing a
> rough consensus that the <private/> element in Carbons or the
> ~equivalent <no-copy/> hint in XEP-0334 cause more trouble than they
> are worth.
> The only use-case I've been able to find is preventing OTR messages
> from being received by clients that cannot decrypt them. It is
> debateable whether receiving garbage is worse than not knowing that
> someone is trying to contact you on another resource.
> As the elements are basically only a workaround for OTR, and OTR is a
> hack, and OTR has its own methods to solve this issue, one could argue
> that we shouldn't be using these elements.
> Does anyone have strong feelings about this?

Aside from OTR specific issues....   and whether there's actually any use case for this:

my view is that <private/> is best used by a carbon-requested client to tell its server not to carbon particular stanzas to its other clients (sharing the same bare JID).... whereas <no-copy/> is a hint to any server who might be making copies.   The former should be trimmed at the sender's client server (assuming it supports carbons).  The latter isn't.

Otherwise we're in-tangling security considerations....

> Regards,
> Matthew
> PS. I don't want to get this discussion tangled up with the
> advancement of Carbons, right now I'd rather just determine whether
> these elements are useful or not.

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