Subject: Re: [Int-area] Call for adoption of draft-winfaa-intarea-broadcast-consider-02

From: Rolf Winter <[email-masked]>
Date: Fri, 2 Sep 2016 14:38:29 +0200

Hi Eliot,

I though a bit more about what you said. I think the suggestions to 
developers were clear in my mind but maybe aren't all that clearly 
formulated. Here are the most important suggestions that I read from the 
text:

- Use IETF-specified protocols if possible
- Avoid using user-specified information inside broadcast/multicast messages
- Avoid persistent IDs in messages
- If you really must use a broadcast/multicast protocol and cannot use 
an IETF-specified protocol, then:
	- Be very conservative in how frequently you send messages
	- Seek advice from IETF-specifies protocols such as message supression 
in mDNS
	- Try to design the protocol in a way that the information cannot be 
correlated with other information in broadcast/multicast messages
	- Let the user configure safe environments if possible (e.g. based on 
the SSID)

The reasoning for the above list is in the text of the document. If we 
spell out the above more clearly and add examples from our experiments, 
would you say the document is ready for adoption? That is something we 
can also do once the document has been adopted as part of the first 
revision.

Best,

Rolf

Am 8/29/16 um 10:13 PM schrieb Eliot Lear:
> Rolf,
>
> Thanks.  Please see below.
>
>
> On 8/29/16 8:57 PM, Rolf Winter wrote:
>>
>>> What is needed are specific recommendations or even the strengthening of
>>> a generalized mechanism, the obvious candidate being mDNS/DNS-SD.  What
>>> specific recommendations would the authors make when using 6761/6762?
>>
>> Using a well-known protocols such as mDNS, DNS-SD, LLMNR etc. is only
>> solving parts of the problem. In our experiments, mDNS - albeit being
>> a standard - was a big problem concerning privacy as it often
>> contained PII. Section 2.3. addresses this.
>
> Precisely my point and this is the real crux of the matter.  It would be
> VERY helpful if you were able to give some very specific examples of
> discovery done wrong and how it would be done right.  It is probably
> worth noting that sometimes this is just moving the problem from
> "impossible to solve" to "impractical to solve", such as when PII moves
> from discovery to an application protocol where the information is sent
> in the clear, and that might even make matters worse, because the
> distance of the stretch of the connection.  Another approach you might
> want to explore is to examine common reasons why identifying information
> ends up in discovery messages and what alternatives would prove better.
>
> Now I realize that one draft can't fix everything, but there needs to be
> enough advice for the developer to act on, and right now I don't think
> there is.
>
>
>>
>>>
>>> Also, Section 2.5 talks about configurability as if that's a good
>>> thing.  Given the opportunity of the user to make a decision in this
>>> space, he or she is likely to make the wrong one.  We know this from
>>> long experience.  Again what is needed is far more specific
>>> recommendations that do not require user interaction.
>>
>> I would argue that some things require user configuration. But that
>> does not necessarily mean editing YAML files or similar which is too
>> technical for the average user. A good example (to me at least) is how
>> e.g. Windows asks a user what kind of network an unknown network is
>> (private, work or public I think are option here). Every user can
>> answer that and Windows decides how to configure itself based on that
>> piece of information. That is enough for potentially privacy leaking
>> protocols where at home a broadcast is supposingly fine, but
>> broadcasting your identity on the airport network is probably not.
>> Making a wrong decision here is also better than no decision I would
>> assume, because many protocols we observed broadcast/multicast
>> irrespective of the network location today. So the user won't be worse
>> off compared to today.
>
> I would suggest then that you require more support for your assertion.
> If you like I can dig up many papers that go the other way, not to
> mention the long sordid history of TLS.
>
>>
>>>
>>> There is probably another avenue of consideration here as well.  It is
>>> probably also helpful to discuss scale.  Use of unique identifiers can
>>> adversely impact scale either within the server implementation or on the
>>> network itself.  There's a hint of this in Section 2.1 re performance
>>> and energy consumption.
>>
>> An the operational experience on the IETF meeting network. We can add
>> text here but some of that would be duplications of the referenced
>> work. But that is fine. On one of the networks where we did our
>> experiments, there was an average rate of 20kbit/s of broadcast and
>> multicast traffic. That does not sound like much, but that is average,
>> including nights and weekends, where there is hardly any traffic.
>
> I think the case Stewart likes to look at is the baseball stadium or the
> mall.
>
> Eliot
>

---

From: Eliot Lear <[email-masked]>
Date: Fri, 2 Sep 2016 16:05:13 +0200

Hi Rolf,

On 9/2/16 2:38 PM, Rolf Winter wrote:
> formulated. Here are the most important suggestions that I read from
> the text:
>
>     - Seek advice from IETF-specifies protocols such as message
> supression in mDNS
>     - Try to design the protocol in a way that the information cannot
> be correlated with other information in broadcast/multicast messages
>     - Let the user configure safe environments if possible (e.g. based
> on the SSID)
>
>
> The reasoning for the above list is in the text of the document.

I do like the above recommendations called out in one place.  That's a
very nice summary.

If it were just a matter of clarity, I wouldn't be concerned about
adoption, because you can fix that in the WG process.  What I'm hoping
for is a bit more texture to this.   And so:
> If we spell out the above more clearly*and add examples from our
> experiments, w*ould you say the document is ready for adoption? That
> is something we can also do once the document has been adopted as part
> of the first revision.

This.  Get some good examples.  I haven't reviewed your experimental
results, but following a few common discovery mechanisms that both do
and do not get it right would be useful.  I would be particularly
interested in situations where the end goal is entirely understandable,
but the method used is just leaky.  I would expect that in some cases,
there may not be alternatives, and in some cases there may be, depending
on the use of the information.  Classing those cases and providing quite
specific recommendations would be very useful.

Eliot

---

From: "Christian Huitema" <[email-masked]>
Date: Fri, 2 Sep 2016 13:35:05 -0700

On Friday, September 2, 2016 7:05 AM, Eliot Lear wrote:
> To: Rolf Winter <[email-masked]>; [email-masked]
> ...
> This.  Get some good examples.  I haven't reviewed your experimental results, 
> but following a few common discovery mechanisms that both do and do not get it 
> right would be useful.  I would be particularly interested in situations where the 
> end goal is entirely understandable, but the method used is just leaky.  I would 
> expect that in some cases, there may not be alternatives, and in some cases there 
> may be, depending on the use of the information.  Classing those cases and providing 
> quite specific recommendations would be very useful.

Yes. And I think Rolf's draft is a good start in that direction. I support adoption as a WG item. And I will be happy to review and help improve...

- -- Christian Huitema