[CFRG] Re: [Ppm] Re: Should we spell out the star topology for VDAFs?

[Brandon Pitman <[e-mail]>]

I think it's OK to just sketch out the star topology, for a few reasons:

1) We don't have a current consumer for this topology.
2) This topology is simpler than the ping-pong topology, and is close to a
direct usage of the VDAF interface -- section 5.2
<https://www.ietf.org/archive/id/draft-irtf-cfrg-vdaf-10.html#section-5.2>
roughly lays out the communication pattern of this topology.

Thanks,
Bran

On Mon, Aug 5, 2024 at 3:34 PM Christopher Patton <cpatton=
[e-mail]> wrote:

> Here is a PR for closing the issue by just sketching the star topology:
> https://github.com/cfrg/draft-irtf-cfrg-vdaf/pull/390
>
> Best,
> Chris P.
>
> On Fri, Aug 2, 2024 at 5:26 PM Christopher Patton <[e-mail]>
> wrote:
>
>> Hi PPM+CFRG,
>>
>> I'd like to get some feedback on what to do about this issue for the VDAF
>> draft:
>> https://github.com/cfrg/draft-irtf-cfrg-vdaf/issues/261
>>
>> Prior to DAP draft 05, we envisioned a "star topology" in which there is
>> a single leader and any number of helpers. The idea was that for each round
>> of preparation, the leader would broadcast the prep message to each of the
>> helpers: each helper would respond with its prep share for the next round,
>> which the leader would use to compute the prep message for the next round,
>> and so on. In draft 05 we decided to specialize the protocol for a single
>> leader and helper and adopt the ping-pong topology [1], which requires
>> fewer round trips over the network to finish.
>>
>> In theory, a future specification could execute a VDAF in a star
>> topology, so it may be useful to spell this out. Note however that not all
>> VDAFs support more than two aggregators: Prio3 does, but Poplar1 doesn't.
>>
>> The VDAF draft spells out ping ponging in full detail. This is necessary
>> because the DAP draft consumes this API directly. Do folks think we should
>> spell out the star topology in the same level of detail?
>>
>> Since we don't currently have a use case for it, I don't think it's
>> necessary to spell out in full detail. I suggest we just sketch it instead.
>>
>> Thanks!
>> Chris P.
>>
>> [1]
>> https://www.ietf.org/archive/id/draft-irtf-cfrg-vdaf-10.html#section-5.8
>>
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