[metrics-team] v3 unique onion address estimates

[David Goulet]

On 18 Dec (10:59:51), Roman Brunner wrote:
> Hi metrics team,
> 
> There exists an estimate for unique v2 .onion addresses for v2 onion
> services. However, for v3, no such estimate exists.
> Lately, the estimates for the v2 addresses started to decrease steadily,
> which I assume to be because of more and more services make the switch to
> v3. Hence it would be interesting to know how many distinct v3 addresses
> are available.
> Is there anything planned to extend this estimate to v3 addresses? And
> towards a possible implementation for v3: do v3 addresses pose any
> additional challenges compared to v2 or could the current statistics
> collection be extended?

Hi!

So yes, v3 are more challenging. The reason is because with v3 descriptors
(posted at the HS directory), do not contain the .onion address. They instead
have what we call a "blinded key" which can only be derived depending on a
time period, a shared random value (created within the consensus every 24h)
and the master identity key of the service (the v3 .onion).

And thus, the client can generated that blinded key by knowing the .onion and
request the blinded key at the directory. One thing that is working for us,
the time period are fixed over a day and we know when the shared random is
created as well.

Thus the only way we can estimate is by keeping an aggregate count of similar
blinded keys a directory sees every 24h (up to the new shared random
creation). And also, another complication, services publish 2 descriptors at
all time that is using the current and previous shared random value in order
to accomodate client with skewed clock.

We'll be able to only estimate the number of v3 addresses that the network
sees. And that that number will be obsfuscated for privacy reasons, like we do
with v2.

More info: https://trac.torproject.org/projects/tor/ticket/23126

All in all, we haven't done this feature in tor just yet.

Hope this help!
David

-- 
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