[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

# Re: [tor-dev] Proposal draft: Better hidden service stats from Tor relays

```"A. Johnson" <aaron.m.johnson@xxxxxxxxxxxx> writes:

> Hi George,
>

Hello!

> I recommend a change to the way that these statistics are
> obfuscated. The problem is that new noise is used every day, and from
> the distribution of the reported bins, the exact location within the
> bin (assuming the stat stats constant) can be reported.
>

Assuming that the underlying value is constant and since our Laplace
distribution is public, the adversary can observe which bin is
reported each time and get a probability distribution for the
underlying value.

This indeed seems plausible under the powerful assumption that the
underlying stat is constant.

> So instead of this
>
>>                   +--------------+    +--------------------+
>>   actual value -> |additive noise| -> |round-up obfuscation| -> public statistic
>>                   +--------------+    +ââââââââââ+
>
> I recommend that you flip the order, so that it is like this
>                   +--------------+    +--------------------+
>   actual value -> |round-up obfuscation| -> |additive noise| -> public statistic
>                   +--------------+    +ââââââââââ+
>
> âAdditive noiseâ in the context of bins is actually just a distribution over bins. You can think of it in two ways:
>   1. Add Laplace noise to the bin center, and then report the bin of the resulting number.

Hm, you mean something like this, right?

+--------------+    +--------------------+    +--------------+
actual value -> |   binning    | -> |  addditive noise   | -> |   binning    | -> public statistic
+--------------+    +ââââââââââ----------+    +--------------+

where the additive noise is applied to the center of the first bin?

I can see how this is better, since the underlying value gets
immediately smoothed by binning. However, it does give me a weird
hacky feeling...

Is this construction something that has been used before?

Thanks for the feedback!

_______________________________________________
tor-dev mailing list
tor-dev@xxxxxxxxxxxxxxxxxxxx
https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev
```

• Follow-Ups: