[tor-dev] Feedback on obfuscating hidden-service statistics

A. Johnson aaron.m.johnson at nrl.navy.mil
Tue Nov 25 22:14:16 UTC 2014

Hi George,

> I posted an initial draft of the proposal here:
> https://lists.torproject.org/pipermail/tor-dev/2014-November/007863.html
> Any feedback would be awesome.

OK, I’ll have a chance to look at this in the next few days.

> Specifically, I would be interested in undertanding the concept of
> additive noise a bit better. As you can see the proposal draft is
> still using multiplicative noise, and if you think that additive is
> better we should change it. Unfortunately, I couldn't find any good
> resources on the Internet explaining the difference between additive
> and multiplicative noise. Could you expand a bit on what you said
> above? Or link to a paper that explains more? Or link to some other
> system that is doing additive noise (or even better its implementation)?

The technical argument for differential privacy is explained in <http://research.microsoft.com/en-us/projects/databaseprivacy/dwork.pdf>.  The definition appears in Def. 2, the Laplace mechanism is given in Eq. 3 of Sec. 5, and Thm. 4 shows why that mechanism achieves differential privacy.

But that stuff is pretty dry. The basic idea is that you’re trying to the contribution of any one sensitive input (e.g. a single user’s data or a single component of a single user’s data). The noise that you need to cover that doesn’t scale with the number of other users, and so you use additive noise.

Hope that helps,

More information about the tor-dev mailing list