Re: de-identification text for Wednesday's call

Shane,

Why hash at all in this case? If you are relying on operational and
administrative controls, you might as well just pledge not to look up
the cookie when you receive it. If you are rotating (and discarding)
salts frequently, then it will have a positive effect, but otherwise I
don't think hashing provides any benefit here.

But this is an aside to our main disagreement about the larger issue
about the role that operational and administrative controls should play.
I agree that they should play a role, but only after de-identification
of data has been achieved. If the result of a DNT:1 request is business
as usual, with minor scrubbing and the caveat that only 4000 engineers
at a large corporation get default access to a specially marked database
instead of 10000, then that will not be a successful standard. (Of
course I welcome more detailed information about operational and
administrative controls.)

One last point I wanted to make is that of course the data sets I
mentioned refer to public data. We don't have access to internal
corporate data sets. There are laws in place to protect the pilfering of
that data, so of course no-one is going to steal data then publish an
academic paper about it, effectively painting a big target on themselves
for federal prosecutors and corporate legal teams. In light of this, the
right empirical question to ask is: of large publicly available data
sets that contain user data and are somewhat akin to log data, how often
are there successful re-identification or attribute disclosure attacks?
Can you point to any public data sets where such an attack has not been
found?

If your argument is instead that public data should be treated
differently from non-public data, then I'd suggest that this is out of
scope for the DNT conversation. DNT is about giving users the choice to
opt out of tracking by companies, which must entail meaningfully curbing
data collection and retention by that company, not merely a request that
a company not make public its collected data. (Indeed, in addition to
being an excessively weak demand by the user, this would in some cases
be a vacuous request, since making that information public is already
prohibited by law.) The de-identification question exists within the
scope of what the companies themselves can do with the data -- is the
data de-identified with respect to the entity that collected the data?

Best,
Dan

On 04/02/2013 11:03 AM, Shane Wiley wrote:
>
> Dan,
>
>  
>
> Once the one-way hash is applied (and other elements of record
> appropriately cleansed) the data is moved to a system that is not
> allowed to be accessed externally.  Its these operational and
> administrative controls that are essential to ensure de-identified
> data is not re-identified at some later time.  I believe you're
> looking only at the technical merits which is only seeing a small
> portion of the overall solution.
>
>  
>
> - Shane
>
>  
>
> *From:*Dan Auerbach [mailto:dan@eff.org]
> *Sent:* Tuesday, April 02, 2013 10:59 AM
> *To:* public-tracking@w3.org
> *Subject:* Re: de-identification text for Wednesday's call
>
>  
>
> On 04/02/2013 08:50 AM, Shane Wiley wrote:
>
>     once the one-way hash function has been applied the data is never
>     again able to be accessed in real-time to modify the user's
>     experience.
>
> I think I'm confused, can you explain this more? How is this possible?
> If you are just hashing a cookie string, your web server receives a
> request that includes a cookie string, you hash that cookie string
> (which is in incredibly fast operation), match the hashed cookie
> against the stored data, and return personalized results.
>
> Or are you salting the hash differently for every request, or
> combining the cookie with an ephemeral piece of data (the timestamp)
> before hashing and then throwing away the timestamp?
>
> Thanks for clarifying, apologies if I'm just being dense.
>
> Dan
>
>
> -- 
> Dan Auerbach
> Staff Technologist
> Electronic Frontier Foundation
> dan@eff.org <mailto:dan@eff.org>
> 415 436 9333 x134


-- 
Dan Auerbach
Staff Technologist
Electronic Frontier Foundation
dan@eff.org
415 436 9333 x134