Search Mailing List Archives


Limit search to: Subject & Body Subject Author
Sort by: Reverse Sort
Limit to: All This Week Last Week This Month Last Month
Select Date Range     through    

[liberationtech] [sunlightlabs] need advice on using hashes for preserving PII's utility for disambiguation while protecting sensitive info

Chris Dary umbrae at gmail.com
Thu Feb 6 13:19:49 PST 2014


It's been a while since I dug into it, but something like an 8-bit
CRC<http://en.wikipedia.org/wiki/Cyclic_redundancy_check>would
probably provide enough disambiguation but would collide often enough
to not be much of a concern for reversing - 256 different values.


On Thu, Feb 6, 2014 at 4:10 PM, Chris Dary <umbrae at gmail.com> wrote:

> Just one thought to throw out: Something that sprang to mind is the idea
> of a check digit or simplified hash that would be redundant enough to
> collide very often if you were trying to reverse, but would still provide
> enough disambiguation that you'd be able to appropriately determine who
> you're dealing with.
>
> You could probably use something similar to the Luhn algorithm for that,
> although I'm not sure how uniform that is:
> http://en.wikipedia.org/wiki/Luhn_algorithm - also, that only ends up
> with a single check digit, which is probably too small for good
> disambiguation. The approach in general might still be helpful though.
>
> -Chris
>
>
> On Thu, Feb 6, 2014 at 3:49 PM, Tom Lee <tlee at sunlightfoundation.com>wrote:
>
>> We've been kicking around an idea at Sunlight that aims to use
>> cryptographic ideas to resolve some of the concerns around the publication
>> of publicly identifiable information in government disclosures. I could use
>> some smart people to tell me what's dumb about it.
>>
>> We often face challenges related to disambiguating entities: is the John
>> Smith who gave political donation A the same John Smith that gave political
>> donation B? One obvious solution to this problem is to push to expand the
>> information that's collected and disclosed -- if we had John's driver's
>> license number (DLN), for instance, it'd be easy to disambiguate these
>> records. But that could introduce privacy concerns for John. One approach
>> to this problem (which I don't think government has tried) is employing a
>> one-way hash.
>>
>> Obviously the input key space for DLNs and most other personal ID numbers
>> is so small that reversing this with a dictionary attack would be trivial.
>> You can add a salt, but only on a per-entity basis (not a per-record basis)
>> if you want to preserve the capacity to disambiguate. That in turns calls
>> for a lookup table in which the input keys are stored, which kind of
>> defeats the point of using a hash (you might as well just assign random
>> output IDs for each input ID). I would worry about government's ability to
>> keep this lookup table secure, and I worry about the brittleness of such a
>> system.
>>
>> Alternately, you can use a single system-wide secret (or set of secrets)
>> to transform inputs into reliable outputs. I think this is less brittle and
>> maybe easier to preserve as a secret, but this system might be too easily
>> reversible given the ability to observe its outputs and know the universe
>> of possible inputs. I'm unsure of the cryptographic options that might be
>> appropriate here.
>>
>> For all I know, the lack of implementations using this kind of one-way
>> transformation isn't about government sluggishness but rather about its
>> feasibility. I'd be very curious to hear folks ideas on this score, though.
>>  My general hunch is that something must be possible -- even a few bits'
>> worth of disambiguating information would be hugely useful to us, and
>> presumably you're not leaking important amounts of information by, say,
>> sharing the last digit of a DLN. So there must be a spectrum of options.
>> But as is probably apparent, I don't think I've got a handle on how to
>> think about this problem rigorously.
>>
>> Tom
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "sunlightlabs" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to sunlightlabs+unsubscribe at googlegroups.com.
>> To post to this group, send email to sunlightlabs at googlegroups.com.
>> Visit this group at http://groups.google.com/group/sunlightlabs.
>> For more options, visit https://groups.google.com/groups/opt_out.
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.stanford.edu/pipermail/liberationtech/attachments/20140206/53a1ee4d/attachment.html>


More information about the liberationtech mailing list