Buckinghamshire CC ANPR cameras

[John Wilson]

On 9 January 2012 16:34, Roland Perry <lists at internetpolicyagency.com> wrote:
> In article <E1RkGz3-0003TK-Ex at skipnote.org>, Chris Edwards
> <chris-ukcrypto at lists.skipnote.org> writes
>
>>> They use the 24 bit hash value returned from the camera not the
>>> registration number
>>
>>
>> I guess hashing a registration is pretty easy to reverse.  With access to
>> the DVLA database of all UK registrations, you simply compute the hash for
>> each one.  This is a one off task.  Once you've done it, you know the
>> registration for any given hash.
>
>
> Unless the hash changes, with for example the date. You'd still get hashes
> consistent enough to work out how fast the traffic's flowing, but each day
> you get a whole new set of hashes.
>
> Although if you knew the date the hash was calculated, you could still
> compare the hash you wanted to reverse with the full table, but it's much
> more to compute and store, and could be accused of being security by
> obscurity.


The hash doesn't change over time. There's a FOI response from the
Highways Agency which confirms that.
(http://www.whatdotheyknow.com/request/48353/response/124187/attach/html/2/FOI%20response%20ref%2013068772.doc.html)

John Wilson