Buckinghamshire CC ANPR cameras

Roland Perry lists at internetpolicyagency.com
Mon Jan 9 16:34:15 GMT 2012

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.
Roland Perry

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