[clug] Unique Id's and CD's

[Robert Edwards]

Karun Dambiec wrote:
> 
> On Thu, 07 May 2009 14:12 +1000, "Robert Edwards" <bob at cs.anu.edu.au>
> wrote:
> 
>>> --
>>> Andrew Janke
>>> (a.janke at gmail.com || http://a.janke.googlepages.com/)
>>> Canberra->Australia    +61 (402) 700 883
>> Of course, none of these solutions guarantee a "unique" id.
>> Depends upon how "unique" you want your ID to be... (ie. in
>> what domain the uniqueness needs to hold).
>>
>> Cheers,
>>
>> Bob Edwards.
>> -- 
> 
> An option is to generate a Universally Unique Identifier,(UUID) or GUID
> following RFC 4122, or some implementation there of, and burn this to a
> copy of the CD.

RFC4122 UUIDs are a great solution, but, again, don't _guarantee_
uniqueness, only allow uniqueness amongst entities who are voluntarily
adopting RFC4122.

Any sort of ID you put on a CD can be put in the same place by someone
else - CD's can't implement a challenge-response authentication scheme
by their very nature. This is the sort of problem that the games and
media distributors have been trying to solve for ever with DRM etc.

If you want an ID for _any_ data CD you will probably need to do some
sort of checksum (md5, sha1 etc.) across the entire disk and live
with the fact that collisions will occur with a small probability.
As others have pointed out, this is time-consuming and computationally
expensive.

If you only want IDs for data CDs that you produce yourself, and you
can live with someone else accidentally/deliberately copying the same
ID, then UUIDs work. You can also place an encrypted string with the
UUID, creation date, author etc. on the CD as well, to increase your
level of confidence.

Cheers,

Bob Edwards.