Had an idea - looking for a math buff to tell me if it's possible with today's technology.

Thu May 19 03:03:46 UTC 2011

Ha! I was wondering this the whole time - if the size of the counter would
make it a zero sum game. That sux! :)

On 19 May 2011 03:52, Brett Frankenberger <rbf+nanog at panix.com> wrote:

> On Thu, May 19, 2011 at 12:26:26AM +0100, Heath Jones wrote:
> > I wonder if this is possible:
> >
> > - Take a hash of the original file. Keep a counter.
> > - Generate data in some sequential method on sender side (for example
> simply
> > starting at 0 and iterating until you generate the same as the original
> > data)
> > - Each time you iterate, take the hash of the generated data. If it
> matches
> > the hash of the original file, increment counter.
> > - Send the hash and the counter value to recipient.
> > - Recipient performs same sequential generation method, stopping when
> > counter reached.
> >
> > Any thoughts?
>
> That will work.  Of course, the CPU usage will be overwhelming --
> longer than the age of the universe to do a large file -- but,
> theoretically, with enough CPU power, it will work.
>
> For a 8,000,000,000 bit file and a 128 bit hash, you will need a
> counter of at least 7,999,999,872 bits to cover the number of possible
> collisions.
>
> So you will need at leat 7,999,999,872 + 128 = 8,000,000,000 bits to
> send your 8,000,000,000 bit file.  If your goal is to reduce the number
> of bits you send, this wouldn't be a good choice.
>
>     -- Brett
>