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@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