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