gelisam

Whether you have two 128-bit hashes or one 256-bit hash, you're still trying to fit 2^n pigeons into (2^128)*(2^128) = 2^256 pigeonholes.

Maybe your intuition is telling you that two hashes must be more secure because if one of the two hash functions turns out to be easy to break, then at least you will still be protected by the other?

I thought of using hashes too, but then I realized that after thousands of years, the program is only going to output a collision, and not the original data.

Checking the first and last few bits reduces the number of collisions, but there are still 2^unchecked_bits/2^160 cyphers which map to the same hash. You could store the number of collisions to skip along with the hash, but that number will be about (unchecked_bits - 161) bits long, so that won't work either.

I used to work at a place where their mission critical software was running on ancient HP-UX boxes which we feared to turn off because we didn't know if they would turn back on. My job was to port this software to modern Ubuntu VMs. Once I was done, we had a celebration in which we turned off the HP-UX boxes forever... except of course there was a bug in my version, so we soon had to turn them back on while I worked on a fix.

To everybody's surprise, the machines did turn back on, but they couldn't connect to the network because a few configuration files were wrong. To our dismay, after we tried to use Vi to edit the first one, we discovered that the ESC key did not work anymore, and we were stuck in edit mode forever! We had to reboot the machine, which takes about an hour on these old machines.

And then of course I configured the files using Ed and saved the day! Surprisingly, I was the youngest programmer there and I was the only one who knew how to use it.