4 ms·
A heuristic. No common magic header and poor compressibility? Likely encrypted.
by pinum 9y ago
A heuristic. No common magic header and poor compressibility? Likely encrypted.
- sillysaurus3 9y agoSince encrypted data is indistinguishable from random noise, I think poor compressibility is actually zero compressibility, isn't it? There are tools to search for TrueCrypt / other encrypted partitions on disks, so it's a solved problem to detect encrypted data. It would be unfortunate if services ban the ability to upload encrypted secrets, though. On the other hand, that'd be good for Tarsnap. I wonder how much it'd cost to store 10TB on it?
- icebraining 9y agoSince encrypted data is indistinguishable from random noise, I think poor compressibility is actually zero compressibility, isn't it? I don't think so. Random noise can take any form - even of a string composed entirely of zeros, which would be trivially compressed. It's just very unlikely that it'll actually be compressible.
- Dylan16807 9y agoRandom noise can't really take any form when you apply the implicit restriction of your search fitting within finite time and space.
- icebraining 9y agoI don't get what you're saying. Searching? For what?
- sillysaurus3 9y agoIt'd take longer than the universe has left to find a string of N zeroes by generating random numbers, for sufficiently large N. And N is surprisingly small.
- icebraining 9y agoSure, but not zero.
- Dylan16807 9y agoYes zero. As zero as zero can possibly be, measuring with the most precise instruments possible. There's an infinitely better chance of both of us being struck by lightning and imagining you found such a number randomly. It wouldn't be zero in certain math worlds. It is zero in the real universe.
- Dylan16807 9y agoThe definition of a random number is in the process of generation. You have to actually generate random numbers if you want to have a random number that meets some criteria. And even with impossibly vast resources, you will never find a random megabyte that compresses well.
- icebraining 9y agoWell, sure, that's what I wrote: "it's very unlikely that it'll actually be compressible." But it's incorrect to claim that random numbers are by definition non-compressible.
- sillysaurus3 9y agoIt was in the context of encryption. Even a 64 digit random number is very unlikely to be compressible, and 64 bytes is about as small of an encrypted partition as you'll ever have.
- dorgo 9y agoThe first billion of digits of Pi might look pretty random, but there might be a short program which genrates them - which can be considered a compressed form. In general, it is impossible to decide how good a given string might be compressed. https://en.wikipedia.org/wiki/Kolmogorov_complexity https://en.wikipedia.org/wiki/Kolmogorov_complexity
- foota 9y agoMight be a short program that generates them? I'm going to go ahead and file that in the understate of the century folder.