5 ms·
If we use a secure cryptographic algorithm which combines different entropy sources and then hashes them together, even a completely insecure additional source
by strenholme 5y ago
If we use a secure cryptographic algorithm which combines different entropy sources and then hashes them together, even a completely insecure additional source of entropy will not reduce the security of /dev/random [1]
If we have 10 different sources of entropy for our random number generator, and only one of them is truly random, our random number generator is still secure.
[1] There’s an issue where /dev/random will have less actual entropy than it think it has, but as long as we have 128 bits[2] or more of actual entropy, the output will still be secure.
[2] 256 bits if worrying about quantum computers or theoretical future computers the size of a continent
- IgorPartola 5y agoWhat exactly is the point of adding 9 known insecure sources if only one is doing the actual useful work? Is it less secure? I guess not. Is it more secure? Doesn’t seem like it.
- BenjiWiebe 5y agoIf you add 9 known not-very-good sources of randomness, it's still better than adding no sources of randomness. Now if your 9 bad sources are 100% predictable, then yes, there's no point in adding them.
- charcircuit 5y agoYou wouldn't. He is just talking about a worst case scenario. He's is saying that as long as one of your sources of randomness is "truly" random you are fine.l
- deleted 5y ago[deleted]
- wizeman 5y ago> Is it more secure? Doesn’t seem like it. Why not? Unless all 9 "insecure" sources are 100% attacker-controlled or broken at the same time, they would still be adding entropy. Each additional source is adding one more hoop for the attacker to have to jump through. The more sources are added, the less the chance that all of them are broken or attacker-controlled at the same time on the same computer. Conversely, if you only have one (presumably good) entropy source it would be much easier for it to be compromised than if you have 10 sources, including the good one (even though some of them are easier to break than others).
- zrm 5y agoSuppose you have 10 sources of entropy and you don't know which ones are good. If you pick one, and you pick the wrong one, you lose. If you use all of them with an algorithm that works as long as any one of them is good, and any one of them is good, you're good.
- CJefferson 5y agoThe question is, which sources are "known secure"? There have been AMD systems where RDRAND is broken and always returns the same value -- I bet those users would have been happy if their webcam got mixed in.
- IgorPartola 5y agoEven if their webcam was pointed at a black wall in a dark room?
- CJefferson 5y agoI just checked and my camera, even if a close the cover and put it under a blanket, still doesn't return straight zeroes. As long as there is some "fuzz" there is something useful to generate randomness. Also, it would be reasonable for the RNG to notice some source is returning input of no value (straight zeroes) and reject it.
- adzm 5y agoYou can actually use a camera sensor as a kind of Geiger counter by blocking normal light eg with foil and measuring fluctuations in the results!