3 ms·

Yep, one of the cool things about entropy is that it always increases. If you keep XORing more information into the seed pool, you only ever increase the total

• dfox 6y ago
  As long as you use reasonably secure way to add entropy into the pool, ie. don't XOR stuff into some kind of pool buffer but use something that at least partly resembles secure hash even for adding entropy (as using full-blown SHA-x to process interrupt timings and similar high volume low quality entropy sources is not exactly practical due to both performance and synchronization issues). Also, total entropy is not necessarily the same thing as attacker's uncertainity of the pool's state. The difference seems mostly theoretical, but there are practical issues for both cases of these two quantities beeing wildy different.
  • loeg 6y ago
    +1 on the mix-with-SHA or something like it paragraph. Re: Entropy; in a system RNG design, entropy is typically considered relative to an attacker. In some very real sense, the "total entropy" of the system is only the unpredictability of the generator to the most knowledgeable attacker.
• loeg 6y ago
  You can't just use naive XOR, but if you take slightly more effort, yes, sure.
• a1369209993 6y ago
  I wasn't one of the downvoters, since your actual point is clear and true, but DO NOT EVER USE XOR TO COMBINE ENTROPY! I cannot emphasize this enough - XOR allows malicous entropy sources to cancel out other entropy. Always use a cryptographically secure hash function, especially when adding entropy from RDRAND.