Le vendredi 01 août 2014 à 20:36:29 +0900, Joel Rees a écrit: > Yes, but, ... > > Most I/O devices are dependent on certain kinds of timing to function. > For instance, if you try to use the timing between cache fills on your > hard disk, and the system for some reason reads a large block of data > on a non-fragmented file, things that were pretty random suddenly are > not. > > And there is a difference between random and arbitrary. If we could > access the bit jitter on the shift register behind the read heads, we > would discover quite of bit of regularity in the apparently random > rises and falls. Likewise, bearings are not perfectly smooth, and > lubricant not perfectly distributed, but the variations are going to > repeat themselves with some regularity. > > Ethernet chatter seems unpredictable, but packets tend to flow in cyclic bursts. > > Pretty much everything in our world has hidden cyclic behavior. > Keyboard hits tend to be much more random, but, even there, a good > typist gets a rhythm going as well. Indeed, the entropy pool isn't as chaotic as it seems, but, with a deterministic machine like a computer, true random numbers can only be retrieved by thermal noise in resistors or similar processes for which a computer isn't designed. Besides, even if /dev/random is only pseudo-random, guessing its output is hard enough to consider it as a true RNG for common operations because, to guess /dev/random output, you would have to know very precise machine parameters, as HDD lubricant distribution, the kind of data you can only gather by deeply probing the system, so deeply that using such a spied machine for RNG would be futile. In short, as partly chaotic is better than totally deterministic, /dev/random can be considered reliable for punctual or day-to-day activity, but it is also obvious that, if our activity needs truly random number generation or heavy stream of at least pseudo random numbers, a dedicated hardware using thermal noise, cosmic rays, nuclear fission or any over per se chaotic phenomenon is greatly recommended. Regards. -- David Guyot Administrateur système, réseau et télécommunications / Sysadmin Europe Camions Interactive / Stockway Moulin Collot F-88500 Ambacourt Tel: +33 (0)3 29 30 47 85 Fax : +33 (0)3 29 31 31 31
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