Messages in this thread |  | | Date | Mon, 20 Aug 2001 21:20:53 -0400 | From | Theodore Tso <> | Subject | Re: /dev/random in 2.4.6 |
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On Mon, Aug 20, 2001 at 04:00:30PM +0000, David Wagner wrote: > > I don't see why not. Apply this change, and use /dev/urandom. > You'll never block, and the outputs should be thoroughly unpredictable. > What's missing?
Absolutely. And if /dev/urandom is not unpredictable, that means someone has broken SHA-1 in a pretty complete way, in which case it's very likely that most of the users of the randomness are completely screwed, since they probably depend on SHA-1 (or some other MAC which is probably in pretty major danger if someone has indeed managed to crack SHA-1).
> (I don't see why so many people use /dev/random rather than /dev/urandom. > I harbor suspicions that this is a misunderstanding about the properties > of pseudorandom number generation.)
Probably. /dev/random is probably appropriate when you're trying to get randomness for a long-term RSA/DSA key, but for session key generation which is what most server boxes will be doing, /dev/urandom will be just fine.
Of course, then you have the crazies who are doing Monte Carlo simulations, and then send me mail asking why using /dev/urandom is so slow, and how can they the reseed /dev/urandom so they can get repeatable, measureable results on their Monte Carlo sinulations....
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