3 ms·

That blog post is old and inaccurate. It propagates myths about CSPRNGs that some have been trying to dispel, particularly Thomas Hühn [1] and djb [2]. /dev/ur

by rspeer 11y ago

That blog post is old and inaccurate. It propagates myths about CSPRNGs that some have been trying to dispel, particularly Thomas Hühn [1] and djb [2]. /dev/urandom is the same cryptographically secure PRNG as /dev/random, except that /dev/random will superstitiously block when it thinks entropy has been "consumed". (CSPRNGs do not meaningfully "consume" entropy.) If you use /dev/random for the mythical warm fuzzies, you might also be misunderstanding other things. Don't be superstitious. Use /dev/urandom. [1] http://www.2uo.de/myths-about-urandom/ http://www.2uo.de/myths-about-urandom/ [2] http://www.mail-archive.com/cryptography@randombit.net/msg04763.html http://www.mail-archive.com/cryptography@randombit.net/msg04...

gizmo686 11y ago
If the system has not gathered any entropy, then /dev/random/ will output predictable numbers. You are consuming random numbers does not meaningfully consume entropy [0]. However, if you try to consume a random number before the system has generated entropy in the first place, then /dev/random will still happily give you non random numbers. Most desktop/servers will store entropy between boots, so this is mostly an issue for embeded to worry about, but still worth keeping in mind. [0] Technically, it is correct to say that we do consume entropy in an information theoretic sense. However, this is not particularly revelent, as the CSPRNG is still (believed to be) secure in a complexity theoretic sense. If it turns out that the CSPRNG is not secure in a complexity theoretic sense, then we have bigger issues to worry about then a broken RNG.
- rspeer 11y ago
  This is a case that the pages I linked cover. Also, you mixed up random and urandom, but no matter. People should not code for the case where their distribution's boot sequence totally fucks up.
- Too 11y ago
  I've seen virtual machines having huge problems with entropy speed for random also, it's not just an issue for embedded.

by rspeer 11y ago

gizmo686 11y ago

If the system has not gathered any entropy, then /dev/random/ will output predictable numbers. You are consuming random numbers does not meaningfully consume entropy [0]. However, if you try to consume a random number before the system has generated entropy in the first place, then /dev/random will still happily give you non random numbers. Most desktop/servers will store entropy between boots, so this is mostly an issue for embeded to worry about, but still worth keeping in mind. [0] Technically, it is correct to say that we do consume entropy in an information theoretic sense. However, this is not particularly revelent, as the CSPRNG is still (believed to be) secure in a complexity theoretic sense. If it turns out that the CSPRNG is not secure in a complexity theoretic sense, then we have bigger issues to worry about then a broken RNG.

rspeer 11y ago
This is a case that the pages I linked cover. Also, you mixed up random and urandom, but no matter. People should not code for the case where their distribution's boot sequence totally fucks up.
Too 11y ago
I've seen virtual machines having huge problems with entropy speed for random also, it's not just an issue for embedded.