5 ms·

> "might generate easily predicted cryptographic keys under certain extremely rare circumstances" no, he's not saying that - he's saying that there's no such t

> "might generate easily predicted cryptographic keys under certain extremely rare circumstances" no, he's not saying that - he's saying that there's no such thing as entropy depletion - and so urandom is secure. Which makes me ask after urandom was created - why EVER bother using /dev/random with it's blocking flaw/deficiency?

sillysaurus3 12y ago
He said there's no such thing as entropy depletion for urandom after it's been seeded. But the seed still has to come from somewhere, and one possible source for that seed is /dev/random.
- nitrogen 12y ago
  /dev/random actually points to the same RNG as /dev/urandom, according to http://www.2uo.de/myths-about-urandom/ http://www.2uo.de/myths-about-urandom/ (and other sources I recall reading but can't find). So you wouldn't use /dev/random to seed /dev/urandom, but you (or the kernel) might use something else to seed both.
X-Istence 12y ago
There is no reason to use /dev/random other than cargo culting devs that believe that /dev/urandom can supposedly run out of entropy. Use /dev/urandom. Don't use /dev/random. On sane systems (FreeBSD for example), /dev/urandom is a symlink to /dev/random and /dev/random only blocks once, upon startup to gather entropy, after that it never blocks!
- obsurveyor 12y ago
  I don't think it's a "cargo cult" if the official docs mention and warn about entropy pool exhaustion.
  - tptacek 12y ago
    The official docs are wrong.
    - obsurveyor 12y ago
      Then submit a patch to fix them.
      - clarry 12y ago
        Instead of telling other people what to do, maybe you should just do it yourself.
      - cpach 12y ago
        Corey Csuhta filed an issue for this four months ago, but no one has responded to it: https://bugzilla.kernel.org/show_bug.cgi?id=71211 https://bugzilla.kernel.org/show_bug.cgi?id=71211
nhaehnle 12y ago
There's no such thing as entropy depletion, but there is such a thing as an insufficiently seeded CSPRNG - which means that /dev/urandom is not secure by design: it does not protect you against that failure mode, and in fact people rely on fragile hacks implemented by distributions to try to seed /dev/urandom properly as soon as possible in the bootup sequence. These hacks could easily break if somebody does not know exactly what they're doing while touching the boot sequence. /dev/random is also stupid, but it does protect you against that particular failure mode.

sillysaurus3 12y ago

He said there's no such thing as entropy depletion for urandom after it's been seeded. But the seed still has to come from somewhere, and one possible source for that seed is /dev/random.

nitrogen 12y ago
/dev/random actually points to the same RNG as /dev/urandom, according to http://www.2uo.de/myths-about-urandom/ http://www.2uo.de/myths-about-urandom/ (and other sources I recall reading but can't find). So you wouldn't use /dev/random to seed /dev/urandom, but you (or the kernel) might use something else to seed both.

X-Istence 12y ago

There is no reason to use /dev/random other than cargo culting devs that believe that /dev/urandom can supposedly run out of entropy. Use /dev/urandom. Don't use /dev/random. On sane systems (FreeBSD for example), /dev/urandom is a symlink to /dev/random and /dev/random only blocks once, upon startup to gather entropy, after that it never blocks!

obsurveyor 12y ago
I don't think it's a "cargo cult" if the official docs mention and warn about entropy pool exhaustion.
- tptacek 12y ago
  The official docs are wrong.
  - obsurveyor 12y ago
    Then submit a patch to fix them.
    - clarry 12y ago
      Instead of telling other people what to do, maybe you should just do it yourself.
    - cpach 12y ago
      Corey Csuhta filed an issue for this four months ago, but no one has responded to it: https://bugzilla.kernel.org/show_bug.cgi?id=71211 https://bugzilla.kernel.org/show_bug.cgi?id=71211

nhaehnle 12y ago

There's no such thing as entropy depletion, but there is such a thing as an insufficiently seeded CSPRNG - which means that /dev/urandom is not secure by design: it does not protect you against that failure mode, and in fact people rely on fragile hacks implemented by distributions to try to seed /dev/urandom properly as soon as possible in the bootup sequence. These hacks could easily break if somebody does not know exactly what they're doing while touching the boot sequence. /dev/random is also stupid, but it does protect you against that particular failure mode.