[Python-Dev] BDFL ruling request: should we block forever waiting for high-quality random bits?

[Stephen J. Turnbull]

Donald Stufft writes:

 > I guess one question would be, what does the secrets module do if
 > it’s on a Linux that is too old to have getrandom(0), off the top
 > of my head I can think of:
 > 
 > * Silently fall back to reading os.urandom and hope that it’s been
 >   seeded.
 > * Fall back to os.urandom and hope that it’s been seeded and add a
 >   SecurityWarning or something like it to mention that it’s
 >   falling back to os.urandom and it may be getting predictable
 >   random from /dev/urandom.
 > * Hard fail because it can’t guarantee secure cryptographic
 >   random.

I'm going to hide behind the Linux manpage (which actually suggests
saving the data in a file to speed initialization at boot) in
mentioning this:

* if random_initialized_timestamp_pre_boot():
      r = open("/dev/random", "rb")
      u = open("/dev/urandom", "wb")
      u.write(r.read(enough_bytes))
      set_random_initialized_timestamp()
  # in theory, secrets can now use os.urandom