Random number generation, simple question.

[Andrew Kuchling]

"Andrew Dalke" <dalke at acm.org> writes:
> What I saw, though, was a compile time option to use /dev/random if
> it exists.  I would have thought that would be enabled by default, but
> it made some comment about how the read will block if there isn't enough
> entropy in the source pool.  Is this ever a problem in real life?

Yes, because the entropy pool is only 4096 bits, and entropy is added
fairly slowly, since an interrupt or other event only adds a few bits
of entropy.  A different device, /dev/urandom, never blocks, so you
can read enough data to theoretically compute the initial state of the
pool.  For generating a long-term thing like an RSA key, this would
matter (or least be psychologically unsettling); for an IV, I think
/dev/urandom would be fine.

--amk