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Re: /dev/random is hot garbage

> On Jul 21, 2019, at 5:03 PM, Joerg Sonnenberger <> wrote:
> On Sun, Jul 21, 2019 at 08:50:30PM +0000, wrote:
>> /dev/urandom is equivalent to /dev/random if there is adequate entropy,
>> but it will also deliver random numbers not suitable for cryptography before that time.
> This is somewhat misleading. The problem is that with an unknown entropy
> state, the system cannot ensure that an attacker couldn't predict the
> seed used for the /dev/urandom stream. That doesn't mean that the stream
> itself is bad. It will still pass any statistical test etc.

That's exactly my point.  If you're interested in a statistically high quality pseudo-random bit stream, /dev/urandom is a gread source.  But if you need a cryptographically strong random number, then you can't safely proceed with an unknown entropy state for the reason you stated, which translates into "you must use /dev/random".

> Note that with the option of seeding the CPRNG at boot time, a lot of
> the distinction is actually moot.

Yes, if at boot time you get enough entropy then /dev/random is unblocked.  The distinction still matters because an application can't know this, so it should express its requirements by choosing the correct device.


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