linux-kernel - Re: [RFC][PATCH 0/6] /dev/random

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Date:	Thu, 21 Apr 2016 17:16:51 +0200
From:	Stephan Mueller <smueller@...onox.de>
To:	Nikos Mavrogiannopoulos <nmav@...tls.org>
Cc:	Ted Tso <tytso@....edu>, Herbert Xu <herbert@...dor.apana.org.au>,
	Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Sandy Harris <sandyinchina@...il.com>
Subject: Re: [RFC][PATCH 0/6] /dev/random - a new approach

Am Donnerstag, 21. April 2016, 15:03:37 schrieb Nikos Mavrogiannopoulos:

Hi Nikos,
> 
> [quote from pdf]
> 
> > ... DRBG is “minimally” seeded with 112^6 bits of entropy.
> > This is commonly achieved even before user space is initiated.
> 
> Unfortunately one of the issues of the /dev/urandom interface is the
> fact that it may start providing random numbers even before the
> seeding is complete. From the above quote, I understand that this
> issue is not addressed by the new interface. That's a serious
> limitation (of the current and inherited by the new implementation),
> since most/all newly deployed systems from "cloud" images generate
> keys using /dev/urandom (for sshd for example) on boot, and it is
> unknown to these applications whether they operate with uninitialized
> seed.

One more item to consider: If you do not want to change to use getrandom(2), 
the LRNG provides you with another means. You may use the 
/proc/sys/kernel/random/drbg_minimally_seeded or drbg_fully_seeded booleans. 
If you poll on those, you will obtain the indication whether the secondary 
DRBG feeding /dev/random is seeded with 112 bits (drbg_minimally_seeded or 256 
bits (drbg_fully_seeded).

Those two booleans are exported for exactly that purpose: allow user space to 
know about initial seeding status of the LRNG.

Ciao
Stephan