linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Stephan Müller" <smueller@chronox.de>
To: James Morris <jamorris@linux.microsoft.com>
Cc: "Mickaël Salaün" <mic@digikod.net>,
	"David Miller" <davem@davemloft.net>,
	"Herbert Xu" <herbert@gondor.apana.org.au>,
	"John Haxby" <john.haxby@oracle.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"Simo Sorce" <simo@redhat.com>,
	linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Mickaël Salaün" <mic@linux.microsoft.com>,
	hpa@zytor.com, tytso@mit.edu
Subject: Re: [PATCH v1] crypto: Make the DRBG compliant with NIST SP800-90A rev1
Date: Wed, 23 Jun 2021 19:27:53 +0200	[thread overview]
Message-ID: <8811360.37IJKxs2K1@positron.chronox.de> (raw)
In-Reply-To: <a4e1c071-32af-9650-e6fd-8943b3a79bb0@linux.microsoft.com>

Am Mittwoch, 23. Juni 2021, 19:00:29 CEST schrieb James Morris:

Hi James,

> On Wed, 23 Jun 2021, Stephan Mueller wrote:
> > > These changes replace the use of the Linux RNG with the Jitter RNG,
> > > which is NIST SP800-90B compliant, to get a proper entropy input and a
> > > nonce as defined by FIPS.
> > 
> > Can you please help me understand what is missing in the current code
> > which
> > seemingly already has achieved this goal?
> 
> The advice we have is that if an attacker knows the internal state of the
> CPU, then the output of the Jitter RNG can be predicted.

Thank you for the hint. And I think such goal is worthwhile (albeit I have to 
admit that if an attacker is able to gain the internal state of a CPU, I would 
assume we have more pressing problems that a bit of entropy).

Anyways, the current code does:

- in regular mode: seed the DRBG with 384 bits of data from get_random_bytes

- in FIPS mode: seed the DRBG with 384 bits of data from get_random_bytes 
concatenated with 384 bits from the Jitter RNG


If I understand the suggested changes right, I would see the following changes 
in the patch:

- in the regular case: 640 bits from get_random_bytes

- in FIPS mode: 256 bits of data from get_random_bytes concatenated with 384 
bits from the Jitter RNG

So, I am not fully sure what the benefit of the difference is: in FIPS mode 
(where the Jitter RNG is used), the amount of data pulled from 
get_random_bytes seems to be now reduced.

Maybe I miss a point here, but I currently fail to understand why the changes 
should be an improvement compared to the current case.

Ciao
Stephan



  reply	other threads:[~2021-06-23 17:28 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-23 12:07 [PATCH v1] crypto: Make the DRBG compliant with NIST SP800-90A rev1 Mickaël Salaün
2021-06-23 14:22 ` Stephan Mueller
2021-06-23 17:00   ` James Morris
2021-06-23 17:27     ` Stephan Müller [this message]
2021-06-23 18:04       ` Mickaël Salaün
2021-06-23 19:10         ` Stephan Mueller
2021-06-24 10:13           ` Mickaël Salaün
2021-06-24 11:50             ` Stephan Mueller
2021-06-25 11:09               ` Mickaël Salaün
2021-06-25 13:50                 ` Stephan Müller
2021-06-25 14:53                   ` Mickaël Salaün
2021-06-23 20:49     ` H. Peter Anvin

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=8811360.37IJKxs2K1@positron.chronox.de \
    --to=smueller@chronox.de \
    --cc=davem@davemloft.net \
    --cc=herbert@gondor.apana.org.au \
    --cc=hpa@zytor.com \
    --cc=jamorris@linux.microsoft.com \
    --cc=john.haxby@oracle.com \
    --cc=konrad.wilk@oracle.com \
    --cc=linux-crypto@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mic@digikod.net \
    --cc=mic@linux.microsoft.com \
    --cc=simo@redhat.com \
    --cc=tytso@mit.edu \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).