Am Samstag, 18. März 2017, 14:43:18 CET schrieb Jeffrey Walton:
> > I am not sure how this statement relates to the quote above. RDSEED is the
> > CBC-MACed output of the flip-flop providing the raw noise.
> > RDRAND is the output of the SP800-90A CTR DRBG that is seeded by the
> > CBC-MAC that also feeds RDSEED. Thus, RDSEED is as fast as the noise
> > source where RDRAND is a pure deterministic RNG that tries to be
> > (re)seeded as often as possible.
> > Both instructions are totally unrelated to the SP800-90A DRBG available to
> > the Linux kernel.
> SP800-90A requires an entropy source to bootstrap the Hash, HMAC and
> CTR generators. That is, the Instantiate and Reseed functions need an
> approved source of entropy. Both RDRAND and RDSEED are approved for
> Intel chips. See SP800-90A, Section 8.6.5
I am aware that SP800-90A makes the claim of having an approved noise source.
But as of now, there is no such thing.
NIST is aware of that issue. To cover that issue during a FIPS 140-2
validation, you have to prove your noise sources to be compliant to SP800-90B.
I performed such noise source assessments as part of the FIPS 140-2
validations of the Intel Sunrise Point or the Qualcomm HW DRBG FIPS 140-2
validations. Also, I completed such assessments for the FIPS 140-2 validations
of the legady /dev/random covering numerous Linux-based cryptographic modules
over the last couple of years.
To get a glimpse of how such assessments for FIPS 140-2 are conducted, please
have a look at the assessment  section 188.8.131.52 starting on page 72 in the
lower half (note that I was the main author of this study). To be honest, the
assessment in  section 5.5 was the main motivation for my LRNG
That said,  section 3.4.1, starting at page 34 bottom, you see the same
SP800-90B test approach that was equally accepted by NIST during formal FIPS
140-2 validations of other noise sources. Hence, I would conclude that my
suggested implementation of the noise source is appropriate for a DRBG to be
compliant to section 8.6.5 of SP800-90A.
But you mention a very important topic: is it and how is it ensured that the
DRBG is appropriately seeded. This issue is discussed in  section 2.1 which
explains the initial, minimal and full seeded stages of the DRBG.