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Date:	Thu, 20 Mar 2014 14:30:33 +0100
From:	Stephan Mueller <smueller@...onox.de>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	aquini@...hat.com, jeremy.wayne.powell@...il.com
Subject: Re: [PATCH v2 1/6] SP800-90A Deterministic Random Bit Generator

Am Donnerstag, 20. März 2014, 09:12:55 schrieb Clemens Ladisch:

Hi Clemens,

> Stephan Mueller wrote:
> > This is a clean-room implementation of the DRBG defined in SP800-90A.
> 
> Why?  I guess it's for certification?

As per SP800-131A, the ANSI X9.31 DRNG is sunset by the end of 2014 and not 
allowed to be used in FIPS 140-2 compliant environments. The kernel crypto API 
implements an ANSI X9.31 DRNG in crypto/ansi_cprng.c as the only DRNG that 
complies with FIPS 140-2 at this time.

Without a replacement for this ANSI X9.31 DRNG, the kernel will not have an 
FIPS 140-2 approved DRNG any more starting from 2015.
> 
> > +static bool drbg_fips_continuous_test(struct drbg_state *drbg,
> > +				     unsigned char *buf)
> > ...
> > +	ret = memcmp(drbg->prev, buf, drbg_blocklen(drbg));
> > +	...
> > +	/* invert the memcmp result, because the test shall pass when the
> > +	 * two compared values do not match */
> > +	if (ret)
> > +		return true;
> > +	else
> > +		return false;
> 
> This looks strange.  The return value of memcmp() is not really
> a boolean, and the code appears not to match the comment because the
> numeric value of ret is not actually inverted.  How about this:

Correct, the comment does not match the code as I had invered the logic of 
drbg_fips_continuous_test as per Rafael's comment. Yet, I did not update the 
comment.
> 
> 	ret = memcmp(...);
> 	...
> 	/* the test shall pass when the compared values are not equal */
> 	return ret != 0;

I will add that change.
> 
> 
> Regards,
> Clemens


Thanks
Stephan
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