Re: [PATCH v2 1/6] SP800-90A Deterministic Random Bit Generator

From: Clemens Ladisch <clemens@ladisch.de>
To: Stephan Mueller <smueller@chronox.de>,
	linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org
Cc: aquini@redhat.com, jeremy.wayne.powell@gmail.com
Subject: Re: [PATCH v2 1/6] SP800-90A Deterministic Random Bit Generator
Date: Thu, 20 Mar 2014 09:12:55 +0100	[thread overview]
Message-ID: <532AA307.504@ladisch.de> (raw)
In-Reply-To: <3662681.npTzbSq3ye@myon.chronox.de>

Stephan Mueller wrote:
> This is a clean-room implementation of the DRBG defined in SP800-90A.

Why?  I guess it's for certification?

> +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:

	ret = memcmp(...);
	...
	/* the test shall pass when the compared values are not equal */
	return ret != 0;

Regards,
Clemens