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

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Date:	Thu, 20 Mar 2014 09:12:55 +0100
From:	Clemens Ladisch <clemens@...isch.de>
To:	Stephan Mueller <smueller@...onox.de>,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org
CC:	aquini@...hat.com, jeremy.wayne.powell@...il.com
Subject: Re: [PATCH v2 1/6] SP800-90A Deterministic Random Bit Generator

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
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