linux-kernel - Re: [PATCH] crypto: ansi_cprng: fix inverted DT increment routine

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Date:	Thu, 13 Nov 2008 13:44:31 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Jarod Wilson <jarod@...hat.com>
Cc:	linux-crypto@...r.kernel.org, herbert@...dor.apana.org.au,
	davem@...emloft.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: ansi_cprng: fix inverted DT increment routine

On Thu, Nov 13, 2008 at 11:36:11AM -0500, Jarod Wilson wrote:
> The ANSI X9.31 PRNG docs aren't particularly clear on how to increment DT,
> but empirical testing shows we're incrementing from the wrong end. A 10,000
> iteration Monte Carlo RNG test currently winds up not getting the expected
> result.
> 
> From http://csrc.nist.gov/groups/STM/cavp/documents/rng/RNGVS.pdf :
> 
> # CAVS 4.3
> # ANSI931 MCT
> [X9.31]
> [AES 128-Key]
> 
> COUNT = 0
> Key = 9f5b51200bf334b5d82be8c37255c848
> DT = 6376bbe52902ba3b67c925fa701f11ac
> V = 572c8e76872647977e74fbddc49501d1
> R = 48e9bd0d06ee18fbe45790d5c3fc9b73
> 
> Currently, we get 0dd08496c4f7178bfa70a2161a79459a after 10000 loops.
> 
> Inverting the DT increment routine results in us obtaining the expected result
> of 48e9bd0d06ee18fbe45790d5c3fc9b73. Verified on both x86_64 and ppc64.
> 
> Signed-off-by: Jarod Wilson <jarod@...hat.com>
> 
> ---
> 
>  crypto/ansi_cprng.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/crypto/ansi_cprng.c b/crypto/ansi_cprng.c
> index 486aa93..a7c703d 100644
> --- a/crypto/ansi_cprng.c
> +++ b/crypto/ansi_cprng.c
> @@ -161,7 +161,7 @@ static int _get_more_prng_bytes(struct prng_context *ctx)
>  	/*
>  	 * Now update our DT value
>  	 */
> -	for (i = 0; i < DEFAULT_BLK_SZ; i++) {
> +	for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
>  		ctx->DT[i] += 1;
>  		if (ctx->DT[i] != 0)
>  			break;
> 
> -- 
> Jarod Wilson
> jarod@...hat.com
> 
> 

Looks good, thanks Jarod!

Acked-by: Neil Horman <nhorman@...driver.com>

-- 
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 *Neil Horman
 *nhorman@...driver.com
 *gpg keyid: 1024D / 0x92A74FA1
 *http://pgp.mit.edu
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