[PATCH] crypto: ansi_cprng: fix inverted DT increment routine

[PATCH] crypto: ansi_cprng: fix inverted DT increment routine

[Jarod Wilson]

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@redhat.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@redhat.com

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

[Neil Horman]

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@redhat.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@redhat.com
> 
> 

Looks good, thanks Jarod!

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

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

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

[Herbert Xu]

On Thu, Nov 13, 2008 at 01:44:31PM -0500, Neil Horman wrote:
> 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@redhat.com>

Patch applied.  Thanks!
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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