Messages in this thread Patch in this message | | | From | Jarod Wilson <> | Subject | [PATCH] crypto: ansi_cprng: fix inverted DT increment routine | Date | Thu, 13 Nov 2008 11:36:11 -0500 |
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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
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