From 91cb1e1432b3d873a0c8831d0dd8022db98ac8b8 Mon Sep 17 00:00:00 2001 From: Joachim Vandersmissen Date: Sun, 6 Aug 2023 14:19:03 -0500 Subject: [PATCH] crypto: jitter - Add clarifying comments to Jitter Entropy RCT cutoff values The RCT cutoff values are correct, but they don't exactly match the ones one would expect when computing them using the formula in SP800-90B. This discrepancy is due to the fact that the Jitter Entropy RCT starts at 1. To avoid any confusion by future reviewers, add some comments and explicitly subtract 1 from the "correct" cutoff values in the definitions. Signed-off-by: Joachim Vandersmissen Reviewed-by: Stephan Mueller Signed-off-by: Herbert Xu --- crypto/jitterentropy.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/crypto/jitterentropy.c b/crypto/jitterentropy.c index c7d7f2caa779..fe9c233ec769 100644 --- a/crypto/jitterentropy.c +++ b/crypto/jitterentropy.c @@ -89,10 +89,14 @@ struct rand_data { unsigned int rct_count; /* Number of stuck values */ /* Intermittent health test failure threshold of 2^-30 */ -#define JENT_RCT_CUTOFF 30 /* Taken from SP800-90B sec 4.4.1 */ -#define JENT_APT_CUTOFF 325 /* Taken from SP800-90B sec 4.4.2 */ + /* From an SP800-90B perspective, this RCT cutoff value is equal to 31. */ + /* However, our RCT implementation starts at 1, so we subtract 1 here. */ +#define JENT_RCT_CUTOFF (31 - 1) /* Taken from SP800-90B sec 4.4.1 */ +#define JENT_APT_CUTOFF 325 /* Taken from SP800-90B sec 4.4.2 */ /* Permanent health test failure threshold of 2^-60 */ -#define JENT_RCT_CUTOFF_PERMANENT 60 + /* From an SP800-90B perspective, this RCT cutoff value is equal to 61. */ + /* However, our RCT implementation starts at 1, so we subtract 1 here. */ +#define JENT_RCT_CUTOFF_PERMANENT (61 - 1) #define JENT_APT_CUTOFF_PERMANENT 355 #define JENT_APT_WINDOW_SIZE 512 /* Data window size */ /* LSB of time stamp to process */