From 46a643763de6d8e39ecf6f76fa79b4d04885aa59 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bodo=20M=C3=B6ller?= Date: Mon, 16 May 2005 01:43:31 +0000 Subject: Implement fixed-window exponentiation to mitigate hyper-threading timing attacks. BN_FLG_EXP_CONSTTIME requests this algorithm, and this done by default for RSA/DSA/DH private key computations unless RSA_FLAG_NO_EXP_CONSTTIME/DSA_FLAG_NO_EXP_CONSTTIME/ DH_FLAG_NO_EXP_CONSTTIME is set. Submitted by: Matthew D Wood Reviewed by: Bodo Moeller --- crypto/bn/bn_lcl.h | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) (limited to 'crypto/bn/bn_lcl.h') diff --git a/crypto/bn/bn_lcl.h b/crypto/bn/bn_lcl.h index 45e19221aa..1c680fc3ce 100644 --- a/crypto/bn/bn_lcl.h +++ b/crypto/bn/bn_lcl.h @@ -163,6 +163,45 @@ extern "C" { +/* BN_mod_exp_mont_conttime is based on the assumption that the + * L1 data cache line width of the target processor is at least + * the following value. + */ +#define MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH ( 64 ) +#define MOD_EXP_CTIME_MIN_CACHE_LINE_MASK (MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH - 1) + +/* Window sizes optimized for fixed window size modular exponentiation + * algorithm (BN_mod_exp_mont_consttime). + * + * To achieve the security goals of BN_mode_exp_mont_consttime, the + * maximum size of the window must not exceed + * log_2(MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH). + * + * Window size thresholds are defined for cache line sizes of 32 and 64, + * cache line sizes where log_2(32)=5 and log_2(64)=6 respectively. A + * window size of 7 should only be used on processors that have a 128 + * byte or greater cache line size. + */ +#if MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH == 64 + +# define BN_window_bits_for_ctime_exponent_size(b) \ + ((b) > 937 ? 6 : \ + (b) > 306 ? 5 : \ + (b) > 89 ? 4 : \ + (b) > 22 ? 3 : 1) +# define BN_MAX_WINDOW_BITS_FOR_CTIME_EXPONENT_SIZE (6) + +#elif MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH == 32 + +# define BN_window_bits_for_ctime_exponent_size(b) \ + ((b) > 306 ? 5 : \ + (b) > 89 ? 4 : \ + (b) > 22 ? 3 : 1) +# define BN_MAX_WINDOW_BITS_FOR_CTIME_EXPONENT_SIZE (5) + +#endif + + /* Pentium pro 16,16,16,32,64 */ /* Alpha 16,16,16,16.64 */ #define BN_MULL_SIZE_NORMAL (16) /* 32 */ -- cgit v1.2.3