diff options
author | Samuel Neves <sneves@dei.uc.pt> | 2014-10-04 00:13:36 +0100 |
---|---|---|
committer | Kurt Roeckx <kurt@roeckx.be> | 2014-10-28 20:54:34 +0100 |
commit | 0d330ce5cc89fb1141e69f19fd4b2eb5e47f2e3b (patch) | |
tree | 92c9396e88d8ea8b40ba70d8841c54252764ee4f /crypto | |
parent | 2a303a583469f480938459cb5da2ba45f5b59ed2 (diff) |
Use only unsigned arithmetic in constant-time operations
Signed-off-by: Kurt Roeckx <kurt@roeckx.be>
Reviewed-by: Emilia Käsper <emilia@openssl.org>
Diffstat (limited to 'crypto')
-rw-r--r-- | crypto/constant_time_locl.h | 16 |
1 files changed, 3 insertions, 13 deletions
diff --git a/crypto/constant_time_locl.h b/crypto/constant_time_locl.h index 7b339a7c31..ccb64082fd 100644 --- a/crypto/constant_time_locl.h +++ b/crypto/constant_time_locl.h @@ -129,17 +129,12 @@ static inline int constant_time_select_int(unsigned int mask, int a, int b); static inline unsigned int constant_time_msb(unsigned int a) { - return (unsigned int)((int)(a) >> (sizeof(int) * 8 - 1)); + return -(a >> (sizeof(unsigned int) * 8 - 1)); } static inline unsigned int constant_time_lt(unsigned int a, unsigned int b) { - unsigned int lt; - /* Case 1: msb(a) == msb(b). a < b iff the MSB of a - b is set.*/ - lt = ~(a ^ b) & (a - b); - /* Case 2: msb(a) != msb(b). a < b iff the MSB of b is set. */ - lt |= ~a & b; - return constant_time_msb(lt); + return constant_time_msb(a^((a^b)|((a-b)^b))); } static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b) @@ -149,12 +144,7 @@ static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b) static inline unsigned int constant_time_ge(unsigned int a, unsigned int b) { - unsigned int ge; - /* Case 1: msb(a) == msb(b). a >= b iff the MSB of a - b is not set.*/ - ge = ~((a ^ b) | (a - b)); - /* Case 2: msb(a) != msb(b). a >= b iff the MSB of a is set. */ - ge |= a & ~b; - return constant_time_msb(ge); + return ~constant_time_lt(a, b); } static inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b) |