Commit d2fa1829 authored by Samuel Neves's avatar Samuel Neves Committed by Kurt Roeckx
Browse files

Use only unsigned arithmetic in constant-time operations 



Signed-off-by: default avatarKurt Roeckx <kurt@roeckx.be>
Reviewed-by: default avatarEmilia Käsper <emilia@openssl.org>
parent d663df23

crypto/constant_time_locl.h

+3 −13
Original line number Diff line number Diff line
@@ -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)