b3b1713a5
Denys Vlasenko
2021-04-26
Subject
tls: in P256 replace constant-time compares with usual ones
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Commit Diff GitHub →
networking/tls_sp_c32.c+9 -14
| @@ -159,17 +159,20 @@ static void sp_256_point_from_bin2x32(sp_point* p, const uint8_t *bin2x32) | |
| p->z[0] = 1; | |
| } | |
| - | /* Compare a with b in constant time. |
| + | /* Compare a with b. |
| * | |
| * return -ve, 0 or +ve if a is less than, equal to or greater than b | |
| * respectively. | |
| */ | |
| static sp_digit sp_256_cmp_10(const sp_digit* a, const sp_digit* b) | |
| { | |
| - | sp_digit r = 0; |
| + | sp_digit r; |
| int i; | |
| - | for (i = 9; i >= 0; i--) |
| - | r |= (a[i] - b[i]) & (0 - !r); |
| + | for (i = 9; i >= 0; i--) { |
| + | r = a[i] - b[i]; |
| + | if (r != 0) |
| + | break; |
| + | } |
| return r; | |
| } | |
| @@ -179,15 +182,7 @@ static sp_digit sp_256_cmp_10(const sp_digit* a, const sp_digit* b) | |
| */ | |
| static int sp_256_cmp_equal_10(const sp_digit* a, const sp_digit* b) | |
| { | |
| - | #if 1 |
| - | sp_digit r = 0; |
| - | int i; |
| - | for (i = 0; i < 10; i++) |
| - | r |= (a[i] ^ b[i]); |
| - | return r == 0; |
| - | #else |
| return sp_256_cmp_10(a, b) == 0; | |
| - | #endif |
| } | |
| /* Normalize the values in each word to 26 bits. */ | |
| @@ -710,8 +705,8 @@ static void sp_256_proj_point_add_10(sp_point* r, sp_point* p, sp_point* q, | |
| sp_256_sub_10(t1, p256_mod, q->y); | |
| sp_256_norm_10(t1); | |
| if (sp_256_cmp_equal_10(p->x, q->x) | |
| - | & sp_256_cmp_equal_10(p->z, q->z) |
| - | & (sp_256_cmp_equal_10(p->y, q->y) | sp_256_cmp_equal_10(p->y, t1)) |
| + | && sp_256_cmp_equal_10(p->z, q->z) |
| + | && (sp_256_cmp_equal_10(p->y, q->y) || sp_256_cmp_equal_10(p->y, t1)) |
| ) { | |
| sp_256_proj_point_dbl_10(r, p, t); | |
| } | |