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authorDenys Vlasenko2021-04-26 21:58:04 +0200
committerDenys Vlasenko2021-04-26 21:58:04 +0200
commit9a40be433de31b8a7fea20b7ebce3dafbedaf504 (patch)
tree932d58daca61e599ca79e71ebffb785146f6766d
parent120401249a37a77cd2d4c71ad20a9a194bfea409 (diff)
downloadbusybox-9a40be433de31b8a7fea20b7ebce3dafbedaf504.zip
busybox-9a40be433de31b8a7fea20b7ebce3dafbedaf504.tar.gz
tls: get rid of constant-time add/sub operations
function old new delta sp_256_sub_10 - 22 +22 static.sp_256_mont_reduce_10 176 178 +2 sp_256_mod_mul_norm_10 1440 1439 -1 sp_256_proj_point_dbl_10 453 446 -7 sp_256_ecc_mulmod_10 1229 1216 -13 static.sp_256_mont_sub_10 52 30 -22 static.sp_256_cond_sub_10 32 - -32 ------------------------------------------------------------------------------ (add/remove: 1/1 grow/shrink: 1/4 up/down: 24/-75) Total: -51 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--networking/tls_sp_c32.c58
1 files changed, 21 insertions, 37 deletions
diff --git a/networking/tls_sp_c32.c b/networking/tls_sp_c32.c
index 8527e78..72a3be5 100644
--- a/networking/tls_sp_c32.c
+++ b/networking/tls_sp_c32.c
@@ -203,26 +203,12 @@ static void sp_256_add_10(sp_digit* r, const sp_digit* a, const sp_digit* b)
r[i] = a[i] + b[i];
}
-/* Conditionally add a and b using the mask m.
- * m is -1 to add and 0 when not.
- */
-static void sp_256_cond_add_10(sp_digit* r, const sp_digit* a,
- const sp_digit* b, const sp_digit m)
-{
- int i;
- for (i = 0; i < 10; i++)
- r[i] = a[i] + (b[i] & m);
-}
-
-/* Conditionally subtract b from a using the mask m.
- * m is -1 to subtract and 0 when not.
- */
-static void sp_256_cond_sub_10(sp_digit* r, const sp_digit* a,
- const sp_digit* b, const sp_digit m)
+/* Sub b from a into r. (r = a - b) */
+static void sp_256_sub_10(sp_digit* r, const sp_digit* a, const sp_digit* b)
{
int i;
for (i = 0; i < 10; i++)
- r[i] = a[i] - (b[i] & m);
+ r[i] = a[i] - b[i];
}
/* Shift number left one bit. Bottom bit is lost. */
@@ -352,7 +338,8 @@ static void sp_256_mul_add_10(sp_digit* r, const sp_digit* a, sp_digit b)
/* Divide the number by 2 mod the modulus (prime). (r = a / 2 % m) */
static void sp_256_div2_10(sp_digit* r, const sp_digit* a, const sp_digit* m)
{
- sp_256_cond_add_10(r, a, m, 0 - (a[0] & 1));
+ if (a[0] & 1)
+ sp_256_add_10(r, a, m);
sp_256_norm_10(r);
sp_256_rshift1_10(r, r);
}
@@ -382,7 +369,8 @@ static void sp_256_mont_add_10(sp_digit* r, const sp_digit* a, const sp_digit* b
{
sp_256_add_10(r, a, b);
sp_256_norm_10(r);
- sp_256_cond_sub_10(r, r, m, 0 - ((r[9] >> 22) > 0));
+ if ((r[9] >> 22) > 0)
+ sp_256_sub_10(r, r, m);
sp_256_norm_10(r);
}
@@ -391,7 +379,8 @@ static void sp_256_mont_dbl_10(sp_digit* r, const sp_digit* a, const sp_digit* m
{
sp_256_add_10(r, a, a);
sp_256_norm_10(r);
- sp_256_cond_sub_10(r, r, m, 0 - ((r[9] >> 22) > 0));
+ if ((r[9] >> 22) > 0)
+ sp_256_sub_10(r, r, m);
sp_256_norm_10(r);
}
@@ -400,28 +389,23 @@ static void sp_256_mont_tpl_10(sp_digit* r, const sp_digit* a, const sp_digit* m
{
sp_256_add_10(r, a, a);
sp_256_norm_10(r);
- sp_256_cond_sub_10(r, r, m, 0 - ((r[9] >> 22) > 0));
+ if ((r[9] >> 22) > 0)
+ sp_256_sub_10(r, r, m);
sp_256_norm_10(r);
sp_256_add_10(r, r, a);
sp_256_norm_10(r);
- sp_256_cond_sub_10(r, r, m, 0 - ((r[9] >> 22) > 0));
+ if ((r[9] >> 22) > 0)
+ sp_256_sub_10(r, r, m);
sp_256_norm_10(r);
}
-/* Sub b from a into r. (r = a - b) */
-static void sp_256_sub_10(sp_digit* r, const sp_digit* a, const sp_digit* b)
-{
- int i;
- for (i = 0; i < 10; i++)
- r[i] = a[i] - b[i];
-}
-
/* Subtract two Montgomery form numbers (r = a - b % m) */
static void sp_256_mont_sub_10(sp_digit* r, const sp_digit* a, const sp_digit* b,
const sp_digit* m)
{
sp_256_sub_10(r, a, b);
- sp_256_cond_add_10(r, r, m, r[9] >> 22);
+ if (r[9] >> 22)
+ sp_256_add_10(r, r, m);
sp_256_norm_10(r);
}
@@ -460,7 +444,8 @@ static void sp_256_mont_reduce_10(sp_digit* a, const sp_digit* m, sp_digit mp)
}
sp_256_mont_shift_10(a, a);
- sp_256_cond_sub_10(a, a, m, 0 - ((a[9] >> 22) > 0));
+ if ((a[9] >> 22) > 0)
+ sp_256_sub_10(a, a, m);
sp_256_norm_10(a);
}
@@ -590,7 +575,6 @@ static void sp_256_map_10(sp_point* r, sp_point* p)
{
sp_digit t1[2*10];
sp_digit t2[2*10];
- int32_t n;
sp_256_mont_inv_10(t1, p->z);
@@ -602,8 +586,8 @@ static void sp_256_map_10(sp_point* r, sp_point* p)
memset(r->x + 10, 0, sizeof(r->x) / 2);
sp_256_mont_reduce_10(r->x, p256_mod, p256_mp_mod);
/* Reduce x to less than modulus */
- n = sp_256_cmp_10(r->x, p256_mod);
- sp_256_cond_sub_10(r->x, r->x, p256_mod, 0 - (n >= 0));
+ if (sp_256_cmp_10(r->x, p256_mod) >= 0)
+ sp_256_sub_10(r->x, r->x, p256_mod);
sp_256_norm_10(r->x);
/* y /= z^3 */
@@ -611,8 +595,8 @@ static void sp_256_map_10(sp_point* r, sp_point* p)
memset(r->y + 10, 0, sizeof(r->y) / 2);
sp_256_mont_reduce_10(r->y, p256_mod, p256_mp_mod);
/* Reduce y to less than modulus */
- n = sp_256_cmp_10(r->y, p256_mod);
- sp_256_cond_sub_10(r->y, r->y, p256_mod, 0 - (n >= 0));
+ if (sp_256_cmp_10(r->y, p256_mod) >= 0)
+ sp_256_sub_10(r->y, r->y, p256_mod);
sp_256_norm_10(r->y);
memset(r->z, 0, sizeof(r->z));