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tls: fix the case of sp_256_mont_tpl_10() leaving striay high bits

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It has no effect on correctness, but interferes with compating internal state
of different implementations.

function                                             old     new   delta
sp_256_proj_point_dbl_10                             443     451      +8
static.sp_256_mont_sub_10                             46      49      +3
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 11/0)               Total: 11 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
2021-10-05 19:45:56 +02:00
parent 81d8af1970
commit 55578f2fb7
3 changed files with 72 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

37
networking/tls_sp_c32.c
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@@ -163,11 +163,13 @@ static void dump_512(const char *fmt, const sp_digit* cr)
a[j] = 0;
for (i = 0; i < 20 && j >= 0; i++) {
b = 0;
a[j--] |= r[i] << s; b += 8 - s;
a[j--] |= r[i] << s;
b += 8 - s;
if (j < 0)
break;
while (b < 26) {
a[j--] = r[i] >> b; b += 8;
a[j--] = r[i] >> b;
b += 8;
if (j < 0)
break;
}
@@ -286,9 +288,10 @@ 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);
if ((r[9] >> 22) > 0)
if ((r[9] >> 22) > 0) {
sp_256_sub_10(r, r, m);
sp_256_norm_10(r);
sp_256_norm_10(r);
}
}
/* Subtract two Montgomery form numbers (r = a - b % m) */
@@ -296,10 +299,12 @@ 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);
if (r[9] >> 22)
sp_256_add_10(r, r, m);
sp_256_norm_10(r);
r[9] &= 0x03fffff; /* truncate to 22 bits */
if (r[9] >> 22) {
sp_256_add_10(r, r, m);
sp_256_norm_10(r);
r[9] &= 0x03fffff; /* truncate to 22 bits */
}
}
/* Double a Montgomery form number (r = a + a % m) */
@@ -317,14 +322,17 @@ 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);
if ((r[9] >> 22) > 0)
if ((r[9] >> 22) > 0) {
sp_256_sub_10(r, r, m);
sp_256_norm_10(r);
sp_256_norm_10(r);
}
sp_256_add_10(r, r, a);
sp_256_norm_10(r);
if ((r[9] >> 22) > 0)
if ((r[9] >> 22) > 0) {
sp_256_sub_10(r, r, m);
sp_256_norm_10(r);
sp_256_norm_10(r);
}
r[9] &= 0x03fffff; /* truncate to 22 bits */
}
/* Shift the result in the high 256 bits down to the bottom. */
@@ -650,6 +658,13 @@ static void sp_256_proj_point_dbl_10(sp_point* r, sp_point* p)
if (r->infinity) /* If infinity, don't double */
return;
if (SP_DEBUG) {
/* unused part of t2, may result in spurios
* differences in debug output. Clear it.
*/
memset(t2, 0, sizeof(t2));
}
/* T1 = Z * Z */
sp_256_mont_sqr_10(t1, r->z /*, p256_mod, p256_mp_mod*/);
/* Z = Y * Z */