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tls: fix (what looks like) a rare corner case bug in P256

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function                                             old     new   delta
static.sp_256_mont_sub_10                             30      46     +16

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2021-10-05 17:31:33 +02:00
parent 92402d5e0a
commit 81d8af1970
1 changed files with 7 additions and 4 deletions
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11
networking/tls_sp_c32.c
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@ -96,11 +96,13 @@ static void sp_256_to_bin_10(sp_digit* r, uint8_t* a)
a[j] = 0;
for (i = 0; i < 10 && 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;
}
@ -297,6 +299,7 @@ static void sp_256_mont_sub_10(sp_digit* r, const sp_digit* a, const sp_digit* b
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) */
@ -864,8 +867,8 @@ static void sp_ecc_secret_gen_256(const sp_digit priv[10], const uint8_t *pub2x3
dump_hex(" %s\n", pub2x32 + 32, 32);
sp_256_point_from_bin2x32(point, pub2x32);
dump_hex("point->x %s\n", point->x, sizeof(point->x));
dump_hex("point->y %s\n", point->y, sizeof(point->y));
dump_512("point->x %s\n", point->x);
dump_512("point->y %s\n", point->y);
sp_256_ecc_mulmod_10(point, point, priv);