From eca5174b5f448d3fc5a9401d76983ce2cf9e2194 Mon Sep 17 00:00:00 2001
From: Andy Polyakov <appro@openssl.org>
Date: Thu, 18 Aug 2016 13:38:42 +0200
Subject: [PATCH] ec/ecp_nistz256.c: get is_one on 32-bit platforms right.
Thanks to Brian Smith for reporting this.
Reviewed-by: Rich Salz <rsalz@openssl.org>
---
crypto/ec/ecp_nistz256.c | 37 ++++++++++++++++++++++---------------
1 file changed, 22 insertions(+), 15 deletions(-)
diff --git a/crypto/ec/ecp_nistz256.c b/crypto/ec/ecp_nistz256.c
index ca44d0aaee..1459980e87 100644
--- a/crypto/ec/ecp_nistz256.c
+++ b/crypto/ec/ecp_nistz256.c
@@ -205,21 +205,29 @@ static BN_ULONG is_equal(const BN_ULONG a[P256_LIMBS],
return is_zero(res);
}
-static BN_ULONG is_one(const BN_ULONG a[P256_LIMBS])
+static BN_ULONG is_one(const BIGNUM *z)
{
- BN_ULONG res;
-
- res = a[0] ^ ONE[0];
- res |= a[1] ^ ONE[1];
- res |= a[2] ^ ONE[2];
- res |= a[3] ^ ONE[3];
- if (P256_LIMBS == 8) {
- res |= a[4] ^ ONE[4];
- res |= a[5] ^ ONE[5];
- res |= a[6] ^ ONE[6];
+ BN_ULONG res = 0;
+ BN_ULONG *a = z->d;
+
+ if (z->top == (P256_LIMBS - P256_LIMBS / 8)) {
+ res = a[0] ^ ONE[0];
+ res |= a[1] ^ ONE[1];
+ res |= a[2] ^ ONE[2];
+ res |= a[3] ^ ONE[3];
+ if (P256_LIMBS == 8) {
+ res |= a[4] ^ ONE[4];
+ res |= a[5] ^ ONE[5];
+ res |= a[6] ^ ONE[6];
+ /*
+ * no check for a[7] (being zero) on 32-bit platforms,
+ * because value of "one" takes only 7 limbs.
+ */
+ }
+ res = is_zero(res);
}
- return is_zero(res);
+ return res;
}
static int ecp_nistz256_set_words(BIGNUM *a, BN_ULONG words[P256_LIMBS])
@@ -741,9 +749,8 @@ static int ecp_nistz256_is_affine_G(const EC_POINT *generator)
{
return (generator->X.top == P256_LIMBS) &&
(generator->Y.top == P256_LIMBS) &&
- (generator->Z.top == (P256_LIMBS - P256_LIMBS / 8)) &&
is_equal(generator->X.d, def_xG) &&
- is_equal(generator->Y.d, def_yG) && is_one(generator->Z.d);
+ is_equal(generator->Y.d, def_yG) && is_one(&generator->Z);
}
static int ecp_nistz256_mult_precompute(EC_GROUP *group, BN_CTX *ctx)
@@ -1331,7 +1338,7 @@ static int ecp_nistz256_points_mul(const EC_GROUP *group,
!ecp_nistz256_set_words(&r->Z, p.p.Z)) {
goto err;
}
- r->Z_is_one = is_one(p.p.Z) & 1;
+ r->Z_is_one = is_one(&r->Z) & 1;
ret = 1;
--
2.25.1