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Timing vulnerability in ECDSA signature generation (CVE-2018-0735)
Preallocate an extra limb for some of the big numbers to avoid a reallocation
that can potentially provide a side channel.
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from #7486)
(cherry picked from commit 99540ec)
https://www.openssl.org/news/secadv/20181029.txt
--- crypto/ec/ec_mult.c.orig 2018-08-14 12:45:07 UTC
+++ crypto/ec/ec_mult.c
@@ -177,8 +177,8 @@ static int ec_mul_consttime(const EC_GRO
*/
cardinality_bits = BN_num_bits(cardinality);
group_top = bn_get_top(cardinality);
- if ((bn_wexpand(k, group_top + 1) == NULL)
- || (bn_wexpand(lambda, group_top + 1) == NULL))
+ if ((bn_wexpand(k, group_top + 2) == NULL)
+ || (bn_wexpand(lambda, group_top + 2) == NULL))
goto err;
if (!BN_copy(k, scalar))
@@ -205,7 +205,7 @@ static int ec_mul_consttime(const EC_GRO
* k := scalar + 2*cardinality
*/
kbit = BN_is_bit_set(lambda, cardinality_bits);
- BN_consttime_swap(kbit, k, lambda, group_top + 1);
+ BN_consttime_swap(kbit, k, lambda, group_top + 2);
group_top = bn_get_top(group->field);
if ((bn_wexpand(s->X, group_top) == NULL)
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