File 0005-Fix-timing-side-channel-in-ECDSA-signature-computati.patch of Package mingw64-openssl

From 7d5cf0f2a1f9ed2aa9b911cc5aaeb09fcb95a635 Mon Sep 17 00:00:00 2001
From: Tomas Mraz <tomas@openssl.org>
Date: Thu, 19 Feb 2026 14:07:20 +0100
Subject: [PATCH 05/11] Fix timing side-channel in ECDSA signature computation

There is a timing signal of around 300 nanoseconds when the top word of
the inverted ECDSA nonce value is zero. This can happen with significant
probability only for some of the supported elliptic curves. In particular
the NIST P-521 curve is affected. To be able to measure this leak, the
attacker process must either be located in the same physical computer or
must have a very fast network connection with low latency.

Attacks on ECDSA nonce are also known as Minerva attack.

Fixes CVE-2024-13176

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/26429)

(cherry picked from commit 63c40a66c5dc287485705d06122d3a6e74a6a203)
(cherry picked from commit 07272b05b04836a762b4baa874958af51d513844)
---
 crypto/bn/bn_exp.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c
index 36b7ba69ad..b346b18dc1 100644
--- a/crypto/bn/bn_exp.c
+++ b/crypto/bn/bn_exp.c
@@ -700,7 +700,8 @@ static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top,
  * out by Colin Percival,
  * http://www.daemonology.net/hyperthreading-considered-harmful/)
  */
-int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
+static
+int bn_mod_exp_mont_fixed_top(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
                               const BIGNUM *m, BN_CTX *ctx,
                               BN_MONT_CTX *in_mont)
 {
@@ -717,10 +718,6 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
     unsigned int t4 = 0;
 #endif
 
-    bn_check_top(a);
-    bn_check_top(p);
-    bn_check_top(m);
-
     if (!BN_is_odd(m)) {
         BNerr(BN_F_BN_MOD_EXP_MONT_CONSTTIME, BN_R_CALLED_WITH_EVEN_MODULUS);
         return (0);
@@ -1192,7 +1189,7 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
             goto err;
     } else
 #endif
-    if (!BN_from_montgomery(rr, &tmp, mont, ctx))
+    if (!bn_from_mont_fixed_top(rr, &tmp, mont, ctx))
         goto err;
     ret = 1;
  err:
@@ -1207,6 +1204,19 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
     return (ret);
 }
 
+int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
+                              const BIGNUM *m, BN_CTX *ctx,
+                              BN_MONT_CTX *in_mont)
+{
+    bn_check_top(a);
+    bn_check_top(p);
+    bn_check_top(m);
+    if (!bn_mod_exp_mont_fixed_top(rr, a, p, m, ctx, in_mont))
+        return 0;
+    bn_correct_top(rr);
+    return 1;
+}
+
 int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont)
 {
-- 
2.53.0