From 401c8d53d8a8cf1e79980e62bda3f946f8e07c14 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Niels=20M=C3=B6ller?= <nisse@lysator.liu.se>
Date: Sat, 13 Mar 2021 16:29:50 +0100
Subject: [PATCH] Analogous fix to ecc_gostdsa_verify.

* ecc-gostdsa-verify.c (ecc_gostdsa_verify): Use ecc_mod_mul_canonical
to compute the scalars used for ecc multiplication.

(cherry picked from commit fbaefb64b90cb45b7075a0ed72a92f2a1fbcd2ab)
---
 ChangeLog            | 3 +++
 ecc-gostdsa-verify.c | 6 +++---
 2 files changed, 6 insertions(+), 3 deletions(-)

#diff --git a/ChangeLog b/ChangeLog
#index fb2d7f66..5f8a22c2 100644
#--- a/ChangeLog
#+++ b/ChangeLog
#@@ -1,5 +1,8 @@
# 2021-03-13  Niels Möller  <nisse@lysator.liu.se>
# 
#+	* ecc-gostdsa-verify.c (ecc_gostdsa_verify): Use ecc_mod_mul_canonical
#+	to compute the scalars used for ecc multiplication.
#+
# 	* ecc-ecdsa-sign.c (ecc_ecdsa_sign): Ensure s output is reduced to
# 	canonical range.
# 
--- a/ecc-gostdsa-verify.c
+++ b/ecc-gostdsa-verify.c
@@ -102,11 +102,11 @@ ecc_gostdsa_verify (const struct ecc_cur
   ecc->q.invert (&ecc->q, vp, hp, vp + 2*ecc->p.size);
 
   /* z1 = s / h, P1 = z1 * G */
-  ecc_mod_mul (&ecc->q, z1, sp, vp);
+  ecc_mod_mul_canonical (&ecc->q, z1, sp, vp, z1);
 
   /* z2 = - r / h, P2 = z2 * Y */
-  ecc_mod_mul (&ecc->q, z2, rp, vp);
-  mpn_sub_n (z2, ecc->q.m, z2, ecc->p.size);
+  mpn_sub_n (hp, ecc->q.m, rp, ecc->p.size);
+  ecc_mod_mul_canonical (&ecc->q, z2, hp, vp, z2);
 
    /* Total storage: 5*ecc->p.size + ecc->mul_itch */
   ecc->mul (ecc, P2, z2, pp, z2 + ecc->p.size);
