From dcda81d796de2f4a16fd7e9e7a5d07baa288f147 Mon Sep 17 00:00:00 2001
From: Niels Möller <nisse@lysator.liu.se>
Date: Tue, 18 Jul 2017 20:52:30 +0200
Subject: [PATCH] Fix for in-place ecc_add_eh.

* ecc-add-eh.c (ecc_add_eh): Fix in-place operation by reordering
two multiplies. Previously, in-place operation resulted in an
invalid call to mpn_mul with overlapping operands. Reported by
Sergei Trofimovich.
---
 ChangeLog    | 7 +++++++
 ecc-add-eh.c | 4 ++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/ecc-add-eh.c b/ecc-add-eh.c
index a16be4c..c07ff49 100644
--- a/ecc-add-eh.c
+++ b/ecc-add-eh.c
@@ -98,8 +98,8 @@ ecc_add_eh (const struct ecc_curve *ecc,
   ecc_modp_mul (ecc, x3, B, z1);
 
   /* y3 */
-  ecc_modp_mul (ecc, B, F, C); /* ! */
-  ecc_modp_mul (ecc, y3, B, z1);
+  ecc_modp_mul (ecc, B, F, z1); /* ! */
+  ecc_modp_mul (ecc, y3, B, C); /* Clobbers z1 in case r == p. */
 
   /* z3 */
   ecc_modp_mul (ecc, B, F, G);
--
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