From 345df93978c41da1ac8047a37f1fed5286883d8d Mon Sep 17 00:00:00 2001
From: Jacob Barthelmeh <jacob@wolfssl.com>
Date: Mon, 19 Dec 2016 14:51:42 -0700
Subject: [PATCH] Bug fix for cache attack

---
 wolfcrypt/src/tfm.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/wolfcrypt/src/tfm.c b/wolfcrypt/src/tfm.c
index e73135a60..71b5735ea 100644
--- a/wolfcrypt/src/tfm.c
+++ b/wolfcrypt/src/tfm.c
@@ -446,12 +446,11 @@ INLINE static void fp_mul_comba_mulx(fp_int *A, fp_int *B, fp_int *C)
       pa = FP_SIZE-1;
    }
 
-   if (A == C || B == C) {
+   /* Always take branch to use tmp variable. This avoids a cache attack for
+    * determining if C equals A */
+   if (1) {
       fp_init(&tmp);
       dst = &tmp;
-   } else {
-      fp_zero(C);
-      dst = C;
    }
 
    TFM_INTEL_MUL_COMBA(A, B, dst) ;