From 26a9435f5c1fa754fe208f3e907bdc752aac922f Mon Sep 17 00:00:00 2001
From: Sean Parkinson <sean@wolfssl.com>
Date: Wed, 15 Nov 2023 13:21:30 +1000
Subject: [PATCH] ECC point double: when z ordinate is 0 point is infinity

Recognize z == 0 as infinity in result of double.
---
 wolfcrypt/src/ecc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/wolfcrypt/src/ecc.c b/wolfcrypt/src/ecc.c
index e38548bc9..179fb6003 100644
--- a/wolfcrypt/src/ecc.c
+++ b/wolfcrypt/src/ecc.c
@@ -7801,6 +7801,13 @@ int ecc_projective_dbl_point_safe(ecc_point *P, ecc_point *R, mp_int* a,
     }
     else {
         err = _ecc_projective_dbl_point(P, R, a, modulus, mp);
+        if ((err == MP_OKAY) && mp_iszero(R->z)) {
+           err = mp_set(R->x, 0);
+           if (err == MP_OKAY)
+               err = mp_set(R->y, 0);
+           if (err == MP_OKAY)
+               err = mp_set(R->z, 1);
+        }
     }
 
     return err;