zero ECC private key stack buffers

Author: JeremiahM37

wolfcrypt/src/port/kcapi/kcapi_ecc.c

@@ -120,6 +120,7 @@ int KcapiEcc_LoadKey(ecc_key* key, byte* pubkey_raw, word32* pubkey_sz,
             if (ret == 0) {
                 ret = kcapi_kpp_setkey(key->handle, priv, keySz);
             }
+            ForceZero(priv, sizeof(priv));
         }
         else {
             /* generate new ephemeral key */
@@ -241,6 +242,7 @@ int KcapiEcc_SharedSecret(ecc_key* private_key, ecc_key* public_key, byte* out,
                 ret = 0;
             }
         }
+        ForceZero(priv, sizeof(priv));
     }
     if (ret == 0) {
     #ifdef KCAPI_USE_XMALLOC
@@ -317,6 +319,7 @@ static int KcapiEcc_SetPrivKey(ecc_key* key)
         }
     }
 
+    ForceZero(priv, sizeof(priv));
     return ret;
 }