From 441f3a7f1f2deeb66efc17f3072892e2c53c2b8c Mon Sep 17 00:00:00 2001
From: Tesfa Mael <tesfa@wolfssl.com>
Date: Mon, 14 Oct 2019 16:43:45 -0700
Subject: [PATCH] Add leading zero for odd number of hex digits

---
 tests/api.c         | 2 +-
 wolfcrypt/src/tfm.c | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/tests/api.c b/tests/api.c
index fa53eef67..7795ff068 100644
--- a/tests/api.c
+++ b/tests/api.c
@@ -24095,7 +24095,7 @@ static void test_wolfSSL_X509_get_serialNumber(void)
     X509_free(x509); /* free's a */
 
     AssertNotNull(serialHex = BN_bn2hex(bn));
-    AssertStrEQ(serialHex, "1");
+    AssertStrEQ(serialHex, "01");
     OPENSSL_free(serialHex);
 
     AssertIntEQ(BN_get_word(bn), 1);
diff --git a/wolfcrypt/src/tfm.c b/wolfcrypt/src/tfm.c
index c5e4aac2b..899503426 100644
--- a/wolfcrypt/src/tfm.c
+++ b/wolfcrypt/src/tfm.c
@@ -4780,6 +4780,12 @@ int mp_toradix (mp_int *a, char *str, int radix)
         ++digs;
     }
 
+    /* For hexadecimal output, add zero when number of digits is odd */
+    if ((digs & 1) && (radix == 16)) {
+        *str++ = fp_s_rmap[0];
+        ++digs;
+    }
+
     /* reverse the digits of the string.  In this case _s points
      * to the first digit [excluding the sign] of the number]
      */