Use default openssl message digest algorithm

res/openssl/barrier.conf

@@ -15,7 +15,7 @@ new_certs_dir = $dir/certs
 certificate = $dir/cacert.pem
 private_key = $dir/private/cakey.pem
 default_days = 365
-default_md = md5
+default_md = default
 preserve = no
 email_in_dn = no
 nameopt = default_ca
@@ -33,7 +33,7 @@ emailAddress = optional
 [req]
 default_bits = 2048 # Size of keys
 default_keyfile = key.pem # name of generated keys
-default_md = md5 # message digest algorithm
+default_md = default # message digest algorithm
 string_mask = nombstr # permitted characters
 distinguished_name = req_distinguished_name
 req_extensions = v3_req