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BACnet Insight

Certificate Handling in BACnet/SC

BACnet/SC Topology.

Certificate user interface example using a WAGO controller.

The aim of this article is to explain the additional security is achieved with certificates, i.e. digital mechanisms behind this are usually proprie-
tasks involved in handling security in heteroge- passports, which are used for two tasks: tary, or to put it another way: every manufac-
neous environments with devices and software ƒ unique identification of the communication turer is doing his own thing. Simplicity is there-
from different manufacturers. partners, fore sometimes bought by being tied to a single
ƒ encryption of the communication so that only vendor.
Hub and spoke the endpoints involved understand it.
The question arises as to how to provide
Communication in BACnet/SC is based on the To fulfil this task, there is a trio of related files BACnet/SC hubs and nodes from different man-
hub and spoke concept, which means that a on each participant in the BACnet/SC network. ufacturers with valid certificates. Fortunately,
device or software acting as a hub (server) is at The root certificate of a so-called Certification there is a helpful and freely available open-
the center. Other BACnet/SC participants con- Authority (CA), the public operational certificate source software tool that can help you with this
nect to it as so-called nodes (clients). In many of the device or software and the correspond- task, XCA by Christian Hohnstädt [1]. It is used in
diagrams, such connections are shown like the ing secret private key. As the name suggests, many BACnet/SC projects as follows:
spokes of a wheel, with the nodes at the ends this should never leave the device and be given 1. one-time creation of a self-signed root
and the hub in the center. In contrast to BACnet/ to a third party. certificate that identifies the so-called
IP, communication is then based on perma- Certification Authority (CA),
nent WebSocket Secure connections (TCP) Handworks 2. generation of signature requests on all
with the hub and no longer on loose messages participating endpoints (hubs and nodes),
(UDP) between the nodes themselves. The term The generation and handling of TLS certificates so-called Certificate Signing Requests (CSR),
‘WebSocket Secure’ deserves special attention is not trivial and requires additional effort when 3. downloading the CSR and importing it into
here. What does this mean and how is security implementing BACnet/SC projects. Many larger XCA,
achieved? manufacturers of control technology systems 4. signing of the CSR with the root certificate
that simultaneously offer hardware and software from 1. resulting in the device certificates,
WSS (WebSocket Secure) is a protocol for secure for management tasks, for example, have rec- called Operational Certificates in BACnet/SC,
bidirectional connections and currently uses the ognized the challenge. Here, the software takes 5. export the CA certificate from 1. and the
TLS 1.3 encryption standard, which is also used over the part of creating certificates and distrib- device certificates from 4. and upload them
for communication via https on the web. The uting them to the devices used. However, the in pairs to the respective participants.

14 14 BACnet Middle East Journal 13 11/24