Security Aspects
There is increasing awareness of the security risks of wireless automation and control products. Users question “How secure is a wireless link compared to running wire?”
There is a lot of comfort in “wire” as a traditional and well understood medium for transferring data. “Wireless”, in comparison, is a relatively new technology, and is a medium without the physical bounds of wire. Wired data stops at the end of the wire – wireless data can spread through the air.
Security is an important aspect of the wireless systems.
What are the security concerns with wireless?
Most concerns center around two aspects:
- Can a wireless link be deliberately jammed to prevent it working?
- Can wireless data be stolen (industrial espionage) or can wireless data be maliciouisly injected (hacking)?
Jamming
Deliberate or non-deliberate jamming occurs when another wireless system causes enough interference to prevent your wireless system operating reliably. The degree of difficulty in doing this depends on the nature of the wireless system.
If the primary wireless system has a high fade margin (or a high signal to noise ratio), then the jamming signal needs to be very strong. For short distance applications found in industrial plants and factories, this means that the interfering antenna needs to be close and will generally be easy to locate.
Fixed frequency channels are easier to jam than spread spectrum, although some forms of spread spectrum do not provide a large advantage. Direct sequence devices can be jammed by higher power direct sequence devices using the same wide channel. Frequency hopping provides the best protection against jamming, with asynchronous hopping having better performance than synchronous hoppers.
Synchronous frequency hopping is where transmitters continually transmit a radio message for receivers to stay in hop-synchronism.
Asynchronous transmitters only transmit when there is data to be transmitted, with receivers continually cycling though the top sequence looking for a transmission “lead-in signature”. Synchronous hoppers can be jammed by strong fixed frequency signal which causes the receivers to lose the transmitter signal each hopping cycle. However it is difficult to jam an asynchronous hopper.
Another system factor affecting vulnerability to jamming is the duty-cycle of the system. It is difficult to create a jamming signal which is present more than 50% of the time. A system which is transmitting continuously (for example, a polling system) can be jammed much easier than a system which uses a more sophisticated event-driven protocol and transmits with a lower duty-cycle. The lower the duty-cycle of a system, the less vulnerable it is to jamming.
Hacking
The best protection against wireless espionage or hacking is encryption of the wireless data. Although sophisticated modulation techniques and spread spectrum provide a high level of protection, this protection disappears if the offender uses the same type of wireless device (with the same modulation or spread spectrum technology) as the target system.
Most modern wireless devices provide some degree of security encryption. There has been a lot of publicity about the weakness of the WiFi WEP encryption, which transmits the encryption keys as part of the encryption scheme. However WEP was not intended for secure industrial application, and there are many other encryption methods which provide very secure protection.
AES (Advanced Encryption Standard) is generally recognized as an “unbreakable” scheme, although this standard requires heavy computing resources and can significantly slow down the operation of wireless devices. Many proprietary encryption schemes provide the same degree of protection without the heavy computing resources – the fact that these schemes are not open to continuous scrutiny and testing gives them a higher level of inherent protection.
Security protection does not need to be 100% secure – the protection needs to make it hard enough for malicious offenders that they will look for an easier alternative to achieve their goals. Modern wireless systems if properly engineered, can provide similar or higher security protection that traditional wired systems.