Vviewpoints
DOI: 10.1145/2492007.2492018
Privacy and security
the air gap:
sCaDa’s enduring
security Myth

As a seCurity practitioner and a controls engineer, I am often asked my views on air gaps as a security strat- egy for supervisory control and data acquisition (SCADA) and industrial control systems (ICS). Air gaps have long been a focus of discussion in industry, and they still continue to generate a lot of interest in the media. In theory, the air gap strategy certainly sounds great. By creating a physical gap between the control network and the business network, the bad guys— criminals, hackers, and worms—are kept out of critical systems.

PhotograPh courteSy of rutherforD aPPleton laboratory anD the ScIence anD technology facIlItIeS councIl (Stfc); httP://WWW.chIlton-comPutIng.org.uk

Before I go any further, I must clarify what I mean when I use the term “air gap”: What I am referring to in this column is the philosophy that says we can truly isolate our critical systems from the outside world. And this is where the myth—and the danger—lies. To begin, I do not believe true air gaps actually exist in the ICS and SCADA world. Moreover, many SCADA security experts have even stronger opinions than me on the subject—for example, see Craig Wright’s blog.a However, I do acknowledge (albeit reluctantly) that not everyone agrees with me on this.

In 2011, for example, we saw a deluge of SCADA and ICS vulnerability

a control system protected by a real air gap: iBm 360/195 playing chess, november 1974.

using the strategies suggested in this
document or isolate the automation
network from all other networks us-
ing an air gap.”
a http://infosecisland.com/blogview/16770-
SCADA-Air-Gaps-Do-Not-Exist.html
notices with advice on addressing the
issue by using an air gap. One example
I have referred to in the past comes
from the original Siemens Security
Advisory addressing the vulnerabili-
ties in Siemens’ SIMATIC S7-1200
PLC line: “In addition, it is important
to ensure your automation network is
protected from unauthorized access

the ‘air Gap Principle’ is history To give credit where credit is due: Siemens removed this recommendation from the advisory (and all