Interested in linking to "Protocol for SCADA field communications"?
You may use the Headline, Deck, Byline and URL of this article on your Web site. To link to this article, select and copy the HTML code below and paste it on your own Web site.
In many cases, confidentiality is a distant third. We would recommend a HMACSHA256 mode if it were available.
I was told that the committee felt that the processing power required to perform the public key calculations in a HMACSHA256 would support encryption. So the committee decided to include encryption. This is one of the ways that security professionals get labeled as unrealistic or paranoid by implementing protection that does not reduce a risk to the organization. There definitely should be encryption modes, but there should be authentication-only modes for asset owners where confidentiality is not required.
The standard wisely defines a mixed mode with both protected and unprotected communication going through a Secure Communication Module (SCM). An asset owner may not want to protect communications to all field sites. Also, mixed mode will support a phased implementation of the AGA-12 boxes.
The serial field communication is typically at a low data rate and may be very time sensitive. Waiting until the entire command is received and the security fields processed prior to sending to a PLC may introduce an unacceptable delay. The AGA 12 standard recognizes this and has holdback and non-holdback modes. Holdback processes the security fields and passes the commands if the signature and HMAC are valid. Non-holdback modes pass the data to the PLC as fast as possible and post processes the signature and HMAC.
Responses to this article will be posted on the DitalBond.com SCADA Blog, along with contrary views and any other interesting feedback I get on this review. What do you think of AGA-12?
|About the Author|
ControlGlobal.com is exclusively dedicated to the global process automation market. We report on developing industry trends, illustrate successful industry applications, and update the basic skills and knowledge base that provide the profession's foundation.