Low-Latency Cryptographic Protection for SCADA Communications

Supervisory Control And Data Acquisition (SCADA) systems are real-time process control systems that are widely deployed throughout critical infrastructure sectors including power, gas, oil, and water. However, SCADA networks generally have little protection from the rising danger of cyber attack. A retrofit solution to protect existing SCADA communications links must assure the integrity of commands and responses that are typically transmitted over serial lines at speeds from 300 to 19200 bits per second, while introducing minimal additional latency into the real-time SCADA traffic. This paper describes the key aspects of a cryptographic protocol for retrofit SCADA link protection that leverages the Cyclic Redundancy Checks (CRC) transmitted by existing SCADA equipment to achieve strong integrity while introducing minimal latency. The protocol is based on a new position embedding encryption mode which, for a b-bit block cipher, ensures that any unauthentic message an adversary can construct (i) includes at least b randomly chosen bits, and therefore, by a new result proved for error detection by systematic shortened cyclic codes, (ii) contains a correct h-bit CRC with probability 2. The low speed of the communications channel limits the rate at which an adversary can make trials, enabling detection of potential attacks before enough trials can be made to achieve any significant likelihood of success. The protocol avoids the need for a decrypting link protection module to buffer decrypted data until an end-of-message integrity check is verified, which would otherwise add significant latency.