Understanding Security in Special-Purpose Digital Radio Communication Systems

Activities that have specialized communication needs which cannot be met by general communication systems such as mobile telephony or wireless networking need specialized communication systems. The thesis investigates the special-purpose digital radio communication systems that have been created to meet specialized needs across a range of fields. Since many of the fields where these communication systems are used are part of critical infrastructures and other important operations, the security of the communication systems may be vital to the security of the operations they support. Despite this, special-purpose digital radio communication systems often have significantly lower levels of security than more commonly used systems, such as mobile telephony or Internet-based protocols. The thesis defines special-purpose digital radio communication systems as a class of systems that, while differing in many ways, have common security properties. The common security themes among the different systems are investigated through focused case studies on two standards: Automatic Link Establishment (ALE) for high-frequency radio and TETRA, a trunked cellular professional mobile radio standard. The case study on ALE uses cryptanalysis to find weaknesses in the cryptography specified by the standard, mirroring similar weaknesses in other standards. In the TETRA case, qualitative interviews reveal how organizations that own TETRA networks make security-related decisions regarding them. The thesis proposes a number of possible explanations for the low level of security in special-purpose digital radio communication systems: lack of security by design, deficient understanding of system dependencies, normal accident dynamics, lack of feedback, and market structure. The thesis is the first to consider the different standards as members of a single class of systems and point out the commonalities.