International Association
for Cryptologic Research

User interaction constitutes a largely unexplored field in protocol analysis, even in instances where the user takes an active role as a trusted third party, such as in the Internet of Things (IoT) device initialization protocols. Initializing the study of computational analysis of 3-party authentication protocols where one party is a physical user, this research introduces the 3-party possession user mediated authentication (3-PUMA) model. The 3-PUMA model addresses active user participation in a protocol which is designed to authenticate possession of a fixed data string – such as in IoT device commissioning. To demonstrate the 3-PUMA model in practice, we provide a computational analysis of the ISO/IEC 9798- 6:2010 standard’s Mechanism 7a authentication protocol which includes a user interface and interaction as well as a device-to-device channel. We show that the security of ISO/IEC 9798-6:2010 Mechanism 7a relies upon a non-standard MAC security notion, which we term existential unforgeability under key collision attacks (EUF-KCA). It is unknown if any standardized MAC algorithm achieves EUF-KCA security, indicating a potential vulnerability in the standard.