Comment on "SRAM-PUF Based Entities Authentication Scheme for Resource-constrained IoT Devices".

The cloud-based Internet of Things (IoT) creates opportunities for more direct integration of the physical world and computer-based systems, allowing advanced applications based on sensing, analyzing and controlling the physical world. IoT deployments, however, are at a particular risk of counterfeiting, through which an adversary can corrupt the entire ecosystem. Therefore, entity authentication of edge devices is considered an essential part of the security of IoT systems. A recent paper of Farha et al. suggested an entity authentication scheme suitable for low-resource IoT edge devices, which relies on SRAM-based physically unclonable functions (PUFs). In this paper we analyze this scheme. We show that, while it claims to offer strong PUF functionality, the scheme creates only a weak PUF: an active attacker can completely read out the secret PUF response of the edge device after a very small amount of queries, converting the scheme into a weak PUF scheme which can then be counterfeited easily. After analyzing the scheme, we propose an alternative construction for an authentication method based on SRAM-PUF which better protects the secret SRAM startup state.