text: Embedded devices in the Internet of Things (IoT) face a wide variety of security challenges. For example, software attackers perform code injection and code-reuse attacks on their remote interfaces, and physical access to IoT devices allows to tamper with code in memory, steal confidential Intellectual Property (IP), or mount fault attacks to manipulate a CPU's control flow. In this work, we present Sponge-based Control Flow Protection (SCFP). SCFP is a stateful, sponge-based scheme to ensure the confidentiality of software IP and its authentic execution on IoT devices. At compile time, SCFP encrypts and authenticates software with instruction-level granularity. During execution, an SCFP hardware extension between the CPU's fetch and decode stage continuously decrypts and authenticates instructions. Sponge-based authenticated encryption in SCFP yields fine-grained control-flow integrity and thus prevents code-reuse, code-injection, and fault attacks on the code and the control flow. In addition, SCFP withstands any modification of software in memory. For evaluation, we extended a RISC-V core with SCFP and fabricated a real System on Chip (SoC). The average overhead in code size and execution time of SCFP on this design is 19.8 and 9.1 , respectively, and thus meets the requirements of embedded IoT devices.
  @cite_16: CFI is a computer security technique that detects runtime attacks by monitoring a program's branching behavior. This work presents a detailed analysis of the security policies enforced by 21 recent hardware-based CFI architectures. The goal is to evaluate the security, limitations, hardware cost, performance, and practicality of using these policies. We show that many architectures are not suitable for widespread adoption, since they have practical issues, such as relying on accurate control flow model (which is difficult to obtain) or they implement policies which provide only limited security.
summary: . Numerous cfi schemes have been introduced in the last 30 years. However, techniques providing fine-grained cfi and code integrity, as required to detect physical attacks, are quite rare @cite_16 .