ZEKRA: Zero-Knowledge Control-Flow Attestation

Abstract

To detect runtime attacks against programs running on a remote computing platform, Control-Flow Attestation (CFA) lets a (trusted) verifier determine the legality of the program's execution path, as recorded and reported by the remote platform (prover). However, besides complicating scalability due to verifier complexity, this assumption regarding the verifier's trustworthiness renders existing CFA schemes prone to privacy breaches and implementation disclosure attacks under "honest-but-curious" adversaries. Thus, to suppress sensitive details from the verifier, we propose to have the prover outsource the verification of the attested execution path to an intermediate worker of which the verifier only learns the result. However, since a worker might be dishonest about the outcome of the verification, we propose a purely cryptographical solution of transforming the verification of the attested execution path into a verifiable computational task that can be reliably outsourced to a worker without relying on any trusted execution environment. Specifically, we propose to express a program-agnostic execution path verification task inside an arithmetic circuit whose correct execution can be verified by untrusted verifiers in zero knowledge. CCS CONCEPTS• Security and privacy → Security protocols; Privacy-preserving protocols; Software security engineering.

Towards Efficient Control-Flow Attestation with Software-Assisted Multi-level Execution Tracing

“…In general, while CFA provides strong security guarantees and verifiable evidence on the correctness of a device's configuration and execution, enforcing control-flow integrity in a practical way is challenging due to the inefficiency of existing tracing solutions. Despite sustained interest in CFA, current approaches try to overcome these limitations by either targeting (custom) optimized generation of CFGs (LO-FAT [5], LiteHAX [6], SCAPI [7] and BLINDTRUST [8]) or leveraging hardware features ( [9], CFIMon [10], µCFI [11], PITTYPAT [12], PT-CFI [13] and C-ITS [14]). That is, current mechanisms require the physical devices to be equipped with specialised hardware components to enable tracing.…”