A Formal Foundation for Secure Remote Execution of Enclaves

June 8, 2022 at 6:57 pm

Paper

Abstract

Recent proposals for trusted hardware platforms, such as Intel SGX and the MIT Sanctum processor, offer compelling security features but lack formal guarantees. We introduce a verification methodology based on a trusted abstract platform (TAP), a formalization of idealized enclave platforms along with a parameterized adversary. We also formalize the notion of secure remote execution and present machine-checked proofs showing that the TAP satisfies the three key security properties that entail secure remote execution: integrity, confidentiality and secure measurement. We then present machine-checked proofs showing that SGX and Sanctum are refinements of the TAP under certain parameterizations of the adversary, demonstrating that these systems implement secure enclaves for the stated adversary models.

Methodology

The enclave is formally modeled, including the program, state (e.g., memory, cache, registers), I/O, execution, and adversaries. The adversaries with privilege, cache access, and memory access are modeled differently.

A trusted abstract platform (TAP) is built for modeling secure remote execution (SRE), which is defined formally and can be meet by satisfying three properties at the same time: Secure Measurement, Integrity, Confidentiality.

Then, to prove that Sanctum and SGX satisfies SRE, the authors prove these architectures refine TAP in Boogie, and therefore meets SRE.

Strength

  • Side-channel and Side-channel attackers are modeled
  • TAP is a general model for various TEEs
  • Formal proof

Weakness

  • The refinement is not accurate enough, i.e., remote attestation seems missing
  • Source code?