ICE: a passive, high-speed, state-continuity scheme

Abstract

The amount of trust that can be placed in commodity computing platforms is limited by the likelihood of vulnerabilities in their huge software stacks. Protected-module architectures, such as Intel SGX, provide an interesting alternative by isolating the execution of software modules. To minimize the amount of code that provides support for the protected-module architecture, persistent storage of (confidentiality and integrity protected) states of modules can be delegated to the untrusted operating system. But precautions should be taken to ensure state continuity: an attacker should not be able to cause a module to use stale states (a so-called rollback attack), and while the system is not under attack, a module should always be able to make progress, even when the system could crash or lose power at unexpected, random points in time (i.e., the system should be crash resilient). Providing state-continuity support is non-trivial as many algorithms are vulnerable to attack, require on-chip non-volatile memory, wear-out existing off-chip secure non-volatile memory and/or are too slow for many applications. We present ICE, a system and algorithm providing state-continuity guarantees to protected modules. ICE's novelty lies in the facts that (1) it does not rely on secure non-volatile storage for every state update (e.g., the slow TPM chip). (2) ICE is a passive security measure. An attacker interrupting the main power supply or any other source of power, cannot break state-continuity. (3) Benchmarks show that ICE already enables state-continuous updates almost 5x faster than writing to TPM NVRAM. With dedicated hardware, performance can be increased 2 orders of magnitude. ICE's security properties are guaranteed by means of a machine-checked proof and a prototype implementation is evaluated on commodity hardware.