Lianying Zhao

He Shuang, Lianying Zhao, David Lie

Web servers service client requests, some of which might cause the web server to perform security-sensitive operations (e.g. money transfer, voting). An attacker may thus forge or maliciously manipulate such requests by compromising a web client. Unfortunately, a web server has no way of knowing whether the client from which it receives a request has been compromised or not -- current "best practice" defenses such as user authentication or network encryption cannot aid a server as they all assume web client integrity. To address this shortcoming, we propose vWitness, which "witnesses" the interactions of a user with a web page and certifies whether they match a specification provided by the web server, enabling the web server to know that the web request is user-intended. The main challenge that vWitness overcomes is that even benign clients introduce unpredictable variations in the way they render web pages. vWitness differentiates between these benign variations and malicious manipulation using computer vision, allowing it to certify to the web server that 1) the web page user interface is properly displayed 2) observed user interactions are used to construct the web request. Our vWitness prototype achieves compatibility with modern web pages, is resilient to adversarial example attacks and is accurate and performant -- vWitness achieves 99.97% accuracy and adds 197ms of overhead to the entire interaction session in the average case.

Lianying Zhao, He Shuang, Shengjie Xu et al.

In recent years, there have emerged many new hardware mechanisms for improving the security of our computer systems. Hardware offers many advantages over pure software approaches: immutability of mechanisms to software attacks, better execution and power efficiency and a smaller interface allowing it to better maintain secrets. This has given birth to a plethora of hardware mechanisms providing trusted execution environments (TEEs), support for integrity checking and memory safety and widespread uses of hardware roots of trust. In this paper, we systematize these approaches through the lens of abstraction. Abstraction is key to computing systems, and the interface between hardware and software contains many abstractions. We find that these abstractions, when poorly designed, can both obscure information that is needed for security enforcement, as well as reveal information that needs to be kept secret, leading to vulnerabilities. We summarize such vulnerabilities and discuss several research trends of this area.

Lianying Zhao, Joseph I. Choi, Didem Demirag et al.

A one-time program (OTP) works as follows: Alice provides Bob with the implementation of some function. Bob can have the function evaluated exclusively on a single input of his choosing. Once executed, the program will fail to evaluate on any other input. State-of-the-art one-time programs have remained theoretical, requiring custom hardware that is cost-ineffective/unavailable, or confined to adhoc/unrealistic assumptions. To bridge this gap, we explore how the Trusted Execution Environment (TEE) of modern CPUs can realize the OTP functionality. Specifically, we build two flavours of such a system: in the first, the TEE directly enforces the one-timeness of the program; in the second, the program is represented with a garbled circuit and the TEE ensures Bob's input can only be wired into the circuit once, equivalent to a smaller cryptographic primitive called one-time memory. These have different performance profiles: the first is best when Alice's input is small and Bob's is large, and the second for the converse.

Lianying Zhao, Mohammad Mannan

Unauthorized data alteration has been a longstanding threat since the emergence of malware. System and application software can be reinstalled and hardware can be replaced, but user data is priceless in many cases. Especially in recent years, ransomware has become high-impact due to its direct monetization model. State-of-the-art defenses are mostly based on known signature or behavior analysis, and more importantly, require an uncompromised OS kernel. However, malware with the highest software privileges has shown its obvious existence. We propose to move from current detection/recovery based mechanisms to data loss prevention, where the focus is on armoring data instead of counteracting malware. Our solution, Inuksuk, relies on today's Trusted Execution Environments (TEEs), as available both on the CPU and storage device, to achieve programmable write protection. We back up a copy of user-selected files as write-protected at all times, and subsequent updates are written as new versions securely through TEE. We implement Inuksuk on Windows 7 and 10, and Linux (Ubuntu); our core design is OS and application agnostic, and incurs no run-time performance penalty for applications. File transfer disruption can be eliminated or alleviated through access modes and customizable update policies (e.g., interval, granularity). For Inuksuk's adoptability in modern OSes, we have also ported Flicker (EuroSys 2008), a defacto standard tool for in-OS privileged TEE management, to the latest 64-bit Windows.