International Association
for Cryptologic Research

Frequently, users on the web need to show that they are, for example, not a robot, old enough to access an age restricted video, or eligible to download an ebook from their local public library without being tracked. Anonymous credentials were developed to address these concerns. However, existing schemes do not handle the realities of deployment or the complexities of real-world identity. Instead, they implicitly make assumptions such as there being an issuing authority for anonymous credentials that, for real applications, requires the local department of motor vehicles to issue sophisticated cryptographic tokens to show users are over 18. In reality, there are multiple trust sources for a given identity attribute, their credentials have distinctively different formats, and many, if not all, issuers are unwilling to adopt new protocols. We present and build zk-creds, a protocol that uses general-purpose zero-knowledge proofs to 1) remove the need for credential issuers to hold signing keys: credentials can be issued to a bulletin board instantiated as a transparency log, Byzantine system, or even a blockchain; 2) convert existing identity documents into anonymous credentials without modifying documents or coordinating with their issuing authority; 3) allow for flexible, composable, and complex identity statements over multiple credentials. Concretely, identity assertions using zk-creds take less than 150ms in a real-world scenario of using a passport to anonymously access age-restricted videos. This paper was published at IEEE Security and Privacy 2023, and the full version can be found at https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=10179430.

Intel's Software Guard Extensions (SGX) promises an isolated execution environment, protected from all software running on the machine. As such, numerous works have sought to leverage SGX to provide confidentiality and integrity guarantees for code running in adversarial environments. In the past few years however, SGX has come under heavy fire, threatened by numerous side channel attacks. With Intel repeatedly patching SGX to regain security, in this paper we set out to explore the effectiveness of SGX's update mechanisms to prevent attacks on real-world deployments. To that aim, we study two commercial SGX applications. First, we investigate the Secret network, an SGX-backed blockchain aiming to provide privacy preserving smart contracts. Next, we also consider PowerDVD, a UHD Blu-Ray Digital Rights Management (DRM) software licensed to play discs on general purpose computers. We show that in both cases vendors are unable to meet security goals originally envisioned for their products, presumably due to SGX's long mitigation timelines and a difficult manual update process. This in turn forces vendors into making difficult security/usability trade offs, resulting in severe security compromises.