International Association
for Cryptologic Research

In 2019, US Attorney General William Barr authored an open letter to Facebook, requesting the company delay its plans to deploy additional end-to-end encryption technology. A key objection raised by the Barr memo was that end-to-end encryption technologies “[put] our citizens and societies at risk by severely eroding a company’s ability to detect and respond to illegal content and activity, such as child sexual exploitation and abuse, terrorism, and foreign adversaries’ attempts to undermine democratic values and institutions.” In addition to reiterating a previous law-enforcement position regarding “exceptional access” to encrypted records, the Barr letter outlined a new request: for technology providers to “​embed the safety of the public in system designs, thereby enabling you to continue to act against illegal content effectively with no reduction to safety, and facilitating the prosecution of offenders and safeguarding of victims.” In the two years since Barr’s letter, the scientific, policy and industrial communities have grappled with the implications of this request. A major topic of concern is whether existing server-side media scanning technologies — used to detect the presence of known child sexual abuse material (CSAM) — can be adapted to work in end-to-end encrypted systems. This work is largely referred to by the term “client-side scanning.” (We use this designation to refer to any system that performs scanning on plaintext at the client, even if some realizations may use two-party protocols.) This debate came to a head in August 2021 when Apple announced the inclusion of a new on-device CSAM scanning technology that is slated for inclusion in iOS 15. In this presentation the authors propose to discuss the background and provide a taxonomy of security and privacy risks related to client-side scanning systems.

Zoom’s platform provides video conferencing services for hundreds of millions of daily meeting participants. They use Zoom to conduct business, learn among classmates scattered by recent events, connect with friends and family, collaborate with colleagues, and in some cases, discuss critical matters of state. Zoom is working hard to improve meeting security for its users. In May 2020, Zoom published an incrementally deployable proposal\footnote{\url{https://github.com/zoom/zoom-e2e-whitepaper}}, describing not only a design for its improved end-to-end encryption (E2EE), but also a plan to build an auditable and persistent notion of identity for all Zoom users, which will provide additional security even against active attacks from a compromised Zoom server. In this talk, I will first describe our improved end-to-end design, report on our progress deploying it, and comment on some lessons we learned along the way. Then, I will look to the future and present our vision for user identity protocols. I will argue why it matters, discuss the issues which make this problem hard, and how we plan to address them.