2022-05-04 Mutual Contact Discovery

Abstract: Messaging services allow new users that join a service to find existing contacts that already use that service through a process called contact discovery. Existing users are similarly informed of new users that are already on their contact list. Current contact discovery protocols either allow the server to reconstruct the social graph (i.e., the graph describing who is a contact of who), which is a serious privacy issue, or use trusted hardware to prevent this. But even in the latter case, privacy is still at stake: when you join and enable contact discovery, anyone already on the service that has your number on their contact list gets notified that you joined. Even if you don’t know that person, or if it is an ex or former colleague that you long parted with and whose contact details you deleted long ago. To solve this, we propose severalmutual contact discovery protocols, that only allow users to discover each other when both are (still) in each other’s contact list. Mutual contact discovery has the additional advantage that it can be implemented in a more privacy friendly fashion (e.g., protecting the social graph from the server) than traditional, one-sided contact discovery, without even relying on trusted hardware.

Meeting with Jaap-Henk: If you would like to talk to Jaap-Henk, please email Hongyu (Hongyu Jin hongyuj@kth.se) with your availability (in-person/on-line) Tuesday afternoon to Thursday afternoon.

Jaap-Henk - please see http://www.cs.ru.nl/~jhh/about.html for his bio and work.