Pairing-free secure-channel establishment in mobile networks with fine-grained lawful interception.

Modern-day mobile communications allow users to connect from any place, at any time. However, this ubiquitous access comes at the expense of their privacy. Currently, the operators providing mobile service to users learn call metadata, and even the contents of those exchanges. A main reason behind this is the Lawful-Interception (LI) requirement, by which serving networks must provide this (meta-)data to authorities, given a warrant. At ESORICS 2021, Arfaoui et al. pioneered a primitive called Lawful-Interception Key-Exchange (LIKE), which achieves the best of both worlds: (provably) privacy-enhanced communications, and fine-grained fine-grained, limited access to user data. Their protocol required pairings and was only applicable in a domestic setting, where the concerned users (Alice and Bob) were subject to the same LI authorities. In this paper we close this gap by proposing a pairing-free LIKE protocol where Alice and Bob are potentially not subject to the same LI authorities.