F-FE — Functional, predicate encryption

F-FE (Functional, predicate encryption) is part of Public-Key Primitives, Key Exchange, Messaging in the UC functionality encyclopedia. Status: open — no accepted UC formulation exists yet.

Simulation-based security for functional encryption is impossible in general once a key holder can make unboundedly many key queries, which is why this functionality remains open despite substantial interest. The closest known UC treatment sidesteps this by assuming trusted hardware rather than realizing FE in the plain model.

References:

• Bhatotia, Kohlweiss, Martinico, and Tselekounis. Steel: Composable hardware-based stateful and randomised functional encryption. In 24th IACR International Conference on Practice and Theory of Public-Key Cryptography (PKC), pages 709–736, 2021. Note: this functionality (F-ESR) relies on a global attested-execution (TEE) hardware assumption to sidestep the impossibility result below — it is not a plain-model FE functionality.
• Boneh, Sahai, and Waters. Functional encryption: Definitions and challenges. In 8th Theory of Cryptography Conference (TCC), 2011.