Paper 2020/1420

Functional Encryption for Quadratic Functions from k-Lin, Revisited

Hoeteck Wee

Abstract

We present simple and improved constructions of public-key functional encryption (FE) schemes for quadratic functions. Our main results are: - an FE scheme for quadratic functions with constant-size keys as well as shorter ciphertexts than all prior schemes based on static assumptions; – a public-key partially-hiding FE that supports NC1 computation on public attributes and quadratic computation on the private message, with ciphertext size independent of the length of the public attribute. Both constructions achieve selective, simulation-based security against unbounded collusions, and rely on the (bi-lateral) k-linear assumption in prime-order bilinear groups. At the core of these constructions is a new reduction from FE for quadratic functions to FE for linear functions.