Multi-input Functional Encryption

Functional encryption (FE) is a powerful primitive enabling fine-grained access to encrypted data. In an FE scheme, secret keys (“tokens”) correspond to functions; a user in possession of a ciphertext ct = Enc(x) and a token TKf for the function f can compute f(x) but learn nothing else about x. An active area of research over the past few years has focused on the development of ever more expressive FE schemes. In this work we introduce the notion of multi-input functional encryption. Here, informally, a user in possession of a token TKf for an n-ary function f and multiple ciphertexts ct1 = Enc(x1), . . . , ctn = Enc(xn) can compute f(x1, . . . , xn) but nothing else about the {xi}. Besides introducing the notion, we explore the feasibility of multi-input FE in the public-key and symmetric-key settings, with respect to both indistinguishability-based and simulation-based definitions of security. ∗ACS. Email: [email protected]. †Department of Computer Science, University of Maryland. Email: [email protected]. This research was sponsored by NSF award #1223623 and by the US Army Research Laboratory and the UK Ministry of Defence under Agreement Number W911NF-06-3-0001. ‡Department of Computer Science, University of Maryland. Email: [email protected]. §Department of Computer Science, University of Maryland. Email: [email protected]. This work is partially supported by NSF award CNS-1314857 and a Google Research Award. ¶Department of Computer Science, Virginia Commonwealth University. Email: [email protected]. This work is partially supported by an NSF CI postdoctoral fellowship, and was mostly done while at the University of Maryland.