## Cryptology ePrint Archive: Report 2013/875

Policy-Based Non-interactive Outsourcing of Computation using multikey FHE and CP-ABE

Michael Clear and Ciaran McGoldrick

Abstract: We consider the problem of outsourced computation that operates on encrypted inputs supplied by multiple independent parties. To facilitate fine-grained access control, it would be desirable if each party could encrypt her input under an appropriate access policy. Moreover, a party should only be authorized to decrypt the result of a computation performed on a set of encrypted inputs if his credentials satisfy the composition of all input policies. There has been limited success so far achieving homomorphic encryption in the functional setting; that is, for primitives such as Ciphertext-Policy Attribute Based Encryption (CP-ABE) and Identity Based Encryption (IBE). We introduce a new primitive that captures homomorphic encryption with support for access policies and policy composition. We then present a generic construction using CP-ABE and multikey Fully-Homomorphic encryption (FHE). Furthermore, we show that a CP-ABE scheme that is homomorphic for circuits of polylogarithmic depth in some parameter $m$ implies a CP-ABE scheme that is homomorphic for circuits of arity $m$ and unbounded depth.

Category / Keywords: public-key cryptography / multikey FHE, CP-ABE, homomorphic encryption

Original Publication (with major differences): SECRYPT 2013 - Proceedings of the 10th International Conference on Security and Cryptography