On the application of generic CCA-secure transformations to proxy re-encryption

Several generic methods exist for achieving CCA-secure public-key encryption schemes from weakly secure cryptosystems, such as the FujisakiOkamoto and REACT transformations. In the context of Proxy ReEncryption (PRE), it would be desirable to count on analogous constructions that allow PRE schemes to achieve better security notions. In this paper, we study the adaptation of these transformations to proxy reencryption and find both negative and positive results. On the one hand, we show why it is not possible to directly integrate these transformations with weakly-secure PRE schemes due to general obstacles coming from both the constructions themselves and the security models, and we identify twelve PRE schemes that exhibit these problems. On the other hand, we propose an extension of the Fujisaki-Okamoto transformation for PRE, which achieves a weak form of CCA-security in the random oracle model, and we describe the sufficient conditions for applying it.