IACR News item: 18 July 2014
Zvika Brakerski, Gil Segev
ePrint ReportWhereas function privacy is inherently limited in the public-key setting, in the private-key setting it has a tremendous potential. Specifically, one can hope to construct schemes where encryptions of messages $m_1, \\ldots, m_T$ together with decryption keys corresponding to functions $f_1, \\ldots, f_T$, reveal essentially no information other than the values $\\{ f_i(m_j)\\}_{i,j\\in [T]}$. Despite its great potential, the known function-private private-key schemes either support rather limited families of functions (such as inner products), or offer somewhat weak notions of function privacy.
We present a generic transformation that yields a function-private functional encryption scheme, starting with any non-function-private scheme for a sufficiently rich function class. Our transformation preserves the message privacy of the underlying scheme, and can be instantiated using a variety of existing schemes. Plugging in known constructions of functional encryption schemes, we obtain function-private schemes based either on obfuscation assumptions, on the Learning with Errors assumption, or even on general public-key encryption (offering various trade-offs between security and efficiency).
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