Paper 2010/626

Public-Key Encryption with Fuzzy Keyword Search: A Provably Secure Scheme under Keyword Guessing Attack

Peng Xu and Hai Jin

Abstract

A lot of interest has been drawn recently into public-key encryption with keyword search (PEKS), which keeps public-key encrypted documents amendable to secure keyword search. However, PEKS resist against keyword guessing attack by assuming that the size of the keyword space is beyond the polynomial level. But this assumption is ineffective in practice. PEKS are insecure under keyword guessing attack. As we observe, the key to defend such attack is to avoid the availability of the exact search trapdoor to adversaries. Accordingly, we compromise the exactness of search trapdoor by mapping at least two different keywords into a fuzzy search trapdoor. We propose a novel concept called public-key encryption with fuzzy keyword search (PEFKS), by which the un-trusted server only obtains the fuzzy search trapdoor instead of the exact search trapdoor, and define its semantic security under chosen keyword attack (SS-CKA) and indistinguishability of keywords under non-adaptively chosen keywords and keyword guessing attack (IK-NCK-KGA). For the keyword space with and without uniform distribution, we respectively present two universal transformations from anonymous identity-based encryption to PEFKS, and prove their SS-CKA and IK-NCK-KGA securities. To our knowledge, PEFKS is the first scheme to resist against keyword guessing attack on condition that the keyword space is not more than the polynomial level.