## Cryptology ePrint Archive: Report 2013/321

Generic Constructions of Secure-Channel Free Searchable Encryption with Adaptive Security

Keita Emura and Atsuko Miyaji and Mohammad Shahriar Rahman and Kazumasa Omote

Abstract: For searching keywords against encrypted data, the public key encryption scheme with keyword search (PEKS), and its an extension called secure-channel free PEKS (SCF-PEKS) have been proposed. In SCF-PEKS, a receiver makes a trapdoor for a keyword, and uploads it on a server. A sender computes an encrypted keyword, and sends it to the server. The server executes the searching procedure (called the test algorithm, which takes as inputs an encrypted keyword, trapdoor, and secret key of the server). In this paper, we extend the security of SCF-PEKS, calling it adaptive SCF-PEKS, wherein an adversary (modeled as a malicious-but-legitimate" receiver) is allowed to issue test queries \emph{adaptively}, and show that adaptive SCF-PEKS can be generically constructed by anonymous identity-based encryption (anonymous IBE) only. That is, for constructing adaptive SCF-PEKS we need not require any additional cryptographic primitive when compared to the Abdalla et al. PEKS construction (J. Cryptology 2008), even though adaptive SCF-PEKS requires additional functionalities. Note that our generic construction needs to apply the KEM/DEM framework (a.k.a. hybrid encryption), where KEM stands for key encapsulation mechanism, and DEM stands for data encapsulation mechanism. We also show that there is a class of anonymous IBE that can be applied for constructing adaptive SCF-PEKS without using hybrid encryption, and propose an adaptive SCF-PEKS construction based on this IBE. Although our second construction is not fully generic, it is efficient compared to the first, since we can exclude the DEM part. Finally, we instantiate an adaptive SCF-PEKS scheme (via our second construction) that achieves a similar level of efficiency for the costs of the test procedure and encryption, compared to the (non-adaptive secure) SCF-PEKS scheme by Fang et al. (CANS2009).

Category / Keywords: public-key cryptography / Public-key Encryption with Keyword Search, Adaptive Security, Anonymous Identity-Based Encryption

Publication Info: Preliminary versions of this paper appear in ISC 2011 and SECRYPT 2012. This is the full and the merged version.