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Achievable CCA2 Relaxation for Homomorphic Encryption
IACR Cryptology ePrint Archive
Homomorphic encryption (HE) protects data in-use, but can be computationally expensive. To avoid the costly bootstrapping procedure that refreshes ciphertexts, some works have explored client-aided outsourcing protocols, where the client intermittently refreshes ciphertexts for a server that is performing homomorphic computations. But is this approach secure against malicious servers? We present a CPA-secure encryption scheme that is completely insecure in this setting. We define a new notiondblp:journals/iacr/AkaviaGHV22 fatcat:olpyubg2tzeu7ph73rxk5xgi5y