This paper proposes a generic construction of CCA-secure fully homomorphic encryption (FHE) scheme.First, we introduce a new primitive called multi-identity fully homomorphic encryption, which works in the multi-identity setting; that is, homomorphic evaluation can performed on ciphertexts created with different identities.Then, we propose an IND-sID-CPA secure multi-identity leveled FHE scheme over lattice.Finally, we present CCA-secure FHE from our proposed multi-identity FHE scheme and strongly EUF-CMA secure signature.The security analysis shows that our FHE scheme is CCA2-secure when the evaluation key is unavailable to the adversary, and remains CCA1-secure when the evaluation key is exposed in the standard model.This paper proposes a generic construction of CCA-secure fully homomorphic encryption (FHE) scheme.First, we introduce a new primitive called multi-identity fully homomorphic encryption, which works in the multi-identity setting; that is, homomorphic evaluation can performed on ciphertexts created with different identities.Then, we propose an IND-sID-CPA secure multi-identity leveled FHE scheme over lattice.Finally, we present CCA-secure FHE from our proposed multi-identity FHE scheme and strongly EUF-CMA secure signature.The security analysis shows that our FHE scheme is CCA2-secure when the evaluation key is unavailable to the adversary, and remains CCA1-secure when the evaluation key is exposed in the standard model.

Joint International Information Technology, Mechanical and Electronic Engineering Conference (JIMEC)Jan 1, 20170 citations

Efficient CCA-Secure Public-Key Encryption Schemes from RSA-Related Assumptions

Colin Boyd, Jaimee Brown, Juan González Nieto

Faculty of Science and Technology; Information Security InstituteJan 1, 20060 citations

CCA-attacks on lattice-based encryption-decryption schemes

Alba Hernández Costoya, Alba Larraya Sancho, Miguel Ángel Marco-Buzunáriz

Abstract This paper presents two distinct chosen-ciphertext attacks (CCA) against lattice-based encryption and decryption schemes, in particular based on the LWE problem, a class of post-quantum cryptographic algorithms. First we attack fully homomorphic encryption-decryption schemes (FHE) exploiting the additional information that the small modulus reduction offers. We compare this attack with the $CPA^D$ attack presented in Checri (2024). Afterwards we present an attack against Kyber.CPAPKE, and another against a weakened version of Kyber.KEM where the cyphertext is not checked for correctness; and compare them to the previous Key Mismatch Attack in Qin (2021). Our work remarks the importance of protecting the decryption function in the different implementations of these cryptographic schemes, and the importance of CCA security in nowadays cryptosystems.Abstract This paper presents two distinct chosen-ciphertext attacks (CCA) against lattice-based encryption and decryption schemes, in particular based on the LWE problem, a class of post-quantum cryptographic algorithms. First we attack fully homomorphic encryption-decryption schemes (FHE) exploiting the additional information that the small modulus reduction offers. We compare this attack with the $$CPA^D$$ attack presented in Checri (2024). Afterwards we present an attack against Kyber.CPAPKE, and another against a weakened version of Kyber.KEM where the cyphertext is not checked for correctness; and compare them to the previous Key Mismatch Attack in Qin (2021). Our work remarks the importance of protecting the decryption function in the different implementations of these cryptographic schemes, and the importance of CCA security in nowadays cryptosystems.

Cryptography and CommunicationsOct 21, 20251 citation

CPA^D

attack presented in Checri (2024). Afterwards we present an attack against Kyber.CPAPKE, and another against a weakened version of Kyber.KEM where the cyphertext is not checked for correctness; and compare them to the previous Key Mismatch Attack in Qin (2021). Our work remarks the importance of protecting the decryption function in the different implementations of these cryptographic schemes, and the importance of CCA security in nowadays cryptosystems.