An Efficient CCA2-Secure Variant of the McEliece Cryptosystem in the Standard Model

Recently, a few chosen-ciphertext secure (CCA2-secure) variants of the McEliece cryptosystem in the standard model were introduced. All the proposed schemes are based on encryption repetition paradigm and use general transformation from CPA-secure scheme to a CCA2-secure one. Therefore, the resulting encryption scheme needs \textit{separate} encryption and has \textit{large} key size compared to the original scheme, which complex public key size problem in the code-based cryptosystems. Thus, the proposed schemes are not sufficiently efficient to be used in practice. In this work, we propose an efficient CCA2-secure variant of the McEliece cryptosystem in the standard model. The main novelty is that, unlike previous approaches, our approach is a generic conversion and can be applied to \textit{any} code-based one-way trapdoor cryptosystem. To further demonstrate the usefulness of our approach, we introduce a direct black-box construction of CCA2-secure scheme from one-way trapdoor functions (OW-TDFs) in the standard model, the lowest-level security notion in the context of public-key cryptography, resolving a problem that has remained unsolved in the past two decades.