  Recently, a few chosen-ciphertext secure (CCA2-secure) variants of the
McEliece public-key encryption (PKE) scheme 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 PKE schemes. 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 PKE
scheme 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} one-way trapdoor function (OW-TDF), the lowest-level security
notion in the context of public-key cryptography, resolving a big fundamental
and central problem that has remained unsolved in the past two decades.
