Paper 2026/1867 Original: eprint.iacr.org/2026/1867 ↗

A Simple Compiler for CCA2-Secure Pseudorandom Codes in the Standard Model

Abstract

Public-key pseudorandom codes (PRCs) combine two seemingly conflicting properties: their codewords are computationally indistinguishable from uniformly random strings, yet a secret-key decoder can recover the encoded message even after a bounded Hamming corruption. Security against chosen-plaintext (CPA) attacks asks that an encoding of a chosen message appears uniform. Security against adaptive chosen-ciphertext (CCA2) attacks additionally gives the adversary adaptive access to a decoding oracle for codewords outside the Hamming ball around the challenge encoding. Döttling et al. (CRYPTO 2026) showed how to realize CCA2-secure PRCs in the standard model through a generic compiler based on the Koppula-Waters hinting pseudorandom generator framework. We give a substantially simpler black-box compiler. Starting from any adaptively $\alpha$-robust, CPA-pseudorandom PRC and using only a secure PRG and an almost perfectly correct IND-CCA2-secure PKE scheme, our compiler constructs an adaptively $\alpha/2$-robust, $\alpha/2$-CCA2-pseudorandom PRC. The compiled PRC has twice the codeword length of the underlying PRC and therefore loses only a factor of two in its relative decoding radius; in particular, it preserves a constant relative decoding radius.