This paper introduces pseudorandom error-correcting codes (PRCs), which are error-correcting codes with the property that any polynomial number of codewords are pseudorandom to any computationally-bounded adversary. PRCs are constructed based on cryptographic assumptions, such as the hardness of LPN (Learning Parity with Noise) and the planted XOR problem. These codes are robust to substitution and deletion errors and can be used for watermarking and steganography. The authors present an undetectable watermarking scheme for language models that is robust to cropping and a constant rate of random substitutions and deletions. This is the first undetectable watermarking scheme that can tolerate a constant rate of errors. They also present a constant-rate stateless steganography scheme with provable steganographic security and robustness to a constant rate of substitutions. The paper shows that PRCs can be used to construct robust, universal steganography schemes. The main contributions include the definition and construction of PRCs, their application to watermarking and steganography, and the proof of their robustness under various error channels. The paper also discusses related work and provides a technical overview of the constructions and proofs.This paper introduces pseudorandom error-correcting codes (PRCs), which are error-correcting codes with the property that any polynomial number of codewords are pseudorandom to any computationally-bounded adversary. PRCs are constructed based on cryptographic assumptions, such as the hardness of LPN (Learning Parity with Noise) and the planted XOR problem. These codes are robust to substitution and deletion errors and can be used for watermarking and steganography. The authors present an undetectable watermarking scheme for language models that is robust to cropping and a constant rate of random substitutions and deletions. This is the first undetectable watermarking scheme that can tolerate a constant rate of errors. They also present a constant-rate stateless steganography scheme with provable steganographic security and robustness to a constant rate of substitutions. The paper shows that PRCs can be used to construct robust, universal steganography schemes. The main contributions include the definition and construction of PRCs, their application to watermarking and steganography, and the proof of their robustness under various error channels. The paper also discusses related work and provides a technical overview of the constructions and proofs.