Invited Papers -- Cryptologists should not ignore the history of Al-Andalusia -- Compact Post-Quantum Signatures from Proofs of Knowledge leveraging Structure for the PKP, SD and RSD Problems -- On Catalan Constant Continued Fractions -- Cryptography -- Full Post-Quantum Datagram TLS Handshake in the Internet of Things -- Moderate Classical McEliece keys from quasi-Centrosymmetric Goppa codes -- QCB is Blindly Unforgeable -- A Side-Channel Secret Key Recovery Attack on CRYSTALS-Kyber Using k Chosen Ciphertexts -- A new keyed hash function based on Latin squares and error-correcting codes to authenticate users in smart home environments -- Attack on a Code-based Signature Scheme from QC-LDPC Codes -- Computational results on Gowers U2 and U3 norms of known S-Boxes -- Multi-Input Non-Interactive Functional Encryption: Constructions and Applications -- Indifferentiability of the Confusion-Diffusion Network and the Cascade Block Cipher -- Quantum Cryptanalysis of 5 rounds Feistel schemes and Benes schemes -- Lattice-based accumulator with constant time list update and constant time verification -- Information Security -- Malicious JavaScript detection based on AST analysis and key feature re-sampling in realistic environments -- Searching for Gemstones: Flawed Stegosystems May Hide Promising Ideas -- A Study for Security of Visual Cryptography -- Forecasting Click Fraud via Machine Learning Algorithms -- An Enhanced Anonymous ECC-based Authentication for Lightweight Application in TMIS -- Discrete Mathematics -- Symmetric 4-adic complexity of quaternary sequences with period 2p n -- Weightwise perfectly balanced functions and nonlinearity -- Chudnovsky-type algorithms over the projective line using generalized evaluation maps -- Coding Theory -- Security enhancement method using shortened error correcting codes -- An UpdatedDatabase of Z4 Codes and an Open Problem about Quasi-Cyclic Codes.

This book constitutes the refereed proceedings of the 4th International Conference on Codes, Cryptology and Information Security, C2SI 2023, held in Rabat, Morocco, during May 29-31, 2023. The 21 full papers included in this book were carefully reviewed and selected from 62 submissions. They were organized in topical sections as follows: Invited Papers, Cryptography, Information Security, Discrete Mathematics, Coding Theory.