The four-volume set LNCS 16268-16271 constitutes the refereed proceedings of the 23rd International Conference on Theory of Cryptography, TCC 2025, held in Aarhus, Denmark, during December 1–5, 2025. The total of 70 full papers presented in the proceedings was carefully reviewed and selected from 242 submissions. They were organized in topical sections as follows: Part I: Secure Computation; Homomorphic Primitives; Proofs; Part II: Foundations; Obfuscation and Functional Encryption; Secret Sharing; Part III: Quantum Cryptography; Signatures and Intractability Assumptions; Part IV: Proofs; Young Researcher Award and Outstanding Paper Awards; Differential Privacy; Times Cryptography and Verifiable Random Function; Secure Computation.