The two-volume set LNCS 12110 and 12111 constitutes the refereed proceedings of the 23rd IACR International Conference on the Practice and Theory of Public-Key Cryptography, PKC 2020, held in Edinburgh, UK, in May 2020. The 44 full papers presented were carefully reviewed and selected from 180 submissions. They are organized in topical sections such as: functional encryption; identity-based encryption; obfuscation and applications; encryption schemes; secure channels; basic primitives with special properties; proofs and arguments; lattice-based cryptography; isogeny-based cryptography; multiparty protocols; secure computation and related primitives; post-quantum primitives; and privacy-preserving schemes.