This book contains revised selected papers from the 30th International Conference on Selected Areas in Cryptography, SAC 2023, held in Fredericton, New Brunswick, Canada, in August 2023. The 21full papers presented in these proceedings were carefully reviewed and selected from 45 submissions. The papers are organized in the following topical sections: Cryptanalysis of Lightweight Ciphers; Side-Channel Attacks and Countermeasures; Post-Quantum Constructions; Symmetric cryptography and fault attacks; Post-Quantum Analysis and Implementations; Homomorphic encryption; Public-Key Cryptography; and Differential Cryptanalysis.