The four-volume proceedings LNCS 13090, 13091, 13092, and 13093 constitutes the proceedings of the 27th International Conference on the Theory and Application of Cryptology and Information Security, ASIACRYPT 2021, which was held during December 6-10, 2021.

Secure and Efficient Software Masking on Superscalar Pipelined Processors.- Fault-Injection Attacks against NIST's Post-Quantum Cryptography Round 3 KEM Cand.- Divided We Stand, United We Fall: Security Analysis of Some SCA+SIFA Countermeasures Against SCA-Enhanced Fault Template Attacks.- Efficient Leakage-Resilient MACs without Idealized Assumptions.- DEFAULT: Cipher Level Resistance Against Differential Fault Attack.- Random Probing Expansion: Quasi Linear Gadgets \& Dynamic Compilers.- Homomorphic Secret Sharing for Multipartite and General Adversary Structures Supporting Parallel Evaluation of Low-Degree Polynomials.- Improved single-round secure multiplication using regenerating codes.- Garbling, Stacked and Staggered: Faster k-out-of-n Garbled Function Evaluation.- Better Security-Efficiency Trade-Offs in Permutation-Based Two-Party Computation.- Two-Round Adaptively Secure MPC from Isogenies, LPN, or CDH.- Reverse Firewalls for Adaptively Secure MPC without Setup.- On Time-LockCryptographic Assumptions in Abelian Hidden-Order Groups.- Astrolabous: A Universally Composable Time Lock Encryption Scheme.- Identity-Based Encryption for Fair Anonymity Applications: Defining, Implementing, and Applying Rerandomizable RCCA-secure IBE.- Simulation-Based Bi-Selective Opening Security for Public Key Encryption.- Key Encapsulation Mechanism with Tight Enhanced Security in the Multi-User Setting: Impossibility Result and Optimal Tightness.- Hierarchical Integrated Signature and Encryption.- Tardigrade: An Atomic Broadcast Protocol for Arbitrary Network Conditions.- Onion Routing with Replies.- Private Join and Compute from PIR with Default.- Generalized Channels from Limited Blockchain Scripts and Adaptor Signatures.- ConTra Corona: Contact Tracing against the Coronavirus by Bridging the Centralized-Decentralized Divide for Stronger Privacy.- Cryptographic Analysis of the Bluetooth Secure Connection Protocol Suite.