Multi-Party Computation -- Game-Theoretic Fairness Meets Multi-Party Protocols: The Case of Leader Election -- Computational Hardness of Optimal Fair Computation: Beyond Minicrypt -- You Only Speak Once: Secure MPC with Stateless Ephemeral Roles -- Fluid MPC: Secure Multiparty Computation with Dynamic Participants -- Secure Computation from One-Way Noisy Communication, or: Anti-Correlation via Anti-Concentration -- Broadcast-Optimal Two Round MPC with an Honest Majority -- Three-Round Secure Multiparty Computation from Black-Box Two-Round Oblivious Transfer -- On the Round Complexity of Black-Box Secure MPC -- ATLAS: Efficient and Scalable MPC in the Honest Majority Setting -- Unconditional Communication-Efficient MPC via Hall's Marriage Theorem -- Non-Interactive Secure Multiparty Computation for Symmetric Functions, Revisited: More Efficient Constructions and Extensions -- Efficient Information-Theoretic Multi-Party Computation over Non-Commutative Rings -- Pushing the Limits of Valiant'sUniversal Circuits: Simpler, Tighter and More Compact -- Oblivious Key-Value Stores and Amplification for Private Set Intersection -- MHz2k: MPC from HE over ℤ2k with New Packing, Simpler Reshare, and Better ZKP -- Sublinear GMW-Style Compiler for MPC with Preprocessing -- Limits on the Adaptive Security of Yao's Garbling -- Lattice Cryptography -- Subtractive Sets over Cyclotomic Rings: Limits of Schnorr-like Arguments over Lattices -- A Compressed Sigma-Protocol Theory for Lattices -- A New Simple Technique to Bootstrap Various Lattice Zero-Knowledge Proofs to QROM Secure NIZKs -- SMILE: Set Membership from Ideal Lattices with Applications to Ring Signatures and Confidential Transactions -- Deniable Fully Homomorphic Encryption from Learning With Errors -- Lattice Cryptanalysis -- Counterexamples to New Circular Security Assumptions Underlying iO -- How to Meet Ternary LWE Keys -- Lattice Reduction with Approximate Enumeration Oracles: Practical Algorithms and Concrete Performance -- Towards faster polynomial-time lattice reduction -- Lower bounds on lattice sieving and information set decoding.

The four-volume set, LNCS 12825, LNCS 12826, LNCS 12827, and LNCS 12828, constitutes the refereed proceedings of the 41st Annual International Cryptology Conference, CRYPTO 2021. Crypto has traditionally been held at UCSB every year, but due to the COVID-19 pandemic it was an online event in 2021. The 103 full papers presented in the proceedings were carefully reviewed and selected from a total of 426 submissions. The papers are organized in the following topical sections: Part I: Award Papers; Signatures; Quantum Cryptography; Succinct Arguments. Part II: Multi-Party Computation; Lattice Cryptography; and Lattice Cryptanalysis. Part III: Models; Applied Cryptography and Side Channels; Cryptanalysis; Codes and Extractors; Secret Sharing. Part IV: Zero Knowledge; Encryption++; Foundations; Low-Complexity Cryptography; Protocols.