Zero Knowledge -- Witness Authenticating NIZKs and Applications -- Towards a Unified Approach to Black-Box Constructions of Zero-Knowledge Proofs -- Compressing Proofs of k-Out-Of-n Partial Knowledge -- Mac'n'Cheese: Zero-Knowledge Proofs for Boolean and Arithmetic Circuits with Nested Disjunctions -- Time- and Space-Efficient Arguments from Groups of Unknown Order -- Encryption++ -- Broadcast Encryption with Size N1/3 and More from k-Lin -- Fine-grained Secure Attribute-based Encryption -- Multi-Input Quadratic Functional Encryption from Pairings -- Functional Encryption for Turing Machines with Dynamic Bounded Collusion from LWE -- Receiver-Anonymity in Reradomizable RCCA-Secure Cryptosystems Resolved -- Foundations -- White Box Traitor Tracing -- Does Fiat-Shamir Require a Cryptographic Hash Function? -- Composition with Knowledge Assumptions -- Non-Interactive Batch Arguments for NP from Standard Assumptions -- Targeted Lossy Functions and Applications -- The t-wise Independence of Substitution-Permutation Networks -- Low-Complexity Cryptography -- Low-Complexity Weak Pseudorandom Functions in AC0[MOD2] -- MPC-Friendly Symmetric Cryptography from Alternating Moduli: Candidates, Protocols, and Applications -- No Time to Hash: On Super-Efficient Entropy Accumulation -- Protocols -- A Logarithmic Lower Bound for Oblivious RAM (for all parameters) -- Oblivious RAM with Worst-Case Logarithmic Overhead -- Puncturable Pseudorandom Sets and Private Information Retrieval with Near-Optimal Online Bandwidth and Time -- Authenticated Key Exchange and Signatures with Tight Security in the Standard Model -- KHAPE: Asymmetric PAKE from Key-Hiding Key Exchange.

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.