Invited Talk -- Which e-voting problems do we need to solve? -- Award Papers -- On the Possibility of Basing Cryptography on EXP6 ≠ BPP -- Linear Cryptanalysis of FF3-1 and FEA -- Efficient Key Recovery for all HFE Signature Variants -- Three Halves Make a Whole? Beating the Half-Gates Lower Bound for Garbled Circuits -- Signatures -- Threshold Schnorr with Stateless Deterministic Signing from Standard Assumptions -- Two-Round Trip Schnorr Multi-Signatures via Delinearized Witnesses -- MuSig2: Simple Two-Round Schnorr Multi-Signatures -- Tighter Security for Schnorr Identification and Signatures: A High-Moment Forking Lemma for Σ-Protocols -- DualRing: Generic Construction of Ring Signatures with Efficient Instantiations -- Compact Ring Signatures from Learning With Errors -- Quantum Cryptography -- A Black-Box Approach to Post-Quantum Zero-Knowledge in Constant Rounds -- On the Concurrent Composition of Quantum Zero-Knowledge -- Multi-theorem Designated-Verifier NIZK for QMA -- On the Round Complexity of Secure Quantum Computation -- Round Efficient Secure Multiparty Quantum Computation with Identifiable Abort -- One-Way Functions Imply Secure Computation in a Quantum World -- Impossibility of Quantum Virtual Black-Box Obfuscation of Classical Circuits -- New Approaches for Quantum Copy-Protection -- Hidden Cosets and Applications to Unclonable Cryptography -- On Tight Quantum Security of HMAC and NMAC in the Quantum Random Oracle Model -- Quantum Collision Attacks on Reduced SHA-256 and SHA-512 -- Succinct Arguments -- Halo Infinite: Proof-Carrying Data from Additive Polynomial Commitments -- Proof-Carrying Data without Succinct Arguments -- Subquadratic SNARGs in the Random Oracle Model -- Sumcheck Arguments and their Applications -- An Algebraic Framework for Universal and Updatable SNARKs.

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.