Non-Interactive Zero Knowledge from Sub-exponential DDH -- On the (in)security of ROS -- New Representations of the AES Key Schedule -- Public-Key Cryptography -- Analysing the HPKE Standard -- Tightly-Secure Authenticated Key Exchange, Revisited -- Aggregatable Distributed Key Generation -- Decentralized Multi-Authority ABE for DNFs from LWE -- Isogenies -- Compact, Efficient and UC-Secure Isogeny-Based Oblivious Transfer -- One-way functions and malleability oracles: Hidden shift attacks on isogenybased protocols -- Sieving for twin smooth integers with solutions to the Prouhet-Tarry-Escott problem -- Delay Encryption -- Post-Quantum Cryptography -- The Nested Subset Differential Attack: A Practical Direct Attack Against LUOV which Forges a Signature within 210 Minutes -- Improved cryptanalysis of UOV and Rainbow -- Cryptanalytic Applications of the Polynomial Method for Solving Multivariate Equation Systems over GF(2) -- Round-Optimal Blind Signatures in the Plain Model from Classical and Quantum Standard Assumptions -- Post-Quantum Multi-Party Computation -- Lattices -- A 2ⁿ/² -Time Algorithm for √n-SVP and √n-Hermite SVP, and an Improved Time-Approximation Tradeoff for (H)SVP -- New Lattice Two-Stage Sampling Technique and its Applications to Functional Encryption - Stronger Security and Smaller Ciphertexts -- On Bounded Distance Decoding with Predicate: Breaking the "Lattice Barrier" for the Hidden Number Problem -- On the ideal shortest vector problem over random rational primes -- Homomorphic Encryption -- Efficient Bootstrapping for Approximate Homomorphic Encryption with Non-Sparse Keys -- High-Precision Bootstrapping of RNS-CKKS Homomorphic Encryption Using Optimal Minimax Polynomial Approximation and Inverse Sine Function -- On the Security of Homomorphic Encryption on Approximate Numbers -- The Rise of Paillier: Homomorphic Secret Sharing and Public-Key Silent OT -- Symmetric Cryptanalysis -- Improved Linear Approximations to ARX Ciphers and Attacks Against ChaCha -- Rotational Cryptanalysis From a Differential-Linear Perspective - Practical Distinguishers for Round-reduced FRIET, Xoodoo, and Alzette -- Automatic Search of Meet-in-the-Middle Preimage Attacks on AES-like Hashing -- A Deeper Look at Machine Learning-Based Cryptanalysis. .

The 3-volume-set LNCS 12696 - 12698 constitutes the refereed proceedings of the 40th Annual International Conference on the Theory and Applications of Cryptographic Techniques, Eurocrypt 2021, which was held in Zagreb, Croatia, during October 17-21, 2021. The 78 full papers included in these proceedings were accepted from a total of 400 submissions. They were organized in topical sections as follows: Part I: Best papers; public-key cryptography; isogenies; post-quantum cryptography; lattices; homomorphic encryption; symmetric cryptanalysis; Part II: Symmetric designs; real-world cryptanalysis; implementation issues; masking and secret-sharing; leakage, faults and tampering; quantum constructions and proofs; multiparty computation; Part III: Garbled circuits; indistinguishability obfuscation; non-malleable commitments; zero-knowledge proofs; property-preserving hash functions and ORAM; blockchain; privacy and law enforcement.