Lossiness and Entropic Hardness for Ring-LWE -- Multi-key Fully-Homomorphic Encryption in the Plain Model -- Constant Ciphertext-Rate Non-Committing Encryption from Standard Assumptions -- Efficient Range-Trapdoor Functions and Applications: Rate-1 OT and CP-ABE for Circuits (and more) in the Symmetric Key Setting -- Optimal Broadcast Encryption from LWE and Pairings in the Standard Model -- Equipping Public-Key Cryptographic Primitives with Watermarking (or: A Hole Is to Watermark) -- Functional Encryption for Quadratic Functions from k-Lin, Revisited -- On Perfect Correctness in (Lockable) Obfuscation -- Can a Public Blockchain Keep a Secret -- Blockchains from Non-Idealized Hash Functions -- Ledger Combiners for Fast Asynchronous Byzantine Agreement with Subquadratic Communication -- Expected Constant Round Byzantine Broadcast under Dishonest Majority -- Round-Efficient Byzantine Broadcast under Strongly Adaptive and Majority Corruptions -- A Lower Bound for One-Round Oblivious RAM -- Lower Bounds for Multi-Server Oblivious RAMs -- On Computational Shortcuts for Information-Theoretic PIR -- Characterizing Deterministic-Prover Zero Knowledge -- NIZK from SNARG -- Weakly Extractable One-Way Functions -- Towards Non-Interactive Witness Hiding -- FHE-Based Bootstrapping of Designated-Prover NIZK -- Perfect Zero Knowledge: New Upperbounds and Relativized Separations.

This three-volume set, LNCS 12550, 12551, and 12552, constitutes the refereed proceedings of the 18th International Conference on Theory of Cryptography, TCCC 2020, held in Durham, NC, USA, in November 2020. The total of 71 full papers presented in this three-volume set was carefully reviewed and selected from 167 submissions. Amongst others they cover the following topics: study of known paradigms, approaches, and techniques, directed towards their better understanding and utilization; discovery of new paradigms, approaches and techniques that overcome limitations of the existing ones, formulation and treatment of new cryptographic problems; study of notions of security and relations among them; modeling and analysis of cryptographic algorithms; and study of the complexity assumptions used in cryptography. Due to the Corona pandemic this event was held virtually.