Enhancing security of cryptographic protocols through better modularization
OA Version
Citation
Abstract
Cryptographic protocols are usually designed using a modular approach, breaking down the task into several smaller tasks that involve constructing several cryptographic primitives. The next step is to identify primitives which serve the purpose and yet are simple enough to be instantiated. Simplicity can be defined in different ways - instantiable from a wider set of assumptions (or information-theoretically secure if possible), relaxed round complexity, and weaker security guarantees. However, finding the right way to break down the protocol into simpler primitives is not always easy. If the primitives are too simple, building the protocol becomes challenging. Conversely, if the primitives are too strong, it can be difficult to build them. Therefore, identifying the correct notion of "simplicity'', choosing the right set of primitives, and building the protocol requires a delicate balance. In this thesis, we revisit three problems in the areas of secure computation (MPC) and non-interactive zero-knowledge (NIZK) and we propose new ways to modularize the problems by relying on simpler primitives: 1. In the setting of two-party computation (2PC) where one of the participating parties is corrupted by a computationally unbounded adversary, we build a round-optimal 2PC protocol using a relaxed version of the oblivious transfer (which is not round-optimal) primitive and a non-interactive commitment scheme. 2. We build a round-optimal MPC protocol that withstands adaptive corruptions using an oblivious transfer which only provides sender and receiver privacy guarantees and satisfies some additional sampling properties. 3. We construct triply adaptive NIZKs which are secure against an adversary that corrupts parties and chooses statements to be proven in an adaptive way. We apply the Fiat-Shamir transform (instantiated using correlation intractable hash functions) to commitment-based Sigma protocols and demonstrate security in a modular way via a new approach for capturing universally-composable non-interactive commitments.
Description
2023
License
Attribution 4.0 International