Scalability and Interoperability of Blockchains

Cryptocurrencies and blockchain technologies allow users to execute payments, smart contracts, and much more in a decentralized way. The increasing adoption of cryptocurrencies since the inception of Bitcoin has raised not only scalability issues but also the need for a more rigorous analysis of their security and privacy. Moreover, because of the emergence of many different cryptocurrencies, the interoperability between them is of great interest as well. One of the research areas of the “Security and Privacy” group is blockchain, and the primary research problems we tackle are summarized below.

Scalability

One of the main problems permissionless blockchains face today is a lack of scalability, which goes far beyond rapidly increasing blockchain sizes. Bitcoin is technically limited to tens of transactions per second, while centralized credit card networks achieve tens of thousands of transactions per second. This problem persists for other blockchains as well. Among the most promising solutions are payment channels, sharding, and rollups. We have previously introduced new payment channel constructions, more efficient payment channel network schemes, interoperable, atomic, and privacy-preserving payment channel hubs, virtual channels, off-chain smart contracts for Bitcoin-like cryptocurrencies, and worked on formalized sharding protocols.

Security & Privacy

Cryptocurrencies have some value associated with them. To ensure that users are not at risk of, for example, losing their money or being exposed to inadequate levels of privacy, cryptocurrencies and protocols built on top of them need to be analyzed rigorously. We focus on formally analyzing protocols, proving them secure, viewing them under the lens of game theory, etc. On a more fundamental note, one interest of us is to define what blockchains are and can achieve under different timing, network, and adversarial models. Moreover, we are interested in post-quantum security.

Interoperability & Expressiveness

Different blockchains have different properties in terms of privacy, expressiveness, transaction throughput, etc. This leads to a very fragmented user base. We analyze and design new cross-chain protocols to interconnect different chains, leverage the properties of other chains, build new applications, or simply perform atomic swaps of tokens between multiple chains while improving efficiency, security, and privacy. Furthermore, we are interested in bringing protocols to blockchains with limited expressiveness, i.e., ones that do not support quasi-Turing complete smart contracts.

Main directions of our research include: