Section: Research Program

Electronic Currencies and the Blockchain

Electronic cash (e-cash) was first proposed in the 1980s but has never been deployed on a large scale. Other means of digital payments are instead largely replacing physical cash, but they do not respect the citizens' right to privacy, which includes their right of anonymous payments of moderate sums. Recently, so-called decentralized currencies, such as Bitcoin, have become a third type of payments in addition to physical cash, and card and other (non-anonymous) electronic payments. The continuous growth of popularity and usage of this new kind of currencies, also called “cryptocurrencies”, have triggered a renewed interest in cryptographic e-cash.

On the one hand, our group investigates “centralized” e-cash, in keeping with the current economic model that has money be issued by (central) banks (while cryptocurrencies use money distribution as an incentive for participation in the system, on which its stability hinges). Of particular interest among centralized e-cash schemes is transferable e-cash, which allows users to transfer coins between each other without interacting with a third party (or the blockchain). Existing efficient e-cash schemes are not transferable, as they require coins to be deposited at the bank after having been used in a payment. Our goal is to propose efficient transferable e-cash schemes.

Another direction concerns (decentralized) cryptocurrencies, whose adoption has grown tremendously over the last few years. While in Bitcoin all transactions are publicly posted on the so-called “blockchain”, other cryptocurrencies such as Zcash respect user privacy, whose security guarantees we have analyzed. Apart from privacy, two pressing challenges for cryptocurrencies, and blockchains in general, are sustainability and scalability. Regarding the former, we are addressing the electricity waste caused by the concept of “proof of work” used by all major cryptocurrencies by proposing alternatives; for the latter, we are working on proposals that avoid the need for all data having to be stored on the blockchain forever.

Blockchains have meanwhile found many other applications apart from electronic money. Together with Microsoft Research, our group investigates decentralized means of authentication that uses cryptography to guarantee privacy.