Practical escrow protocol for cryptocurrencies

Abstract

Escrow protocol for cryptocurrencies is a two-party protocol that enables the fair exchange of goods or services with digital coins. An escrow protocol allows digital coins to be escrowed (i.e., locked) in a way that only the seller can claim the coins (when the deal is completed) or the buyer can claim the coin (when the deal is canceled) with the help of a trusted third party (TTP). Existing escrow protocols for cryptocurrencies are built based on various approaches with various security and efficiency trade-offs. In this thesis, we introduce a new approach based on verifiably encrypted signature (VES), a specific kind of digital signature whose validity can be verified in encrypted form. Escrow protocols constructed from our approach enjoy many desirable features, including (a) round-efficient; (b) privacy-preserving for participants; and (c) minimal TTP involvement. ECDSA is the signature scheme adopted by major cryptocurrencies such as Bitcoin and Ethereum. To construct escrow protocols for these cryptocurrencies based on our approach, we develop an efficient verifiably encrypted ECDSA, which may be of independent interest. Besides ECDSA, EdDSA and Schnorr digital signatures are adopted in popular cryptocurrencies. To build escrow protocols to fit these popular cryptocurrencies, we generalize the above signature schemes as an EdDSA-like signature and propose a generic construction of verifiably encrypted signature scheme for EdDSA-like signature. We conduct a thorough complexity analysis of the escrow protocol obtained from the above VES schemes and demonstrate its feasibility.