Paper 2026/2495

Issuer-Independent Decentralized Exchange for E-Cash

Abstract

Despite decades of cryptographic advances, electronic cash (e-cash) remains largely confined to payments and lacks the broader decentralized financial applications built around cryptocurrencies. As a step toward broadening its application layer, we present an issuer-independent e-cash exchange in which a liquidity provider holds inventories of two independently issued e-cash currencies and users trade between them without requiring either issuer to participate in individual swaps. Our design combines a blockchain settlement layer, which automates the exchange and makes its execution publicly verifiable, with an exchange-compatible e-cash protocol. Classical e-cash must be adapted to this setting in two respects: payments must become publicly verifiable by the exchange, and the additional privacy risks created by public execution must be addressed. We formalize these new privacy requirements and construct a compact e-cash realization with publicly verifiable payments and aggregate anonymous reissue. We prove the security and privacy properties of the resulting exchange protocol under the stated cryptographic and issuer-functionality assumptions.