A universal system for fair non-repudiable certified e-mail without a trusted third party

Abstract

Certified e-mail delivery is a quickly emerging field with significant legal benefits for e-commerce and e-government. Existing service-providers provide individual solutions that rely on a trusted third party and are in general limited in their scope and interoperability; as a consequence, they are unsuitable for cross-border application as required by transnational unions like the EU.In contrast to existing service-providers, we present a working system for certified e-mail that does not rely on a trusted third party for fair non-repudiation of receipt. We achieve fair non-repudiation of receipt through a novel protocol that involves splitting an encrypted message into a chain of parts, which the addressee gradually acquires, generating proof-of-receipt for each individual part. The protocol cryptographically prevents the addressee from obtaining the message in case they terminate the protocol prematurely.The universality of the presented system makes it feasible for unobtrusive operation using existing user agents and e-mail providers. The system is presented as a proof-of-concept implementation for the open-source Mozilla Thunderbird user agent.