International Association
for Cryptologic Research

Many cryptographic protocols exist that enable two parties to exchange items (e.g., e-commerce) or agree on something (e.g., contract-signing). In such settings, disputes may arise. Official arbitration refers to the process of resolving disputes between two (or more) parties by a trusted and authorized Judge, based on evidence provided. As an example, consider the secure cloud storage scenario where there needs to be an official arbitration process between the client and the server in case of data loss or corruption. Without such a mechanism that can be officially used by the Judge in the court, the barrier on the enterprise adoption of such systems is high.

In this paper we first formally define official arbitration, and then provide several general purpose official arbitration protocols. Later, we focus on secure cloud storage, and provide efficient official arbitration schemes that can be used on top of any secure cloud storage scheme. We furthermore present a completely automated system where the Judge can just be a computer instead of a human being. All our constructions have security proofs, and we conclude with performance measurements showing that our overhead for official arbitration is roughly 2 ms and 80 bytes for each update on the stored data.