Secure Quasi-Realtime Collaborative Editing over Low-Cost Storage Services

Abstract. A realtime collaborative editor facilitates concurrent edit-ing of a document by multiple authors. It is desired that the document be shared only among the authors, and protected from the potentially curious server. Existing approaches have taken two distinct paths – cen-tralized server based approaches that achieve high concurrency and meet real-time requirement but compromise on security and incur high server cost, and peer-to-peer based approaches that support security but com-promise on users ’ convenience and mobility. In this paper, we observe that by relaxing the realtime requirement, we can achieve security, re-duce server cost and yet exploit the conveniences of the centralized set-ting. In particular, we consider generic low-cost storage servers in the cloud that provide storage integrity but do not guarantee low-latency. Essentially, our method breaks the document into small encrypted re-gions that are stored on the server and coordinates the authors ’ access. Although two authors are unable to concurrently modify a same region, the system is able to provide “quasi-realtime ” experience. By relaxing the requirement to quasi-realtime, the difficulties in achieving document consistency, and the requirement on resources are significantly reduced. We give a proof-of-concept implementation on top of Dropbox, a com-mercial cloud storage service. Preliminary user studies show that the system is effective.