Dominik Leibenger

A storage-efficient cryptography-based access control solution for subversion

Version control systems are widely used in software development and document management. Unfortunately, versioning confidential files is not normally supported: Existing solutions encrypt the transport channel, but store data in plaintext within a repository. We come up with an access control solution that allows secure versioning of confidential files even in the presence of a malicious server administrator. Using convergent encryption as a building block, we enable space-efficient storage of version histories despite secure encryption. We describe an implementation of our concept for the Subversion (SVN) system, and evaluate storage efficiency and runtime of this implementation. Our implementation is compatible with existing SVN versions without requiring changes to the storage backend.

sec-cs: Getting the Most out of Untrusted Cloud Storage

We present sec-cs, a hash-table-like data structure for contents on untrusted storage that is provably secure and storage-efficient. We achieve authenticity and confidentiality with zero storage overhead using deterministic authenticated encryption. State-of-the-art data deduplication approaches prevent redundant storage of shared parts of different contents irrespective of whether relationships between contents are known a priori.,,,,Instead of just adapting existing approaches, we introduce novel (multi-level) chunking strategies, ML-SC and ML-CDC, which are significantly more storage-efficient than existing approaches in presence of high redundancy.,,,,We prove sec-css security, publish an implementation, and present evaluation results indicating suitability for, e.g., future backup systems that should preserve many versions of files on little available storage.

Confidentiality and Authenticity for Distributed Version Control Systems - A Mercurial Extension

Version Control Systems (VCS) are a valuable tool for software development and document management. Both client/server and distributed (Peer-to-Peer) models exist, with the latter (e.g., Git and Mercurial) becoming increasingly popular. Their distributed nature introduces complications, especially concerning security: it is hard to control the dissemination of contents stored in distributed VCS as they rely on replication of complete repositories to any involved user. We overcome this issue by designing and implementing a concept for cryptography-enforced access control which is transparent to the user. Use of field-tested schemes (end-to-end encryption, digital signatures) allows for strong security, while adoption of convergent encryption and content-defined chunking retains storage efficiency. The concept is seamlessly integrated into Mercurial-respecting its distributed storage concept-to ensure practical usability and compatibility to existing deployments.

Privacy Challenges in the Quantified Self Movement - An EU Perspective

Abstract The gathering of data about oneself (such as running speed, pulse, breathing rate, food consumption, etc.) is rapidly becoming more popular, and has lead to the catch phrase “Quantified Self” (QS). While this trend creates opportunities both for individuals and for society, it also creates risks, due to the data’s personal and often sensitive nature. Countering these risks, while keeping the benefits of QS services, is a task both for the legal system and for the technical community. However, it should also take users’ expectations into account. We therefore analyze the legal situation of QS services based on European law and the privacy policies of some major service providers to clarify the practical consequences for users. We present the result of a study concerning the users’ views on privacy, revealing a conflict between the user’s expectations and the providers’ practices. To help resolve the conflict, we discuss how existing and future privacy-enhancing technologies can avoid the risks associated with QS services.

Triviback: A Storage-Efficient Secure Backup System

The importance of frequent backups is uncontroversial. Their creation is simpler than ever today thanks to widespread availability of cheap cloud storage. Common backup solutions, however, tend to be either insecure, inflexible or inefficient in typical backup scenarios.,,,,In this paper, we present triviback, a lightweight and almost trivial, yet powerful solution for outsourcing backups to untrusted cloud storage. Based on recent research results on secure data deduplication, triviback combines strong confidentiality, authenticity and availability guarantees with flexibility and efficiency in terms of low storage and communication costs: Triviback supports efficient preservation of many (overlapping) backup states with storage costs comparable to (insecure) state-of-the-art version control systems (VCS)—while supporting full storage reclamation on deletion of arbitrary backup states.,,,,We prove the security of our contribution, publish a ready-to-use implementation and perform an extensive evaluation of storage and communication costs.