Zachary N. J. Peterson

Provable data possession at untrusted stores

We introduce a model for provable data possession (PDP) that allows a client that has stored data at an untrusted server to verify that the server possesses the original data without retrieving it. The model generates probabilistic proofs of possession by sampling random sets of blocks from the server, which drastically reduces I/O costs. The client maintains a constant amount of metadata to verify the proof. The challenge/response protocol transmits a small, constant amount of data, which minimizes network communication. Thus, the PDP model for remote data checking supports large data sets in widely-distributed storage system. We present two provably-secure PDP schemes that are more efficient than previous solutions, even when compared with schemes that achieve weaker guarantees. In particular, the overhead at the server is low (or even constant), as opposed to linear in the size of the data. Experiments using our implementation verify the practicality of PDP and reveal that the performance of PDP is bounded by disk I/O and not by cryptographic computation.

Remote data checking using provable data possession

We introduce a model for provable data possession (PDP) that can be used for remote data checking: A client that has stored data at an untrusted server can verify that the server possesses the original data without retrieving it. The model generates probabilistic proofs of possession by sampling random sets of blocks from the server, which drastically reduces I/O costs. The client maintains a constant amount of metadata to verify the proof. The challenge/response protocol transmits a small, constant amount of data, which minimizes network communication. Thus, the PDP model for remote data checking is lightweight and supports large data sets in distributed storage systems. The model is also robust in that it incorporates mechanisms for mitigating arbitrary amounts of data corruption. We present two provably-secure PDP schemes that are more efficient than previous solutions. In particular, the overhead at the server is low (or even constant), as opposed to linear in the size of the data. We then propose a generic transformation that adds robustness to any remote data checking scheme based on spot checking. Experiments using our implementation verify the practicality of PDP and reveal that the performance of PDP is bounded by disk I/O and not by cryptographic computation. Finally, we conduct an in-depth experimental evaluation to study the tradeoffs in performance, security, and space overheads when adding robustness to a remote data checking scheme.

Ext3cow: a time-shifting file system for regulatory compliance

The ext3cow file system, built on the popular ext3 file system, provides an open-source file versioning and snapshot platform for compliance with the versioning and audtitability requirements of recent electronic record retention legislation. Ext3cow provides a time-shifting interface that permits a real-time and continuous view of data in the past. Time-shifting does not pollute the file system namespace nor require snapshots to be mounted as a separate file system. Further, ext3cow is implemented entirely in the file system space and, therefore, does not modify kernel interfaces or change the operation of other file systems. Ext3cow takes advantage of the fine-grained control of on-disk and in-memory data available only to a file system, resulting in minimal degradation of performance and functionality. Experimental results confirm this hypothesis; ext3cow performs comparably to ext3 on many benchmarks and on trace-driven experiments.

Securing electronic medical records using attribute-based encryption on mobile devices

We provide a design and implementation of self-protecting electronic medical records (EMRs) using attribute-based encryption on mobile devices. Our system allows healthcare organizations to export EMRs to locations outside of their trust boundary. In contrast to previous approaches, our solution is designed to maintain EMR availability even when providers are offline, i.e., where network connectivity is not available. To balance the needs of emergency care and patient privacy, our system is designed to provide fine-grained encryption and is able to protect individual items within an EMR, where each encrypted item may have its own access control policy. We implemented a prototype system using a new key- and ciphertext-policy attribute-based encryption library that we developed. Our implementation, which includes an iPhone app for storing and managing EMRs offline, allows for flexible and automated policy generation. An evaluation of our design shows that our ABE library performs well, has acceptable storage requirements, and is practical and usable on modern smartphones.

Geolocation of data in the cloud

We introduce and analyze a general framework for authentically binding data to a location while providing strong assurances against cloud storage providers that (either accidentally or maliciously) attempt to re-locate cloud data. We then evaluate a preliminary solution in this framework that combines constraint-based host geolocation with proofs of data possession, called constraint-based data geolocation (CBDG). We evaluate CBDG using a combination of experiments with PlanetLab and real cloud storage services, demonstrating that we can bind fetched data to the location originally hosting it with high precision. We geolocate data hosted on the majority of our PlanetLab targets to regions no larger than 118,000 km^2, and we geolocate data hosted on Amazon S3 to an area no larger than 12,000 km^2, sufficiently small to identify the state or service region.

Security through play

The US Naval Postgraduate School and University of Washington each independently developed informal security-themed tabletop games. [d0x3d!] is a board game in which players collaborate as white-hat hackers, tasked to retrieve a set of valuable digital assets held by an adversarial network. Control-Alt-Hack is a card game in which three to six players act as white-hat hackers at a security consulting company. These games employ modest pedagogical objectives to expose broad audiences to computer security topics.

Verifiable audit trails for a versioning file system

We present constructs that create, manage, and verify digital audit trails for versioning file systems. Based upon a small amount of data published to a third party, a file system commits to a version history. At a later date, an auditor uses the published data to verify the contents of the file system at any point in time. Audit trails create an analog of the paper audit process for file data, helping to meet the requirements of electronic record legislation, such as Sarbanes-Oxley. Our techniques address the I/O and computational efficiency of generating and verifying audit trails, the aggregation of audit information in directory hierarchies, and constructing verifiable audit trails in the presence of lost data.

Building regulatory compliant storage systems

In the past decade, informational records have become entirely digital. These include financial statements, health care records, student records, private consumer information and other sensitive data. Because of the delicate nature of the data these records contain, Congress and the courts have begun to recognize the importance of properly storing and securing electronic records. Examples of legislation include the Health Insurance Portability and Accountability Act (HIPAA) of 1996, the Gramm-Leach-Bliley Act (GLBA) of 1999, and the more recent Federal Information Security Management Act (FISMA) and Sarbanes-Oxley Act (SOX) of 2002. Altogether, there exist over 4,000 acts and regulations that govern digital storage, all with a varying range of requirements for maintaining electronic records.