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Defeating Vanish with Low-Cost Sybil Attacks Against Large DHTs
, 2009
"... Researchers at the University of Washington recently proposed Vanish [19], a system for creating messages that automatically “self-destruct ” after a period of time. Vanish works by encrypting each message with a random key and storing shares of the key in a large, public distributed hash table (DHT ..."
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Researchers at the University of Washington recently proposed Vanish [19], a system for creating messages that automatically “self-destruct ” after a period of time. Vanish works by encrypting each message with a random key and storing shares of the key in a large, public distributed hash table (DHT). Normally, DHTs expunge data older than a certain age. After they expire, the key is permanently lost, and the encrypted data is permanently unreadable. Vanish is an interesting approach to an important privacy problem, but, in its current form, it is insecure. In this paper, we defeat the deployed Vanish implementation, explain how the original paper’s security analysis is flawed, and draw lessons for future system designs. We present two Sybil attacks against the current Vanish implementation, which stores its encryption keys in the million-node Vuze BitTorrent DHT. These attacks work by continuously crawling the DHT and saving each stored value before it ages out. They can efficiently recover keys for more than 99 % of Vanish messages. We show that the dominant cost of these attacks is network data transfer, not memory usage as the Vanish authors expected, and that the total cost is two orders of magnitude less than they estimated. While we consider potential defenses, we conclude that public DHTs like Vuze probably cannot provide strong security for Vanish. Update – September 28, 2009 After we shared these findings with the Vanish team, they released a software update that attempts to defend against our attacks [20] and a report detailing potential countermeasures [18]. We respond to these developments in the update section at the end of this paper. 1
FADE: Secure Overlay Cloud Storage with File Assured Deletion”,
, 2010
"... Abstract. While we can now outsource data backup to third-party cloud storage services so as to reduce data management costs, security concerns arise in terms of ensuring the privacy and integrity of outsourced data. We design FADE, a practical, implementable, and readily deployable cloud storage s ..."
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Abstract. While we can now outsource data backup to third-party cloud storage services so as to reduce data management costs, security concerns arise in terms of ensuring the privacy and integrity of outsourced data. We design FADE, a practical, implementable, and readily deployable cloud storage system that focuses on protecting deleted data with policy-based file assured deletion. FADE is built upon standard cryptographic techniques, such that it encrypts outsourced data files to guarantee their privacy and integrity, and most importantly, assuredly deletes files to make them unrecoverable to anyone (including those who manage the cloud storage) upon revocations of file access policies. In particular, the design of FADE is geared toward the objective that it acts as an overlay system that works seamlessly atop today's cloud storage services. To demonstrate this objective, we implement a working prototype of FADE atop Amazon S3, one of today's cloud storage services, and empirically show that FADE provides policy-based file assured deletion with a minimal trade-off of performance overhead. Our work provides insights of how to incorporate value-added security features into current data outsourcing applications.
1 Secure Overlay Cloud Storage with Access Control and Assured Deletion
"... Abstract—We can now outsource data backups off-site to third-party cloud storage services so as to reduce data management costs. However, we must provide security guarantees for the outsourced data, which is now maintained by third parties. We design and implement FADE, a secure overlay cloud storag ..."
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Abstract—We can now outsource data backups off-site to third-party cloud storage services so as to reduce data management costs. However, we must provide security guarantees for the outsourced data, which is now maintained by third parties. We design and implement FADE, a secure overlay cloud storage system that achieves fine-grained, policy-based access control and file assured deletion. It associates outsourced files with file access policies, and assuredly deletes files to make them unrecoverable to anyone upon revocations of file access policies. To achieve such security goals, FADE is built upon a set of cryptographic key operations that are self-maintained by a quorum of key managers that are independent of third-party clouds. In particular, FADE acts as an overlay system that works seamlessly atop today’s cloud storage services. We implement a proof-of-concept prototype of FADE atop Amazon S3, one of today’s cloud storage services. We conduct extensive empirical studies, and demonstrate that FADE provides security protection for outsourced data, while introducing only minimal performance and monetary cost overhead. Our work provides insights of how to incorporate value-added security features into today’s cloud storage services. Keywords—access control, assured deletion, backup/recovery, cloud storage 1
X-Vine: Secure and Pseudonymous Routing Using Social Networks
"... Distributed hash tables suffer from several security and privacy vulnerabilities, including the problem of Sybil attacks. Existing social network-based solutions to mitigate the Sybil attacks in DHT routing have a high state requirement and do not provide an adequate level of privacy. For instance, ..."
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Cited by 17 (3 self)
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Distributed hash tables suffer from several security and privacy vulnerabilities, including the problem of Sybil attacks. Existing social network-based solutions to mitigate the Sybil attacks in DHT routing have a high state requirement and do not provide an adequate level of privacy. For instance, such techniques require a user to reveal their social network contacts. We design X-Vine, a protection nmechanism for distributed hash tables that operates entirely by communicating over social network links. As with traditional peer-to-peer systems, X-Vine provides robustness, scalability, and a platform for innovation. The use of social network links for communication helps protect participant privacy and adds a new dimension of trust absent from previous designs. X-Vine is resilient to denial of service via Sybil attacks, and in fact is the first Sybil defense that requires only a logarithmic amount of state per node, making it suitable for large-scale and dynamic settings. X-Vine also helps protect the privacy of users social network contacts and keeps their IP addresses hidden from those outside of their social circle, providing a basis for pseudonymous communication. We first evaluate our design with analysis and simulations, using several real world large-scale social networking topologies. We show that the constraints of X-Vine allow the insertion of only a logarithmic number of Sybil identities per attack edge; we show this mitigates the impact of malicious attacks while not affecting the performance of honest nodes. Moreover, our algorithms are efficient, maintain low stretch, and avoid hot spots in the network. We validate our design with a PlanetLab implementation and a Facebook plugin.
Comet: An active distributed key-value store
"... Distributed key-value storage systems are widely used in corporations and across the Internet. Our research seeks to greatly expand the application space for key-value storage systems through application-specific customization. We designed and implemented Comet, an extensible, distributed key-value ..."
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Distributed key-value storage systems are widely used in corporations and across the Internet. Our research seeks to greatly expand the application space for key-value storage systems through application-specific customization. We designed and implemented Comet, an extensible, distributed key-value store. Each Comet node stores a collection of active storage objects (ASOs) that consist of a key, a value, and a set of handlers. Comet handlers run as a result of timers or storage operations, such as get or put, allowing an ASO to take dynamic, application-specific actions to customize its behavior. Handlers are written in a simple sandboxed extension language, providing properties of safety and isolation. We implemented a Comet prototype for the Vuze DHT, deployed Comet nodes on Vuze from PlanetLab, and built and evaluated over a dozen Comet applications. Our experience demonstrates that simple, safe, and restricted extensibility can significantly increase the power and range of applications that can run on distributed active storage systems. This approach facilitates the sharing of a single storage system by applications with diverse needs, allowing them to reap the consolidation benefits inherent in today’s massive clouds. 1
Lost in translation: Understanding the possession of digital things in the cloud
- In CHI ’12: Proceedings of the International Conference on Human factors in Computing Systems
, 2012
"... {asellen, r.harper, ..."
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CleanOS: Limiting mobile data exposure with idle eviction
- In OSDI
, 2012
"... Mobile-device theft and loss have reached gigantic proportions. Despite these threats, today’s mobile devices are saturated with sensitive information due to operating systems that never securely erase data and applications that hoard it on the vulnerable device for performance or convenience. This ..."
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Mobile-device theft and loss have reached gigantic proportions. Despite these threats, today’s mobile devices are saturated with sensitive information due to operating systems that never securely erase data and applications that hoard it on the vulnerable device for performance or convenience. This paper presents CleanOS, a new Android-based operating system that manages sensitive data rigorously and maintains a clean environment at all times. To do so, CleanOS leverages a key property of today’s mobile applications – the use of trusted, cloudbased services. Specifically, CleanOS identifies and tracks sensitive data in RAM and on stable storage, encrypts it with a key, and evicts that key to the cloud when the data is not in active use on the device. We call this process idle eviction of sensitive data. To implement CleanOS, we used the TaintDroid mobile taint-tracking system to identify sensitive data locations and instrumented Android’s Dalvik interpreter to securely evict that data after a specified period of non-use. Our experimental results show that CleanOS limits sensitive-data exposure drastically while incurring acceptable overheads on mobile networks. 1
Keypad: An Auditing File System for Theft-Prone Devices
"... This paper presents Keypad, an auditing file system for theftprone devices, such as laptops and USB sticks. Keypad provides two important properties. First, Keypad supports finegrained file auditing: a user can obtain explicit evidence that no files have been accessed after a device’s loss. Second, ..."
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Cited by 15 (3 self)
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This paper presents Keypad, an auditing file system for theftprone devices, such as laptops and USB sticks. Keypad provides two important properties. First, Keypad supports finegrained file auditing: a user can obtain explicit evidence that no files have been accessed after a device’s loss. Second, a user can disable future file access after a device’s loss, even in the absence of device network connectivity. Keypad achieves these properties by weaving together encryption and remote key storage. By encrypting files locally but storing encryption keys remotely, Keypad requires the involvement of an audit server with every protected file access. By alerting the audit server to refuse to return a particular file’s key, the user can prevent new accesses after theft. We describe the Keypad architecture, a prototype implementation on Linux, and our evaluation of Keypad’s performance and auditing fidelity. Our results show that Keypad overcomes the challenges posed by slow networks or disconnection, providing clients with usable forensics and control for their (increasingly) missing mobile devices.
Practical Robust Communication in DHTs Tolerating a Byzantine Adversary
"... There are several analytical results on distributed hash tables (DHTs) that can tolerate Byzantine faults. Unfortunately, in such systems, critical operations such as data retrieval and message sending incur significant communication costs. For example, a simple scheme used in many Byzantine fault-t ..."
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Cited by 14 (3 self)
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There are several analytical results on distributed hash tables (DHTs) that can tolerate Byzantine faults. Unfortunately, in such systems, critical operations such as data retrieval and message sending incur significant communication costs. For example, a simple scheme used in many Byzantine fault-tolerant DHT constructions of n nodes requires O(log 3 n) messages; this is likely impractical for real-world applications. Currently, the best known message complexity is O(log 2 n) in expectation; however, the corresponding protocol suffers from prohibitive costs owing to hidden constants in the asymptotic notation and to setup costs. In this paper, we focus on reducing the communication costs against a computationally bounded adversary. We employ threshold cryptography and distributed key generation to define two protocols both of which are more efficient than existing solutions. In comparison, our first protocol is deterministic with O(log 2 n) message complexity and our second protocol is randomized with expected O(log n) message complexity. Further, both the hidden constants and setup costs for our protocols are small and no trusted third party is required. Finally, we present results from microbenchmarks conducted over PlanetLab showing that our protocols are practical for deployment under significant levels of churn and adversarial behaviour. 1.
Parenting from the Pocket: Value Tensions and Technical Directions for Secure and Private Parent-Teen Mobile Safety
"... An increasing number of high-tech devices, such as driver monitoring systems and Internet usage monitoring tools, are advertised as useful or even necessary for good parenting of teens. Simultaneously, there is a growing market for mobile “personal safety ” devices. As these trends merge, there will ..."
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Cited by 13 (3 self)
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An increasing number of high-tech devices, such as driver monitoring systems and Internet usage monitoring tools, are advertised as useful or even necessary for good parenting of teens. Simultaneously, there is a growing market for mobile “personal safety ” devices. As these trends merge, there will be significant implications for parent-teen relationships, affecting domains such as privacy, trust, and maturation. Not only the teen and his or her parents are affected; other important stakeholders include the teen’s friends who may be unwittingly monitored. This problem space, with less clearcut assets, risks, and affected parties, thus lies well outside of more typical computer security applications. To help understand this problem domain and what, if anything, should be built, we turn to the theory and methods of Value Sensitive Design, a systematic approach to designing for human values in technology. We first develop value scenarios that highlight potential issues, benefits, harms, and challenges. We then conducted semi-structured interviews with 18 participants (9 teens and their parents). Results show significant differences with respect to information about: 1) internal state (e.g., mood) versus external environment (e.g., location); 2) situation (e.g., emergency vs. non-emergency); and 3) awareness (e.g., notification vs. non-notification). The value scenario and interview results positioned us to identify key technical challenges – such as strongly protecting the privacy of a teen’s contextual information during ordinary situations but immediately exposing that information to others as appropriate in an emergency – and corresponding architectural levers for these technologies. In addition to laying a foundation for future work in this area, this research serves as a prototypical example of using Value Sensitive Design to explicate the underlying human values in complex security domains.
