2,748 research outputs found
Fundamental Limits on Communication for Oblivious Updates in Storage Networks
In distributed storage systems, storage nodes intermittently go offline for
numerous reasons. On coming back online, nodes need to update their contents to
reflect any modifications to the data in the interim. In this paper, we
consider a setting where no information regarding modified data needs to be
logged in the system. In such a setting, a 'stale' node needs to update its
contents by downloading data from already updated nodes, while neither the
stale node nor the updated nodes have any knowledge as to which data symbols
are modified and what their value is. We investigate the fundamental limits on
the amount of communication necessary for such an "oblivious" update process.
We first present a generic lower bound on the amount of communication that is
necessary under any storage code with a linear encoding (while allowing
non-linear update protocols). This lower bound is derived under a set of
extremely weak conditions, giving all updated nodes access to the entire
modified data and the stale node access to the entire stale data as side
information. We then present codes and update algorithms that are optimal in
that they meet this lower bound. Next, we present a lower bound for an
important subclass of codes, that of linear Maximum-Distance-Separable (MDS)
codes. We then present an MDS code construction and an associated update
algorithm that meets this lower bound. These results thus establish the
capacity of oblivious updates in terms of the communication requirements under
these settings.Comment: IEEE Global Communications Conference (GLOBECOM) 201
SoK: Cryptographically Protected Database Search
Protected database search systems cryptographically isolate the roles of
reading from, writing to, and administering the database. This separation
limits unnecessary administrator access and protects data in the case of system
breaches. Since protected search was introduced in 2000, the area has grown
rapidly; systems are offered by academia, start-ups, and established companies.
However, there is no best protected search system or set of techniques.
Design of such systems is a balancing act between security, functionality,
performance, and usability. This challenge is made more difficult by ongoing
database specialization, as some users will want the functionality of SQL,
NoSQL, or NewSQL databases. This database evolution will continue, and the
protected search community should be able to quickly provide functionality
consistent with newly invented databases.
At the same time, the community must accurately and clearly characterize the
tradeoffs between different approaches. To address these challenges, we provide
the following contributions:
1) An identification of the important primitive operations across database
paradigms. We find there are a small number of base operations that can be used
and combined to support a large number of database paradigms.
2) An evaluation of the current state of protected search systems in
implementing these base operations. This evaluation describes the main
approaches and tradeoffs for each base operation. Furthermore, it puts
protected search in the context of unprotected search, identifying key gaps in
functionality.
3) An analysis of attacks against protected search for different base
queries.
4) A roadmap and tools for transforming a protected search system into a
protected database, including an open-source performance evaluation platform
and initial user opinions of protected search.Comment: 20 pages, to appear to IEEE Security and Privac
Communication Cost for Updating Linear Functions when Message Updates are Sparse: Connections to Maximally Recoverable Codes
We consider a communication problem in which an update of the source message
needs to be conveyed to one or more distant receivers that are interested in
maintaining specific linear functions of the source message. The setting is one
in which the updates are sparse in nature, and where neither the source nor the
receiver(s) is aware of the exact {\em difference vector}, but only know the
amount of sparsity that is present in the difference-vector. Under this
setting, we are interested in devising linear encoding and decoding schemes
that minimize the communication cost involved. We show that the optimal
solution to this problem is closely related to the notion of maximally
recoverable codes (MRCs), which were originally introduced in the context of
coding for storage systems. In the context of storage, MRCs guarantee optimal
erasure protection when the system is partially constrained to have local
parity relations among the storage nodes. In our problem, we show that optimal
solutions exist if and only if MRCs of certain kind (identified by the desired
linear functions) exist. We consider point-to-point and broadcast versions of
the problem, and identify connections to MRCs under both these settings. For
the point-to-point setting, we show that our linear-encoder based achievable
scheme is optimal even when non-linear encoding is permitted. The theory is
illustrated in the context of updating erasure coded storage nodes. We present
examples based on modern storage codes such as the minimum bandwidth
regenerating codes.Comment: To Appear in IEEE Transactions on Information Theor
Social-Aware Stateless Forwarding in Pocket Switched Networks
Several social-aware routing protocols for pocket switched networks have been recently introduced in the literature. The main idea underlying these protocols is to exploit state information (e.g., history of past encounters) to deduce information on the social structure of the network, and to optimize routing based on this information. While social-aware routing protocols have been shown to have superior performance to social-oblivious, stateless routing protocols such as, e.g., BinarySW, the improvement comes at the cost of considerable storage overhead required on the nodes, which is instead not required for stateless approaches. So, whether the benefits of social-aware routing protocols would still be present when storage capacity at the nodes is constrained is not clear. In this paper we present SANE, the first forwarding mechanism that combines the advantages of both social-aware and stateless approaches. SANE is based on the observation-that we validate on real-world traces-that individuals with similar interests tend to meet more often. In our approach, individuals (network members) are characterized by their interest profile, a compact representation of their interests. By implementing a simple interest profile similarity based forwarding rule, SANE is free of network state information, thus overcoming the storage capacity problem with existing social-aware approaches. Through extensive experiments, we show the superiority of social-aware, stateless forwarding over existing stateful, social-aware and stateless, social-oblivious routing approaches. An important byproduct of our interest-based approach is that it easily enables innovative routing primitives, such as interest-casting. An interest-casting protocol is also introduced in this paper, and extensively evaluated through experiments based on both real-world and synthetic mobility traces
Updating Content in Cache-Aided Coded Multicast
Motivated by applications to delivery of dynamically updated, but correlated
data in settings such as content distribution networks, and distributed file
sharing systems, we study a single source multiple destination network coded
multicast problem in a cache-aided network. We focus on models where the caches
are primarily located near the destinations, and where the source has no cache.
The source observes a sequence of correlated frames, and is expected to do
frame-by-frame encoding with no access to prior frames. We present a novel
scheme that shows how the caches can be advantageously used to decrease the
overall cost of multicast, even though the source encodes without access to
past data. Our cache design and update scheme works with any choice of network
code designed for a corresponding cache-less network, is largely decentralized,
and works for an arbitrary network. We study a convex relation of the
optimization problem that results form the overall cost function. The results
of the optimization problem determines the rate allocation and caching
strategies. Numerous simulation results are presented to substantiate the
theory developed.Comment: To Appear in IEEE Journal on Selected Areas in Communications:
Special Issue on Caching for Communication Systems and Network
Hardware-Assisted Secure Computation
The theory community has worked on Secure Multiparty Computation (SMC) for more than two decades, and has produced many protocols for many settings. One common thread in these works is that the protocols cannot use a Trusted Third Party (TTP), even though this is conceptually the simplest and most general solution. Thus, current protocols involve only the direct players---we call such protocols self-reliant. They often use blinded boolean circuits, which has several sources of overhead, some due to the circuit representation and some due to the blinding. However, secure coprocessors like the IBM 4758 have actual security properties similar to ideal TTPs. They also have little RAM and a slow CPU.We call such devices Tiny TTPs. The availability of real tiny TTPs opens the door for a different approach to SMC problems. One major challenge with this approach is how to execute large programs on large inputs using the small protected memory of a tiny TTP, while preserving the trust properties that an ideal TTP provides. In this thesis we have investigated the use of real TTPs to help with the solution of SMC problems. We start with the use of such TTPs to solve the Private Information Retrieval (PIR) problem, which is one important instance of SMC. Our implementation utilizes a 4758. The rest of the thesis is targeted at general SMC. Our SMC system, Faerieplay, moves some functionality into a tiny TTP, and thus avoids the blinded circuit overhead. Faerieplay consists of a compiler from high-level code to an arithmetic circuit with special gates for efficient indirect array access, and a virtual machine to execute this circuit on a tiny TTP while maintaining the typical SMC trust properties. We report on Faerieplay\u27s security properties, the specification of its components, and our implementation and experiments. These include comparisons with the Fairplay circuit-based two-party system, and an implementation of the Dijkstra graph shortest path algorithm. We also provide an implementation of an oblivious RAM which supports similar tiny TTP-based SMC functionality but using a standard RAM program. Performance comparisons show Faerieplay\u27s circuit approach to be considerably faster, at the expense of a more constrained programming environment when targeting a circuit
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