Sublinear Computation Research Articles

EPMDA-FED: Efficient and Privacy-Preserving Multidimensional Data Aggregation Scheme With Fast Error Detection in Smart Grid

Smart grids bring advantages of reliabilty and high efficiency by real-time communication technologies in contrast to the traditional grids. However, smart grids also raise concerns about privacy and security for the individual fine-grained information collection. In order to guarantee privacy and securtiy in the grids, we propose an efficient and privacy-preserving multidimensional data aggregation scheme without a third trusted party and supporting fast error detection, named EPMDA-FED, in the paper. Firstly, we adopt Chinese Remainder Theorem to pack multidimensional data and encrypt the processed data using the keys generated by the negotiation among users and the control center. Secondly, our scheme is efficient for encryption without high-cost additive homomorphic public key encryption scheme, such as Paillier cryptosystem and supporting batch verification with fast error detection. Our proposed error detection algorithm is quite efficient with sublinear computation complexity. Besides, through security analysis, EPMDA-FED is semantically secure against collusion attack and the consistency of negotiated key, authenticity and data integrity of the users’ reports are guaranteed. Finally, performance evaluation shows EPMDA-FED is more efficient than existing competing approaches in terms of computation and communication overhead.

Authenticated Dictionaries

Authenticated dictionaries are a widely discussed paradigm to enable verifiable integrity for data storage on untrusted servers, such as today’s widely used “cloud computing” resources, allowing a server to provide a “proof,” typically in the form of a slice through a cryptographic data structure, that the results of any given query are the correct answer, including that the absence of a query result is correct. Persistent authenticated dictionaries (PADs) further allow queries against older versions of the structure. This research presents implementations of a variety of different PAD algorithms, some based on Merkle tree-style data structures and others based on individually signed “tuple” statements (with and without RSA accumulators). We present system throughput benchmarks, indicating costs in terms of time, storage, and bandwidth as well as considering how much money would be required given standard cloud computing costs. We conclude that Merkle tree PADs are preferable in cases with frequent updates, while tuple-based PADs are preferable with higher query rates. For Merkle tree PADs, red-black trees outperform treaps and skiplists. Applying Sarnak-Tarjan’s versioned node strategy, with a cache of old hashes at every node, to red-black trees yields the fastest Merkle tree PAD implementation, notably using half the memory of the more commonly used mutation-free path copying strategy. For tuple PADs, although we designed and implemented an algorithm using RSA accumulators that offers constant update size, constant storage per update, constant proof size, and sublinear computation per update, we found that RSA accumulators are so expensive that they are never worthwhile. We find that other optimizations in the literature for tuple PADs are more cost-effective.

Recognizing partially visible objects using feature indexed hypotheses

A common task in computer vision is to recognize the objects in an image. Most computer vision systems do this by matching models for each possible object type in turn, recognizing objects by the best matches. This is not ideal, as it does not take advantage of the similarities and differences between the possible object types. The computation time also increases linearly with the number of possible objects, which can become a problem if the number is large. A new recognition method is described: feature indexed hypotheses, which takes advantage of the similarities and differences between object types and is able to handle cases, where there are a large number of possible object types, in sublinear computation time. A two-dimensional occluded parts recognition system using this method is described.