Hybrid application support for mobile information systems

The wide-spread presence of wireless networks and the availability of mobile devices has enabled the development of mobile applications that take us a step closer to accomplishing Weiser’s vision of ubiquitous computing (Weiser, 1991). Unfortunately however, network connectivity is still not given anywhere and at any time. To increase the benefit of mobile applications, the next logical step is to provide support for an offline modethat allows to continuously work with an application, even when the device is not connected to a network. In this paper typical problems of replicating data are explained, possible solutions are discussed and two architectural patterns that could be used to implement hybrid support are illustrated

Reconciling Graphs and Sets of Sets

We explore a generalization of set reconciliation, where the goal is to reconcile sets of sets. Alice and Bob each have a parent set consisting of $s$ child sets, each containing at most $h$ elements from a universe of size $u$. They want to reconcile their sets of sets in a scenario where the total number of differences between all of their child sets (under the minimum difference matching between their child sets) is $d$. We give several algorithms for this problem, and discuss applications to reconciliation problems on graphs, databases, and collections of documents. We specifically focus on graph reconciliation, providing protocols based on set of sets reconciliation for random graphs from $G(n,p)$ and for forests of rooted trees

Fuzzy Extractors: How to Generate Strong Keys from Biometrics and Other Noisy Data

We provide formal definitions and efficient secure techniques for - turning noisy information into keys usable for any cryptographic application, and, in particular, - reliably and securely authenticating biometric data. Our techniques apply not just to biometric information, but to any keying material that, unlike traditional cryptographic keys, is (1) not reproducible precisely and (2) not distributed uniformly. We propose two primitives: a "fuzzy extractor" reliably extracts nearly uniform randomness R from its input; the extraction is error-tolerant in the sense that R will be the same even if the input changes, as long as it remains reasonably close to the original. Thus, R can be used as a key in a cryptographic application. A "secure sketch" produces public information about its input w that does not reveal w, and yet allows exact recovery of w given another value that is close to w. Thus, it can be used to reliably reproduce error-prone biometric inputs without incurring the security risk inherent in storing them. We define the primitives to be both formally secure and versatile, generalizing much prior work. In addition, we provide nearly optimal constructions of both primitives for various measures of ``closeness'' of input data, such as Hamming distance, edit distance, and set difference.Comment: 47 pp., 3 figures. Prelim. version in Eurocrypt 2004, Springer LNCS 3027, pp. 523-540. Differences from version 3: minor edits for grammar, clarity, and typo

Key-value storage system synchronization in peer-to-peer environments

Data synchronization is the problem of bringing multiple versions of the same data on different remote devices to the most up to date version. This thesis looks into the particular problem of key-value storage systems synchronization between mobile devices in a peer-to-peer environment. In this research, we describe, implement and evaluate a new key-value storage system synchronization algorithm using a 2-phase approach, combining approximate synchronization in the first phase and exact synchronization in the second phase. The 2-phase architecture helps the algorithm achieve considerable boost in performance in all three major criteria of a data synchronization algorithm, namely synchronization time, processing time and communication cost, while still being suitable to operate in a peer-to-peer environment. The performance increase makes it feasible to employ database synchronization technique in a wider range of mobile applications, especially those operating on a slow peer-to-peer network

Lossless Differential Compression for Synchronizing Arbitrary Single-Dimensional Strings

Differential compression allows expressing a modified document as differences relative to another version of the document. A compressed string requires space relative to amount of changes, irrespective of original document sizes. The purpose of this study was to answer what algorithms are suitable for universal lossless differential compression for synchronizing two arbitrary documents either locally or remotely. Two main problems in differential compression are finding the differences (differencing), and compactly communicating the differences (encoding). We discussed local differencing algorithms based on subsequence searching, hashtable lookups, suffix searching, and projection. We also discussed probabilistic remote algorithms based on both recursive comparison and characteristic polynomial interpolation of hashes computed from variable-length content-defined substrings. We described various heuristics for approximating optimal algorithms as arbitrary long strings and memory limitations force discarding information. Discussion also included compact delta encoding and in-place reconstruction. We presented results from empirical testing using discussed algorithms. The conclusions were that multiple algorithms need to be integrated into a hybrid implementation, which heuristically chooses algorithms based on evaluation of the input data. Algorithms based on hashtable lookups are faster on average and require less memory, but algorithms based on suffix searching find least differences. Interpolating characteristic polynomials was found to be too slow for general use. With remote hash comparison, content-defined chunks and recursive comparison can reduce protocol overhead. A differential compressor should be merged with a state-of-art non-differential compressor to enable more compact delta encoding. Input should be processed multiple times to allow constant a space bound without significant reduction in compression efficiency. Compression efficiently of current popular synchronizers could be improved, as our empiral testing showed that a non-differential compressor produced smaller files without having access to one of the two strings

Efficient PDA Synchronization

Modern Personal Digital Assistant (PDA) architectures often utilize a wholesale data transfer protocol known as "slow sync" for synchronizing PDAs with Personal Computers (PCs). This approach is markedly inefficient with respect to bandwidth usage, latency, and energy consumption, since the PDA and PC typically share many common records. We propose, analyze, and implement a novel PDA synchronization scheme (CPIsync) predicated upon recent information-theoretic research. The salient property of this scheme is that its communication complexity depends on the number of differences between the PDA and PC, and is essentially independent of the overall number of records. Moreover, our implementation shows that the computational complexity and energy consumption of CPIsync is practical, and that the overall latency is typically much smaller than that of slow sync or alternative synchronization approaches based on Bloom filters. Thus, CPIsync has potential for significantly improving synchronization protocols for PDAs and, more generally, for heterogeneous networks of many machines