Mummoorthy Murugesan

Efficient privacy-preserving similar document detection

Similar document detection plays important roles in many applications, such as file management, copyright protection, plagiarism prevention, and duplicate submission detection. The state of the art protocols assume that the contents of files stored on a server (or multiple servers) are directly accessible. However, this makes such protocols unsuitable for any environment where the documents themselves are sensitive and cannot be openly read. Essentially, this assumption limits more practical applications, e.g., detecting plagiarized documents between two conferences, where submissions are confidential. We propose novel protocols to detect similar documents between two entities where documents cannot be openly shared with each other. The similarity measure used can be a simple cosine similarity on entire documents or on document fragments, enabling detection of partial copying. We conduct extensive experiments to show the practical value of the proposed protocols. While the proposed base protocols are much more efficient than the general secure multiparty computation based solutions, they are still slow for large document sets. We then investigate a clustering based approach that significantly reduces the running time and achieves over 90% of accuracy in our experiments. This makes secure similar document detection both practical and feasible.

Similar Document Detection with Limited Information Disclosure

Similar document detection plays important roles in many applications, such as file management, copyright protection, and plagiarism prevention. Existing protocols assume that the contents of files stored on a server (or multiple servers) are directly accessible. This assumption limits more practical applications, e.g., detecting plagiarized documents between two conferences, where submissions are confidential. We propose novel protocols to detect similar documents between two entities where documents cannot be openly shared with each other. We also conduct experiments to show the practical value of the proposed protocols.

k-out-of-n oblivious transfer based on homomorphic encryption and solvability of linear equations

Oblivious Transfer (OT) is an important cryptographic tool, which has found its usage in many crypto protocols, such as Secure Multiparty Computations, Certified E-mail and Simultaneous Contract Signing . In this paper, we propose three k-out-of-n OT (OT_k^n) protocols based on additive homomorphic encryption. Two of these protocols prohibit malicious behaviors from a receiver. We also achieve efficient communication complexity bounded by O(l* n) in bits, where l is the size of the encryption key. The computational complexity is comparable to the most efficient existing protocols. Due to the semantic security property, the sender cannot get receivers selection. When the receiver tries to retrieve more than k values, the receiver is caught cheating with 1-(1/m) probability (Protocol II) or the receiver is unable to get any value at all (Protocol III). We introduce a novel technique based on the solvability of linear equations, which could find its way into other applications. We also provide an experimental analysis to compare the efficiency of the protocols.

Secure Content Validation

Information dissemination in electronic form has improved drastically over the past few years. New technologies in Web feeds allow the uses to get notified automatically when new contents are available. Tliough the speedy availability of information is a positive trend, theres also the concern about the validity of information. Let us consider a content producer, who creates and publishes an article based on information from confidential sources. When any of these confidential sources becomes invalid, it is imperative that the end-user who relies on the content of the article be informed. As time passes, the article would have reached many who are often non-traceable to be informed. Given this selling, we develop models for ensuring the confidentiality and secrecy of sources, and also allow the end-user to perform certain operations in reasoning about the validity of articles. We present three types of models, and protocols that solve this problem efficiently.