Duy Nguyen

Web searching accounts for one of the most frequently performed computations over the Internet as well as one of the most important applications of outsourced computing, producing results that critically affect users ’ decision-making behaviors. As such, verifying the integrity of Internet-based searches over vast amounts of web contents is essential. In this paper, we provide the first solution to this general security problem. We introduce the concept of an authenticated web crawler and present the design and prototype implementation of this new concept. An authenticated web crawler is a trusted program that computes a special “signature ” S over a collection of web contents it visits. Subject to this signature, web searches can be verified to be correct with respect to the integrity of their produced results. But this signature serves more advanced purposes than just content verification: It allows the verification of complicated queries on web pages, such as conjunctive keyword searches, which are vital for the functionality of online web-search engines today. In our solution, along with the web pages that satisfy any given search query, the search engine also returns a cryptographic proof. This proof, together with the signature S, enables any user to efficiently verify that no legitimate web pages are omitted from the result computed by the search engine, and that no pages that are non-conforming with the query are included in the result. An important property of our solution is that the proof size and the verification time are proportional only to the sizes of the query description and the query result, but do not depend on the number or sizes of the web pages over which the search is performed. Our authentication protocols are based on standard Merkle trees and the more involved bilinear-map accumulators. As we experimentally demonstrate, the prototype implementation of our system gives a low communication overhead between the search engine and the user, and allows for fast verification of the returned results on the user side.