Privacy Preserving Evaluation of a Web-Based Questionnaire

Abstract

This thesis focuses on methods of evaluation of web-based multiple choice type questionnaire, such as online examination and online surveys, in a privacy preserving process. Two styles of questionnaire are discussed, their structure, and different approaches of their evaluation, along with discovering methods to evaluate them using cryptographic protocols. The motivation to pursue this study originates mainly from [1] where the two types of questionnaire are elaborated and how a user can attempt to select either single option or multiple options, to answer each question in a questionnaire, based on what the survey hosting party has defined. This thesis aims to present a complete picture of evaluating the two kinds of questionnaires in a privacy preserving manner. Evaluation of surveys with more than one allowed answer choice is used from paper [1] and is stated as it is in chapter 4, and is based on Secure Voting Protocol from [3]. For evaluating questionnaire with exactly one allowed answer choice, we discuss why secure voting isn’t beneficial and a new solution is then proposed in chapter 5 which is based on the idea of Private Set Intersection-Cardinality (PSI-CA). The two approaches are discussed thoroughly in terms of problem definition, security and privacy requirements, followed by the cryptographic means to achieve them and then the study is concluded with their correctness and security analysis along with associated experimental data.