Personal choice and challenge questions: a security and usability assessment

Mike Just, David Aspinall

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    69 Citations (Scopus)


    Challenge questions are an increasingly important part of mainstream authentication solutions, yet there are few published studies concerning their usability or security. This paper reports on an experimental investigation into user-chosen questions. We collected questions from a large cohort of students, in a way that encouraged participants to give realistic data. The questions allow us to consider possible modes of attack and to judge the relative effort needed to crack a question, according to an innovative model of the knowledge of the attacker. Using this model, we found that many participants were likely to have chosen questions with low entropy answers, yet they believed that their challenge questions would resist attacks from a stranger. Though by asking multiple questions, we are able to show a marked improvement in security for most users.

    Original languageEnglish
    Title of host publicationProceedings of the 5th Symposium on Usable Privacy and Security (SOUPS)
    PublisherAssociation for Computing Machinery (ACM)
    Number of pages11
    ISBN (Print)9781605587363
    Publication statusPublished - 2009


    • usability
    • computer security
    • challenge questions


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