@inproceedings {INPROC-2014-81,
    author = {Stefan Schneegass and Frank Steimle and Andreas Bulling and Florian Alt and Albrecht Schmidt},
    title = {{SmudgeSafe: Geometric Image Transformations for Smudge-resistant User Authentication}},
    booktitle = {Proceedings of the 2014 ACM International Joint Conference on Pervasive and Ubiquitous Computing},
    publisher = {ACM},
    institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany},
    pages = {775--786},
    type = {Conference Paper},
    month = {January},
    year = {2014},
    isbn = {978-1-4503-2968-2},
    doi = {10.1145/2632048.2636090},
    keywords = {finger smudge traces, graphical passwords, touch input},
    language = {English},
    cr-category = {H.5.2 Information Interfaces and Presentation User Interfaces,
                   K.6.5 Security and Protection},
    department = {University of Stuttgart, Institute of Visualisation and Interactive Systems, Visualisation and Interactive Systems},
    abstract = {Touch-enabled user interfaces have become ubiquitous, such as on ATMs or
      portable devices. At the same time, authentication using touch input is
      problematic, since finger smudge traces may allow attackers to reconstruct
      passwords. We present SmudgeSafe, an authentication system that uses random
      geometric image transformations, such as translation, rotation, scaling,
      shearing, and flipping, to increase the security of cued-recall graphical
      passwords. We describe the design space of these transformations and report on
      two user studies: A lab-based security study involving 20 participants in
      attacking user-defined passwords, using high quality pictures of real smudge
      traces captured on a mobile phone display; and an in-the-field usability study
      with 374 participants who generated more than 130,000 logins on a mobile phone
      implementation of SmudgeSafe. Results show that SmudgeSafe significantly
      increases security compared to authentication schemes based on PINs and lock
      patterns, and exhibits very high learnability, efficiency, and memorability.},
    url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2014-81&engl=1}
 }