Check out the new USENIX Web site.

USENIX Home . About USENIX . Events . membership . Publications . Students
13th USENIX Security Symposium — Abstract

Pp. 135–150 of the Proceedings

Graphical Dictionaries and the Memorable Space of Graphical Passwords

Julie Thorpe and Paul van Oorschot, Carleton University

Abstract

In commonplace textual password schemes, users choose passwords that are easy to recall. Since memorable passwords typically exhibit patterns, they are exploitable by brute-force password crackers using attack dictionaries. This leads us to ask what classes of graphical passwords users find memorable. We postulate one such class supported by a collection of cognitive studies on visual recall, which can be characterized as mirror symmetric (reflective) passwords. We assume that an attacker would put this class in an attack dictionary for graphical passwords and propose how an attacker might order such a dictionary. We extend the existing analysis of graphical passwords by analyzing the size of the mirror symmetric password space relative to the full password space of the graphical password scheme of Jermyn et al. (1999), and show it to be exponentially smaller (assuming appropriate axes of reflection). This reduction in size can be compensated for by longer passwords: the size of the space of mirror symmetric passwords of length about L+5 exceeds that of the full password space for corresponding length L ≤ 14 on a 5 ~ 5 grid. This work could be used to help in formulating password rules for graphical password users and in creating proactive graphical password checkers.
  • View the full text of this paper in HTML and PDF.
    Click here if you have forgotten your password Until August 2005, you will need your USENIX membership identification in order to access the full papers. The Proceedings are published as a collective work, © 2004 by the USENIX Association. All Rights Reserved. Rights to individual papers remain with the author or the author's employer. Permission is granted for the noncommercial reproduction of the complete work for educational or research purposes. USENIX acknowledges all trademarks within this paper.

  • If you need the latest Adobe Acrobat Reader, you can download it from Adobe's site.
To become a USENIX Member, please see our Membership Information.

?Need help? Use our Contacts page.

Last changed: 27 July 2004 aw
Technical Program
Security '04 Home
USENIX home