1. Graphical Dictionaries Presentation by Roger Kahn1 Graphical Dictionaries & Memorable Space of Graphical Passwords

2. Graphical Dictionaries Presentation by Roger Kahn2 Memorable Space of Graphical Passwords Based on Article by Thorpe, van Oorschot USENIX 2004 Contains References to The Design and Analysis of Graphical Passwords by Jermyn et. al

3. Graphical Dictionaries Presentation by Roger Kahn3 Memorable Space of Graphical Passwords Purpose of Paper Define a class of memorable graphical passwords Map it on the DAS scheme from Jermyn et al (Moti ’ s lecture)

4. Graphical Dictionaries Presentation by Roger Kahn4 Memorable Space of Graphical Passwords Textual Passwords Passwords chosen are usually ones that are easy to remember Concrete words easier to remember Text Password space used (with high probability) vulnerable to dictionary attacks since it ’ s a relatively small subset of total password space

5. Graphical Dictionaries Presentation by Roger Kahn5 Memorable Space of Graphical Passwords Graphical Passwords Recall by people of pictures is better than words – including concrete nouns Presumably better since memorable password space and total password space is larger

6. Graphical Dictionaries Presentation by Roger Kahn6 Memorable Space of Graphical Passwords Recall of Pictures that are symmetric are far better Recall of pictures symmetric around some truly vertical or horizontal axis is still better due to mirror symmetry Studies indicate that horizontal and vertical symmetry that are centered is still better

7. Graphical Dictionaries Presentation by Roger Kahn7 Memorable Space of Graphical Passwords Are Types of images recalled better than others? The paper criticizes the visual recall studies due to short recall times in the tests Suggestion that recall is far better than studied

8. Graphical Dictionaries Presentation by Roger Kahn8 Memorable Space of Graphical Passwords DAS Scheme Review User defined Drawings Repeatable Drawings Start and End Points for drawing Stroke – Movement of the pen on grid between clearly defined points movements on border not accepted Password - List of successive points which stroke goes through separated by pen-up Stroke goes from neighbor to neighbor

9. Graphical Dictionaries Presentation by Roger Kahn9 Memorable Space of Graphical Passwords DAS Scheme Review(cont ’ d) If current point is (x,y) neighbors are (x,y+1), (x,y-1), (x+1,y), (x-1, y) Stroke length is # of neighbors drawn through until pen-up Password Length is the sum of the stroke lengths Password Space for L max =2 on 5X5 grid is 2 58 8 Character password < 2 53

10. Graphical Dictionaries Presentation by Roger Kahn10 Memorable Space of Graphical Passwords Proposed Class of Memorable Graphical Passwords Purpose of Study Mirror Symmetrical graphical passwords selected Psychological Studies show recall improved over time toward mirror symmetrical images Need to remember less(½ of image plus symmetry axis) Objects viewed and recalled better than pictures

11. Graphical Dictionaries Presentation by Roger Kahn11 Memorable Space of Graphical Passwords Class I of memorable Passwords Mirror Symmetry about a reflection axis (Vertical or Horizontal) which cuts a 2D set of grid cells of size 5x5 Each Component may be a pair of mirror symmetric components as well Naming Leaves open possibility for future types

12. Graphical Dictionaries Presentation by Roger Kahn12 Memorable Space of Graphical Passwords

13. Graphical Dictionaries Presentation by Roger Kahn13 Memorable Space of Graphical Passwords

14. Graphical Dictionaries Presentation by Roger Kahn14 Memorable Space of Graphical Passwords

15. Graphical Dictionaries Presentation by Roger Kahn15 Memorable Space of Graphical Passwords Class I of memorable Passwords(cont ’ d) Assumption: User draws password such that the composite stroke of each mirror symmetric component are drawn symmetrically Assumption taken since temporal order of password affects ability of user to recall password One to many relationship between stroke order and drawing

16. Graphical Dictionaries Presentation by Roger Kahn16 Memorable Space of Graphical Passwords Symmetric Encoding Example

17. Graphical Dictionaries Presentation by Roger Kahn17 Memorable Space of Graphical Passwords Symmetry Example

18. Graphical Dictionaries Presentation by Roger Kahn18 Memorable Space of Graphical Passwords Continuous, Enclosed, Disjoint Cases

19. Graphical Dictionaries Presentation by Roger Kahn19 Memorable Space of Graphical Passwords Continuous, Enclosed, Disjoint Cases

20. Graphical Dictionaries Presentation by Roger Kahn20 Memorable Space of Graphical Passwords Smaller Password Spaces Class Ia – Subset of Class I passwords whos components are symmetric (individually or pairwise) Class Ib – Subset of Class Ia. Symmetric around Vertical and Horizontal Axes

21. Graphical Dictionaries Presentation by Roger Kahn21 Memorable Space of Graphical Passwords Quantifying Memorable Password Space General Approach # of passwords given a maximum stroke length This paper ’ s method include only symmetric strokes Stroke set is the number of symmetric strokes from start to end of length l. # of permutations of 4 directions while symmetric around a valid axis Parameters are path diversions, room between current point and the grid bound

22. Graphical Dictionaries Presentation by Roger Kahn22 Memorable Space of Graphical Passwords Approximate Size of Class I Passwords Class I dictionary size very close to the size of the full password space Class Ia, Ib much more vulnerable to Brute-Force attacks. It ’ s a much smaller password space.

23. Graphical Dictionaries Presentation by Roger Kahn23 Memorable Space of Graphical Passwords

24. Graphical Dictionaries Presentation by Roger Kahn24 Memorable Space of Graphical Passwords Questions and Discussion rogerka@eng.tau.ac.il

25. Graphical Dictionaries Presentation by Roger Kahn25 Memorable Space of Graphical Passwords Assignment Why are the password subclasses more vulnerable to a brute force dictionary attacks? What is easier for Humans to recall pictures or words? What types of pictures and words are the easiest to recall? What is a stroke?