1. Usable Privacy and
Security Engineering &
Public Policy
Lorrie Faith Cranor
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2. Usable privacy and security research
bridges privacy/security and usability/HCI
Usable Privacy&
Security/Privacy Usability/HCI Security
Humans are a secondary Humans are the primary Human factors and
constraint to constraint, security are both primary
security/privacy security/privacy rarely constraints
constraints considered
Humans considered Concerned about human Concerned about both
primarily in their role as error but not human normal users and
adversaries/attackers attackers adversaries
Involves threat models Involves task models, Involves threat models
mental models, cognitive AND task models,
models mental models, etc.
Focus on security Focus on usability Considers usability and
metrics metrics security metrics together
User studies rarely done User studies common User studies common,
often involve deception +
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active adversary

3. User-selected graphical passwords
Usable Privacy&
Security/Privacy Usability/HCI Security
What is the space of Howdifficult is it for a All the security/privacy
possible passwords? user to create, and usability HCI
remember, and enter a questions
How can we make the graphical password?
password space larger to How long does it take? How do usersselect
make the password graphical passwords?
harder to guess? How hard is it for users How can we help them
to learn the system? choose passwords
How are the stored harder for attackers to
passwords secured? Are users motivated to predict?
put in effort to create
Can an attacker gain good passwords? As the password space
knowledge by observing increases, what are the
a user entering her Is the system accessible impacts on usability
password? using a variety of factors and predictability
devices, for users with of human selection?

4. How can we make secure systems
more usable?
• Make it “just work”
– Invisible security
– Automation
• Make security/privacy
understandable
– Make it visible
– Make it intuitive
– Use metaphors that users
can relate to
– Human-centered design
• Train the user
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5. Better together
• Examining security/privacy and usability together is often critical for
achieving either
• Examples
– Passwords
• Users cope with some measures to increase password security by behaving
in predictable ways
• Some efforts to make passwords easier also make it much easier for an
attacker to guess a password
– Access control
• The way access control settings are visualized in a user interface and the
underlying semantics of how rule conflicts are resolved both contribute to
users’ ability to configure the system to accurately enforce the desired policy
– Privacy tools
• Users who misunderstand how to use privacy tools don’t configure them
properly
• Some simple privacy tools don’t provide much protection
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6. References
• S. Komanduri, R. Shay, P.G. Kelley, M.L. Mazurek, L. Bauer, N.
Christin, L.F. Cranor, and S. Egelman.Ofpasswords and people:
Measuring the effect of password-composition policies.CHI 2011.
• R.W. Reeder, L. Bauer, L.F. Cranor, M.K. Reiter, and K. Vaniea.
More than skin deep: Measuring effects of the underlying model on
access-control system usability. CHI 2011.
• P.G. Leon, B. Ur, R. Balebako, L.F. Cranor, R. Shay, and Y. Wang.
Why Johnny Can't Opt Out: A Usability Evaluation of Tools to Limit
Online Behavioral Advertising. CHI 2012.
See also related papers listed at http://cups.cs.cmu.edu/
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