An Inconvenient Trust
User Attitudes toward Security and Usability
Tradeoffs for Key-Directory Encryption Systems

Patrick Gage Kelley@patrickgage

Assistant Professor, Computer Sciencejoint work with researchers at University of Maryland:
Wei Bai, Doowon Kim, Moses Namara, Yichen Qian,and Dr. Michelle L. Mazurek
first published in June at theSymposium on Usable Privacy and Security SOUPS

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What is End-to-End Encryption?

What is End-to-End Encryption?
Hackers
Governments
Misbehaving Employees/CompanyItselfPA RT I C I PA N T S

80%
BetweenAges of18-34

Occupation:
40% reported
jobs or majors
in computing,math andengineering

Gender:Male 60%
Female 40%52

PA RT I C I PA N T S[1]Security Expertise

Only 2 out of 52 scored 3or higher (out of 5.5)
52

[1] L. J. Camp, T. Kelley, and P. Rajivan. Instrument for measuring computing and security
expertise. Technical Report TR715, Indiana University, Feb. 2015.

PA RT I C I PA N T S
Security Expertise[1]Only 2 out of 52 scored 3 or higher (out of 5.5)

Have your ever registered a domain name?
Have your ever created a database?
Have you ever used SSH?
Have you ever configured a firewall?

[1] L. J. Camp, T. Kelley, and P. Rajivan. Instrument for measuring computing and security
expertise. Technical Report TR715, Indiana University, Feb. 2015.

PA RT I C I PA N T S
Security Expertise[1]Only 2 out of 52 scored 3 or higher (out of 5.5)

If you know, please describe what a "security certificate"is in the context of the Internet, otherwise write "Don't know."

If you know, please describe what is meant by "phishing''
otherwise write "Don't know"[1] L. J. Camp, T. Kelley, and P. Rajivan. Instrument for measuring computing and security
expertise. Technical Report TR715, Indiana University, Feb. 2015.

Secure

Easy to Use

Secure

Ideal

Easy to Use

Secure

Ideal

Easy to Use

Secure

Ideal

Exchange

Easy to UseExchange Model[1]exchanging public locks

manually out of band

[1] W. Tong, S. Gold, S. Gichohi, M. Roman, and J. Frankle. Why King George III can encrypt. 2014

Exchange (PGP-like)
Model

SecureIdeal

Exchange

End users exchange
public locks manuallyout of band.
The usability has been
improved, but still not
popular.

Easy to Use

Secure

Ideal

Exchange
Registration

Easy to Use

Registration Modelcentral server stores public locks

Registration Model
A central server Secure
will be responsible for
distributing publiclocks.
Alarms some security
experts because of thetrust (and governmentleverage) over that
central server

Ideal

Exchange
Registration

Easy to Use

How dogeneral users consider thesecurity and usability tradeoffs
between exchange andregistration models?

METHODOLOGY

Participants
Email list-servs
Online platforms, e.g. Craigslist
Flyerswithin-subjects design:

METHODOLOGY

Participants
Email list-servs
Online platforms, e.g. Craigslist
Flyerswithin-subjects design:First Model
High-level concepts
Complete email tasks
Learn about security
Feedback

Second Model
High-level concepts
Complete email tasks
Learn about security
Feedback

METHODOLOGYExchange Mnoitartsi
RegodelMailvelopeledMo

METHODOLOGYEmail Tasks for Introducing Concepts
1. Generate/Register public lock/private key pair

METHODOLOGYEmail Tasks for Introducing Concepts
2. Exchange email with Alice*Participants don’t need to exchange public locks in theregistration model

METHODOLOGYEmail Tasks for Introducing Concepts
3. Exchange email with Bob and Carl

*Participants don’t need to exchange public locks in theregistration model

METHODOLOGYEmail Tasks for Introducing Concepts
4. Imagine exchanging email with ten people*Participants don’t need to exchange public locks in theregistration model

METHODOLOGYEmail Tasks for Introducing Concepts
5. Think about misconfigurations

a. Lose Alice’s public lock*b. Lose own private key
c. Publicize own private key*There is no such task in registration model

METHODOLOGY

Security Learning: Exchange Model“This threat doesn’t happen usually, because itrequires Mallet to have much power andresources to achieve this.”

METHODOLOGY

Security Learning: Registration Model“[In primary registration model] you need totrust the email provider”

METHODOLOGY[1]Security Learning: Registration Model CaaS“[In CaaS model] you need to trust the twoparties don’t collaborate.”[1] S. Fahl, M. Harbach, T. Muders, and M. Smith. Confidentiality as a Service – usable security for the cloud. In Trust, Security and Privacy inComputing and Communications (TrustCom), 2012 IEEE 11th International Conference on, pages 153–162, June 2012.

METHODOLOGY[1]Security Learning: Registration Model CaaS“[In CaaS model] you need to trust the twoparties don’t collaborate.”[1] S. Fahl, M. Harbach, T. Muders, and M. Smith. Confidentiality as a Service – usable security for the cloud. In Trust, Security and Privacy inComputing and Communications (TrustCom), 2012 IEEE 11th International Conference on, pages 153–162, June 2012.

METHODOLOGY[1]Security Learning: Registration Model Auditing“[In auditing model] you need to trust theauditors and/or the software on your devices.”[1] M. S. Melara, A. Blankstein, J. Bonneau, E. W. Felten, and M. J. Freedman. CONIKS: Bringing key transparency to end users.
In 24th USENIX Security Symposium (USENIX Security 15), pages 383–398. USENIX Association, Aug. 2015.

PA RT I C I PA N T S

80%
BetweenAges of18-34

Occupation:
40% reportedjobs or majors
in computing,math andengineering

Gender:Male 60%Female 40%[1]
Security Expertise

52

Only 2 out of 52scored 3 or higher(out of 5.5)

Analysis
Quantitative Analysis
5-point Likert scale responses
Cumulative-link mixed regression model (CLMM)
Qualitative Analysis
Open coding independently by two researchers
Met to resolve all differences

R E S U LT S

Sending and receiving encrypted email
to 10 people would be difficult(intellectually challenging)
Exchange, First
Exchange, Second
Registration, First
Registration, Second
Number of Participants

R E S U LT S

Sending and receiving encryptedemail to 10 people would be
cumbersome (tedious)
Exchange, First
Exchange, Second
Registration, First
Registration, Second
Number of Participants

36

R E S U LT S

Exchange model was
dramatically more cumbersome
and somewhat more difficult.

R E S U LT S“(The exchange model is) time
consuming, especially sending urgent
emails. I have no choice but to wait for(the correspondent’s public lock).”— ES9

R E S U LT S

Security Comparison
The Perceived Security Gap Is Small
Manual effort
may lead tovulnerability

Exchange

Registration

Some concernbut generallytrustedR E S U LT S

This model effectively protected myprivacy
Exchange, First
Exchange, Second
Registration, First
Registration, Second
Number of Participants40

R E S U LT S

48 (out of 52) trusted the exchange model.
38 trusted the registration model.
The order participants saw eachmodel played a significant role:
participants who saw
registration model first weremore comfortable with it.

R E S U LT S

Exchange model: manual effort may lead to vulnerability
More than half wereconcerned about thesecurity of the medium
used to exchange locks.

“There are too many exchanges between different people.
Exchanging [locks] to many people may go wrong.”— RT7

R E S U LT S(Primary) Registration model:
some concern but generally trusted
10 participants trusted their own email provider.
7 participants were specific about which kind ofproviders they would trust:“(Big companies like) Google and Yahoo!
don’t do such things [violate users’ privacy],
unless the government forces them to do so.
In general, it’s secure."— RT10R E S U LT S

CaaS and auditing models: some
additional perceived security forregistration“(In CaaS Model) If one party is screwedup, you have another one to protect[your email]. You are still safe.”—ES8“(In Auditing Model) Obviously it’s extra
secure. Other parties are verifying it."—ET13

R E S U LT S

CaaS and auditing models:
still some concerns“(In CaaS Model) Involving more
systems may complicate thesystem, so it is less trustful.”— RS1“(In Auditing Model) I want to know
who these auditors are, . . . Their
reputations, and whether they are truly
independent.”— RS9R E S U LT S

Rate your willingness to use thismodel in the future
Exchange
Registration
Number of Participants

No significant difference between
two models for personal use.

R E S U LT S

When they would use the models
Registration model
more broad use

Exchange model
high-security info only
at a small scale only

15 would use in

1 would use in general email
0 large scale

general email orlarge scale

R E S U LT S

Handling Misconfigurations

All Correct75%

Largely Correct

13%

Other12%R E S U LT S

Handling Misconfigurations
Losing private key?
One participant mentioned recovering keys from a backup(such as a USB drive) rather than generating a new key pair.
“I will send my email to a third person I trust, and ask that
person to encrypt the email for me and send to myrecipients. Similarly, he will decrypt the [response] email
for me and forward it to me.”R E S U LT S

Participants explicitly made tradeoffs
among security and usability features.
RT13, who said he would not use the exchange model,
commented that “The negotiating process maybe givesme safer feelings, more protection. But on the other
hand . . . the disadvantage is it is time consuming,
cumbersome, tedious, more complicated, and this is theprice I have to pay for more protection."

It is possible to explain the highlevel concepts and risks ofencryption to users.
Place users in the context, and trust
their decisions.
They can think about tradeoffs
effectively.

The registration model is moreconvenient than the exchange
model, BUT the perceived security
gap between them is small.
We used a near-best-case method for
explaining encryption.

It is possible to explain the highlevel concepts and risks ofencryption.
Place users in the context,
and trust their decisions.
They can think about tradeoffs
effectively.
The registration model is moreconvenient than the exchange
model, BUT the perceived security
gap between them is small.

An Inconvenient Trust
User Attitudes toward Security
and Usability Tradeoffs for KeyDirectory Encryption Systems

with Wei Bai, Doowon Kim, Moses
Namara, Yichen Qian, andDr. Michelle L. Mazurek

Patrick Gage Kelley@patrickgage

An Inconvenient Trust

Icon credits

Gregor ČrešnarAdriana Danaila

User Attitudes toward Security
and Usability Tradeoffs for KeyDirectory Encryption Systems

with Wei Bai, Doowon Kim, Moses
Namara, Yichen Qian, andDr. Michelle L. Mazurek

Patrick Gage Kelley
Icon Fair@patrickgage