1. © 2009 IBM Corporation
Trust Measurement and Management
Alan Hartman – IBM Haifa Research Lab
20 June 2012
Open Research Issues

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Agenda
 Motivation
 Defining Trust
 Relationship between Risk and Trust
 Basic Trust Management Scenario
 More Complex Scenarios
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Why measure and manage trust?
Distrust and caution are the parents of security. - Benjamin
Franklin
The trust of the innocent is the liar’s most useful tool. -
Stephen King
Trust, but verify. – Ronald Reagan

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Definition of trust
 Trust is: An expectation about a future behaviour of
another person … depending on the degree of trust
and the extent of the associated risk (Kasselbaum
Ph. D. Thesis in Sociology)
 Trust is: A function with three parameters:
–Trust(Trustee, Trustor, ActivityOutcome), whose
value is the probability (degree of trust) that
Trustor believes that Trustee will produce
ActivityOutcome in the future
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Relationship between trust and risk
 Rational behavior: If the payoff is positive, then take the
risk
 Also rational: If the worst case is too awful, don’t take the
risk
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 Working Hypothesis: A decision (by the Trustor) on whether to offer
the Trustee the opportunity to participate in an Activity with the
Trustor is based on both Trust and Risk
 Payoff is: a measure of the expected utility to the
Trustor associated with all possible outcomes of an
activity.
Payoff(Trustor, Activity) = sum over all Outcomes
(Trust( Trustee, Trustor, ActivityOutcome ) * Value(Outcome))

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Academic Interest in Trust
 Sociology
–Who trusts the Internet?
–What are the factors that influence a person to trust
interactions in cyberspace?
 Economics
–What motivates trust and cooperation?
–What reputation and incentive mechanisms to promote
trust?
 Management
–Creating and maintaining trust – as part of leadership
 Computer Science
–Creating trust in computing infrastructure and services
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Basic Trust Management Scenario
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1. Build Trust
2. Shake Trust
3. Restore Trust

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Building Trust
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Trustor A trusts Trustee B to produce Outcome C with confidence level P0

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ShakingTrust
An Event E occurs which
causes P0 to decrease to P'
which is below the threshold
Pt determined by Trustee B
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Trust Restoration
 Trustee B takes mitigation
action M and measures new
trust level P ''
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Basic Scenario For Trust Management
1) Initial condition: Trustor A trusts Trustee B to
produce outcome C with confidence level P0
2) Either an Event E occurs which causes P0 to
decrease to P' which is below the threshold Pt
determined by Trustee B Or P0 < Pt in the first
place
3) Loop on i:
I. B takes mitigation action Mi and measures
confidence level Pi (Assume Mi are ordered
in decreasing order of cost effectiveness)
II. Until Pi >= Pt, or no cost effective mitigation
actions remain in the arsenal of B

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Research Challenges for Trust Management
• How to measure P for a given A, B, and C
• How to determine an appropriate threshold Pt for a
given A, B, C
• What are appropriate mitigation actions Mi for a
given A, B, C, E
• How to detect and report trust breach events E
• How to measure cost effectiveness of Mi
• When to give up – i.e. what is the law of
diminishing returns in the context of A, B, C, E,
and P0, P1, P2, ...Pi

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Measuring Trustworthiness of ICT Systems
Quantifying Trustworthiness
Using Quantifiable Properties*
Dependability
Security
Performability
13 *University of Kansas, Resilinets Wiki

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Measuring Trustworthiness of Individuals or
Organizations
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Quantifiable Properties
Trustworthy actions
Observed
Reported by trusted source
Evidence
Trustworthy reputation
Reputation measure
Trusted reputation system
Membership of trusted organization
Trusted guarantor

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Mutual trust scenario
Alice trusts BigBank to maintain the integrity of
her credit card with P=99%
BigBank trusts Alice to be honest with it with
Q=95%
E is an unauthorized credit card transaction
from Alice's account – reported to BigBank by
Alice (P'=85%, Q'=75%)
What actions should Alice and BigBank take to
rebuild mutual trust?
What is the protocol for mutual trust
negotiation?

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B2B trust scenario
OmahaInsurance is negotiating with IBM to
outsource their health insurance claims
processing
Trust is held between IBM and Omaha and
also between Omaha and its customers
Event = break in to IBM office in Bangalore
Action C is contract negotiation between IBM
and Omaha

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Trust me, I’m a doctor
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