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7. Using Trust for Role-Based Access Control (RBAC)


Step1: get opinion1 = b1, d1, u1 and issuer field from evidence statement E1 ... Specify trust constraints that a user/issuer must satisfy to obtain a role ... – PowerPoint PPT presentation

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Title: 7. Using Trust for Role-Based Access Control (RBAC)

7. Using Trust for Role-Based Access Control
Prof. Bharat Bhargava Center for Education and
Research in Information Assurance and Security
(CERIAS) and Department of Computer
Sciences Purdue University http//www.cs.purdue.ed
u/people/bb bb_at_cs.purdue.edu Collaborators in the
RAID Lab (http//raidlab.cs.purdue.edu) Prof.
Leszek Lilien (former Post Doc) Dr. Yuhui Zhong
(former Ph.D. Student)
This research is supported by CERIAS and NSF
grants from IIS and ANIR.
Using Trust for Role-Based Access Control -
  • 1) Access Control in Open Systems
  • 2) Proposed Access Control Architecture
  • 2.1) Basics
  • 2.2) RBAC TERM server
  • 3) TERM server
  • 3.1) Basic
  • 3.2) Evidence Model
  • 3.3) Architecture
  • Credential Management (CM)
  • Evidence Evaluation (EE)
  • Role Assignment (RA)
  • Trust Information Management (TIM)
  • 3.4) Prototype TERM server

1) Access Control in Open Systems (1)
  • Open environment (like WWW,
    WiFi networks)
  • User who may not be known in advance
  • Still must determine the permission set for an
    unknown user
  • Common approach
  • Grant access based on users properties
    demonstrated by digital credentials
  • Problems with credentials
  • Holding credentials does not assure user
  • Evidence provided by different credential issuers
    should not be uniformly trusted (apply
    degrees of trust)

1) Access Control in Open Systems (2)
  • A solution for problems with credentials
  • Trust should be used by access control mechanisms
  • To limit granting privileges to potentially
    harmful users
  • How to establish trust ?
  • In particular with newcomer devices
  • What do we need to know about a pervasive device,
    in order to make a trust decision?
  • Using trust for attribute-based access control
  • Identity-based access control is inadequate in
    open environments (e.g., vulnerable to
  • Multi-dimensional attribute set to determine
    trust level

2.1) Proposed Access Control Architecture - Basics
  • Authorized Users
  • Validated credentials (first-hand experience and
    second-hand recommendations)
  • AND
  • Trust based on history of cooperative and
    legitimate behavior
  • Other Users
  • Lack of required credentials
  • OR
  • Lack of trust resulting from history of
    non-cooperative or malicious behavior

2.2) Proposed Access Control Architecture - RBAC
TERM Server
  • Role-based access control (RBAC)
  • Trust-enhanced role-mapping (TERM) server
    cooperates with RBAC

3.1) TERM Server - Basic Concepts (1)
  • Evidence
  • Credentials
  • Statement about some properties of a subject
  • Examples X.509, PICS rating
  • Issuers opinion
  • Allows issuer to express confidence w.r.t. her
    statement (recommendation)
  • Widely used in daily life
  • Example Reviewers familiarity with topic on
    review forms
  • Not supported by current credentials
  • Evidence
  • Associate issuers opinion with credentials
  • Reliability of evidence
  • Trust w.r.t. evidence from the viewpoint of the
    relying entity (i.e. TERM server)
  • Combination of the trust w.r.t. the issuer and
    the issuers opinion

3.1) TERM Server - Basic Concepts (2)
  • Trust based on interpretation of observations of
    users behaviors
  • Inherently uncertain
  • Users behavior affected by multiple reasons
  • Example Reasons why a user provides incorrect
  • Dishonesty / Error / Other reasons
  • Trust context
  • Trust is context-specific
  • Example Bob trusts his doctor w.r.t. health
    problems but not w.r.t. flying with him
  • Different trust characteristics are emphasized in
    different contexts
  • Trust characteristisc may have different meanings
    in different contexts
  • Research questions
  • How to represent contexts?
  • How to propagate trust among contexts?
  • Trust in a user and issuer (of recommendations)
  • Trusting a user belief that user is cooperative
  • Trusting an issuer believe evidence provided by

3.2) TERM Server Evidence Model (1)
  • Direct experience
  • Users or recommendation issuers behavior
    observed by TERM
  • First-hand information
  • Recommendation
  • Recommenders opinion w.r.t. trust in a
  • Second-hand information

3.2) Evidence Model (2)
  • Design considerations
  • Accommodate different forms of evidence in an
    integrated framework
  • Support reliability evaluation
  • Evidence type
  • Specify information required by this kind of
  • (et_id, (attr_name, attr_domain, attr_type) )
  • E.g. (student, name, string, mand,
    university, string, mand, department, string,
  • Evidence
  • Evidence is an instance of an evidence type

3.2) Evidence Model (3)
  • Opinion
  • (belief, disbelief, uncertainty)
  • Probability expectation of Opinion
  • Belief 0.5 uncertainty
  • Characterizes the degree of trust represented by
    an opinion
  • Alternative representation
  • Fuzzy expression
  • Uncertainty vs. vagueness
  • Evidence statement
  • ltissuer, subject, evidence, opiniongt

3.3) TERM Server Architecture (1)
  1. Credential Management (CM) simply transforms
    different formats of credentials to evidence
  2. Evidence Evaluation (EE) - evaluates reliability
    of evidence statements
  3. Role Assignment (RA) - maps roles to users based
    on evidence statements and role assignment
  4. Trust Information Management (TIM) - evaluates
    user/issuers trust information based on direct
    experience and recommendations

a) CM - Credential Management
  • Transforms different formats of credentials to
    evidence statements

b) EE - Evidence Evaluation
  • Develop an algorithm to evaluate reliability of
  • Issuers opinion cannot be used as reliability of
  • Two types of information used
  • Evidence Statement
  • Issuers opinion
  • Evidence type
  • Trust w.r.t. issuer for this kind of evidence type

Evidence Evaluation Algorithm
  • Input evidence statement E1 ltissuer, subject,
    evidence, opinion1gt
  • Output reliability RE(E1) of evidence statement
  • Step1 get opinion1 ltb1, d1, u1gt and issuer
    field from evidence statement E1
  • Step2 get the evidence statement about issuers
    testify_trust E2 ltterm_server, issuer,
    testify_trust, opinion2gt from local database
  • Step3 get opinion2 ltb2, d2, u2gt from evidence
    statement E2
  • Step4 compute opinion3 ltb3, d3, u3 gt
  • (1) b3 b1 b2
  • (2) d3 b1 d2
  • (3) u3 d1 u1 b2 u1
  • Step5 compute probability expectation for
    opinion3 lt b3, d3, u3 gt
  • PE (opinion3) b3 0.5 u3
  • Step6 RE (E1) PE (opinion3)

c) RA - Role Assignment
  • Design a declarative language for system
    administrators to define role assignment policies
  • Specify content and number of evidence statements
    needed for role assignment
  • Define a threshold value characterizing the
    minimal degree of trust expected for each
    evidence statement
  • Specify trust constraints that a user/issuer must
    satisfy to obtain a role
  • Develop an algorithm to assign roles based on
  • Several policies may be associated with a role
  • The role is assigned if one of them is satisfied
  • A policy may contain several units
  • The policy is satisfied if all units evaluate to

RA Algorithm for Policy Evaluation
  • Input evidence set E and their reliability, role
  • Output true/false
  • P ? the set of policies whose left hand side is
    role A
  • while P is not empty
  • q a policy in P
  • satisfy true
  • for each units u in q
  • if evaluate_unit(u, e, re(e)) false for all
    evidence statements e in E
  • satisfy false
  • if satisfy true
  • return true
  • else
  • remove q from P
  • return false

RA Algorithm for Unit Evaluation
  • Input evidence statement E1 ltissuer, subject,
    evidence, opinion1gt and its reliability RE (E1),
    a unit of a policy U
  • Output true/false
  • Step1 if issuer does not hold the IssuerRole
    specified in U or the type of evidence does not
    match evidence_type in U then return false
  • Step2 evaluate Exp of U as follows
  • (1) if Exp1 Exp2 Exp3 then
  • result(Exp1) max(result(Exp2), result(Exp3))
  • (2) else if Exp1 Exp2 Exp3 then
  • result(Exp1) min(result(Exp2), result(Exp3))
  • (3) else if Exp1 attr Op Constant then
  • if Op ? EQ, GT, LT, EGT, ELT then
  • if attr Op Constant true then
    result(Exp1) RE(E1)
  • else result(Exp1) 0
  • else if Op NEQ then
  • if attr Op Constant true then
    result(Exp1) RE(E1)
  • else result(Exp1) 1- RE(E1)
  • Step3 if min(result(Exp), RE(E1)) ? threshold in
  • then output true else output false

d) TIM - Trust Information Management
  • Evaluate current knowledge
  • Current knowledge
  • Interpretations of observations
  • Recommendations
  • Developed algorithm that evaluates trust towards
    a user
  • Users trustworthiness affects trust towards
    issuers who introduced user
  • Predict trustworthiness of a user/issuer
  • Current approach uses the result of evaluation as
    the prediction

3.4) Prototype TERM Server
Defining role assignment policies
Loading evidence for role assignment
Software http//www.cs.purdue.edu/homes/bb/NSFtru
Our Research at Purdue
  • Web Site http/www.cs.purdue.edu/homes/bb
  • Over one million dollars in current support from
  • NSF, Cisco, Motorola, DARPA
  • Selected Publications
  • B. Bhargava and Y. Zhong, "Authorization Based on
    Evidence and Trust", in Proc. of Data Warehouse
    and Knowledge Management Conference (DaWaK),
    Sept. 2002.
  • E. Terzi, Y. Zhong, B. Bhargava, Pankaj, and S.
    Madria, "An Algorithm for Building User-Role
    Profiles in a Trust Environment", in Proc. of
    DaWaK, Sept. 2002 .
  • A. Bhargava and M. Zoltowski, Sensors and
    Wireless Communication for Medical Care, in
    Proc. of 6th Intl. Workshop on Mobility in
    Databases and Distributed Systems (MDDS), Prague,
    Czechia, Sept. 2003.
  • B. Bhargava, Y. Zhong, and Y. Lu, "Fraud
    Formalization and Detection", in Proc. of DaWaK,
    Prague, Czech Republic, Sept. 2003.

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