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Timed Constraint Programming: A Declarative Approach to Usage Control. Radha Jagadeesan, Will Marrero, Corin Pitcher (DePaul University) Vijay Saraswat (IBM Research). Usage Control. Scope of Usage Control [Park, Sandhu 2002] Traditional access control Trust management

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timed constraint programming a declarative approach to usage control

Timed Constraint Programming:A Declarative Approach to Usage Control

Radha Jagadeesan, Will Marrero, Corin Pitcher (DePaul University)

Vijay Saraswat (IBM Research)

usage control
Usage Control
  • Scope of Usage Control [Park, Sandhu 2002]
    • Traditional access control
    • Trust management
    • Digital rights management
  • Temporal aspects of UCON policies
    • Terminate ongoing sessions when resource consumption is too high
    • Change access rights during an emergency
    • Enforcement of dynamic separation of duty concerns

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

this talk
This Talk
  • Policy algebra for Usage Control, following timed concurrent constraint programming paradigm
    • Declarative
    • Default constraint programming addresses negative authorization requirements
    • Reactive computing addresses history-sensitive requirements
  • Policy analysis
    • Equational reasoning
    • Model checking

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

outline
Outline
  • Motivation
  • Policy algebra
    • Untimed
    • Timed
  • Policy analysis

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

ucon traditional access control
UCON: Traditional Access Control
  • Can a subject perform an action on an object?
  • Policy captured as an access matrix and enforced by a monitor
  • Centralized authority

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

access control lists acls
Access Control Lists (ACLs)
  • Access Control Lists (ACLs) associated with objects
  • Problem: ACL management is too burdensome
  • Solution: make use of the object hierarchy

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

acls with inheritance
ACLs with Inheritance
  • On hierarchically structured objects, MS Windows permits inheritance with ACLs.
  • Reduces redundancy
  • Inheritance is optional, so we can always start from the empty ACL if necessary

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

acls with inheritance1
ACLs with Inheritance
  • Suppose that Alice should not be able to access File 1
  • Failing to inherit from Dir 3 to File 1 causes loss of access to Bob and Charlie
  • Bob and Charlie must be added back explicitly

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

acls with negative entries
ACLs with Negative Entries
  • Negative ACL entries reduce redundancy
  • But conflicts must be resolved, e.g.,
    • By order
    • By prioritization of negative entries

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

declarative components
Declarative Components
  • Deduction can be used to describe
    • Existing access control systems – for analysis
    • New access control systems – for implementation and analysis
  • Constraints used in policies for NSA’s SELinux to restrict permissible domain transitions

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

ucon trust management
UCON: Trust Management
  • Trust Management: decentralized authorities
    • PolicyMaker [Blaze, Feigenbaum, Lacy]
    • SPKI/SDSI [Ellison, Rivest et al]
    • RT family [Li, Mitchell]
  • RT1c – deduction and constraints

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

ucon digital rights management
UCON: Digital Rights Management
  • Familiar examples:
    • Movie can be played just once
    • Movie can be played repeatedly within 24 hours of first play
  • More generally, history-sensitive policies that control ongoing access to resources
  • Non-trivial behavior in the accessing state of a session

initial

state

requesting

accessing

end

denied

revoked

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

ucon digital rights management1
UCON: Digital Rights Management
  • Sessions may affect one another
    • In the event of an attack, revoke existing web sessions and only allow administrators to login via a local console
    • Ryutov and Neuman’s GAA-API provides similar capabilities
  • Broad applicability
    • Officer on traffic duty receives limited access to FBI database if query to state database flags driver as a “person of interest” [Anon, NSA]
    • Doctor may perform an operation only when the patient has signed a consent form [Park & Sandhu]

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

separation of duty
Separation of Duty
  • The Separation of Duty (SoD) principle limits the harm that can be caused by one person acting alone
  • Example policy: no-one can approve their own purchase requests
  • Static SoD – no-one can be both an approver and a purchaser (too restrictive)
  • History-based SoD – the desired policy (requires runtime monitoring)

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

the chinese wall security policy
The Chinese Wall Security Policy
  • Brewer and Nash’s Chinese Wall security policy is a history-based SoD specified in terms of conflict of interest
  • A law firm working as both prosecution and defense counsel must partition staff carefully and prevent information leaks
  • Staff are initially unassigned
  • Upon reading a prosecution file, they are forbidden from accessing defense files in the future
  • Generally, resources are assigned owners, and the owners may be in conflict
  • Prevents accidental or malicious leakage by users / Trojan horses, but not water fountain gossip

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

outline1
Outline
  • Motivation
  • Policy algebra
    • Untimed
    • Timed
  • Policy analysis

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

policy algebra
Policy Algebra
  • Existing declarative policy algebras for untimed policies
  • Existing work on timed policies lacks notions such as multiform time and preemption identified by the reactive systems community
  • Adapt existing work on an approach to reactive systems using Timed Default concurrent constraint programming

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

outline2
Outline
  • Motivation
  • Policy algebra
    • Untimed
    • Timed
  • Policy analysis

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

untimed fragment 3 valued logic
Untimed Fragment: 3-Valued Logic
  • 3-valued logic
    • true – grant access
    • false – deny access
    •  - neither grant nor deny access
  • Operators:
    • P and Q
    • P or Q
    • not (P)
    • P def Q
    • P left Q

Q

P

Q

P

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

untimed fragment constraint store
Untimed Fragment: Constraint Store
  • Concurrent constraint programming paradigm
    • From store-as-valuation to store-as-constraint
    • Constraint system includes entailment relation
    • “read” becomes “ask”, using entailment to query store
    • “write” becomes “tell”, adding to the store
  • Ask: if a then P else Q
    • Runs P if “a” is entailed by the store
    • Otherwise runs Q
  • Tell: discussed later

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

untimed fragment functions
Untimed Fragment: Functions
  • Policy language permits (recursive) functions
  • Policy function CheckAccess with username parameter u
    • CheckAccess(u) ::

if uStudents then true else 

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

access control lists
Test negative entries on current path p

Test positive entries on current path p

Test inherited rights from parent directory, if any

Otherwise access is denied

CheckACL(u,p) ::

(if uNegACL(p) then false)

def

(if uPosACL(p) then true)

def

(if p≠/  pInherits then

CheckACL(u,parent(p))

)

def

false

Access Control Lists

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

outline3
Outline
  • Motivation
  • Policy algebra
    • Untimed
    • Timed
  • Policy analysis

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

reactive systems
Reactive Systems
  • Reactive systems continuously react to their environment at a speed determined by their environment [Halbwachs]
  • Well-established theory and tools, e.g., Esterel, Lustre, Signal

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

reactive systems1
Reactive Systems
  • View temporal policies as reactive systems [McDougall et al]
  • The environment is the security monitor
    • Queries whether requests should be granted
    • Passes relevant events to the policy, e.g., time passing or attack detected

Environment

Policy

query(…)

false

event(…)

query(…)

true

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

timed concurrent constraint programming
Timed Concurrent Constraint Programming
  • Timed cc and Timed Default cc – extensions of concurrent constraint programming for reactive systems
  • Each time instant (reacting to environmental stimulus) has its own store
  • Process residual remains for next time instant

ask / tell

store0

P0

ask / tell

store1

P1

ask / tell

store2

P2

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

timed fragment operators
Timed Fragment: Operators
  • next(tell(a)) – tells constraint a to store in next time instant
  • hence(P) – runs fresh copy of P at every subsequent time instant
  • time P on-present a (time P on-absent a)– runs P when a is (is not) entailed by the store
  • Other temporal operators are definable
    • always(P)
    • first a do P
    • P until a

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

example timed policy change
Example: Timed Policy Change
  • Prevent access to files during time frame delimited by start / stop events
    • System load becomes too high
    • Intrusion detection system identifies an attack
    • Deletion / modification of files forbidden during criminal investigation

CheckACLTimedPolicyChange(u,p) ::

(if pAffected  Started then false)

def CheckACL(u,p)

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

example timed policy change1
Example: Timed Policy Change
  • Upon a Start event, tell Started to future stores
  • Stop event preempts execution of inner process

always (

if Start then

(always (next (tell (Started)))) until Stop

)

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

the chinese wall security policy1
The Chinese Wall Security Policy
  • Assume an owner function and a conflict relation conf in the constraint system

CheckACLWithCW(u,p) ::

(if CheckACL(u,p) then

if X. ((conf(X,owner(p)) /\ read(u,X)) else

true

left

always (next(tell(read(u,owner(p))))))

def false

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

outline4
Outline
  • Motivation
  • Policy algebra
    • Untimed
    • Timed
  • Policy analysis

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

policy analysis
Policy Analysis
  • Does a policy behave as we expect?
  • Two approaches
    • Equational reasoning based on a bisimilarity relation
    • Model checking

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

equational reasoning
Equational Reasoning
  • A policy is a process that reacts to additions to the store, and produces an output result (true, false, or )
  • By coinduction, define bisimilarity as the greatest relation that cannot distinguish processes using
    • Same additions to the store for both processes
    • Observing the output result
  • Theorem: bisimilarity is a congruence

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

model checking
Model Checking
  • Goal: reuse existing technology if possible
  • Construct a transition system for a policy, where transitions indicate queries (with response) or events supplied by the environment
  • With recursion and finiteness restrictions, the transition system is finite
    • By a translation into Timed Default cc and a theorem due to Saraswat, Jagadeesan, Gupta

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

model checking1
Model Checking
  • Interesting properties can be expressed using linear temporal logic (LTL)
  • Simple safety (from Li, Mitchell, Winsborough 2003): Does there exist a reachable state in which a (presumably untrusted) principal u has access to a resource p?
    • G (¬grant(u,p))
  • Analysis with state-dependent restrictions, e.g., for the Chinese Wall policy with a finite set of users and two resources p1 and p2 that are in conflict
    • u. G (grant(u,p1)  G (¬grant(u,p2)))

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

summary
Summary
  • There is a need for history-sensitive policies
  • Constraints already appear in security theory and practice
  • This paper: a temporal policy algebra
    • Combines constraint entailment and negation
    • Declarative timed features from reactive programming languages
  • Policy analysis via coinductive equational reasoning and model checking

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

future work
Future Work
  • Implementation in progress (based on jcc)
  • Case studies
  • Practical model checking?

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

slide38
Thank You!

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

properties
Properties

PPDP 2005 - Timed Constraint Programming: A Declarative Approach to Usage Control

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