margrave: xacml verification and change-impact analysis kathi fisler, wpi shriram krishnamurthi,...

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Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

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Page 1: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Margrave: XACML Verification and Change-Impact Analysis

Kathi Fisler, WPIShriram Krishnamurthi, Brown

Leo Meyerovich, BrownMichael Carl Tschantz, Brown

Page 2: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Running Example

Roles:Faculty, Student

Resources:InternalGrades, ExternalGrades

Actions:Assign, View, Receive

Page 3: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Properties

1. There do not exist members of Student who can Assign ExternalGrades

2. Faculty can Assign both InternalGrades and ExternalGrades

3. No combination of roles exists whose user can both Receive and Assign ExternalGrades

Page 4: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 1

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

Page 5: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 1, Properties 1-3

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

1. There do not exist members of Student who can Assign ExternalGrades

2. Faculty can Assign both InternalGrades and ExternalGrades

3. No combination of roles exists whose user can both Receive and Assign ExternalGrades

Page 6: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Output

Error!

Counterexample:Student simultaneously requests to – Receive ExternalGrade – Assign ExternalGrade

XACML: attributes represent sets

Page 7: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 2

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• Attributes for action and requested resources are constrained as singletons

Page 8: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 2, Properties 1-3

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• Attributes for action and requested resources are constrained as singletons

1. There do not exist members of Student who can Assign ExternalGrades

2. Faculty can Assign both InternalGrades and ExternalGrades

3. No combination of roles exists whose user can both Receive and Assign ExternalGrades

Page 9: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Output

Error!

Counterexample:Faculty - Student requests …

But a Faculty isn’t also a Student

Page 10: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 3

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• Attributes for action and requested resources are constrained as singletons

• Faculty are disjoint from Students

Page 11: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 3, Properties 1-3

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• Attributes for action and requested resources are constrained as singletons

• Faculty are disjoint from Students

1. There do not exist members of Student who can Assign ExternalGrades

2. Faculty can Assign both InternalGrades and ExternalGrades

3. No combination of roles exists whose user can both Receive and Assign ExternalGrades

Page 12: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Output

Success!

Page 13: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 4

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• TAs have the same privileges as Faculty

• Attributes for action and requested resources are constrained as singletons

• Faculty are disjoint from Students

Page 14: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 4, Properties 1-3

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• TAs have the same privileges as Faculty

• Attributes for action and requested resources are constrained as singletons

• Faculty are disjoint from Students

1. There do not exist members of Student who can Assign ExternalGrades

2. Faculty can Assign both InternalGrades and ExternalGrades

3. No combination of roles exists whose user can both Receive and Assign ExternalGrades

Page 15: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Output

Error!

Counterexample:• Student - TA can Assign

ExternalGrades• Student - TA is not a Faculty

TAs are tricky!

Page 16: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 5

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• TAs can View and Assign InternalGrades but not ExternalGrades

• Attributes for action and requested resources are constrained as singletons

• Faculty are disjoint from Students

Page 17: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 5, Properties 1-3

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• TAs can View and Assign InternalGrades but not ExternalGrades

• Attributes for action and requested resources are constrained as singletons

• Faculty are disjoint from Students

1. There do not exist members of Student who can Assign ExternalGrades

2. Faculty can Assign both InternalGrades and ExternalGrades

3. No combination of roles exists whose user can both Receive and Assign ExternalGrades

Page 18: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Output

Success!

Page 19: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 6

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• TAs can View and Assign InternalGrades but not ExternalGrades

• FacultyFamily can Receive ExternalGrades

• Singleton and disjointness constraints

Page 20: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 6, Properties 1-3• Requests for Students to

Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• TAs can View and Assign InternalGrades but not ExternalGrades

• FacultyFamily can Receive ExternalGrades

• Singleton and disjointness constraints

1. There do not exist members of Student who can Assign ExternalGrades

2. Faculty can Assign both InternalGrades and ExternalGrades

3. No combination of roles exists whose user can both Receive and Assign ExternalGrades

Page 21: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Output

Error!

Counterexample:• Faculty can Assign ExternalGrades• FacultyFamily can Receive

ExternalGrades• The same person generates both

Page 22: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Design Flow

• Verification catches subtle corner-cases

• Testing without the test cases: property represents a set of test cases

• The disadvantage is usually cost (there’s another one we’ll get to later…)

Page 23: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Performance

• Parsing: 355ms (cold cache) – 70ms (warm)

• Longest verification: 10ms; most were faster than timer could measure

• Memory: baseline of 4.7Mb, no increase

[Athlon XP 1800+, 1.5GHz, 512Mb]

Page 24: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Implementation

Page 25: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Multi-Terminal Decision Diagrams

• Faculty (f) can assign (a) grades (g)• Students (s) can receive (r) grades (g)

Page 26: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Rules and Rule Combination

Page 27: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Constraints

• Represented by boolean expressions

• Easy to combine booleans with MTDDs

• Adds new terminal: EC (Excluded by Constraint)

Page 28: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Properties?!?

Page 29: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policies Without Properties

• Working policy P1

• Modified policy P2

• Testing reveals intended change

• But…

Page 30: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 4 – Policy 3

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• TAs have the same privileges as Faculty

• Attributes for action and requested resources are constrained as singletons

• Faculty are disjoint from Students

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• Attributes for action and requested resources are constrained as singletons

• Faculty are disjoint from Students

Page 31: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Output

• Eight combinations grant access

• Four involve ExternalGrades

• Adding TAs should not have affected this!

Page 32: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 5 – Policy 3

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• TAs can View and Assign InternalGrades but not ExternalGrades

• Attributes for action and requested resources are constrained as singletons

• Faculty are disjoint from Students

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• Attributes for action and requested resources are constrained as singletons

• Faculty are disjoint from Students

Page 33: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Output

All changes involve only

• TAs• InternalGrades

Therefore, we can be confident about the edit

Page 34: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Policy 6 – Policy 5• Requests for Students to

Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• TAs can View and Assign InternalGrades but not ExternalGrades

• FacultyFamily can Receive ExternalGrades

• Singleton and disjointness constraints

• Requests for Students to Receive ExternalGrades succeed

• Requests for Faculty to Assign or View ExternalGrades succeed

• TAs can View and Assign InternalGrades but not ExternalGrades

• Singleton and disjointness constraints

Page 35: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Output

All changes involve Receiving grades

Some changes involve the Faculty role

Is there an error?

Page 36: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Exploring Changes

• We can query and verify differenceseg: Did a change affect ExternalGrades?

• Properties of differences may be stronger than properties of the entire system

• Exploration may eventually lead to identifying system properties

Page 37: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Case Study

Page 38: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Application

Continue: paper submission and reviewSoftvis 2005, CSFW 2005, FOAL 2005, ISSTA 2004, LMO

2005, TAV-WEB 2004, PADL 2004/3/2/1, FDPE 2003, Scheme 2003/2, ...

• Roles: Admin, Chair, PC Member, Subrev…• Actions: Submit, Review, Broadcast, …• Resources: Papers, Reviews,

Configurations

Page 39: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Performance

• Policy has 50 MTDD variables• Raw policy has 1268 MTDD nodes• Constraints shrink it to 817 nodes• Parsing/constraining: 2.07s• Twelve properties: each < 10ms• Memory: 316,288 bytes over baseline• Change: 2ms, 1133 nodes, 16.3Kb

memory

Page 40: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Conclusion

Page 41: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Tool Output1:/Subject, role, Faculty/ 2:/Subject, role, Student/ 3:/Resource, resource-class, ExternalGrades/ 4:/Resource, resource-class, InternalGrades/ 5:/Action, command, Assign/ 6:/Action, command, View/7:/Action, command, Receive/ 8:/Subject, role, TA/12345678{00010101 N->P00011001 N->P00100101 N->P00101001 N->P01010101 N->P01011001 N->P01100101 N->P01101001 N->P}

Page 42: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

Perspective

• Verification can be cheap enough to fit into the design flow and encourage policy exploration

• Change impact– useful in itself finds some errors without

properties– query/verif. is a bonus lightweight formal method

• Think about continuous verification and change impact reports

Page 43: Margrave: XACML Verification and Change-Impact Analysis Kathi Fisler, WPI Shriram Krishnamurthi, Brown Leo Meyerovich, Brown Michael Carl Tschantz, Brown

XACML analysis:http://www.cs.brown.edu/research/plt/software/margrave/

Conference manager:http://continue.cs.brown.edu/