Antigone: Security Policy Management in Group Communication

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Antigone Security Policy Management in Group
Communication

• Patrick McDaniel
• EECS, University of Michigan
• April 30, 2001

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Outline

• Problem Statement
• Ismene Group Policy Management
• Antigone Communication Infrastructure
• Implementation and Applications

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Scenario 1
Telecommuters
Consultants
Confidentiality Integrity Authenticity Authorizati
on
Customers
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Scenario 2
Confidentiality Integrity Authenticity Authorizati
on Commitment
Satellite Offices
Contract Negotiation
Arbitrator
Legal Representatives
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Problem

• How do we develop and enforce a group session
  security policy appropriate for the run-time
  environment and membership within a single
  framework?
• Session requirements may be unique
• Each entity may have unique abilities and
  constraints
• The structure and needs of the group may change
  dramatically over time

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(Our) definition of session policy

• ... a statement of the entirety of security
  relevant parameters and facilities used to
  implement the group.

• who are the entities allowed to participate and
  in what capacity (authorization and access
  control)
• which mechanisms will be used to achieve mission
  critical goals (provisioning)
• Note historically not restricted to
  electronically distributed

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Related Work

• Policy Management
• IPsec SPS, Policy Working Group
• Group/Coalition Policy Management
• MSME, GSAKMP, DCCM, SMuG/MSEC
• Authorization and Access Control
• GAA-API, Extended ACLs, and many more
• Trust management
• REFEREE, PolicyMaker, KeyNote, SPKI/SDSI,
  Strongman

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Contributions

• Investigation of Policy Group
• Policy Design Space
• Policy Determination (Ismene)
• Policy Enforcement (Antigone)

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Goals

• Policy Determination
• Flexibly express conditional session requirements
• Support reconciliation of member policies
• Allow assessment of session policy with local
  requirements
• Efficiently derive/evaluate policy
• Policy Enforcement
• Provide efficient, secure (unreliable) group
  communication
• Support a wide range of security
  services/policies
• Easily integrate new services/policies

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The Antigone/Ismene Approach
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Outline

• Problem Statement
• Ismene Group Policy Management
• Antigone Communication Infrastructure
• Implementation and Applications

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Secure Group Policy Dimensions

• Session rekeying policy
• How and when to rekey?
• Data Security policy
• Content guarantees
• Membership policy
• Distribution/accuracy of membership
• Process failure policy
• Failures detected/recovered from?
• Authorization and Access Control

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Example Policy Confidentiality

• Confidentiality Policy All code reviews using
  the distributed editor must be confidential.
• session GroupType(codeReview),
• Application(DistEdit)
• config(datahandler(guarconf))
• Policy states the requirements appropriate for
  application, data sensitivity, membership, and
  other aspects of the environment

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Example Policy Group Participation

• Group Participation Policy Only members of the
  legal department can participate in contract
  negotiations.
• join GroupType(contractNegotiation),
• credential( cert, cert.issuerCA,
• cert.type"X.509",
• cert.ORGLegalDept" )
  accept
• Any number of possible services may be used for
  stating authorization and access control

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An Antigone Group
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Ismene Policy Description Language (IPDL)

• Clause (policy) tag (if) conditionals
  (then) consequences
• Tags identify sub-policies that must be
  satisfied,
• Conditionals test the environment (predicate)
• Consequences apply policy
• E.g., All Contract negotiations must use a
  leave-sensitive LKH key management service.
  Other sessions should use KEK key management.
• groupprot GroupType(contractNegotiation)
• config(lkhkeymgmt(sensleave))
  
• groupprot config(kekkeymgmt())

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Consequences

• Describes results of positive evaluation of
  conditionals
• Tags
• Configuration
• config(lkhkeymgmt())
• config(lkhkeymgmt(keytime10secs))
• Pick Statements
• pick(config(lkhkeymgmt(keytime10secs)),
• config(kekkeymgmt(keytime5secs)) )

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Provisioning Policy Evaluation

• provision keymgt, dhandler, fprot
• keymgt GroupType(contractNegotiation)
• config(lkhkeymgt())
• keymgt config(kekkeymgt())
• dhandler GroupType(contractNegotiation)
• config(dhnd(cryptaes))
• dhandler pick(config(dhnd(cryptdes),
• config(dhnd(cryptrc4)))
• fprot config(chainfp()), fpparms
• fpparms groupsize(gt100) config(chainfp(hbperio
  d5))
• fpparms config(chainfp(hbperiod3))

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Authorization and Access Control

• Credentials are modeled sets of attributes
• E.g., X.509 Certificates consist of attributes
  for subject/common name,
• Credential conditions test the existence of
  credentials with specific attributes
• Authorization and Access Control Clauses
• join day(Monday), config(kekkeymgt()),
• credential(tick,tick.servicecontractc
  onference,
  tick.serverbigco.com)
• accept
• IPDL represents a closed world

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Integrating External Authorization and Access
Control

• Current approach designed to express simple
  authorization and access control
• Some applications may require more sophistication
• Using external policy infrastructure (e.g.
  KeyNote)
• join KeyNote(requestor, attrset, grppol,
  creds)
• accept

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Policy Reconciliation

• The group and each local policy is evaluated
  (result config, pick, AuthA-Cntl statements)

• Example
• kekkeymgt(), chainfp(hbperiod5),
• pick(config(dhnd(cryptdes),
• config(dhnd(cryptrc4)))
• Reconciliation Given evaluated group and local
  policies, how do we arrive at single
  configuration?

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Provisioning Reconciliation Strategies

• Option 1 Prioritized local policies, implemented
• Option 2 Finding largest satisfiable subgroup
• (NP-complete) ReductionMAX2SAT

Group policy a, b, pick(c,d), pick(e,f) Local
policy A d, pick(e,f) Local policy B d,
pick(e,g)
Policy Instantiation a,b,d,e
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Authorization and Access Control Reconciliation
Strategies

• How do we reconcile the authorization and access
  control statements to arrive at a definition
  satisfying all local policies
• OR (if any policy would accept)
• AND (if all policies accept)

• Group policy
• join C1 accept
• join C2 accept
• Local policy A
• join C3 accept
• Local policy B
• join C4 accept

Policy Instantiation join ((C1 or C2) and c3
and c4) accept
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Compliance

• Is the session policy instantiation in consistent
  with my local policy?
• Provisioning compliance (containment),
• Simple search P-time
• Authorization and Access Control
• For all actions/conditions, is the group policy
  more specific (less permissive) than local policy
• Closely related problem of secure
  interoperatibility is NP Gong and Qian, 1994
• Note reconciled policies are trivially
  compliant

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Ismene Summary

• IPDL is a language for expressing group policy
• Provisioning and access control flexibly
  specified
• Policies sensitive to changing conditions
• Algorithm Efficiency
• Other features
• Analysis, reconfig,

Participant Reconciliation Provisioning Compliance AACtrl Compliance
Initiator/ Reconciled Member P Known a priori Known a priori
Unreconciled Member None P P
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Outline

• Problem Statement
• Ismene Group Policy Management
• Antigone Communication Infrastructure
• Implementation and Applications

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Antigone

• Group communication framework implementing policy
  though the the flexible composition of security
  mechanisms
• Composition directed by the security policy
  specification

• Study of the requirements and enforcement of
  group policy

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Antigone

• Policy Enforcement Architecture
• Given a group policy, coordinates the
  provisioning and enforcement of available
  services
• Mechanism
• is a basic service used to implement the group
• E.g., Data-handler (MSEC, GSAKMP, )
• Event-based architecture
• Security relevant events are detected and
  distributed to interested mechanisms
• Policy directs reaction to observed events

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Antigone Architecture
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Policy Enforcement
SE
SE
SE
SE
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Features/Optimizations

• Message construction/marshalling
• Implementing the many mechanism protocol variants
  difficult (e.g., AH, ESP, MESP, )
• Generalized message handling
• Internal buffer handling
• Messages are frequently created/destroyed
• Internal heap of often used/resized buffer
  objects
• Minimization of byte copying, key context
  switching

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Throughput and Latency
Latency
Throughput
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Antigone Overhead

• Constant overhead (50usec /message)

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Antigone Summary

• Framework for enforcing group policy
• Supports a wide range of security services
• Event based architecture
• Easy integration of new services and policies
• Efficient implementation
• Low per packet overhead (50usec)
• High throughput

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Outline

• Problem Statement
• Ismene Group Policy Management
• Antigone Communication Infrastructure
• Implementation and Applications

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Implementation Status

• Antigone
• API six libraries, implementing various
  security, group management, and transport level
  services
• Language grammar, apcc compiler
• 30,000 lines of C code
• Supports a wide range of secure group
  communication mechanisms (e.g., OpenSSL)
• Currently alpha
• Experimenting/optimizing/developing
• Freely available
• http//antigone.eecs.umich.edu

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Applications

• AMirD secure filesystem replication
• Filesystem state updated over secure control
  group

• Simultaneous groups distribute files implementing
  policies appropriate for their content
• Secure Group Messaging Service
• Group based secure instant messaging (I.e., ICQ,
  MS-M)
• Native Antigone - Bump-in-the stack
• Secure existing applications

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Conclusions

• Ismene language and infrastructure for flexible
  and efficient policy determination
• Flexible conditional statements of provisioning
  and authorization and access control
• Efficient reconciliation and analysis (and
  compliance)
• Antigone framework for the flexible and
  efficient enforcement of group security policy
• Unreliable group communication service
• Easy integration of new services and policies
• Low latency, high throughput group communication
• Applications illustrate the Antigone policy
  approach

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Contact Information

• Comments, questions are welcomed
• pdmcdan_at_eecs.umich.edu
• Antigone/Ismene Website
• http//antigone.eecs.umich.edu/