Enforcing SSoD policies by SMER Constraints

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Enforcing SSoD policies by SMER Constraints

• Hong Chen

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Motivation

• Terminology
• SoD Separation of Duty
• RBAC Role-Based Access Control
• SMER Static Mutually Exclusive Role
• SoD is important in RBAC systems
• Directly enforcing SoD in RBAC is difficult
• We can use SMER to enforce RBAC

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Definitions (1)

• Domains
• U the set of all possible users
• R the set of all possible roles
• P the set of all possible permissions
• RBAC state

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Definitions (2)

• SSoD policy
• SSoD safety
• SMER constraint
• RBAC state satisfies SMER constraint
• Enforcing SSoD by SMER

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Example
Example borrowed from Ninghui Li, Ziad Bizri,
and Mahesh V. Tripunitara On Mutually-Exclusive
Roles and Separation of Duty, ccs 2004
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Current Research Result

• Directly enforcing SSoD policies in RBAC is
  intractable
• Enforcing SMER constraints is efficient
• Verification problem is intractable
• Generation of singleton SMER constraints
• Precise enforcement is not always possible

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Enforcing is not enough

• Compatibility
• Example
• C1 and C2 both enforce E
• C1 is not a good choice

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Comparing SMER constraints

• Compare two SMER constraints
• C1 is at least as restrictive as C2 under RH
  (denoted by ) if and only if
• If both C1 and C2 are in a set of SMERs and C1 is
  more restrictive than C2, than we can simply
  remove C2 from the set

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Generation of SMER constraints(1)

• Naïve Generation 2(2n)
• Even for small n, not efficient
• Generating all set of SMERs that can minimally
  implement given SSoD policies
• Starting from most restrictive SMERs

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Generation of SMER constraints(2)
Most Restrictive set of SMERs
Restrictive
SMERs that implement SSoD
SMERs that minimally implement SSoD
SMERs that do not implement SSoD
Not Restrictive
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Summary

• Notion of implementation
• Comparison between different SMERs
• Comparison between different SSoDs
• Algorithm to generate all set of SMERs that
  minimally implement SSoD

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Future Work

• When can we precisely implement SSoD?
• More efficient generation algorithm
• How to choose from a set of implementations?
• How to compare different SMER constraints
  according to the given SSoD policies?