the extended schematic protection model (espm)
DESCRIPTION
The Extended Schematic Protection Model (ESPM). Ravi Sandhu Laboratory for Information Security Technology George Mason University www.list.gmu.edu [email protected]. Recap. HRU has undecidable safety under very weak assumptions Bi-conditional monotonic Take-Grant and variations - PowerPoint PPT PresentationTRANSCRIPT
© 2004 Ravi Sandhuwww.list.gmu.edu
The Extended Schematic Protection Model(ESPM)
Ravi SandhuLaboratory for Information Security Technology
George Mason [email protected]
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© 2004 Ravi Sandhuwww.list.gmu.edu
Recap
• HRU has undecidable safety under very weak assumptions• Bi-conditional monotonic
• Take-Grant and variations• Efficiently decidable safety• Unexpected aggregate policy
• Schematic protection model (SPM)• Useful demarcation of efficiently decidable safety
– Decidable for acyclic attenuating schemes• polynomial in size of initial state• exponential in number of types (for dense cc relation)• open question: acyclic non-attenuating
– Undecidable for cyclic schemes • Copy flag and demand operation turn out to be redundant• SPM can simulate Bell LaPadula multilevel security
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SPM creation
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ESPM joint creation
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Monotonic HRU command
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ESPM simulation
1. Parameter list generation• Marshall parameter set of size Ji
2. Validating the conditional3. Simulating the HRU command body
• Simulating creates– Unconditional create with alive right, so X/alive dom(X) is
required for X to participate in any command
• Simulating enters– straightforward
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ESPM types
• p: proxy entity type• Px/r dom(Py) for Px, Py of type p in ESPM system iff r [Py,Px] in HRU system
• {aj | j=1…Jmax}: agent types• Represent ESPM proxy entity in jth parameter of HRU command
• {vi | i=1…I}: validator types• Represent a collection of Ji entities in instance of HRU commandi
• Created by joint creation with agent types as parents• {tk
i | k=1…Ki, i=1…I}: term types• Simulate truth value of each term in each HRU command
• {cmi | m=1…Mi, i=1…I}: create types
• Simulate creates for each HRU command• {en
i | n=1…Ni, i=1…I}: enter types• Simulate enters for each HRU command
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© 2004 Ravi Sandhuwww.list.gmu.edu
ESPM creation
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© 2004 Ravi Sandhuwww.list.gmu.edu
ESPM attenuating loopsIf type(ui) = type(v)
Except that one such parent can have attenuating rulecrpj(u1, u2, …, uN, v) = pj/R2
j c/R1j
crc(u1 , u2, …, uN, v) = pj/R3j c/R4
j
soR1
j R2j and R3
j R2j and R4
j R1j
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ESPM unfolded state
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ESPM unfolded state
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ESPM safety analysis
• exponential in types (like SPM)
• exponential in size of initial state (unlike SPM)
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ESPM safety analysis
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Expressive power of SPM and ESPM
• both are monotonic• ESPM is equivalent to monotonic HRU
• HRU can simulate ESPM• ESPM can simulate HRU
• ESPM with double-parent creation is equivalent to ESPM• ESPM is at least as expressive as SPM
• ESPM can simulate SPM trivially
• it turns out that SPM is less expressive than ESPM (and thereby less expressive than monotonic) HRU
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Monotonic access graph model
• nodes are strongly typed• type of a node cannot change
• edges are strongly typed• type of an edge cannot change
• graph operations• initial state operations• node operations
– multi-parent– creates new edges from each parent to child
• edge operations– cannot create new nodes– must be monotonic (edges cannot be removed)
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Simulation: scheme B simulates scheme A
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Scheme A has double-parent creation
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Double-parent creation in scheme A
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Double-parent creation in scheme A
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Failed simulation in scheme B with single-parent creation and identical initial state
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Failed simulation in scheme B with single-parent creation and arbitrary initial state
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© 2004 Ravi Sandhuwww.list.gmu.edu
Failed simulation in scheme B with single-parent creation and arbitrary initial state
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© 2004 Ravi Sandhuwww.list.gmu.edu
Failed simulation in scheme B with single-parent creation and arbitrary initial state
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Multi-parent creation does not add power in non-monotonic systems
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Multi-parent creation
• Adds power to monotonic models
• Perhaps should be viewed as a non-monotonic binding operation