On the Expressive Power of the Unary Transformation Model by Ravi Sandhu Srinivas Ganta Center for Secure Information Systems George Mason University
Mar 26, 2015
On the Expressive Power of the UnaryTransformation Model
by
Ravi SandhuSrinivas Ganta
Center for Secure Information SystemsGeorge Mason University
Outline
• Introduction / Motivation
• Transformation Model
• Example
• Expressive Power
• Conclusion
NMT
• Can enforce lots of diverse policies
• Has simple implementation
• Cannot adequately express the document release example
(Sandhu & Suri, Oakland 92)
Document Release Example
• A scientist prepares a document and can release it only after getting approval from a patent-officer.
Transformation Model (TRM)
• Protection state in TRM is viewed in terms of the familiar access matrix
• Protection state of the system is given by the tuple (OBJ, SUB, t, AM)
• The specification for changing the protection state is given by an authorization scheme
ACCESS MATRIX
subjects
objects
u : s
f : o
r wown
Authorization Scheme
• A set of access rights R.
• Disjoint sets of subject and object types, TS and TO, respectively.
• A collection of three classes of state changing commands: Transformation commands, Create commands and Destroy commands
Transformation Commands
Command name (S1:s1,....Sn:sn, O:o) if predicate then sequence of primitive operations enter/delete r into [S, O] end
Command transfer-ownership (S1:s, S2:s, O:o) if own [S1,O]
thenenter own in [S2,O]deleterown from [S1,O]
end
Example:
Create Commands
Command create (S1:s1, O:o) create object O enter own in [S1, O] end
Destroy Commands
Command destroy (S1:s1, O:o) destroy object O end
if own [S1,O] then
• A set of rights R
• A set of disjoint subject and object types TS and TO respectively
• A set of state-changing transformation, creation and destroy commands
• The initial state
TRM SUMMARY
Document Release Example
• A document cannot be released by a scientist without first obtaining approval from a patent-officer.
• Types = { sci, po, doc}
• Rights = {read, write, own, review, pat-ok, pat-reject, release}
• Command create-doc (S:sci, O:doc) create object O enter own in [S,O] enter read in [S,O] enter write in [S,O] end
Create Command
Document Release Example
S: sci
P: po
O :doc
ownreadwrite
• command rqst-review (S:sci, P:po, O:doc) if own [S,O] then enter review in [P,O] delete write from [S,O] end
write [S,O]
Request Review
Get-Approval/Rejection
• command get-approval (S:sci, P:po, O:doc) if own [S,O] then enter pat-ok in [S,O] delete review from [P,O] end
review [P,O]
• command get-rejection (S:sci, P:po, O:doc) if own [S,O] then enter pat-reject in [S,O] delete review from [P,O] end
review [P,O]
Release / Revise Document
• command release-doc (S:sci, O:doc) if pat-ok [S,O] then enter release in [S,O] delete pat-ok from [S,O] end
• command revise-doc (S:sci, O:doc) if pat-reject [S,O] then enter write in [S,O] delete pat-reject from [S,O] end
Expressive Power
TRM BTRM
• The document release example has commands which test for atmost two cells of the matrx.
• Binary Transformation Model
•
(Sandhu & Ganta, Oakland 94)
Expressive Power
• UTRM TRM
• UTRM BTRM
?
?
UTRM BTRM
• requires every subject in the simulation to be of a different type.
• Esorics 94
UTRM BTRM
• if every subject cannot be of a different type
Conclusion
• UTRM BTRM impractical simulation in general
• UTRM < BTRM for all practical purposes