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2. Topics. Problems with BLP ModelsCovert ChannelsComposing BLP modelsDeterministic NoninterferenceUnwinding theoremACL Interpretation of NoninterferenceRestating Noninterference w.r.t. AC matrix modelPolicy Changes over timeComposing deterministic noninterference secure systemsNondeducibil
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1. 1 Covert ChannelsNon-interference and Policy Composition
Chapter 8, Chapter 17
2. 2 Topics Problems with BLP Models
Covert Channels
Composing BLP models
Deterministic Noninterference
Unwinding theorem
ACL Interpretation of Noninterference
Restating Noninterference w.r.t. AC matrix model
Policy Changes over time
Composing deterministic noninterference secure systems
Nondeducibility
Composing deducibly secure systems
Generalized noninterference
Composing generalized noninterference
Restrictiveness
Composing restrictive system
3. 3 Covert channels Alice: TS user
Bob: unclassified user
Alice cannot pass information (i.e. write down) to Bob directly
Can use an indirect way to pass information
On a single CPU system both start submitting jobs
If Alice wants to communicate:
0 to Bob, occupy the CPU for even units of time
1 to Bob occupy the CPU for odd units of times
4. 4 Composing BLP models