**Reading**: Chapters 15.2.2, 16.1, 16.3

Analyzing a cipher requires being able to spot patterns. See how good you are. What is the pattern in the following?

- Privilege in Languages
- Nesting program units
- Temporary upgrading of privileges

- Information Flow
- What is it?
- Entropy-based analysis: flows from
*x*to*y*if*H*(*x*|_{s}*y*) <_{t}*H*(*x*|_{s}*y*) where system starts in state_{s}*s*, transitions to state*t* - Examples:
,*y*:=*x**x*:=*y*+*z*,**if***x*= 1**then***y*:= 0**else***y*:= 1

- Compiler-Based Mechanisms
- Labels on variables; all examples use Bell-LaPadula style labels
- Review lub(
*X*,*Y*), glb(*X*,*Y*)

- Review lub(
- Certifying sets of statements
- Declarations
- Assignments
- Compound statements
- Conditional statements
- Iterative statements

- Labels on variables; all examples use Bell-LaPadula style labels

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