Fundamental Ideas I

• From Paulson: analz and synth

• If S is a set of message fields,

  analz(S) is the set of its components that the attacker can obtain
  
  synth(S) is the set of fields that the attacker can construct from it
  analz(S) is the smallest set T such that

  1. T includes S
  
  2. if {X, Y} in T then X in T and Y in T
  3. if {X}K in T and K in T then X in T

  Example: analz({{{X}K2, Y}K1, K1}) = {same, plus {{X}K2, Y}, {X}K2, Y}
  synth(S) is the smallest set T such that

  1. T includes S
  
  2. if X in T and Y in T then {X, Y} in T
  3. if X in T and K in T then {X}K in T

• The attacker can forge any message in synth(analz(S)) from S

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