Nessett’s Critique

• Awkward example in [Nes90]

  A -> B: {T, Kab}Ka-1 --> B sees {T, A <-Kab-> B}Ka-1
  

• Assumptions

  (A1) B bel Ka-> A
  
  (A2) A bel A <-Kab-> B
  (A3) B bel fresh(T)
  (A4) B bel A controls A <-Kab-> B

• Goal: B bel A <-Kab-> B

• Proof:

  B bel A said (T, A <-Kab-> B) A1, rule 1
  
  B bel fresh(T, A <-Kab-> B) A3, rule 5
  B bel A bel (T, A <-Kab-> B) rule 2
  B bel A <-Kab-> B A4, rule 3

• Problem: Ka is a public key, so Kab is exposed.

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