HES2011 - Mate Soos - Craking Industry Ciphers at a Whim

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HES2011 - Mate Soos - Craking Industry Ciphers at a Whim

  1. 1. Breaking Industrial Ciphers at a Whim M ATE S OOS P RESENTATION AT HES’11
  2. 2. Story line1 HiTag2: reverse-engineered proprietary cipher2 Analytic tools are needed to investigate them3 CryptoMiniSat: free software tool to test ciphers (and to break them) 2
  3. 3. Philips HiTag2 Cipher For access control: cars, army buildings Proprietary: reverse-engineered by Karsten Nohl and Sean O’Neil Feedback linear(!), filter non-linear 3
  4. 4. SAT SolversInput: CNF, an “and of or-s’ (x1 ∨ ¬x3 ) ∧ (¬x2 ∨ x3 ) ∧ (x1 ∨ x2 ) Crypto-problem needs conversionUses DPLL(ϕ) algorithm 1 If (formula ϕ trivial) return SAT/UNSAT 2 ret ← DPLL(ϕ with v ← true) 3 If (ret = SAT) return SAT 4 ret ← DPLL(ϕ with v ← false) 5 If (ret = SAT) return SAT 6 return UNSAT 4
  5. 5. Toy Example (¬x1 ∨ ¬x2 ∨ x3 ) ∧ (¬x1 ∨ x2 ) ∧ (¬x1 ∨ ¬x2 ) Clause 1 Clause 2 Clause 31 Guess: x1 = True2 Clause 2: x2 = True3 Clause 3: impossible! Reverse guess.4 x1 = False5 Good, everything is satisfied! 5

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