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Breaking Industrial Ciphers at a Whim               M ATE S OOS         P RESENTATION AT HES’11
Story line1   HiTag2: reverse-engineered proprietary cipher2   Analytic tools are needed to investigate them3   CryptoMini...
Philips HiTag2 Cipher For access control: cars, army buildings Proprietary: reverse-engineered by Karsten Nohl and Sean O’...
SAT SolversInput: CNF, an “and of or-s’      (x1 ∨ ¬x3 )    ∧   (¬x2 ∨ x3 )   ∧    (x1 ∨ x2 )      Crypto-problem needs co...
Toy Example          (¬x1 ∨ ¬x2 ∨ x3 )   ∧     (¬x1 ∨ x2 )   ∧   (¬x1 ∨ ¬x2 )              Clause 1               Clause 2...
HES2011 - Mate Soos - Craking Industry Ciphers at a Whim
HES2011 - Mate Soos - Craking Industry Ciphers at a Whim
HES2011 - Mate Soos - Craking Industry Ciphers at a Whim
HES2011 - Mate Soos - Craking Industry Ciphers at a Whim
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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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