Paper 2003/217

Chemical Combinatorial Attacks on Keyboards

Eric Brier, David Naccache, and Pascal Paillier


This paper presents a new attack on keyboards. \smallskip The attack consists in depositing on each keyboard key a small ionic salt quantity ({\sl e.g.} some NaCl on key 0, some KCl on key 1, LiCl on key 2, SrCl$_2$ on key 3, BaCl$_2$ on key 4, CaCl$_2$ on key 5...). As the user enters his PIN, salts get mixed and leave the keyboard in a state that leaks secret information. Nicely enough, evaluating the entropy loss due to the chemical trace turns out to be a very interesting combinatorial exercise. \smallskip Under the assumption that mass spectroscopic analysis can reveal with accuracy the mixture of chemical compounds generated by the user, we show that, for moderate-size decimal PINs, the attack would generally disclose the PIN. \smallskip The attack may apply to door PIN codes, phone numbers dialed from a hotel rooms, computer keyboards or even ATMs. \ss While we did not implement the chemical part of the attack, a number of mass spectrometry specialists confirmed to the authors its feasibility.

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Publication info
Published elsewhere. chemistry attack keyboard combinatorics entropy
Contact author(s)
david naccache @ gemplus com
2003-10-09: received
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      author = {Eric Brier and David Naccache and Pascal Paillier},
      title = {Chemical Combinatorial Attacks on Keyboards},
      howpublished = {Cryptology ePrint Archive, Paper 2003/217},
      year = {2003},
      note = {\url{}},
      url = {}
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