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Algebraic Side-Channel Attacks Beyond the Hamming Weight Leakage Model

Algebraic Side-Channel Attacks Beyond the Hamming Weight Leakage Model. Yossi Oren , Mathieu Renauld , François-Xavier Standaert and Avishai Wool CHES Workshop, Leuven, September 2012. Outline. What is Template-TASCA? How do you use it?. Review: solvers and optimizers.

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Algebraic Side-Channel Attacks Beyond the Hamming Weight Leakage Model

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  1. Algebraic Side-Channel Attacks Beyond the Hamming Weight Leakage Model Yossi Oren, Mathieu Renauld, François-Xavier Standaert and Avishai Wool CHES Workshop, Leuven, September 2012

  2. Outline • What is Template-TASCA? • Howdo you use it?

  3. Review: solvers and optimizers Goal function Set of m logical statements over n variables x1, …,xn Solver Optimizer Satisfying assignment Optimal

  4. Cryptanalysis using solvers • Modern crypto is strong enough to withstand Algebraic Cryptanalysis using solvers [MM00] • If we add side-channel information the key can be recovered quickly and efficiently [RS09] • Physical limitations of the attack setup introduce errors which can be overcome by replacing solvers with optimizers [OKPW10] Oren, Kirschbaum, Popp and Wool,CHES 2010 Massacci and Marraro, Journal of Automated Reasoning 2000 Renauld and Standaert, INSCRYPT 2009

  5. Our contributions • We extend ASCA from a priori (HW) leakage model towards any profiled model • The resulting attack methodology, called Template-TASCA (alt. Template-Set-ASCA), combines the low data complexity of algebraic attacks and the versatility of template attacks • Our results apply both to solvers and to optimizers

  6. Versatility of Template-TASCA Template Decoder Power trace Secret Key Solver/ Optimizer Hamming weights Secret Key

  7. Versatility of Template-TASCA Power Trace EM Trace Whatever Aposteriori probability vectors Template Decoder Hamming weights Solver/ Optimizer Secret Key

  8. Two cases of successful key recovery

  9. Solvers and Optimizers • Solvers are fast, optimizers are versatile

  10. Solvers and Optimizers • Solvers cannot operate over the entire solution space (need additional heuristics)

  11. Shopping list • Device under test (DUT) • Template decoder • Optimizer (or solver) • Cipher equations • Leak equations

  12. Start like template… • In offline phase, create template decoders for many intermediate states • In online phase, apply decoders to power trace, obtaining multiple aposteriori probability vectors

  13. … end like TASCA • Pass probability vectors, together with device description, to optimizer or solver • The output will be the state (and key) which optimally matches the probabilities of all the intermediate values:

  14. Summary • Using Template-TASCA and Template-Set-ASCA, crypto devices can be attacked with very low data complexity • Any leak can be used, as long as a “soft decoder” exists for it • This is theoretically a very strong attack – can it have impact on real world devices?

  15. Thank you! http://iss.oy.ne.ro/Template-TASCA

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