[Resource Topic] 2022/1202: Disorientation faults in CSIDH

Welcome to the resource topic for 2022/1202

Disorientation faults in CSIDH

Authors: Gustavo Banegas, Juliane Krämer, Tanja Lange, Michael Meyer, Lorenz Panny, Krijn Reijnders, Jana Sotáková, Monika Trimoska


We investigate a new class of fault-injection attacks against the CSIDH family of cryptographic group actions. Our disorientation attacks effectively flip the direction of some isogeny steps. We achieve this by faulting a specific subroutine, connected to the Legendre symbol or Elligator computations performed during the evaluation of the group action. These subroutines are present in almost all known CSIDH implementations. Post-processing a set of faulty samples allows us to infer constraints on the secret key. The details are implementation specific, but we show that in many cases, it is possible to recover the full secret key with only a modest number of successful fault injections and modest computational resources. We provide full details for attacking the original CSIDH proof-of-concept software as well as the CTIDH constant-time implementation. Finally, we present a set of lightweight countermeasures against the attack and discuss their security.

ePrint: https://eprint.iacr.org/2022/1202

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I gave a talk on this last Friday, with slides available here. Video should be up soon-ish

Talk by K.Reijnders at the isogeny days in Leuven.

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