Paper 2022/1097

Post-Quantum Security of the (Tweakable) FX Construction, and Applications

Gorjan Alagic, University of Maryland, College Park
Chen Bai, University of Maryland, College Park
Jonathan Katz, University of Maryland, College Park
Christian Majenz, Technical University of Denmark
Patrick Struck, University of Regensburg

The FX construction provides a way to increase the effective key length of a block cipher E. We prove security of a tweakable version of the FX construction in the post-quantum setting, i.e., against a quantum attacker given only classical access to the secretly keyed construction while retaining quantum access to E, a setting that seems to be the most relevant one for real-world applications. We then use our results to prove post-quantum security—in the same model—of the (plain) FX construction, Elephant (a finalist of NIST's lightweight cryptography standardization effort), and Chaskey (an ISO-standardized lightweight MAC).

Available format(s)
Secret-key cryptography
Publication info
Contact author(s)
galagic @ umd edu
cbai1 @ umd edu
jkatz2 @ gmail com
chmaj @ dtu dk
patrick struck @ ur de
2022-08-29: approved
2022-08-24: received
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      author = {Gorjan Alagic and Chen Bai and Jonathan Katz and Christian Majenz and Patrick Struck},
      title = {Post-Quantum Security of the (Tweakable) FX Construction, and Applications},
      howpublished = {Cryptology ePrint Archive, Paper 2022/1097},
      year = {2022},
      note = {\url{}},
      url = {}
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