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

TitlePost-Quantum Security of the (Tweakable) FX Construction, and Applications
Publication TypeJournal Article
Year of Publication2022
AuthorsAlagic, G, Bai, C, Katz, J, Majenz, C, Struck, P
Date Published8/29/2022

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