Cryptanalysis of TFHE-Friendly Cipher FRAST
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Dateien
Autor:in (Körperschaft)
Publikationsdatum
2026
Typ der Arbeit
Studiengang
Typ
01A - Beitrag in wissenschaftlicher Zeitschrift
Herausgeber:innen
Herausgeber:in (Körperschaft)
Betreuer:in
Übergeordnetes Werk
IACR Transactions on Symmetric Cryptology
Themenheft
DOI der Originalpublikation
Link
Zugehörige Forschungsdaten
Reihe / Serie
Reihennummer
Jahrgang / Band
2026
Ausgabe / Nummer
1
Seiten / Dauer
119-147
Patentnummer
Verlag / Herausgebende Institution
Ruhr-Universität Bochum
Verlagsort / Veranstaltungsort
Auflage
Version
Programmiersprache
Abtretungsempfänger:in
Praxispartner:in/Auftraggeber:in
Zusammenfassung
FRAST is a TFHE-friendly stream cipher that was published at FSE 2025. The cipher is defined over Z16, and makes extensive use of negacyclic S-boxes over Z16 as they are less costly in TFHE. Like many FHE-friendly ciphers, FRAST randomizes some of its components to increase its security against statistical attacks. In the case of FRAST, some S-boxes are randomized using an XOF that takes a nonce as input. In this work, we point out a strong structural property of the full FRAST permutation, which leads to a much simpler alternative representation of the primitive. We study the consequences of this representation and find a weak key space of non-negligible size (i.e., much larger than 2128) on which every ciphertext leaks one bit of plaintext. This corresponds to a distinguishing attack on the full FRAST in the weak-key setting. In particular, we emphasize that, apart from the structural property, the usage of negacyclic S-boxes further leads to a much larger weak-key space for our attack.Finally, we provide a general framework to mount a linear attack on FRAST in the average key setting. We briefly describe our approach in the end of the paper, and observe that standard assumptions expected to work in the context of linear cryptanalysis do not hold in the case of FRAST: our experiments indicate that a linear attack in the average key setting does not work as expected.
Schlagwörter
Fachgebiet (DDC)
Veranstaltung
Startdatum der Ausstellung
Enddatum der Ausstellung
Startdatum der Konferenz
Enddatum der Konferenz
Datum der letzten Prüfung
ISBN
ISSN
2519-173X
2569-2925
2569-2925
Sprache
Englisch
Während FHNW Zugehörigkeit erstellt
Ja
Zukunftsfelder FHNW
Publikationsstatus
Veröffentlicht
Begutachtung
peer-reviewed
Open Access-Status
Diamond
Lizenz
Zitation
Bak, A., Ghosh, S., Liu, F., Meier, W., Ni, J., & Perrin, L. (2026). Cryptanalysis of TFHE-Friendly Cipher FRAST. IACR Transactions on Symmetric Cryptology, 2026(1), 119–147. https://doi.org/10.46586/tosc.v2026.i1.119-147