QCB is Blindly Unforgeable

Jannis Leuther; Stefan Lucks

Paper 2023/1653

QCB is Blindly Unforgeable

Jannis Leuther

, Bauhaus University, Weimar

Stefan Lucks

, Bauhaus University, Weimar

Abstract

QCB is a proposal for a post-quantum secure, rate-one authenticated encryption with associated data scheme (AEAD) based on classical OCB3 and \(\Theta\)CB, which are vulnerable against a quantum adversary in the Q2 setting. The authors of QCB prove integrity under plus-one unforgeability, whereas the proof of the stronger definition of blind unforgeability has been left as an open problem. After a short overview of QCB and the current state of security definitions for authentication, this work proves blind unforgeability of QCB. Finally, the strategy of using tweakable block ciphers in authenticated encryption is generalised to a generic blindly unforgeable AEAD model.

Note: In an earlier version of this paper [18], a claim from [2] was repeated, that blind unforgeability (BU) implies plus-one unforgeability (PO) [8]. This claim, which would have indicated that our result is strictly stronger than the PO unforgeability result from [5], has been withdrawn in an updated version of [2]. This withdrawal does not undermine the contribution of our paper. On the contrary, both BU and PO seem to be important security notions of independent importance. As it turns out, QCB satisfies both notions: QCB is both PO unforgeable (proven in [5]) and BU unforgeable (proven in our paper).

Metadata

Available format(s): PDF
Category: Secret-key cryptography
Publication info: Published elsewhere. Minor revision. C2SI 2023: Codes, Cryptology and Information Security
DOI: 10.1007/978-3-031-33017-9_6
Keywords: Post-Quantum Cryptography QCB Blind Unforgeability AEAD Symmetric Cryptography
Contact author(s): jannis leuther @ uni-weimar de
stefan lucks @ uni-weimar de
History: 2023-12-08: revised; 2023-10-25: received; See all versions
Short URL: https://ia.cr/2023/1653
License: CC BY

BibTeX

@misc{cryptoeprint:2023/1653,
      author = {Jannis Leuther and Stefan Lucks},
      title = {{QCB} is Blindly Unforgeable},
      howpublished = {Cryptology {ePrint} Archive, Paper 2023/1653},
      year = {2023},
      doi = {10.1007/978-3-031-33017-9_6},
      url = {https://eprint.iacr.org/2023/1653}
}