Paper 2022/1776

Offset-Based BBB-Secure Tweakable Block-ciphers with Updatable Caches

Arghya Bhattacharjee, Indian Statistical Institute
Ritam Bhaumik, French Institute for Research in Computer Science and Automation
Mridul Nandi, Indian Statistical Institute

A nonce-respecting tweakable blockcipher is the building-block for the OCB authenticated encryption mode. An XEX-based TBC is used to process each block in OCB. However, XEX can provide at most birthday bound privacy security, whereas in Asiacrypt 2017, beyond-birthday-bound (BBB) forging security of OCB3 was shown by Bhaumik and Nandi. In this paper we study how at a small cost we can construct a nonce-respecting BBB-secure tweakable blockcipher. We propose the OTBC-3 construction, which maintains a cache that can be easily updated when used in an OCB-like mode. We show how this can be used in a BBB-secure variant of OCB with some additional keys and a few extra blockcipher calls but roughly the same amortised rate.

Available format(s)
Secret-key cryptography
Publication info
Published elsewhere. Indocrypt 2022
OCBtweakable block-cipherauthenticated encryptionupdatable offsetsbeyond-birthday-bound security
Contact author(s)
bhattacharjeearghya29 @ gmail com
ritam bhaumik @ epfl ch
mridul nandi @ gmail com
2022-12-31: approved
2022-12-29: received
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Creative Commons Attribution-NonCommercial-ShareAlike


      author = {Arghya Bhattacharjee and Ritam Bhaumik and Mridul Nandi},
      title = {Offset-Based BBB-Secure Tweakable Block-ciphers with Updatable Caches},
      howpublished = {Cryptology ePrint Archive, Paper 2022/1776},
      year = {2022},
      note = {\url{}},
      url = {}
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