Update on GIFT-COFB

[Kazuhiko Minematsu]

Dear all,

GIFT-COFB team would like to announce an update on our security
analysis of GIFT-COFB.
Please find the attached specification document (v1.2). The algorithm
is not changed.
Short summary:
- The specification document revised the security bound by
incorporating the recent analysis shown by Inoue et al. (ePrint
2022/001).
- We confirmed that the proof could be fixed as suggested by 2022/001,
working with Akiko Inoue,
who now joins GIFT-COFB team.
- The resulting bound maintains our bit security claims and shows the
tightness of 2022/001.
- The revised proof is shown in an updated ePrint of GIFT-COFB (2020/738).

We also included the invalidity of recent biclique analysis on GIFT,
as posted earlier, and revised several subsections for improving
readability.

https://eprint.iacr.org/2022/001
https://eprint.iacr.org/2020/738

Best regards,
Kazuhiko on behalf of GIFT-COFB team