Challenge archive: SekaiCTF 2022 - FaILProof Revenge

Challenge: FaILProof Revenge
Event: SekaiCTF - 2022
Year: 2022
Category: Cryptography
Authors: deuterium
Mode: offline
Article: https://deut-erium.github.io/challenges/sekaictf-2022/failproof-revenge/
Text: https://deut-erium.github.io/challenges/sekaictf-2022/failproof-revenge/challenge.txt
JSON: https://deut-erium.github.io/challenges/sekaictf-2022/failproof-revenge/challenge.json

Original description:
I am sure it's failproof now, I have increased the security levels too!

Notes:
- The flag module is needed only to generate a new instance. Solve from the source and the two lines in output.txt; no server is needed.
- This fixed output was generated for the post with the unchanged original program and event flag. It is not a recording from the competition.
- This is a static archive. No live challenge service or runtime simulation is provided here.

Challenge files (primary):
- source.py (archived server source) (source.py; server-source)
  URL: https://deut-erium.github.io/assets/challenges/sekaictf-2022-failproof-revenge/source.py
  Bytes: 1200
  SHA-256: 7451a6b5ee870999277b61e9fe5c23b08428ed2a9f8a6f9f025b85e545fd110d
  Upstream provenance: https://raw.githubusercontent.com/project-sekai-ctf/sekaictf-2022/383b16da68c438c5d516e6f00b2716210141f7a4/crypto/failproof-revenge/challenge/app/source.py
- Fixed instance (output.txt) (output.txt; fixed-instance)
  URL: https://deut-erium.github.io/assets/challenges/sekaictf-2022-failproof-revenge/output.txt
  Bytes: 9008
  SHA-256: 447bcf2520cceda24115e5d31faff6c1ef0fe1334b46bc05bf5488a6745d01fc

Licenses (local copies):
- AGPL-3.0: https://deut-erium.github.io/assets/challenges/licenses/AGPL-3.0.txt
  Bytes: 34523
  SHA-256: 8486a10c4393cee1c25392769ddd3b2d6c242d6ec7928e1414efff7dfb2f07ef
  Upstream provenance: https://raw.githubusercontent.com/project-sekai-ctf/sekaictf-2022/383b16da68c438c5d516e6f00b2716210141f7a4/LICENSE
- CC BY-NC-SA 4.0: https://deut-erium.github.io/assets/challenges/licenses/CC-BY-NC-SA-4.0.txt
  Bytes: 19119
  SHA-256: 14d2138e3a8bd9448254f171b8e17130bf7104d2fd843ab0b924bd105fd00d5a
  Upstream provenance: https://raw.githubusercontent.com/project-sekai-ctf/sekaictf-2022/383b16da68c438c5d516e6f00b2716210141f7a4/LICENSE.content.md

SPOILERS - organizer files and solutions
Spoilers: organizer files and upstream source, archive, or solution links may reveal answers. Modified downloads are identified below.
Source: https://github.com/project-sekai-ctf/sekaictf-2022/blob/383b16da68c438c5d516e6f00b2716210141f7a4/crypto/failproof-revenge/README.md
Archive: https://github.com/project-sekai-ctf/sekaictf-2022/tree/383b16da68c438c5d516e6f00b2716210141f7a4/crypto/failproof-revenge
Solution: https://github.com/project-sekai-ctf/sekaictf-2022/tree/383b16da68c438c5d516e6f00b2716210141f7a4/crypto/failproof-revenge/solution