Challenge archive: SekaiCTF 2025 - Law and Order

Challenge: Law and Order
Event: SekaiCTF - 2025
Year: 2025
Category: Cryptography
Authors: deuterium
Mode: interactive
Article: https://deut-erium.github.io/challenges/sekaictf-2025/law-and-order/
Text: https://deut-erium.github.io/challenges/sekaictf-2025/law-and-order/challenge.txt
JSON: https://deut-erium.github.io/challenges/sekaictf-2025/law-and-order/challenge.json

Description excerpt:
My friends were the FROST to implement sharing signatures for flag and ensured to always include me but somehow it's still not working?

Notes:
- The organizers report that the released handout was an incorrect version. The archived server source and solution are for the corrected version; they do not match the released handout.
- The original remote service is retired. Browser practice offers corrected (default) and released variants with a public dummy reward.
- The original remote service is retired. Browser practice runs locally with the public dummy reward practice{local_dummy_reward}, not an event flag or authoritative score. No TCP endpoint is provided.

Browser practice: https://deut-erium.github.io/challenges/sekaictf-2025/law-and-order/#browser-practice
Runtime: law-and-order
Variants: corrected, released (first is default)
Mode describes the original interactive I/O. Start practice from the article, not a TCP client.

Challenge files (primary):
- chall.py (released handout, incorrect version) (released-chall.py; handout)
  URL: https://deut-erium.github.io/assets/challenges/sekaictf-2025-law-and-order/released-chall.py
  Bytes: 9209
  SHA-256: 76f203c72a553a10ee134c0b03094e9b0ab6a709d0f4c0bc2ec55ea25fcd13f2
  Upstream provenance: https://raw.githubusercontent.com/project-sekai-ctf/sekaictf-2025/683dd81ae520581add40ec21c4819866e28cbde4/crypto/law-and-order/dist/chall.py
- chall.py (corrected server source) (corrected-chall.py; server-source)
  URL: https://deut-erium.github.io/assets/challenges/sekaictf-2025-law-and-order/corrected-chall.py
  Bytes: 9407
  SHA-256: 2bdeeeaf9326a11a26e56bb6a35ffb25907385d649c426492e2e6645ccf19b37
  Upstream provenance: https://raw.githubusercontent.com/project-sekai-ctf/sekaictf-2025/683dd81ae520581add40ec21c4819866e28cbde4/crypto/law-and-order/challenge/app/chall.py

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-2025/blob/683dd81ae520581add40ec21c4819866e28cbde4/crypto/law-and-order/README.md
Archive: https://github.com/project-sekai-ctf/sekaictf-2025/tree/683dd81ae520581add40ec21c4819866e28cbde4/crypto/law-and-order
Solution: https://github.com/project-sekai-ctf/sekaictf-2025/tree/683dd81ae520581add40ec21c4819866e28cbde4/crypto/law-and-order/solution