Challenge archive: SekaiCTF 2022 - Diffecient

Challenge: Diffecient
Event: SekaiCTF - 2022
Year: 2022
Category: Cryptography
Authors: deuterium
Mode: interactive
Article: https://deut-erium.github.io/challenges/sekaictf-2022/diffecient/
Text: https://deut-erium.github.io/challenges/sekaictf-2022/diffecient/challenge.txt
JSON: https://deut-erium.github.io/challenges/sekaictf-2022/diffecient/challenge.json

Original description:
Welcome to the Diffecient Security Key Database API, for securely and efficiently saving tons of long security keys! Feel *free* to query your security keys, and pay a little to add your own to our state-of-the-art database.

We trust our product so much that we even save our own keys here!

Notes:
- The archive has server source but no separate player handout. The linked file imports a secret module; organizer files are under the spoiler section.
- 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-2022/diffecient/#browser-practice
Runtime: diffecient
Variants: default (first is default)
Mode describes the original interactive I/O. Start practice from the article, not a TCP client.

Challenge files (primary):
- diffecient.py (archived server source) (diffecient.py; server-source)
  URL: https://deut-erium.github.io/assets/challenges/sekaictf-2022-diffecient/diffecient.py
  Bytes: 4221
  SHA-256: bf4668f888f33cea4280e878300f3f738a8e46ae7a9ed25ba507844f65d3b245
  Upstream provenance: https://raw.githubusercontent.com/project-sekai-ctf/sekaictf-2022/383b16da68c438c5d516e6f00b2716210141f7a4/crypto/diffecient/challenge/app/diffecient.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-2022/blob/383b16da68c438c5d516e6f00b2716210141f7a4/crypto/diffecient/README.md
Archive: https://github.com/project-sekai-ctf/sekaictf-2022/tree/383b16da68c438c5d516e6f00b2716210141f7a4/crypto/diffecient
Solution: https://github.com/project-sekai-ctf/sekaictf-2022/tree/383b16da68c438c5d516e6f00b2716210141f7a4/crypto/diffecient/solution