│ Category: Miscellaneous
│ Author: Imattas aka Zemi
│ Flag: byuctf{wh0_kn3w_h4sh_w4snt_h4sh}
│ Source Path: misc/hash_psycho
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--[ Challenge Description ]--
-- text --
Brand new authentication server, zero security vulnerabilities
`nc psycho.chal.cyberjousting.com 1353`
[hash_psycho.py]
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--[ Provided Materials ]--
- Repository folder
https://github.com/BYU-CSA/BYUCTF-2025/tree/main/misc/hash_psycho
- misc/hash_psycho/README.md
https://github.com/BYU-CSA/BYUCTF-2025/blob/main/misc/hash_psycho/README.md
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--[ Recon / Initial Analysis ]--
This page imports the BYUCTF 2025 source material for the Miscellaneous
challenge Hash Psycho. The prompt is kept separate from the solve notes, and
upstream artifacts are linked so the challenge can be replayed from the original
repository.
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--[ Vulnerability / Observation ]--
The useful observation comes from the imported solve notes below. I kept the
original technical path intact while normalizing the page metadata, challenge
grouping, and author attribution for the Volume 2 writeup archive.
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--[ Exploitation / Solution ]--
Source: misc/hash_psycho/README.md
https://github.com/BYU-CSA/BYUCTF-2025/blob/main/misc/hash_psycho/README.md
Python default int hash() actually is equivalent to % (2**61-1). You can
therefore forge a hash value that is just 1337+(2**61-1) (2305843009213695288)
and voila, flag.
-- python --
>>> 1337 == hash(1337+(2**61-1))
True
Flag - byuctf{wh0_kn3w_h4sh_w4snt_h4sh}
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--[ Full Exploit Script ]--
No standalone exploit script was present in the selected source material.
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--[ Key Takeaways ]--
- The BYUCTF 2025 challenge material is preserved with local archive formatting.
- The page author is normalized to Imattas aka Zemi.
- The source repository remains linked for handouts, services, and solve
artifacts.