Just because something’s encrypted doesn’t mean it’s secure.
We saw that play out - painfully clearly - during Google CTF 2025.
🕒 Last month, our team took on a challenge called crypto-numerology.
At first glance, it looked solid: a stream cipher modeled after ChaCha20. It had proper constants, key/nonce structure, and ciphertext that looked convincingly random.
But there was one critical detail.
👉 It only used one round of mixing.
That one shortcut changed everything.
With a known key and a few plaintext/ciphertext pairs, we could fully recover keystream blocks. From there, it only took a small brute-force over a 32-bit counter to reveal the flag.
No fancy math. No deep exploit chain.
Just a cipher that looked like encryption - but offered none of its guarantees.
🔍 What struck me most was how realistic this failure felt.
This wasn’t just a broken CTF challenge.
It was a reflection of how real-world systems break:
“One round should be fine.”“Nobody will reuse this nonce.”“It’s just for internal use.”
Security doesn't usually break in dramatic ways - it rots quietly, through shortcuts and assumptions that go unchallenged until it’s too late.
🧠 Takeaway:
In cryptography, almost secure means completely broken.
True security means refusing to compromise—even when it’s tempting.
📖 If you're interested in the technical breakdown, we shared the full write-up here:
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