🔐 Encryption ≠ Security

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:
🔗 https://ctftime.org/writeup/40328