Challenge
Category: General Skills · Points: 200 · CTF: picoCTF 2026
We’re given a single encoded string and told it has gone through multiple layers of encoding. No hints on which ones or in what order.
Analysis
The string looks like Base64 at first glance — but decoding it once doesn’t give plaintext. It’s clearly nested. Rather than guessing the order manually, throwing it into CyberChef’s Magic operation lets it auto-detect the encoding stack.
Magic identified the sequence as:
- From Base64
- From Hex
- URL Decode
- ROT13
Approach
Replicate the chain in CyberChef with these operations in order:
| Step | Operation | Settings |
|---|---|---|
| 1 | From Base64 | Alphabet: A-Za-z0-9+/=, Remove non-alphabet chars: ✓ |
| 2 | From Hex | Delimiter: Auto |
| 3 | URL Decode | Treat + as space: ✓ |
| 4 | ROT13 | Rotate upper + lower case, Amount: 13 |
Pasting the input string and running the chain outputs the flag directly.
Key Takeaway
When a challenge says “multiple encodings” with no further hints, CyberChef’s Magic operation is the fastest way to fingerprint the stack. Each encoding layer on its own is trivially reversible — the only challenge is identifying the correct order.
Flag
picoCTF{nested_enc0ding_66b54257}