Neven Marić
Hidden Investigations CTF 2026

CryptoHidden Investigations CTF 2026

Cipher Cascade

cipher_cascade.txt contains a header stating the layer order (outermost to innermost): Reverse -> Base64 -> Hex -> ???. The unknown innermost layer turned out to be ROT13.

  • crypto
  • encoding
  • base64
  • hex
  • rot13
  • multi-layer

What this one teaches

  • When one layer produces output that almost looks like the flag prefix (e.g. uvPGS ≈ hiCTF), the remaining transformation is usually a simple substitution cipher like ROT13.
  • Peel encoding layers one at a time, verifying each step's output before moving on — the header told you three of the four layers.

Task description

An encrypted transmission was intercepted from a rogue operator. Intelligence suggests the message was encrypted using multiple layers of encoding — a cascade of ciphers, each wrapped around the last. Can you peel back every layer and reveal the hidden flag?

Layers

  1. Encoded message (starts =Q2NxcTM2...): reverse the string -> NzU3NjUwNDc1MzdiNzkz...=
  2. Base64 decode -> 75765047537b79346c33655f6f6c5f79346c33655f68616a3161717d
  3. Hex decode -> uvPGS{y4l3e_ol_y4l3e_haj1aq}
  4. The ??? layer: ROT13 (uvPGS -> hiCTF, the flag prefix gives it away) -> hiCTF{l4y3r_by_l4y3r_unw1nd}
The flagRevealhiCTF{l4y3r_by_l4y3r_unw1nd}

This CTF was possibly solved, and the writeup most likely written by an LLM. Apologies for inconsistencies.