MONOID

rev

---

Challenge

The binary produces a hex blob from the flag through a small, fully reversible per-byte pipeline: repeating-key XOR followed by a subtract-with-wraparound.

Solution

Reverse the pipeline in the opposite order it was applied — hex-decode the blob to raw bytes, undo the subtraction (add 67 back, mod 128, per byte), then undo the repeating-key XOR with "#!s3kur1ty". Both steps are self-inverse-adjacent (mod-128 addition undoes mod-128 subtraction, and XOR undoes XOR), so running the same key/offset over the ciphertext bytes recovers the flag directly.