zwesty
Write-ups / Day 17 / Android
Day 17 · Sat, Oct 17 · Android

Name Collapse

Prey slaughtered

APK structure, character permutations

STTMClaude Homebase Both

Flags are shortened to their first 8 and last 4 characters because they're unique per team.

Challenge ID
mobile-android-day-17-name-collapse (+ /time_trial, /mastery)
Solved
2026-10-17, all three modes, by 09:11:15 ET (unranked)
Player
Zwesty (solo), with Claude Code (Opus 5.5): our automated morning solver (a scheduled script on our Kali VM), then a Claude helper agent for this lane

The challenge

Find the backend answer code (ANS- + 16 uppercase hex) for the named case. The APK's puzzle asset uses a new codec, indexed.

Safety

The APK was only unzipped and read; nothing was installed or run.

What was in the files

assets/huntress_puzzle.json held data (20 characters, the code scrambled) and order, a full permutation of 0–19: character i of data belongs at position order[i].

The modes

  • Morning solver: clean stop: its new unknown-codec fallback (built the night before) tries transforms of data, but not reorderings, so it found no reading and stopped without sending anything.
  • Claude helper agent: added indexed (and its "gather" and decoy-insertion forms, accepting only a unique valid reading) to the pre-built Android solver. Tests 9/9 incl. all 174 saved APKs identical; a regression rehearsal showed 0 changed.
Single Solve   CORRECT 09:10:12  flag b2465198…
Time Trial     CORRECT 09:11:08  flag 7e909505…   plain start (unranked)
Mastery        CORRECT 09:11:15  flag 464dee22…   5/5 sets, plain start (unranked)

Time to solve

All three modes were solved by 09:11:15 ET, each on the first submit, once the new codec was added. Both timed runs were plain starts and so unranked.

Takeaways

  • The fallback needs reorderings as well as transforms, since split (Days 5/10) and indexed both use an order list. Added for future days.
  • The timed runs were started without the ranked option, so they went unranked; a ranked pass was still open at the time of writing.