Food for Thought · Huntress CTF 2026

The challenge

"A very small language has quite a lot to say."

answer_id	Question	Format
`message`	"Decode the assigned blob completely. What exact answer slug does its final non-empty decoded line instruct you to submit?"	pattern: "three lowercase words separated by hyphens, followed by a hyphen and a two-digit number; submit the slug only"; trimmed

The Mastery asked the same question once per blob (set1.message … set128.message).

Reading the prompt: what it said we'd need

Clue	What it pointed to	What I did about it
"A very small language"	A minimal programming language, not an encoding	The blob used only `+`, `-`, and `.`: Brainfuck's command set (eight commands in all)
"has quite a lot to say"	The program prints the message	Run it as data: count the cell up and down, print a character on each `.`
"Food for Thought" (title)	Brainfuck's name, politely	Confirmed the reading
"submit the slug only" (format)	The answer is the slug alone	Same as the last few days; no trailer in any of today's blobs

What was in the files

Single Solve: blob.txt, 3,406 bytes, one line with no line break: 1,677 +, 1,620 -, and 109 ., nothing else (no <, >, [, ], or ,). So it works on one cell: move the value up or down to the next character's code, print, repeat. The first 78 + and a . print N. The 109 printed characters read "Nice work decoding this warmup! To solve, submit this exact answer to the Game Master: happy-comet-blossom-79".
Time Trial: blob.txt, 3,473 bytes, the same template (1,706 +, 1,657 -, 110 .) with a different slug (dandy-blanket-beaver-21).
Mastery: one zip of 128 blobs (105,200 bytes; 92,576 unpacked). Each blob has 26 lines in the history pattern of the earlier days: line 23 Ascii85 (Day 23), line 24 netstrings (Day 24), line 25 code points (Day 25), and line 26 Brainfuck (today), 200 characters on blob-01.txt.

So the timed variants used the same template with different values; only the program length changed with the sentence.

Single Solve

The solver: stopped, nothing sent

started_at  2026-10-26 09:00:54.417 ET   (solver; artifact 01-blob.txt, 3,406 bytes)
deadline    none (Single Solve)
answers     none
result      STOP: no instruction line found (per-line with reverse, Day 10 decoders, whole-blob reverse, search; atbash;
            caesar search; new-layer search; trailer reading); not submitting. Timed modes not started.

This stop was correct. None of the solver's readings knew Brainfuck, and its 3-move "new-layer search" didn't find it, so any value sent would have been a guess.

By hand (Claude)

A blob of nothing but + - . is readable at a glance as Brainfuck. Claude ran it through a step-limited interpreter (as data, with a hard step cap), read the sentence above, and sent the one answer it gave: happy-comet-blossom-79.

started_at  2026-10-26 09:00:54.417 ET   (same attempt, submitted by Claude)
answers     1   happy-comet-blossom-79
result      CORRECT   flag a509003f…eb7f   (09:02:20.583)

The flag is from the Game Master's reply in our request log.

The solver update (Claude)

Claude built a new Warmups solver on top of the previous one (which already had a trailer reading added after Day 25): - One new reading, brainfuck_text, added to the solver's text decoders at cost 1, as an established reading and not a fallback (a lesson from Day 22). So it runs in the whole-blob search, on every Mastery line, and under the stacked readings. - Strict and bounded. The input (or each non-empty line) must be only Brainfuck commands (whitespace ignored), must print at least once, and must not read input (,). The interpreter has a 2,000,000-step limit and a 30,000-cell tape; unbalanced brackets or a pointer off the tape reject the input. The program is treated as data, never run as code. - Line 26 added to the strict per-line layer list, so the trailer reading also knows line 26 (the Day 25 lesson: a new layer goes into that list too, or a trailer on the new line is left out). - Each Mastery set is still solved on its own, as before. - Our rehearsal tool gained a Brainfuck layer, so synthetic blobs can use it.

Checks before the timed runs: - Its tests: the first run was 9 of 10. The multi-line case failed because a whole-blob run carries the cell value from one line into the next; per-line programs are now always tried as well. Then 10 of 10 (the real Single blob, the interpreter's bounds, plain text untouched, Brainfuck over and under Base64, code points still read, the strict day-26 layer, per-set). - A regression rehearsal against the previous day's puzzles plus synthetic blobs: 131 saved attempts, slowest 1.02 s, per-set identical; against the previous solver 130 identical, 1 newly solved (today's Single), 0 changed; synthetic 60 of 60 with the Brainfuck layer.

The reading was written between 09:03:50 and 09:04:06 ET and the rehearsal layer at 09:04:14, so the reading, tests, and rehearsal took about two and three-quarter minutes after the Single.

Time Trial

CORRECT on the first attempt, ranked (unique_attempts_remaining: 255, variant_fresh: true).

started_at  2026-10-26 09:05:09.319 ET
deadline    2026-10-26 09:05:39.319 ET   (30 s)
answers     1   dandy-blanket-beaver-21
start        129 ms after started_at
artifact     494 ms after started_at   (3,473 bytes)
solve        504 ms after started_at   (10 ms)
submit      1195 ms after started_at
result      CORRECT   flag e7db3b56…acbf   (09:05:09.949)

Mastery

CORRECT on the first attempt, ranked (128 sets, 145 s clock; Day 25 had 123 sets and 140 s).

started_at  2026-10-26 09:05:15.669 ET
deadline    2026-10-26 09:07:40.669 ET   (145 s)
answers     128
start        125 ms after started_at
artifact     779 ms after started_at
solve       1189 ms after started_at   (410 ms)
submit      2057 ms after started_at
result      CORRECT   flag 1c6884ef…7f39   (09:05:17.007)

All 128 answers had the plain slug form: no Mastery blob had a trailer today, so the full-trailer answer form added after Day 25 is still unconfirmed. No retries, no rejected values, no rate limit. Afterwards this solver became our default Warmups solver for the following days.

Time to solve

All three modes were solved by 09:05:17 ET, 5 min 17 s after release (4 min 23 s from the first start request on this lane). The Single Solve was decoded by hand at 09:02:20; the Time Trial and Mastery were both ranked and each went through on the first submit.

Takeaways

The new layer is still the slowest part of a Warmups morning. Day 25's code points took 2 min 37 s from the first start; today's Brainfuck took 4 min 23 s, most of it building and testing the bounded interpreter rather than the decode.
Hand first, reader second. The Single went in at 09:02:20 by hand, about 1 min 26 s after the stop; the reading was built and rehearsed afterwards, so both ranked runs were first attempts.
Stopping was right. The solver's searches found nothing and it sent nothing.
A language is not an encoding: bound it. A Brainfuck reading is an interpreter, so it needs a step cap, a tape limit, and bracket checks, and it must refuse input (,). Treated that way, it is as safe as any other decoder.
Test multi-line blobs per line. A program run over the whole blob carries the cell from line to line; the first test run caught it (9/10), and per-line programs are now always tried.
Add every new layer to the strict per-line list as well. Today's line 26 entry means a trailer on that line won't be left out. No trailer came today, so that form is still waiting for its first confirmation.
Next pre-builds: other tiny esoteric languages with plain-text output (Brainfuck variants that swap the command characters, Ook!, whitespace-only programs), as strict, bounded readings.