glitch — TJCTF 2026

Description

Do not resist the g̵͕̗͑̅l̶̢̂̚ḭ̶̐͗t̴͔̞̒͐c̸̭͈̄h̷̨̞͊͠. Wrap flag in tjctf{}

A PNG image (1920×1080, 8-bit palette mode, 156 colors) showing a glitched test pattern with horizontal color bands and heavy noise/glitch artifacts overlaid. The goal is to extract the flag hidden in the color pattern.

Analysis

The image contains horizontal color bands spanning the width of the image, overlaid with significant noise and glitch effects. Several rabbit holes exist:

1. Stego analysis — LSB extraction, bit-plane analysis, palette index manipulation all yield nothing meaningful.
2. Block-based extraction — Averaging 16×16 RGB blocks produces printable ASCII streams in a wedge-shaped region, but these don't decode to anything useful via Ascii85/Base85/BasE91.
3. Channel difference streams — R-B and G-B differences over the wedge region show structured alphabets (32 and 16 distinct symbols respectively), but no valid encoding was found.

The key breakthrough comes from the challenge description: "Do not resist" is a wordplay on "resistor". The horizontal color bands represent resistor color codes.

Resistor Color Code Mapping

The standard resistor color code assigns digits 0-9 to colors:

Color	Digit
Black	0
Brown	1
Red	2
Orange	3
Yellow	4
Green	5
Blue	6
Violet/Purple	7
Gray	8
White	9

The image contains 28 horizontal color bands (not 13 as it appears at first glance — thin bands can be missed due to the noise overlay and aggressive denoising merging them with neighbors). These 28 bands are read in pairs, where each pair forms a two-digit decimal number that maps to an ASCII character.

Solution

Step 1: Identify the 28 color bands

Careful segmentation of the image (avoiding aggressive median filtering that merges thin bands) reveals 28 distinct horizontal color bands from top to bottom.

Step 2: Map band pairs to ASCII

Pair	Color 1	Color 2	Digits	Decimal	ASCII
1	Blue	Gray	6, 8	68	D
2	Green	Brown	5, 1	51	3
3	Gray	Orange	8, 3	83	S
4	Yellow	White	4, 9	49	1
5	Violet	Brown	7, 1	71	G
6	Violet	Gray	7, 8	78	N
7	Yellow	Orange	4, 3	43	+
8	Gray	Yellow	8, 4	84	T
9	Blue	White	6, 9	69	E
10	Blue	Violet	6, 7	67	C
11	Violet	Red	7, 2	72	H
12	White	Green	9, 5	95	_
13	Green	Gray	5, 8	58	:
14	Yellow	Brown	4, 1	41	)

Result: D3S1GN+TECH_:)

Step 3: Solve script

#!/usr/bin/env python3
"""
TJCTF 2026 - glitch
Resistor color code decoding from horizontal color bands in a glitched PNG.
"""

# Standard resistor color code: color -> digit
digits = {
    "black": "0", "brown": "1", "red": "2", "orange": "3",
    "yellow": "4", "green": "5", "blue": "6", "violet": "7",
    "gray": "8", "white": "9",
}

# 28 bands read top-to-bottom, grouped into 14 pairs
pairs = [
    ("blue", "gray"),      # 68 -> D
    ("green", "brown"),    # 51 -> 3
    ("gray", "orange"),    # 83 -> S
    ("yellow", "white"),   # 49 -> 1
    ("violet", "brown"),   # 71 -> G
    ("violet", "gray"),    # 78 -> N
    ("yellow", "orange"),  # 43 -> +
    ("gray", "yellow"),    # 84 -> T
    ("blue", "white"),     # 69 -> E
    ("blue", "violet"),    # 67 -> C
    ("violet", "red"),     # 72 -> H
    ("white", "green"),    # 95 -> _
    ("green", "gray"),     # 58 -> :
    ("yellow", "brown"),   # 41 -> )
]

message = "".join(chr(int(digits[a] + digits[b])) for a, b in pairs)
flag = f"tjctf{{{message}}}"
print(flag)
# tjctf{D3S1GN+TECH_:)}