day 14 - Tiny Runes

One of Santa's Little Helpers received an unusual Christmas wish, a copy of the yet to be released Deus Hex game. All they managed to find were fragments from the dialogue system. Can you decode the last one?

Download: advent2019-tiny-runes.tar.gz

Recon

We are provided the following files:

-rw-r--r--   1 spotless  spotless   965 Nov 29 00:17 lines1.bin
-rw-r--r--   1 spotless  spotless   399 Nov 29 20:55 lines1.png
-rw-r--r--   1 spotless  spotless    74 Nov 26 01:30 lines1.txt
-rw-r--r--   1 spotless  spotless  1161 Nov 29 00:45 lines2.bin
-rw-r--r--   1 spotless  spotless   834 Nov 29 20:55 lines2.png
-rw-r--r--   1 spotless  spotless   166 Nov 26 01:31 lines2.txt
-rw-r--r--   1 spotless  spotless  1033 Nov 29 00:45 lines3.bin
-rw-r--r--   1 spotless  spotless   616 Nov 29 20:55 lines3.png
-rw-r--r--   1 spotless  spotless   108 Nov 26 01:31 lines3.txt
-rw-r--r--   1 spotless  spotless   985 Nov 29 00:45 lines4.bin

lines4.bin does not have a .txt and .png version, we are most likely suppose to generate those ourselves.

File structure

File starts with a TiNyMeTa header and also seems to contain a PNG:

00000000: 5469 4e79 4d65 5461 0000 0010 0000 0002  TiNyMeTa........
00000010: 0008 0008 080c 0052 0002 0034 5478 5472  .......R...4TxTr
00000020: 0000 0301 8950 4e47 0d0a 1a0a 0000 000d  .....PNG........
00000030: 4948 4452 0000 0040 0000 0060 0103 0000  IHDR...@...`....
00000040: 0097 0be6 ab00 0000 0650 4c54 4500 0000  .........PLTE...
00000050: f0d1 c563 8e08 7e00 0002 b649 4441 5478  ...c..~....IDATx
00000060: da25 5241 641c 6114 feb6 7da6 1123 62c5  .%RAd.a...}..#b.
00000070: fa0f 2b5d 6bc5 1a3d 8c88 556b b322 a71c  ..+]k..=..Uk."..

Extracting it gives us a mapping of characters:

tail -c +37 lines4.bin > chars.png

LiNe

At the bottom of the .bin file, we can observe:

00000310: 0707 9205 d0b7 2b6c e400 0000 0049 454e  ......+l.....IEN
00000320: 44ae 4260 824c 694e 6500 0000 3c05 0101  D.B`.LiNe...<...
00000330: 0b05 0607 0102 0704 0806 0704 0500 0904  ................
00000340: 0804 0205 0704 0801 0601 0b01 0305 0804  ................
00000350: 0805 0103 0a05 0804 0807 0404 0806 0205  ................
00000360: 0b03 0b01 0705 0806 074c 694e 6500 0000  .........LiNe...
00000370: 6805 0103 0a04 0806 0903 0700 0500 0a01  h...............
00000380: 0b00 0502 0704 0806 0707 0404 0806 0205  ................

Where LiNe is (possibly) locations to the chars found in the extracted PNG file.

We assume: LiNe<payload length><x,y><x,y><x,y>

Code

import struct

f = open("lines4.bin", "rb")
bindata = f.read()
f.close()

# from PNG
charmap = """
Q?0\\H$Y,
R-L^KJ*k
s#_/m=f9
7d-NE4qr
Pi*v`&XA
n3I'0*;Z
wGpB8cSj
Fg:eby"v
%+ 1 !M@
h{2xW.D}
tUICTz6u
Io>a5l<\'
""".strip().split("\n")

spl = bindata.split(b"LiNe")
flag = ""

for segment in spl[1:]:
    payload_length = struct.unpack(">L", segment[:4])[0]
    data = segment[4:][:payload_length]
    coords = [(ord(data[z]), ord(data[z+1])) for z in range(0, payload_length, 2)]

    for x, y in coords:
        char = charmap[y][x]
        flag += char

print(flag)

Output:

Jock: "0h my God! JC! A flag!"
JC Denton: "A flag! A0TW{wh4t_4_r0tt3n_fi13_f0rm4t}"

Flag

A0TW{wh4t_4_r0tt3n_fi13_f0rm4t}