Matryoshka doll

Problem

Matryoshka dolls are a set of wooden dolls of decreasing size placed one inside another. What's the final one? Image: this

• Image

Solution

1. The problem suggests files places inside of other files, so let's run binwalk dolls.jpg.

   DECIMAL       HEXADECIMAL     DESCRIPTION
   --------------------------------------------------------------------------------
   0             0x0             PNG image, 594 x 1104, 8-bit/color RGBA, non-interlaced
   3226          0xC9A           TIFF image data, big-endian, offset of first image directory: 8
   272492        0x4286C         Zip archive data, at least v2.0 to extract, compressed size: 378956, uncompressed size: 383938, name: base_images/2_c.jpg
   651614        0x9F15E         End of Zip archive, footer length: 22

   Sure enough, there are several files.

2. We can extract the files by running binwalk --dd='.*' dolls.jpg and then cd _dolls.jpg.extracted.

3. After some trial and error, the correct solution is to extract the zip file, cd base_images, and then repeat step 3 on 2_c.jpg.

4. Now that you are in _2_c.jpg.extracted, extract the zip file and repeat step 3.

5. Repeat the above steps of extracting and binwalking until you end up at this path: _dolls.jpg.extracted/base_images/_2_c.jpg.extracted/base_images/_3_c.jpg.extracted/base_images/_4_c.jpg.extracted/136DA-(1). There is a flag.txt file in this directory that contains the flag.

Flag

picoCTF{336cf6d51c9d9774fd37196c1d7320ff}