Description

[Printer] - 30 points
The UFO was forged on one of the universe's most advanced printers - do you know which make and model? Enter the answer as Make Model.

[Layer by Layer] - 70 points
Do you know how GCode files work? Maybe you can find a hidden message along the layers. Flag format: CTF{answer}

Introduction

Well, what do we have here? The file I am given is called unidentifi3d.gcode. But first, what even is a .gcode?

Phew, turns out that it isn't some challenge-specific code; it is code used in manufacturing. An important snippet from this article:

The G-code commands instruct the machine where to move, how fast to move, and what path to follow.

Great! My first guess is that this gcode would "draw" out the flag for me.

Solving the challenge: Part 1

After a little Googling, I found this website that can help read this code. Dumping the code in the website gave me this weird drawing:

At the bottom of the page, there are sliders. Sliding back and forth, I catch a glimpse of this:

I see the word Flying_sau. Is that short for Flying_saucer? Let me try that.

Oh, it unexpectedly worked. Looks like this is the key for the second part of the challenge.

Flag: CTF{Flying_saucer}

After doing a little research, it turns out that the sliders indicate layers of scaffolding. Interestingly, 3D printers print objects by stacking 2D layers upon layers till the 3D object is created. As it turns out, one of the layers happens to be the flag. Now to solve the first part of the challenge.

Solving the challenge: Part 2

The first challenge asks for the make and model. To summarise this article:

• Make: Who is the manufacturer of the product? [Apple]
• Model: What is the product? [Iphone X]

Looking at the end of the .gcode file, I find this:

;SETTING_3 {"global_quality": "[general]\\nversion = 4\\nname = Extra Fast #2\\n
;SETTING_3 definition = geeetech_A10M\\n\\n[metadata]\\ntype = quality_changes\\
;SETTING_3 nsetting_version = 16\\nquality_type = verydraft\\n\\n[values]\\nsupp
;SETTING_3 ort_enable = True\\n\\n", "extruder_quality": ["[general]\\nversion =
;SETTING_3 4\\nname = Extra Fast #2\\ndefinition = fdmprinter\\n\\n[metadata]\\
;SETTING_3 ntype = quality_changes\\nsetting_version = 16\\nposition = 0\\nquali
;SETTING_3 ty_type = verydraft\\n\\n[values]\\n\\n", "[general]\\nversion = 4\\n
;SETTING_3 name = Extra Fast #2\\ndefinition = fdmprinter\\n\\n[metadata]\\ntype
;SETTING_3 = quality_changes\\nsetting_version = 16\\nposition = 1\\nquality_ty
;SETTING_3 pe = verydraft\\n\\n[values]\\n\\n"]}

I have a hunch that this metadata contains the model which "manufactured" the flag.
Great! As it turns out, geeetech A10M is the name of the model.

Flag: geeetech A10M

Interesting things to note

• This may be the first flag I have found that contains a space instead of an underscore
• I just want to acknowledge the little inside joke that the admins were trying to reference. Because who built the pyramids?