speeds_and_feeds.md

speeds and feeds

• Challenge information
• Solutions
• References

Challenge information

Points: 50
Tags: picoCTF 2021, Reverse Engineering
Author: RYAN RAMSEYER

Description:
There is something on my shop network running at nc mercury.picoctf.net 59953, but I can't tell what it is. 
Can you?

Hints:
1. What language does a CNC machine use?

Challenge link: https://play.picoctf.org/practice/challenge/116

Solutions

Analyze the output

We start by connecting to the service and watch the output

┌──(kali㉿kali)-[/mnt/…/picoCTF/picoCTF_2021/Reverse_Engineering/speeds_and_feeds]
└─$ nc mercury.picoctf.net 59953
G17 G21 G40 G90 G64 P0.003 F50
G0Z0.1
G0Z0.1
G0X0.8276Y3.8621
G1Z0.1
G1X0.8276Y-1.9310
G0Z0.1
G0X1.1034Y3.8621
G1Z0.1
G1X1.1034Y-1.9310
G0Z0.1
G0X1.1034Y3.0345
G1Z0.1
G1X1.6552Y3.5862
G1X2.2069Y3.8621
G1X2.7586Y3.8621
G1X3.5862Y3.5862
G1X4.1379Y3.0345
G1X4.4138Y2.2069
G1X4.4138Y1.6552
G1X4.1379Y0.8276
G1X3.5862Y0.2759
G1X2.7586Y0.0000
<---snip--->

A LOT of output in some unknown format. Let's save the output in a local file

┌──(kali㉿kali)-[/mnt/…/picoCTF/picoCTF_2021/Reverse_Engineering/speeds_and_feeds]
└─$ nc mercury.picoctf.net 59953 > speeds_and_feeds_output.txt

Now it's time to research what kind of format this is...
It looks like it is something called G-code.

Next, we need to find an online interpreter for it. NC Viewer is one.

Get the flag

In NC Viewer, click on the New File icon and paste in the output from the speeds_and_feeds_output.txt file above.
Then click the PLOT button.

The result should look something like this:

Zoom out and re-position the grid and you have the whole flag.

For additional information, please see the references below.

References

• Wikipedia - G-code