Ph0wn 2018 - Wanna drink? Move your arm!

Category: Prog

Challenge description

In these challenge we were provided with an SSH access to a Lego robotic arm. We used Python in our solution, but a different approach is available on Duks’ blog.

Ph0wn aliens have abducted my coke and put it in the fridge. But, now, I am thirsty. Open the door with the robotic arm, and you will get a free coke … and a flag! Fortunately, the aliens have left a few instructions in case they would format their internal memory.

• You first must request access to the robot by giving your IP address, one team at a time. Then you can connect to the robot on ph0wn2018-robot with IP address 10.210.17.146
• Once connected, you must make a program to move the arm and open the door. The door must rotate of 180 degrees to get the can. Knocking down the fridge is prohibited (you must get the can without destroying the fridge, you vandals!)
• The flag is NOT in the robot system, it is printed on the coke can. Oh, by the way, a very powerful lazer beam will strike your own computer if you were to erase to content of the system, or if you get the can without using the robotic arm. Last but not least, they have noted the login/password on a post-it just next to the printed manual:
• Login: robot
• Password: maker The flag has the usual format.

Author: ludoze

Challenge resolution

Once connected to the device, we had to identify what to do. A quick Google search showed that such kind of robot can be managed using Python scripting with the ev3dev package. Fortunately, we had a Python interpreter installed on the robot with the ev3dev package.

After taking a look at the ev3dev documentation, we were able to call the ev3dev.core.list_motors() function to retrieve the names of the three motors available on the robotic arm. A first one for up/down movement, a second for rotation and the last one managing the pinch.

There are many ways to move a motor. We decided to use a function which moves the motor for a certain duration at a certain speed:

from ev3dev.core import *

motor = Motor('motor_name')
motor.run_timed(time_sp=300, speed_sp=-750)

And it moved!

Note that the sense of rotation can be changed by setting speed_sp to a negative or positive value.

Then we just had to move the robotic arm until we were able to open the fridge

Author: @Crypt0_M3lon

Post date: 2018-12-17