Virtual Machine 0

~# cat Question

Can you crack this black box? We grabbed this design doc from enemy servers: Download. We know that the rotation of the red axle is input and the rotation of the blue axle is output. The following input gives the flag as output: Download.

FILES: Virtual-Machine-0.zip, input.txt

Unzipping Virtual-Machine-0.zip, gives us Virtual-Machine-0.dae. We can open a COLLADA file using blender. Using the tools in blender, we can dismantle the items around to reveal the two red and blue gear.

The challenge description told us how to get the flag. We need to see how many times the red gear goes around the blue gear. The driver gear (the bigger one) has 40 teeths, while the driven gear (the smaller one) has 8 teeths. So, if the driver gear makes 1 rotation, the driven gear will make 5 rotations. Multiplying this number in python with input.txt, converting the value to hex and then ASCII yields the flag.

x = 39722847074734820757600524178581224432297292490103995916782275668358702105
x = x * 5
hex_x = hex(x)
flag = bytes.fromhex(hex_x[2:]).decode('ascii')
print(flag)

Flag: picoCTF{g34r5_0f_m0r3_5ca97824}