CTFs | FCSC2023 | Intro | Comparaison

Context

We are given:

• the code of the machine (machine.py)
• a code to translate the assembly code into hex format in order to send it to the server (assembly.py)
• the code present on the server (challenge.py)

This challenge is an introduction to assembly code. The harder was to understand the syntax of the asm code they created.

Here is the python code I created:

from assembly import assembly

# create the assembly code
code = """
CMP R5, R6
JNZA different
MOV R0, #0x0
JA end


different:
    MOV R0, #0x1

end:
    MOV R0, R0  // instruction inutile pour éviter un "warning"

STP
"""

# create the assembly object
asm = assembly(code.split("\n"))

print(asm)

R5 and R6 contains the 2 values that we have to compare.

We compare the two values. If they are equal, we set the value of R0 to 0 and jump to the end.

If they are different, we jump to the label “different” and set the value of R0 to 1.

Let’s look at the output:

It seems that our code has been translated to hex without problem.

Let’s send it to the server:

One more flag 🙂!