Un courrier suspect
In this challenge, we are given this CIRC file. By looking on the internet, I found that the tool Logisim could open such files. When we open the file we get this:
So we go to the first part and now we have the first part of the flag 404CTF{L3_:
We now go to the second section:
The second and third sections are linked, so we look at what we have in the third section:
We need to fill the matrix with the entry of the Multiplexer of the part 2 by order of their arrival in the multiplexer. Here is an example of the first four:
So the final hexadecimal values we need to set in the matrix are 4d 30 6d 33 6e 54 5f 33 53 74 5f 56 33 6e 55 33. We can now spam the CTRL+T to tick several times, and the text field completes itself:
We now have the second part of the flag M0m3nT_3St_V3nU_.
We now go to the 4th part:
As we can see, it’s like in the second part, so in the black box of the part 4 i just re-created the part 3 and set the input in the same way we did earlier. This time the hexadecimal string is 44 33 5f 35 34 6d 75 73 33 72 7d:
As we did previously, we tick the clock with CTRL+T and we get the last part of the flag:
The last part of the flag is _D3_54mus3r}.
The final flag is 404CTF{L3_M0m3nT_3St_V3nU_D3_54mus3r}