We are given a binary file that asks for the correct pin. One the hints suggests us to read about [timing attacks](https://en.wikipedia.org/wiki/Timing_attack) and i did.

What the program is doing is comparing each character of the correct pin and the user input, the moment a character is wrong the program stops, which allows this kind of attack.

So for example if pin = 12345678
we can guess the right numbers by checking the time it takes
for the program to run
0000000 -- took 10ns the character is wrong and stopped.
1000000 -- took 100ns compared the character and its right.
1100000 -- took 100ns compared the first character but stopped at the second.
1200000 -- took 200ns compared both characters and found they are right.

The time increases for each right character.

I wrote a shell script to generate each number and to show the time it took to execute the program, but i couldn't make it completely automatic so i still had to add the right number to the program.

for i in {0..9}
echo $pin
time ./pin_checker <<< $pin
Once the execution was finished i checked for the iteration with the highest user time value and added that number to the pin variable, after doing that 8 times i ended up with this pin **48390513**.

❯ nc saturn.picoctf.net 52680
Verifying that you are a human...
Please enter the master PIN code:
Password correct. Here's your flag:

Original writeup (https://github.com/DoomHackCTF/WriteUps/tree/main/picoCTF2022/Forensics/SideChannel).