Cyber Apocalypse 2021

Serial Logs

Solved by : Nigamelastic

• .sal files are saleae logic analyzer files.
• I got this as reference https://dystopia.sg/allesctf20-PWNkemon/ so i downloaded the sla logic analyzer https://www.saleae.com/downloads/
• from here after installing, i opened the sal files which i could and then the following:
• I imported the value i am pretty sure if i find the right analyzer it should work

• by far for this challenge async serial works the best
• challenge states raspberry pi which has a baud rate of 115200
• after some pondering i realized that there are some errors in parity on fixing them and using the 115200 in async serial we get the hex converting which gives us this:

https://www.dropbox.com/s/ztqoa16wvp6rvf6/message.txt?dl=0

• found this : https://6e726d.github.io/Challenge/Ekoparty15/
• this writeup explains how to get the baud rate
• open the SAL file and zoom

• zoom

• zoom

• zoom

• until you see the smallest unit of the digital wave then measure it: as its 13.498

• since it is in μ we will divide it by 1000000
• so 1000000/13.498 = 74085.049637
• I obviously used 74000 as bit rate, converted the hex to ascii with the tool itself and it gave me the flag:

CHTB{wh47?!_f23qu3ncy_h0pp1n9_1n_4_532141_p2070c01?!!!52}