Hw - Serial logs
For this challenge, we have a Saleae Logic project export. Giving the name of the challenge, and the channel 1, we will use the serial Async
with the default settings:
Some logs appear then in the console:
[...more logs...]
[LOG] Connection from 6edec472e9754574d91f460e170b825bacee5f121b73805dffa4f2a5a7d23d7f
[LOG] Connection from 316636cf0500c22f97fa261585b72a48c4625aca7868f0f6ee253937620ac15c
[LOG] Connection from 4b1186d29d6b97f290844407273044e5202ddf8922163077b4a82615fdb22376
[LOG] Connection from 4b1186d29d6b97f290844407273044e5202ddf8922163077b4a82615fdb22376
[LOG] Connection from 4b1186d29d6b97f290844407273044e5202ddf8922163077b4a82615fdb22376
[ERR] Noise detected in channel. Swithcing baud to backup value
And after this error, there is garbage on the console output. This last message teach us that the channel baud has been changed from 115200
to some unknown value. After tried some common default values without success, we will try to figure out the baud by analysing the capture.
For this, we first take a charactere that could be found in the damaged communication.
So the timing for the first bit of communication is 8.48μs
.
We then compute \( f = \frac{1}{8.48\times 10^{-6}}\) where f is the baud value of the communication (which is roughly like a frequency)
We then measure the timing of the next first bits. We found a timing of 13.46μs
. So by trying the same computation that above, we find a baud of 74294
. Trying this setting, the flag appears at the end of the logs.