# BSidesSF CTF 2017 - Latlong (Forensics 150)
>Transmission Received.
>This challenge was created by our pal @arirubinstein.>He was not informed of the flag format, so expect this one to be look something like flag{...}
The file seems to be an audio file and at first I thought it was a 56Kbps "Dial-up modem noise" (who used to connect to the Internet some years ago, will definitely remember).
But luckily, shortly after the admins posted an hint:
>Hint - "Ax25 will lead you in the direction"
AX.25 (Amateur X.25) is a data link layer protocol suite and designed for use by amateur radio operators.
So it was clear that we had to decode the file using the protocol [specification](https://www.tapr.org/pub_ax25.html).
I started reading the protocol specification, and I was going to implement a decoder, but I was sure I could find something already implemented.
I found this decoder on GitHub: [Invasive](https://github.com/h2so5/Invasive)
And opening the file audio with this decoder showed the flag:
![flag](./latlong.png)