One of the WCTF SDR challenges at Shmoocon 2014 involved decoding an ICMP packet that had been converted into base64. The end goal is to get to doing live tcpdump capture via SDR and using the PiFM as the x-mitter, much like a remote bug would exist. In preparation for future cons, here is how you can replicate something simple for now.
#install tcpdump and minimodem
apt-get install tcpdump minimodem
#start grabbing packets in 10 second intervalstimeout 10 tcpdump -A'port not 22' | minimodem --tx-f-8 1200 -f send.wav && ./pifm send.wav 80.0
#shutdown the x-mittouch /tmp/empty && /home/pi/pifm /tmp/empty
What’s Happening
Here, we’re simple capturing all ASCII characters that tcpdump has grabbed, kicking it out to minimodem and then transmit. Simple enough. For the reception, and if you’re lame like me (using Ubuntu), you can use the following commands to demod it.