Can a powerline network adapter be more easily used to listen to traffic on another router?

Question

A roommate of mine asked me to connect a powerline adapter to the network. The ethernet cable of the adapter is connected to an Apple Airport Express router which is connected to a Frontier Internet cable modem. I have another router from Frontier connected to the Frontier Internet cable modem.

Adapter > Airport > ISP Cable Modem > ISP router

However all of the electric plugs for everything are plugged into a multi-outlet surge protector which in turn is plugged into the powerline adapter, and the powerline adapter is plugged into the home's wall outlet.

So since my rudimentary understanding of a powerline adapter is that they use the electricity to transmit data, my question is does the person with the receiving end of the powerline adapter connection have an "easier" time sniffing traffic of a person connected to the Frontier router? (let's assume the person is practicing good wifi security and has a strong password, etc.). Mostly I'm worried by plugging the Frontier router power plug into the surge protector which in turn is plugged into the powerline adapter, I'm not really keeping the traffic "separated" and the roommate on the receiving end of the powerline adapter now will be able to "easily read" the traffic data going into/from the Frontier router.

Answer 1

You are missing a key detail: devices do not transmit data on the powerline unless designed to. So just plugging in does not expose data on the power line.

Answer 2

Does the person with the receiving end of the powerline adapter connection have an "easier" time sniffing traffic of a person connected to the Frontier router?

Not if the person on the receiving end is using encryption. If the user connects to all web sites that he/she visits using SSL/TLS (and the same when using IMAP, POP3, SMTP, etc., for email, and similar for any other services that they are using) then traffic cannot be easily sniffed regardless of the transport layer being used - be it powerline adapter, ethernet, wifi, or other.

Answer 3

The powerline adapter is plugged into a switch port on the airport. Since it's a switched port, only traffic destined for the powerline adapter segment would pass... plus some broadcast-type traffic.

If your PC is connected to a different port on the airport, or is connecting via WiFi, it's unlikely traffic would be sent to the switch ports where your roommates PC is connected via powerline adapter.

Sniffing traffic on the powerline adapter would only show corresponding traffic sent to the connected port on the airport. It would not be all traffic that the airport is handling.

Also, someone on the powerline... or the airport... can't sniff traffic on the frontier router. They can only sniff traffic that hits their local interface. If they wanted to sniff traffic on the frontier router, they would have to be connected to the frontier router and have low-level access to sniff everything it's kernel is passing... unlikely scenario in most consumer/home router environments.