Etherify 5 – switching the switches

Recently i’ve published:

Etherify – bringing the ether back to ethernet

Etherify 3 – the PI 4’s dirty little secret

Etherify 4 – back to earth with “normal” ethernet hardware

please read these articles first, before reading this one.

Etherify 4 used ethernet interfaces from two air-gapped laptops connected together via ethernet to transmit information via radio.

Etherify 5 uses two Linksys LGS318 switches connected together.  The intra-switch  link speed is changed via SNMP via the script. Changing the speed to 100Mbit/s results in a detectable signal around 50MHz, while changing to 10Mbit/s turns off this signal.

This demonstrates that network devices can also be used to exfiltrate data from air-gapped networks. The particular network device and port can be selected based upon being close to an attacker, or having hardware that radiates more etc (such as out-of-spec ethernet cables).

Other frequencies might yield a better signal, however 50MHz was near amateur radio frequencies, and was selected because i already had antennas  and other equipment for this band. The frequency is dependent on the actual hardware being used, always check a wide band of frequencies, previously i’ve found strong enough signals in the 125MHz-625MHz range (this extends it down to 50MHz, and probably lower).

Modulation is done via slow morse code (QRSS CW).

Transmit setup

Two Linksys  LGS318 connected via ports 17 using a 1m ethernet cable were used to transmit. uses a default factory config.

The has autonegotiation on the transmitting port disabled (port 17):

CLI v1.0
set system
voice vlan oui-table add 0001e3 Siemens_AG_phone________
voice vlan oui-table add 00036b Cisco_phone_____________
voice vlan oui-table add 00096e Avaya___________________
voice vlan oui-table add 000fe2 H3C_Aolynk______________
voice vlan oui-table add 0060b9 Philips_and_NEC_AG_phone
voice vlan oui-table add 00d01e Pingtel_phone___________
voice vlan oui-table add 00e075 Polycom/Veritel_phone___
voice vlan oui-table add 00e0bb 3Com_phone______________
hostname switcheca015
snmp-server server
snmp-server community public ro view Default
snmp-server community private rw view Default
interface vlan 1
ip address
no ip address dhcp
interface gigabitethernet17
speed 10
no negotiation

Receive setup

A laptop running gqrx and an usb rtl-sdr receiver was used. The gqrx output was connected via pulseaudio to DL4YHF Spectrum Lab running under wine. Spectrum Lab is used to display a high resolution spectrogram. The receiver used a 50/144/432MHz whip antenna from Yaesu FT817, because it was avaliable.

Deluxe mobile TEMPEST receiver
Deluxe mobile TEMPEST receiver


Changing the interface speed will result in changing the signal radiated by the interface.

This is the signal at 5m distance at 50MHz:

The above spectrogram shows part of the message being sent (“etherify 5 demo”).


While the previous etherify demos used Raspberry PI 4 and laptops,  this shows that it is possible to run etherify from network hardware, such as an ethernet switch. The Linksys LG318 switch is not a big enterprise switch, but is pretty well designed to not cause interference (good shielding etc).

When trying this on other hardware, please check as much spectrum as possible to find the leaked signal (at least from 10MHz to 1GHz). The best frequency is not always obvious, and depends how the device generates it’s clocks internally, which frequencies will leak out more etc.

Using network infrastructure hardware enables transmission of data from an interface that is closer to the receiver, or radiates better (due to asymetry in the ethernet cable, bad hardware etc).

The “software” side is intentionally a very primitive silly hack.

Happy air-gap jumping 🙂

If you cite this, please include the webpage address and attribute Jacek Lipkowski (SQ5BPF). Email can be sent to my_callsign @ this_domain.