A US engineer has devised a seemingly foolproof and cheap way to encrypt messages using the natural noise caused by electrons flowing along a wire.

Data messages can be sent intermittently and camouflaged by this 'thermal noise'. It appears to be better than quantum key distribution (QKD) technology.

The engineer is Laszlo Kish of US-based Texas A&M University. In his plan the sender and receiver both have the same pair of resistors attached to the physical cable; one produces a high resistance, the other a low one. As a voltage passes along the wire so-called thermal noise is generated and its amount varies with the resistance on the wire.

At either end of the line fast random choices of resistor are made and a monitor at the other end detects high or low noise if the resistor at that end is the same. A medium noise level is detected if different resistors are chosen at each end. This happens one half of the time and single digit messages can be sent in this period. The message is a binary one or zero depending upon which end is reading the message and whether its resistor choice is high or low, meaning the choice at the other end is the opposite, which signals '1' or '0'.

To snoopers eavesdropping on the line it just appears that the thermal noise level varies randomly. If they do realize that medium noise levels signal a message they don't know the binary digit value because they don't know the resistor setting at either end of the line. Thirdly, the very act of tapping the line alters the thermal noise level so the fact of the eavesdropping is detectable. It seems almost ridiculously simple and secure.

A prototype device has been built by Kish and his team. With its 99.98 percent message reception accuracy and 2000 kilometre distance QKD technology is out-performed. The team calculated that fewer than one two thousandth of the bits sent were actually vulnerable to snoopers.

QKD technology is based on optical fibres carrying photons between quantum encryption devices. Device message reception accuracy is adversely affected by vibration, heat and dust, and they are much more expensive than the estimated $US100 of a Kish device.

QKD technology has been proposed as a highly secure way of sending encryption keys between parties wishing to send and receive data securely. Kish technology appears to have the edge and, if it is fast enough, might even be used for sending the raw data itself.