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Are fiber optics secure?

One of today’s topics at Nato´s on-going cyber symposium in Mons, Begium, was interception possibility of fiber optic networks.

An optical fiber is a flexible and transparent fiber made by glass or plastic with a diameter comparable to that of a human hair. Optical fibers are used to transmit light between the two ends of the fiber and are used in fiber-optic communications over long distances and at high bandwidth.

There still seems to be an idea among different parties that fiber optics should be considered ”secure” in terms of eavesdropping. Nothing could be more wrong. For more than a decade by know, the knowledge about fiber tapping has been widely spread. For instance, a vast amount of data from undersea cables, or you could say the Internets ”backbone”, has been tapped for a long period by the powerful intelligence agencies – verified by leaked Snowden documents.


fiber optics


Basically four different fiber tapping methods applies

Fiber bending

An optical detector is put on the cable that has to be bent as much as possible. Only 1% of the signal strength is lost due to the bending, and transmission will not be disturbed, because of the high transmission margins. An alternative to bending is to use a fiber clamp attached on the straight fiber. They are commercially available and the cost is below 1000 US dollar.


Evanescent coupling

Requires access to the actual fiber optic transmitter, but the cost for the device is very low and signal loss is kept to a minimum.


V-groove cut

A physical cut in the optical fiber is performed to get access to the light in the core. However this is a risky method because of the sensitive nature of the fiber.



The fiber´s light could be reflected in other directions as well, by affecting the fiber with a strong laser, meaning that you don´t even have to get direct contact with the fiber.

In many cases the reason for a short break in connectivity will never be investigated, meaning that there is a low risk of detection when compromising the fiber optics. ”It fixed itself” is a good enough approach for many ISP´s, instead of trying to figure out what really happened.

So, different interception techniques for fiber optic networks are a reality. The question then is how to protect the valuable data.


Cable surveillance and monitoring

Cable surveillance and monitoring with different methods is a possibility. However, the accuracy of the results will depend on natural variations like bending angles of the fiber, temperature in the ground and which mode the transmitter was working on.

The only way to be sure about the integrity of the data transmitted over the fiber optic network is – as always – to use accurate end-to-end encryption. From a trusted vendor.

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