BendBright and Cyber Security

How to tap optical fibres and how to prevent data breaches Optical fibres guide light within their core using the principle of total reflection. A fibre consists of a central ‘core’ where the light propagates, surrounded by optical cladding acting as a mirror to keep the light within the core. In telecommunications, the vast majority of deployed fibres (>60%) are single-mode fibres called ‘standard’, complying with the international ITU-T standard for transmission fibres – G.652.D. Such fibres exhibit optimum bandwidth and transmission characteristics to allow the optical systems connected at their extremities to virtually transport an unlimited data capacity as system generations evolve. (Hundreds of laser channels were each able to carry 10 Gbit/s 10 years ago, then 40 Gbit/s, then 100 Gbit/s and now 400 Gbit/s, and soon more). These G.652.D standard single-mode fibres were initially developed and introduced for long-distance and straight links, making them intrinsically sensitive to bending effects. Put simply, when bent, such fibres leak some light outside of their guide (see Figure 2), which hackers can exploit to tap transmitted signals. They capitalise on this weakness of G.652.D fibres under bend, using very simple tools to create a small bend in the fibre to extract the light and redirect it to the attackers’ computers on a diverted route through a coupler (see Figures 1a and 1b). Cladding Total reflection Core Figure 2 Figure 1b fewmm Coating (typ. 250, 200, or 180µm) Jacket Cladding Active fibre optic cable Lost light <1% Optical photo detector 1 Bend tapping device 2 Optical- electrical converter 3 Laptop 4 Figure 1a