Fibre-optic cables may be used to eavesdrop up to 1km away, study says


21st Century wire tap? Spies could use fibre-optic broadband cables to EAVESDROP on people from over half a mile away, study shows

  • Scientists have developed a system that picks up sound from fibre-optic cables 
  • Fibre-optic cables use light pulses to transmit data and are used for broadband
  • But they are sensitive to changes in environmental pressure caused by sound
  • This security flaw may let snoopers eavesdrop on confidential conversations

Fibre-optic cables could be used to eavesdrop on people over half a mile away by detecting changes in light that occur when they speak, a new study shows. 

Researchers in China have developed a system that picks up sound at one end of a fibre-optic cable and transmits the audio at the other end. 

Fibre-optic cables use pulses of light to transmit data and are used to deliver full fibre broadband to people’s homes. 

But they’re sensitive to changes in environmental pressure, which could be caused by acoustic waves, such as sound from someone speaking – a potential security risk.

Modern fibre optic cables, which use pulses of light to transmit data, deliver full fibre broadband (file photo)

The new study was conducted by researchers at Tsinghua University, Beijing and published on the pre-print server arXiv. 

‘Optical fibre networks are widely deployed all over the world, which not only facilitates data transmission but also provides an opportunity to obtain additional information,’ they say in their paper.

WHAT ARE FIBRE OPTIC CABLES?

Fibre optic cables involve tiny tubes that are about as thick as a human hair and are reflective on the inside.

They transfer information by sending flashes of light through the tubes.

This bounces off the reflective walls and along the cable. 

These flashes of data are then received and interpreted at the other end.  

‘These applications of optical fibre networks, including earthquake detection, urban traffic flow monitoring, underground geological structure exploration, have positive impacts on people’s production and life. 

‘However, it also brings some potential security problems, which should be considered carefully.’

One type of broadband network architecture using optical fibre is known as fibre to the premises (FTTP).

As the name suggests, this is where fibre-optic cables run all the way to a premises, whether it be a house, flat building or office. 

According to the current layout mode of FTTP, fibre up to several meters will be installed in residents’ homes. 

But sound signals could be modulated onto the light wave that the fibre transmits, without installing any additional equipment in the resident’s home.

This would allow other people to eavesdrop and recover them at remote places along the fibre link. 

‘Optical fibres are very sensitive to vibration,’ Luc Thévenaz at the Swiss Federal Institute of Technology in Lausanne, Switzerland, who wasn’t involved in the study, told New Scientist. 

For their study, the Chinese team created a system that detects changes in light that occur when someone speaks near optical fibre. Diagram from the paper presents the eavesdropping scheme

For their study, the Chinese team created a system that detects changes in light that occur when someone speaks near optical fibre. Diagram from the paper presents the eavesdropping scheme

‘So any fibre placed in a building is actually a sort of microphone that can tap any kind of conversation.’  

For their study, the Chinese team created a system that detects changes in light that occur when someone speaks near optical fibre.

The system picks up sound at one end of the fibre and emits sound at the other end, based on changes in the transmitted light.

In lab experiments, the audio at the end wasn’t perfectly clear, but it could be made easier to understand with existing computer speech enhancement methods, the researchers claim. 

They say the eavesdropping method requires ‘complicated equipment and strict conditions’, but add that ‘secret stealing behaviour will always done regardless of cost’. 

Such a method could be disastrous for company headquarters fitted with fibre optics, as they could have confidential information leaked from snooped conversations. 

The researchers have suggested several ways to prevent eavesdropping, including materials such as metal and glass to coat the fibre, which would reduce changes in light caused by sound.

FIBRE OPTIC TECHNOLOGY: A PRIMER 

Everywhere on Earth, hair-thin optical fibres carry large amounts of information from different places. 

Optical fibres are a technology that uses glass or plastic threads (fibres) to transmit data. 

A fibre optic cable comprises a bundle of these threads, each of which is capable of transmitting messages modulate onto light waves. 

Fibre optics enable more information to be carried due to some of its properties which include low cost, immunity from disturbances that can affect electrical wires and wireless communication systems, and the fact that they are much thinner an lighter than metal wires. 

Optical fibres have played an important role in the rapid growth of world-wide communications in the last 25 years, and are important in enabling the growth of the internet.   

One type of broadband network architecture using optical fibre is known as fibre to the premises (FTTP).

As the name suggests, this is where fibre-optic cables run all the way to a premises, whether it be a house, flat building or office. 

According to the current layout mode of FTTP, fibre up to several meters will be installed in residents’ homes.  

Full-fibre broadband, which offers speeds of up to 1000Mbps (megabits per second), allows for better quality video calls and higher resolution movie streaming.

Full-fibre broadband is currently available to around one quarter of Brits but it will take at least two decades before it reaches every home in the UK. 

Full fibre means that the fibre optic connection goes all the way to the property, rather then just to the local telephone exchange, with copper cable completing the ‘last mile’ connection. 

Full fibre will provide the fastest broadband speeds to date – around one gigabit per second (Gbps) – capable of downloading TV shows or movies in seconds.  

According to Broadband Compared, 25Mbps is the minimum download speed for steaming a 4K movie on both Netflix and Amazon Prime Video.   



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