Many users do not realise that when they use a mobile phone the wireless part of the link, which is secured by the mobile network operators, is only between the mobile phone and the base station closest to the caller and recipient. In between, the signal travels through ordinary phone lines. At this point it is possible for conversations to be accessed by unauthorised parties.
Previous attempts to make mobile phone conversations totally secure have been successful but have relied on a special GSM data service that has resulted in some operational problems.
In particular, these solutions have required expensive dedicated handsets and subscriptions, and calls between different countries can be unreliable. The University of Surrey system is the first true end-to-end secure GSM system that does not rely on a special GSM data service.
Encryption techniques are not new, but until now it has been impossible to use these with mobile phones. Traditional landline encryption systems convert voice messages directly into digital data, which is then transmitted.
But current mobile phones have a much lower digital information transmission capacity than landlines. In order to provide good speech quality at much reduced digital information rates, mobile phones assume that the signal to be transmitted is plain speech, and cannot therefore recognise or transmit the data signals of encrypted speech.
Scientists at the University of Surrey have overcome this problem by modulating encrypted speech patterns into audio streams that both mobile and landline technology will accept.
The University of Surrey said its system is the first of its kind in the world, and it is being developed by university spin-off company MulSys for potential users.
Ahmet Kondoz, a professor in the University of Surrey's Centre for Communication System Research, said, "This is the first true end-to-end GSM secure voice transmission technology that uses the GSM voice channel to transmit encrypted speech.
"By using the standard voice channel, it will offer unprecedented levels of security and quality of service for mobile secure communications."