Quantum communications are not 100 per cent secure, researchers have concluded, and its lasers that are used to intercept the signals.
Referred to as bright light hacking, the photon detectors used in quantum communications can be remotely controlled as well as blinded by a strong light pulse. The blinding of the detector means it does not register, with a certain probability, the photon it was meant too.
‘Even if the detectors were blinded, for instance, as long as they produce the right correlations, a secret key can be extracted from them,’ said Renato Renner, a researcher at the Institute for Theoretical Physics in Zurich.
Quantum communication uses quantum key distribution for encryption. This involves a secret key that is shared between two distant parties. The key is distributed as bits of quantum data, so if an eavesdropper tries to intercept the message, in theory, the bits will be disturbed and the receiver and sender will know the transmission has been compromised. If the key is not disturbed, it can be used to encode messages that are sent over an insecure channel.
Renner and his colleagues have been calculating the failure probability of certain quantum encryption schemes. The numbers would allow users to estimate how likely it would be that an adversary could read their secret messages, information that is critical for ensuring the overall security of quantum communications. Renner will present the research at the Conference on Lasers and Electro Optics in San Jose, California.
Bright light hacking was first demonstrated in 2010. Since then physicists have been trying to find ways to calculate the security of quantum encryption schemes without making assumptions about the reliability of the devices. The security ultimately depends on three assumptions, the initial secrecy of the password, the validity of quantum theory, and the reliability of the devices in the quantum communication system.