Credit: University of Twente
NEWS QUANTUM TECHNOLOGY
Secure communication with 7 bits per photon Fast development of quantum computing increases the risk of breaking cryptography. At the University of Twente, researchers developed a new method using photons for secure key generation, resulting in transmission speeds of up to 7 bits per photon. Antoinette Brugman
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ryptography is a necessary step in securing communication of sensitive data. The fast development of quantum computing risks to break existing cryptography in the near future. This threatens the security of future communication but also of recent communication that has been stored. Therefore, new methods using quantum technology are being developed for data encryption that can’t be broken by quantum computers. The new method developed at the University of Twente (UT) is a more sophisticated version of an existing system: Quantum Key Distribution (QKD). Commercial QKD systems are available already from several vendors. They use single particles of light – photons – that can be transmitted over the fiberglass cable grid, in a grid of two polarization directions perpendicular to each other. One direction representing 0, the other 1.
Randomly switching between bases
The QKD system randomly sends its information using two different bases: one with a grid in the horizontal and vertical direction (rectilinear), the other with a rotated grid (diagonal). To detect the photons, the receiver randomly switches between the same two bases. However, correct detection is only possible if the right grid is used. After sending all the photons, both sides 58
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exchange the sequence of the alternating basis they used – this can be openly done over the Internet. Thus, both the sender and the receiver know which measurements were done in the same basis and, therefore, which photons sent were properly detected. The receiver only keeps these measurements and deletes the others. As a result, both sides have a unique row of photon UT researchers, led by professor Pepijn Pinkse, developed a new method using photons for secure key generation. Credit: University of Twente
positions forming the secret key to encrypt and decrypt their communication. If an attacker intercepts the communication, either that particular photon is lost – and nothing is detected by the receiver – or a new photon is inserted that probably wasn’t sent in the right basis. The sender and receiver use a small fraction of the photons measured in the correct ba-
