Digital signatures allow users to verify the source of digital messages while simultaneously providing a guarantee of their integrity. The present widely used digital signature schemes typically have security based on the perceived computational complexity of inverting certain mathematical functions. However, advances in mathematical and computational analysis may render these schemes insecure.
Quantum digital signatures offer comparable security functionality based on the fundamentals of quantum physics. Previous experimental demonstrations of quantum digital signatures operated over relevantly short distances in laboratory environments. Researchers in IPaQS at Heriot-Watt University (in colloboration with the National institute of Information and Communications Technology in Japan) have reported the first demonstration of quantum digital signatures over 90 kilometres of installed optical fibre in an urban environment.