A Solution for Post Quantum Security Using Existing Communications Infrastructures

The application of quantum cryptographic methods to existing communications infrastructures can be extremely difficult owing to the complex nature of quantum transmission methods. The premise of this thesis is an examination of methods to combine quantum-safe
security with standard protocols, such as phase shift keying. Use is made of an algorithm previously presented by Ueli Maurer which allows for the distillation of a mutual symmetric cryptographic key from some shared secret information (Maurer, 1993). This algorithm is examined extensively and incorporated into a complete protocol which
can be applied to pre-existing communications using phase shift keying. Primarily, one must consider the theoretical noise capabilities. In order to ensure the security of these communications the properties of microwaves are characterised and established as quantum-limited
coherent states with a fractional excess noise on measurement.
Side channel attacks are more prolific when one considers the quantum measurement attack vector, especially when one considers that the full extent of these attacks in not yet known. If the same security could be extracted from the distillation algorithm, without relying upon quantum mechanics as the resource, then a universal standard
for widespread implementation could be produced. The properties of random numbers are shown to be a sufficent resource for the advantage distillation algorithm which provides a strong candidate for a possible post-quantum secure universal standard.
The security of this (and various other protocols), however, relies upon the presence of an ‘impenetrable’ safe-house for trusted parties to prepare their cryptogrpahic resource (whether it be quantum or randomnumbers). A side channel attack is examined which is based on the possibility of signal leakage from a shielded room. The use of the vector potential elucidates a possible method for signals to be detected outside a Faraday shielded enclosure - methods for performing this
detection are examined and a characterisation of the properties of the leakage is performed. Leakage is detected from a shielded room at the National Authority for Counter Eavesdropping. It is concluded that a threat exists from this. However, there are possibilities for counteracting this using certain dielectric materials which need to be
explored further.
Overall, it is established that advances have been made towards developing a post-quantum secure cryptographic method, which can be straight forwardly implemented in a variety of existing infrastructures using phase shift keying protocols, and even in a universal implementation using random numbers as a secure resource.