Quantum Cryptography uses the laws of Quantum Mechanics to create new cryptographic
primitives. Most of these primitives are still theoretical, as they rely on quantum computer
processing techniques which are not possible with today’s technology. However, one
primitive -Quantum Key Distribution (QKD) - is achievable today, and can provide
unconditionally secure communications. Despite this, QKD has met with mixed reactions
within the cryptographic community, and has not yet been widely adopted.

This paper considers the reasons for this: relevant QKD protocols are described, and their
strengths and weaknesses are examined to see where the competing claims for its security
and applicability arise. This is followed by a brief overview of practical QKD research work:
the EU-funded SECOQC quantum network project, and low-cost free space QKD
technology. This then enables the commercial potential of QKD systems to be explored.

The conclusion from this study is somewhat mixed. There is a basic problem facing QKD:
there are tried and tested “classical” solutions in all the application areas where it could be
used. An extensive infrastructure is needed to support QKD implementations, so any
security enhancements from QKD systems may be prohibitively expensive. But there are
areas where it could provide a real benefit by addressing weaknesses in classical
applications.

Commercial success will depend on the perceived benefits of installing security “based on
the laws of physics alone”, rather than security levels per se, and on how acceptable the
general public and business find the technology. There will be a place for QKD in the
cryptographers’ toolbox, but it may only be a small niche with very specific application
requirements.