  We propose to analyse quantum protocols by applying formal verification
techniques developed in classical computing for the analysis of communicating
concurrent systems. One area of successful application of these techniques is
that of classical security protocols, exemplified by Lowe's discovery and fix
of a flaw in the well-known Needham-Schroeder authentication protocol. Secure
quantum cryptographic protocols are also notoriously difficult to design.
Quantum cryptography is therefore an interesting target for formal
verification, and provides our first example; we expect the approach to be
transferable to more general quantum information processing scenarios. The
example we use is the quantum key distribution protocol proposed by Bennett and
Brassard, commonly referred to as BB84. We present a model of the protocol in
the process calculus CCS and the results of some initial analyses using the
Concurrency Workbench of the New Century (CWB-NC).
