  In this paper we review a number of issues on the security of quantum key
distribution (QKD) protocols that bear directly on the relevant physics or
mathematical representation of the QKD cryptosystem. It is shown that the
cryptosystem representation itself may miss out many possible attacks which are
not accounted for in the security analysis and proofs. Hence the final security
claims drawn from such analysis are not reliable, apart from foundational
issues about the security criteria that are discussed elsewhere. The cases of
continuous-variable QKD and multi-photon sources are elaborated upon.
