  We present how the mechanisms of quantum Darwinism allow for the leakage of
information in the standard BB84 quantum key distribution protocol, a
paradigmatic prepare and measure quantum cryptography scenario.
  We work within the decoherence theory framework and employ the model of
measurements provided by quantum Darwinism. We investigate how much of the
information about the results crucial for the cryptographic key to be kept
secret is leaked during the quantum measurement process and subsequently how
much of that information might be later obtained by an eavesdropper using a
type of a so-called Van Eck side-channel wiretapping.
  We also show how the security can be affected by different ways of organizing
the surrounding environment into layers, e.g. rooms or other divisions
affecting the spread of quantum information in the environment and its
interaction, paving a venue to potential enhancements, and insight into proper
engineering of shieldings for cryptographical devices.
