  We perform a comprehensive analysis of practical quantum cryptography (QC)
systems implemented in actual physical environments via either free-space or
fiber-optic cable quantum channels for ground-ground, ground-satellite,
air-satellite and satellite-satellite links. (1) We obtain universal
expressions for the effective secrecy capacity and rate for QC systems taking
into account three important attacks on individual quantum bits, including
explicit closed-form expressions for the requisite amount of privacy
amplification. Our analysis also includes the explicit calculation in detail of
the total cost in bits of continuous authentication, thereby obtaining new
results for actual ciphers of finite length. (2) We perform for the first time
a detailed, explicit analysis of all systems losses due to propagation, errors,
noise, etc. as appropriate to both optical fiber cable- and satellite
communications-based implementations of QC. (3) We calculate for the first time
all system load costs associated to classical communication and computational
constraints that are ancillary to, but essential for carrying out, the pure QC
protocol itself. (4) We introduce an extended family of generalizations of the
Bennett-Brassard (BB84) QC protocol that equally provide unconditional secrecy
but allow for the possibility of optimizing throughput rates against specific
cryptanalytic attacks. (5) We obtain universal predictions for maximal rates
that can be achieved with practical system designs under realistic
environmental conditions. (6) We propose a specific QC system design that
includes the use of a novel method of high-speed photon detection that may be
able to achieve very high throughput rates for actual implementations in
realistic environments.
