The last two decades have witnessed an exciting advanced research field that stems from non-classical atomic theory, quantum mechanics. This field promises an important applicability in secure data communications, known as quantum cryptography. Quantum cryptography takes advantage of the inherent random polarization state of single photons, which is not reproducible by a third party or an eavesdropper located between the source and the destination. Thus, when polarization states of photons are associated with binary logic an algorithm may intelligently developed according to which a cryptographic key is disseminated by the source terminal to the destination. This is a process known as quantum key distribution. However, as photons propagate in a non-linear medium such as fiber, their polarization state does not remain intact and thus the quantum key distribution and quantum cryptography becomes vulnerable to attacks. In this paper we consider the applicability of quantum cryptography in a pragmatic fiber-optic medium and in a popular communication network topology. We identify major weaknesses for each step of the quantum key distribution process, and also potential attacks to incapacitate quantum cryptography in fiber communications, so that better countermeasure strategies can be developed.