  Quantum Key Distribution or QKD provides symmetric key distribution using the
quantum mechanics/channels with new security properties. The security of QKD
relies on the difficulty of the quantum state discrimination problem. We
discover that the recent developments in $\mathcal{PT}$ symmetry can be used to
expedite the quantum state discrimination problem and therefore to attack the
BB84 QKD scheme. We analyze the security of the BB84 scheme and show that the
attack significantly increases the eavesdropping success rate over the previous
Hermitian quantum state discrimination approach. We design and analyze the
approaches to attack BB84 QKD protocol exploiting an extra degree of freedom
provided by the $\mathcal{PT}$-symmetric quantum mechanics.
