  We study the possible application of the decoy state method on a basic two
way quantum key distribution (QKD) scheme to extend its distance. Noting the
obvious advantage of such a QKD scheme in allowing for single as well as double
photon contributions, we derive relevant lower-bounds on the corresponding
gains in a practical decoy state implementation using two intensities for decoy
states. We work with two different approaches in this vein and compare these
with an ideal infinite decoy state case as well as the simulation of the
original.
