  We propose a novel upconversion (sum frequency generation) based
quantum-optical setup that can be employed as a receiver (Bob) in practical
quantum key distribution systems. The pump governing the upconversion process
is produced and utilized inside the physical receiver, making its access or
control unrealistic for an external adversary (Eve). This pump facilitates
several properties which permit Bob to define and control the modes that can
participate in the quantum measurement. Furthermore, by manipulating and
monitoring the characteristics of the pump pulses, Bob can detect a wide range
of quantum hacking attacks launched by Eve.
