  Quantum Key Distribution (QKD) enables two parties to establish a common
secret key that is information-theoretically secure by transmitting random bits
that are encoded as qubits and sent over a quantum channel, followed by
classical information processing steps known as information reconciliation and
key extraction. Transmission of information over a quantum channel introduces
errors that are generally considered to be due to the adversary's tempering
with the quantum channel and needs to be corrected using classical
communication over an (authenticated) public channel. Commonly used
error-correcting codes in the context of QKD include cascade codes, low-density
parity check (LDPC) codes, and more recently polar codes. In this work, we
explore the applicability of designing of a polar code encoder based on a
channel reliability sequence. We show that the reliability sequence can be
derived and used to design an encoder independent of the choice of decoder. We
then implement our design and evaluate its performance against previous
implementations of polar code encoders for QKD as well as other typical
error-correcting codes. A key advantage of our approach is the modular design
which decouples the encoder and decoder design and allows independent
optimization of each. Our work leads to more versatile polar code-based error
reconciliation in QKD systems that would result in deployment in a broader
range of scenarios.
