The goal of this note is to explain the reconciliation problem for
continuous-variable quantum key distribution protocols with a discrete
modulation. Such modulation formats are attractive since they significantly
simplify experimental implementations compared to protocols with a Gaussian
modulation. Previous security proofs that relied crucially on the Gaussian
distribution of the input states are rendered inapplicable, and new proofs
based on the entropy accumulation theorem have emerged. Unfortunately, these
proofs are not compatible with existing reconciliation procedures, and
necessitate a reevaluation of the reconciliation problem. We argue that this
problem is nontrivial and deserves further attention. In particular, assuming
it can be solved with optimal efficiency leads to overly optimistic predictions
for the performance of the key distribution protocol, in particular for long
distances.Comment: 11 pages, 1 figur