The black paper of quantum cryptography: real implementation problems

TL;DR

This paper reviews practical challenges and security issues in quantum key distribution, emphasizing that real-world implementations face trust and threat concerns that complicate claims of absolute security.

Contribution

It clarifies common misconceptions about QKD security, analyzes practical implementation issues, and discusses the potential divergence between practical and theoretically secure quantum cryptography.

Findings

Practical QKD implementations involve trust elements similar to classical cryptography.

Recent threats to QKD security are identified but are potentially addressable.

The field may split into practical and theoretically secure approaches.

Abstract

The laws of physics play a crucial role in the security of quantum key distribution (QKD). This fact has often been misunderstood as if the security of QKD would be based only on the laws of physics. As the experts know well, things are more subtle. We review the progresses in practical QKD focusing on (I) the elements of trust that are common to classical and quantum implementations of key distribution; and (II) some threats to security that have been highlighted recently, none of which is unredeemable (i.e., in principle QKD can be made secure). This leads us to guess that the field, similar to non-quantum modern cryptography, is going to split in two directions: those who pursue practical devices may have to moderate their security claims; those who pursue ultimate security may have to suspend their claims of usefulness.