Foiling covert channels and malicious classical post-processing units in quantum key distribution

Abstract: Existing security proofs of quantum key distribution (QKD) suffer from two fundamental weaknesses. First, memory attacks have emerged as an important threat to the security of even device-independent quantum key distribution (DI-QKD), whenever QKD devices are re-used. This type of attacks constitutes an example of covert channels, which have attracted a lot of attention in security research in conventional cryptographic and communication systems. Second, it is often implicitly assumed that the classical post-processing units of a QKD system are trusted. This is a rather strong assumption and is very hard to justify in practice. Here, we propose a simple solution to these two fundamental problems. Specifically, we show that by using verifiable secret sharing and multiple optical devices and classical post-processing units, one could re-establish the security of QKD. Our techniques are rather general and they apply to both DI-QKD and non-DI-QKD.