  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.
