not the $\sigma(j)$-th QKD round has aborted, Eve could obtain the $j$-th bit value of the first QKD session key. Alternatively, Eve might also leak the key material produced in a certain QKD round by simply hiding it in the public discussion of subsequent QKD runs. We refer the reader to Ref. [@mem_attack] for more details. Memory attacks are a fundamental threat to the security of DI-QKD.[]{data-label="mem_att"}](fig_memory_attack){width="0.95\columnwidth"}

Despite its conceptual beauty, DI-QKD is however not foolproof. Indeed, one cannot expect that all QKD users will have expertise in experimental quantum optics and electronics. So, unless Alice and Bob manufacture their own QKD devices themselves, it could be very hard for them to guarantee that the devices are indeed honest. For instance, it was shown in [@mem_attack] that DI-QKD is highly vulnerable to the so-called memory attacks. In this type of attacks, a hidden memory device (planted by the eavesdropper, Eve, in say Alice’s setup during the manufacturing or initial installation of the QKD system) stores up the key material generated in each QKD session and then leaks this information to Eve in subsequent QKD runs. This situation is illustrated in Fig. \[mem\_att\]. Importantly, such leakage of key information could be 