  Quantum key distribution(QKD) allows the legitimate partner to establish a
secret key whose security only depends on physical laws. In recent years,
research on QKD by employing insecure measurement devices, namely
measurement-device-independent QKD (MDI-QKD) is increased. MDI-QKD removes all
attacks on measurement devices and thus an untrusted third party can be
employed for measuring. However, a weakness of previous MDI-QKD protocols is
the need for joint measurements such as Bell measurements whose efficiency is
low in practice. On the other hand, can all QKD protocols become
measurement-device-independent remains a problem. In this paper, we present a
scheme making prepare-measure QKD protocols become MDI-QKD protocols, called
$'measurement-device-independenization'$, which does not need to employ joint
measurements and could be efficiently implemented by weak coherence sources.
The protocol might look like the detector-device-independent(DDI) protocols but
it is also secure under the Trojan horse attack. To illustrate this, we
investigate the photon-number-adding(PNA) attack and present a scheme, called
$'photon-number-purification'$, which can also be employed to close loopholes
for previous protocols such as DDI and plug-and-play ones.
