Implementation of the security test of fiber based DV QKD receivers/single-photon detectors exploiting an OTDR A portable dual-wavelength (1310 nm e 1550 nm) Single-Photon Optical-Time-Domain-Reflectometer (SP-OTDR) is available, which can be used to evaluate backflash emissions from single-photon detectors. The SP-OTDR can be used also to evaluate the effectiveness of the countermeasures of the QKD devices against Trojan-horse attacks injecting light in QKD. Wavelength: 1310 and 1550nm Requirements: device to be tested: single-mode fiber based DV-QKD receiver, and on-off single-photon detectors used in DV-QKD system at telecom