Satellite Quantum Communications When Man-in-the-Middle Attacks Are Excluded

Abstract

An application of quantum communications is the transmission of qubits to create shared symmetric encryption keys in a process called Quantum Key Distribution (QKD). Contrary to publicprivate key encryption, symmetric encryption is safe from (quantum) computing attacks, i.e. it provides forward security and is thus attractive for secure communications. In this paper we argue that for free-space quantum communications, especially with satellites, if one assumes that man-inthe-middle attacks can be detected by classical channel monitoring techniques, simplified quantum communications protocols and hardware systems can be implemented that offer improved key rates. We term these protocols photon key distribution (PKD) to differentiate them from the standard QKD protocols. We identify three types of photon sources and calculate asymptotic secret key rates for PKD protocols and compare them to their QKD counterparts. Results show that PKD protocols have roughly a factor of two higher rates as only one measurement basis is used and due to the relaxed security assumptions can establish keys at very high losses whereas in QKD the privacy amplification process becomes prohibitive.

Advances in space quantum communications

“…From a purely engineering perspective, conventional laser communications are considered more secure than radio-based systems due to the much narrower diffraction limited beam divergences of optical links [249]. It is also necessary to examine the necessity for the full QKD mechanism when line-of-sight is guaranteed between transmitter and receiver, using other means, such as optical beacons, radar and optical observation [250]. In such cases, the concerns would be malicious Trojan-horse attacks by light injection into the receiver, or harvesting scattered light into the adversary's detector [251,252].…”

Quantum technology for military applications

“…However, this is not possible for the quantum channel where it would be detected promptly. One possible attack is a man-in-the-middle type attack [240,241], since the early quantum network parties can have a problem with authentication or trusted repeaters. Other types of attacks are considered at the quantum physics level; for example, a photon number splitting attack relies on utilising coherent laser pulses for the quantum channel [81] or the Trojan-horse attacks [82], or the collecting of scattered light and its detection [242].…”

Applicability of Squeezed- and Coherent-State Continuous-Variable Quantum Key Distribution over Satellite Links

“…Alternatively and taking into account the fact that the excess noise atop of the calibrated electronic noise of the detector appears most likely due to the imperfect estimation of a noiseless quantum channel, one may assume passive eavesdropping such that no untrusted channel excess noise is present. In the case of satellite-based links, where line of sight between the sender and the receiver suggests the absence of equipment capable of active eavesdropping, this is a particularly sensible assumption and it was applied recently for feasibility study of DV QKD over satellite links [ 45 ]. We also take this assumption into account in CV QKD by assuming the excess noise to be trusted (i.e., being out of control by an eavesdropper) and including it in the state purification using the scheme similar to the entangling cloner with a strongly unbalanced coupling to the signal prior to detection [ 37 ].…”