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Quantum Key Distribution (QKD) aims to solve the problem of key exchange by the use of quantum mechanics and thus offers the potential of ensuring “unconditional secure” key exchange for encrypted communication. For the identification of practical scenarios for QKD from space and in particular with regard to the limited computational/communication resources available on a satellite the following 4 objectives are covered by the project activities:
QTL has a strong scientific background related to space-based quantum key distribution implicating an overview of scientific literature and the technology relevant for QKD implementations, in particular for space applications. Concerning the timely satisfaction of the requirements of the activity, the preliminary results already presented show that the basic software framework is already existing at QTL. Additionally, essential QKD protocols are already integrated, and large parts of the software can be reused for the integration of additional QKD protocols. Based on these facts, we don’t anticipate challenges that could have a severe impact on the work carried out during the activity.
While classical link budget calculations are widely known and sufficient for calculating the received photon rate, calculating the secure key rate strongly depends on many parameters of used QKD protocol, the post-processing and the performance of the QKD hardware (transmitter and receiver). Knowledge and tools to calculate the secure key rate for a given optical link scenario are therefore important for assessing different QKD service architectures.
The basic software framework is already existing at QTL; some important QKD protocols are integrated and are ready to be used. In addition to calculations/optimizations directly related to the individual QKD protocols, the software features simulations/calculations of relevant parameters related to the optical quantum channel. It consists of 4 modules.
Module 1 allows us to calculate and optimize relevant parameters regarding the optical quantum channel (e.g., link distance, elevation angle, beam-size on ground, etc.) depending on a set of input parameters (e.g. orbital parameters, wavelength, up- or downlink, etc.).
The second module allows to simulate the expected experimental measurement results during the exchange phase of the quantum signal.
Module 3 takes into account “finite-size effects” and covers the analysis of the amount of classical communication that is required for the individual post-processing steps as well as the amount of pre-shared quantum key needed for the authentication of the classically exchanged messages. Consequently, the net secure key gain can be obtained.
The optimal mean photon numbers in a decoy-state DV-QKD protocol strongly depends on the noise in the quantum channel. Module 4 will set out a solution to this problem with the help of numerical optimization of the net-secure key gain.
The software framework consists of 4 modules:
Module 1: Optical Quantum Channel
Module 2: Protocol specific performance and security analysis
Module 3: Post-Processing
Module 4: Optimization
QTL’s software framework constitutes a relevant part for simulating the performance of selected QKD protocols but is not subject to any IP Rights.
Duration: 6 months
completed with the acceptance of all deliverable items at the Mid Term Review
completed with the final presentation and acceptance of the End-of-Contract documentation
Based on a broad literature research, the three most promising QKD protocols among the currently known and secure ones have been selected. It was shown that these protocols can reliably fulfil the theoretical assumptions in a practical scenario, even in harsh environmental conditions. Hence, they can safely be regarded as information-theoretically secure and thus protected by quantum physics laws. To further analyse the impact of the specific characteristics of the protocols, the employed satellite constellation (LEO, MEO, GEO), and other relevant technology-related parameters, QTLabs developed a simulation software for the different QKD protocols. As a result of a first broad performance study it was shown that suitable amounts of secure quantum key can be generated in general and that the technology is ready for further development towards space readiness.
The current study, however, did not investigate the immense potential that lies in the general mission design, which constitutes an important next step for further investigations.