Satellite-relayed QKD
In the previous post, the notion of free-space QKD was introduced. It mentions how two channels — quantum and classical, are used to distribute keys in free-space QKD using satellites and ground stations. Owing to the extensive dispersion of ground stations across a wide geographical area, significant round trip times can reduce the duration of key validity, primarily when a single satellite is tasked with disseminating keys to ground stations positioned at geographically distant sites. Furthermore, the skewed allocation of keys by satellites to ground stations could further exacerbate the reduction in key distribution. Consequently, the utilization of satellite-relayed QKD presents a dual advantage: it mitigates the round trip time and enhances the extent of keys distributed.
The mechanism involves the satellite transmitting keys from the source satellite to the terminal satellite while consecutively encrypting and decrypting these keys through the intermediary satellite. Subsequently, the terminal satellite is responsible for dispersing the keys to the corresponding ground station. The common keys are ultimately shared between the source and terminal ground stations.
For every pair of adjacent satellites situated along the forwarding trajectory, an Inter-Satellite Link (ISL) is established. This link continually generates and stores keys within the key pools of neighboring satellites. These stored keys in the pools encrypt and decrypt the keys slated for future forwarding. This process ensures a continuous and secure flow of keys along the relayed path. The scheme’s effectiveness is in significantly minimizing the round trip time, thus extending the cryptographic period of keys and concurrently addressing the imbalance in key distribution by employing a collaborative and relayed distribution model.
In essence, satellite-relayed QKD overcomes the limitations posed by large round trip times and imbalanced key distribution that could otherwise undermine the security and efficiency of key transmission over substantial distances. The multi-step process involving intermediate satellites for encryption and decryption and the establishment of ISLs guarantees a seamless and robust key distribution system that effectively addresses these challenges.
Note: This article is a part of my Womanium Online Quantum Media Project. Find out about it here .
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