# Category:Trusted Repeater Network Stage

The very first and initial network stage has trusted quantum repeaters, i.e. we do not study the scenerio where repeaters could be accessible to a dishonest party (Eve). Quantum Repeaters are used to transmit quantum information over long distances. As quantum channels are inherently lossy so, to reach longer distances, intermediate nodes called quantum repeaters are necessary. These repeaters are placed at calculated intervals along the quantum channel, allowing qubits to be transmitted over arbitrarily long distances. In its simplest form, a quantum repeater works by first generating entanglement between the repeater and each of the end nodes individually. This stage has possibility of having at-least two nodes connected by repeaters and a sequence of short distance links that connect intermediary repeaters. The two ends can receive quantum-generated codes but cannot send or receive quantum states as end-to-end transmission of qubits is not allowed. Any two end users can share an encryption key and here the trusted repeater would have access to keys as well. Each pair of adjacent nodes uses Quantum Key Distribution to exchange encryption keys. These pairwise keys allow the end nodes to generate their own key which would be longer in length, provided that all intermediary nodes are trusted. The first step towards upgrading these networks could be Measurement Device Independent Quantum Key Distribution (MDI-QKD), which is a QKD protocol that is secure even with untrusted measurement devices.

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