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+# Quantum Key Distribution Protocol
+
+## Overview
+
+Quantum Key Distribution (QKD) is a secure communication method that uses quantum mechanics to distribute encryption keys between two parties. The security of QKD is based on the principles of quantum mechanics, specifically the behavior of quantum bits (qubits).
+
+## Key Principles
+
+1. **Quantum Superposition**: Qubits can exist in multiple states simultaneously, allowing for the encoding of information in a way that is fundamentally different from classical bits.
+
+2. **Quantum Entanglement**: Two qubits can be entangled, meaning the state of one qubit is directly related to the state of another, regardless of the distance between them.
+
+3. **No-Cloning Theorem**: It is impossible to create an identical copy of an arbitrary unknown quantum state, ensuring that any attempt to intercept the key will disturb the quantum states and be detectable.
+
+## Protocol Steps
+
+1. **Preparation**: The sender (Alice) prepares a series of qubits in a specific quantum state (e.g., using polarization states of photons).
+
+2. **Transmission**: Alice sends the qubits to the receiver (Bob) over a quantum channel.
+
+3. **Measurement**: Bob measures the received qubits using randomly chosen bases. He records the results of his measurements.
+
+4. **Basis Reconciliation**: After the transmission, Alice and Bob communicate over a classical channel to compare the bases they used for measurement. They discard the results where their bases did not match.
+
+5. **Key Generation**: The remaining bits, where their bases matched, form the shared secret key.
+
+6. **Error Checking**: Alice and Bob can perform error checking to ensure that no eavesdropping has occurred. If the error rate is above a certain threshold, they may discard the key and start over.
+
+7. **Key Usage**: The shared key can now be used for symmetric encryption of messages using classical encryption algorithms (e.g., AES).
+
+## Conclusion
+
+Quantum Key Distribution provides a theoretically secure method for key exchange, leveraging the principles of quantum mechanics. It is a crucial component of quantum secure messaging systems, ensuring that communication remains confidential and secure against eavesdropping.