C-DOT's fiber-based indigenous Quantum Key Distribution (QKD) system and PRL's Free Space QKD system were successfully integrated, forming India’s 1^st end-to-end quantum communication link.

1. Centre for Development of Telematics (C-DOT) is the telecom Research and Development wing of the Department of Telecommunications.
2. Physical Research Laboratory (PRL) is a research institute under the Department of Space.

 Background 

1. The rapid progress in quantum computers and quantum algorithms has put the security of the existing classical techniques of data security at risk.
2. This is because the huge computational power of quantum computers can easily break the secrecy of the key used for encryption/decryption. 
3. The huge computational power of quantum computers can pose a threat to the security of the existing communication and data security infrastructure if any adversary gains access to quantum computers. 
4. An emerging branch of quantum technology namely quantum communications can address this threat.

 Quantum Key Distribution (QKD) 

1. QKD, also known as Quantum Cryptography, is a method for creating secure communication.
2. It enables the distribution and sharing of secret keys needed for cryptographic protocols.

3. Significance:

• Cryptography is about secure communication techniques that ensure only the sender and intended receiver can access the message.
• In an untrusted network like the Internet, cryptographic algorithms and protocols are crucial for security.
• QKD will support start-ups and small-medium enterprises in quantum information.
• It allows security agencies to develop a quantum communication network using indigenous technology.
• The encryption is unbreakable due to the unique nature of photon transmission.
• Attempting to intercept data leaves a trace because a photon cannot be perfectly copied or measured without disturbance.

4. Difference from Conventional Cryptography:

• Traditional cryptosystems rely on complex mathematical algorithms for data encryption.
• Quantum communication's security is based on the laws of Physics, offering a different level of security.

5. QKD can be deployed through various mediums such as optical fiber, free space, and satellites to ensure end-to-end security in communication networks.
6. QKD has widespread applications in strategic sectors like defence, government communications, pharmaceutical and healthcare industries, financial services, data centres and telecommunication networks.

 Categories of Quantum Key Distribution (QKD) 

1. Prepare-and-Measure Protocols:

• These protocols involve measuring unknown quantum states.
• They help detect eavesdropping (spying) and assess potential data interception.

2. Entanglement-based Protocols:

• These protocols use quantum states where two objects are linked together.
• Entanglement means one object's measurement affects the other.
• This method ensures detection of any changes made by an eavesdropper (spy).

 Working of Quantum Key Distribution 

1. In Quantum Key Distribution (QKD), encryption keys are sent as 'qubits' in an optical fiber.

• Qubits are like regular bits in a binary system.

2. Optical fibers transmit data faster and over longer distances compared to other mediums, using total internal reflections.
3. QKD needs interactions between legitimate users, which must be authenticated using cryptographic methods.
4. It allows distant users without a shared long secret key to create a common random string of secret bits, called a secret key.
5. QKD turns an authenticated communication channel into a secure one.
6. Illegitimate (illegal) attempts to read the transmission disturb the qubits encoded on photons, causing transmission errors. Legitimate users are immediately alerted to these errors, ensuring security.

 About Quantum Communications 

1. Quantum communications is part of Quantum Technology, alongside Quantum Computing, Quantum Sensors, and Quantum Materials.
2. It's based on principles like superposition, entanglement, and tunnelling from Quantum mechanics.
3. Applications include secure communication, computing, simulation, healthcare, and cryptography.

 Initiatives for Quantum Technology in India 

1. National Mission on Quantum Technologies and Applications (NM-QTA)
2. Quantum-Enabled Science and Technology (QuEST)
3. Quantum Frontier mission of Prime Minister Science, Technology & Innovation Advisory Council (PM-STIAC)
4. National Mission on Interdisciplinary Cyber-Physical Systems (NM-ICPS)

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