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Innovation and Digital Transformation for a Sustainable World

which will be combined with a secret key . This process Table 2 – Summary of Quantum Communication Protocols
known as encryption transforms plaintext into ciphertext .
Cryptographically it can be represented as = ( ). No Name of Protocol Year Working Principle
1 BB84 1984 Heisenberg uncertainty
On the subsequent step, Alice will send the ciphertext
2 E91 1991 Quantum entanglement
to Bob through the public channel.After is obtained, Bob
3 BBM92 1992 Heisenberg uncertainty
decoding the same secret key by means of a corresponding
4 SSP 1999 Heisenberg uncertainty
decryption algorithm , and then the original plaintext
5 Secret Sharing 1999 Quantum entanglement
message is recovered, which is shown as = ( ).
6 DPS 2003 Quantum entanglement
Key confidentiality is the fundamental basis of classical 7 SARG04 2004 Heisenberg uncertainty
cryptography. If an intruder does not have the key, he should 8 COW 2004 Quantum entanglement
not be able to read the cipher. 9 KMB09 2009 Heisenberg uncertainty
10 SR CV-QKD 2015 Continuous-variable QKD
3.2 Principles of Quantum Cryptography 11 Twin-Field QKD 2018 rate–distance limit
12 LLP 2019 Quantum entanglement
Quantum cryptography [7] is a discipline within quantum 13 Knapsack Encoding 2020 Super increasing knapsack
information science field that actually uses fundamental laws 14 QKE 2022 Quantum compression
of quantum mechanics to attain secure communication. The 15 Modified BB84 2023 Heisenberg uncertainty
general idea behind QC comes down to the concept of 16 PHQKD-MF 2024 High-dimensional QKD
qubits, quantum bits with the superposition states described
shared secret key between two parties which are supposed to
by | ⟩ = |0⟩+ |1⟩, where and are complex probabilities
2
2
with normalization | | + | | = 1. Quantum cryptography be Alice and Bob while being spied on by an eavesdropper
protocols, Quantum key Distribution (QKD) being an who might be denoted as Eve at times. In the transmission
phase of quantum transmitting, Alice chooses a bit string “a”
example, leverage the elementary quantum properties such as
= ( 1 , ..., ) and a random sequence of basis “s” ∈ {⊕, ⊗}
entanglement and indeterminancy for developing information
where “n” is larger than “N”. Alice will encode her bit with
transmission channels that cannot be deciphered by the
the support of the bases she has selected in the polarisation of
attackers. For example, in the BB84 protocol, the qubits
photons and send the latter to Bob. Bob is Alice’s counterpart
that Alice prepares are in one of two bases (|0⟩ and |1⟩, or
′
′
|+ ⟩ and |− ⟩) which are then sent to Bob, who measures them and he has to use either the (+) basis or the (∗) basis to
measure each photon and then the observed bits are classical
randomly in one of the bases. By means of calculating a part
ones. Given that he gets a bit string = ( 1 , ..., ).
of their bases for measurement and using error correction
The set of values = { 1 , ..., } and = { 1 , ..., }
and privacy amplification methods, Alice and Bob decode a
is called the raw (ordinary) key pair. Bob now reveals its
shared secret key from the rest qubits. This mechanism takes
bases. Alice checks, quickly correlates, and discards the
advantage of the principles of quantum mechanics to secure
parts that do not correlate. Parties assess the estimated
communication from eavesdropping.
error rate and ensure data reconciliation and privacy by
applying information reconciliation and privacy amplification
4. QUANTUM KEY DISTRIBUTION (QKD)
techniques.
PROTOCOLS
Quantum-key distribution (QKD) takes advantage of one of 4.2 E91
the fundamental quantum mechanics features for creating a
A.Ekert was the first person to introduce this protocol
secret key. Its security rely on intrinsic randomness inherent
[9]. He employed the expanded Bell’s theorem to test the
in quantum states and measurements. QKD takes benefit
eavesdropping. In this protocol firstly, from a prime source,
of no-cloning theorem that ensures uniqueness of key and
Alice and Bob receive their entangled photons in one of
Heisenberg’s Uncertainty Principle that detects any attempt
four utmost entangled states ( 1 to 4 ). Assume the source
of eavesdropping. Involving Alice and Bob, QKD follows
generates an EPR pair:
two phases: quantum transmission and post-processing. A
quantum communication system will need a quantum channel 1
which would carry photons having their polarization encoded, = √ (|10⟩ + |01⟩) (1)
2
as well as a classical channel for message exchange. Coding
of classical bits (0 or 1) can be carried out with a polarized Alice now measures her particle among any of the 45°, 90°,
photon, and filtering or using crystals ensures data security. and 0° degree bases that she obtained from the entangled
pair. Bob then counts the particle he got from the entangled
4.1 BB84 Protocol pair using any 45°, 90°, or 135°degree base. Following that,
Bob and Alice remove the particles from different bases and
The BB84 protocol [8] patented by Charles Bennett and measure the particles in the same base. They get a common
Gilles Brassard in 1984 sparkled the quantum key distribution key if the bases are the same. The term "shifted key" refers
(QKD) field, which gave birth to the new era in secure to any bits or particles that are still present. In the end, Alice
communication in the quantum realm. It depends on the and Bob Check the system and the final decision is taken by
innate randomness of the quantum mechanics to create a interchanging.
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