With the advent of efficient quantum algorithms and technological advances, design of quantum circuits has gained importance. In this paper, Quantum circuit using standard quantum gates is constructed for the transmission of quantum encrypted check bits. The proposed scheme is analogous to the first QKD (quantum key distribution) protocol, (BB84) where the check bits are used to detect the level of noise and evesdropping on the channel. The gates used in this work are easily realizable and the encoding and decoding of classical information bits is extended for multiple bits using dense coding scheme.
With the advent of efficient quantum algorithms and technological advances, design of quantum circuits has gained importance. In this paper, Quantum circuit using standard quantum gates is constructed for the transmission of quantum encrypted check bits. The proposed scheme is analogous to the first QKD (quantum key distribution) protocol, (BB84) where the check bits are used to detect the level of noise and evesdropping on the channel. The gates used in this work are easily realizable and the encoding and decoding of classical information bits is extended for multiple bits using dense coding scheme.
The focus of this study is to develop a novel method of encoding the qubits and use as secret key in public key cryptography. In BB 84 protocol, 50% of the random number (generated at source) is used as secret key and the remaining bits are used as “check bits”. The check bits are used to detect the presence of eve as well as the nature of quantum channels. In this protocol, random qubits are encoded using different type of polarizations like horizontal, veritical and diagonal. In the proposed quantum encoder, basic quantum gates are used to encode the random secret key along with the check bits. Quantum key distribution, (a cryptographic mechanism) relies on the inherent randomness of quantum mechanics and serves as an option to replace techniques made vulnerable by quantum computing. However, it is still subject to clever forms of eavesdropping and poses a significant challenge to implementation. To study the challenges, quantum circuits are first simulated using QCAD.
Classical cryptosystem, which is based on mathematical complexity and irrationally time-consuming to decode, is endangered with the inception of quantum computers empowered with unprecedented computational processing along with sophisticated quantum algorithms. Thus requiring quantum cryptography and Quantum Key Distribution (QDK) protocol for secured key distribution. This thesis work contributes to the field of cryptography. First of all, it shows unconditionally secured QKD which is bound by quantum mechanics laws. It is minimal or moreover almost negligible chances of escaping the eavesdropper i.e. almost zero probability. Next, it shows the modified existing QKD protocol named BB84 protocol. The main drawback of the existing protocol is that it is less efficient concerning photon utilization as we know perfect single-photon generation is still challenging to current technology. In this work, the modified protocol has been presented and it is shown the simulated output using the Aer Provider backend ‘aer_simulator’ provided by Qiskit. With the generated key, message is encoded, transmitted and decoded in real quantum computer with backend ‘ibmq_manila’. The errors generated and analyzed and found that without interference in the channel, maximum only upto 15% errors have been generated from the noise of quantum circuit and are in acceptable range but in presence of interference, error rates surpass the acceptable range i.e. 20% error margin and hence the interference in the channel is detected.
In the 1980s it was first realized that quantum–mechanical phenomena can be exploited directly for the manipulation, storage and transmission of information. The discovery of quantum algorithms for prime factorization [18] and unstructured search [7], which outperformed the best classical algorithms for these tasks significantly, opened up new vistas for computer science and gave an initial thrust to the emerging field of quantum computation. To implement a quantum algorithm, however, a large scale quantum computer is necessary and such a device has yet to be built. Research in quantum information, on the other hand, has shown that quantum effects can be harnessed to provide efficient and highly secure communication channels, which can be built using current technology. Entangled quantum states, superpositions and quantum measurement are among the characteristics of the subatomic world which nature puts at our disposal; these and related phenomena enable the development of novel techniques for computation and communication with no rival in classical computing and communication theory. The focus in this paper is on communication protocols involving the use of such phenomena. Quantum protocols have particularly important applications in cryptography. Several quantum protocols have been proposed for cryptographic tasks such as oblivious transfer, bit commitment and key distribution [8,13]. The BB84 protocol for quantum key distribution [2,14], which allows two users to establish a common secret key using a single quantum channel, has been shown to be unconditionally secure against all attacks [11]. Other quantum protocols include procedures for
Quantum cryptography is anticipated to drive substantial advancements in cybersecurity. The impending arrival of quantum cryptography compromises current encryption methods, possibly compromising the effectiveness of traditional key management-based security protocols. One fundamental Quantum Key Distribution (QKD) protocol, BB84, encounters challenges when operating with fewer Quantum bits (Qubits) and bases that only support up to 8 Qubits. This limitation weakens the system’s security, making brute force, intercept, and resend attacks less challenging. Consequently, this study proposes a method to enhance the security of the BB84 protocol, to reduce susceptibility to attacks and eavesdropping. The improved BB84 protocol utilizes 9, 12, and 16 quantum bits along with two, and three bases to significantly bolster security. This allows authorized parties to eliminate the use of compromised keys. Additionally, the study implements the E91 QKD protocol utilizing the Entanglement Pair Generation (EPR) method to produce secure keys. While the existing E91 protocol ensures security through Bell’s theorem and Bell’s inequality, it overlooks the impact of noise, leading to inaccuracies in eavesdropper detection. To address this, the study introduces an additional security measure. Whenever an eavesdropper attempts to measure the quantum state, the proposed E91 protocol collapses its state from$\vert 10\rangle to\vert 11\rangle ,settingthefirstQubitto\vert 1\rangle andtheotherQubitto\vert 0\rangle $, thus providing the eavesdropper with incorrect information, accompanied by a phase angle of$15\pi $/8. This leads to a misconception, preventing eavesdroppers from obtaining useful details about transferred quantum states. Additionally, considering that the proposed E91 protocol relies on entangled particles and utilizes double Qubit gates, which are inherently noisier than single Qubit gates and more susceptible to quantum decoherence, this study employs error mitigation techniques during the final measurement to predict outcomes more efficiently.
Quantum key distribution (QKD) can provide an unconditionally secure communication encryption method. Continuous-variable QKD (CVQKD) requires extracting the key from the noisy channel, leading to higher requirements for the error-correcting codes used in multidimensional reconciliation. We extend the quasi-cyclic low-density parity-check of the radio design for the global 5G mobile communication technology standard to achieve error correction under lower signal-to-noise ratio on integrated hardware. A field programmable gate array (FPGA) chip is used to realize the approximate lower triangular matrix encoding algorithm, and the core module only has the circular shift register, which reduces the encoding complexity, improves the encoding efficiency, and reduces the hardware resource consumption. For extended super-long code words, the decoding algorithm requires additional hardware resources to implement, which the previous algorithm cannot meet. Therefore, we present a hardware implementation of offset minimum sum algorithm (OMSA), which can avoid operations of complex mathematical formula. The offset factor of OMSA reduce the error caused by the low accuracy of calculation on the hardware. The update of the decoding information is layered in a partially parallel way in the matrix to achieve the cross processing of node information. It speeds up the transmission of information between different nodes and the convergence of decoding algorithm of low-complexity parallel structure. Simulation results show that the maximum theoretical coordination efficiency is 85% when the code with block length is 69632 at a bit rate of 22/68 and the signal-to-noise ratio asymptotic threshold is 0.7. Using an FPGA, ∼0.1 frame error rate was achieved, but with a zero-bit error rate, the optimal achievable secret key rate is about 200 Kbps at 30-km distance theoretically. For a 200-MHz system clock on the successfully decoded block, 125 Gbps encoding throughput and 472 Kbps decoding throughput was achieved, better than the theoretical key rate of prototype of CVQKD.
We introduce noise-adaptive quantum key distribution (QKD) protocols, in which the honest parties optimize the encoding (state preparation) and decoding (measurement basis) operations according to the noise models affecting the honest subsystems induced by an eavesdropper. This extends conventional QKD schemes that employ fixed encoding and decoding strategies independent of the noise characteristics of the communication channel. We investigate three representative protocols: entanglement-based secure dense coding (SDC), the entanglement-free Lucamarini and Mancini (LM05), and a two-way prepare-and-measure Bennett Brassard (BB84) protocols. Using entropic uncertainty relations, we derive the corresponding secret key rates for both adaptive and conventional non-adaptive scenarios under collective attacks. For independent but identical noise acting on the forward and backward transmission channels, as well as for correlated and non-Markovian environments, we identify classes of channels for which adaptive schemes yield enhanced secret key rates for the considered protocols. In contrast, we also determine Pauli channels, including depolarizing and bit flip channels, for which adaptive strategies provide no benefit. We further show that these optimal sets are generally non-unique and can differ substantially from the unitaries that maximize dense-coding capacity in the absence of security constraints. Our results establish noise-adaptive encoding and decoding as a powerful framework for improving secure communication over realistic noisy quantum channels.