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Experimental Verification of the Quantum Key Distribution with an eavesdropper and qiskit implementation

Arupjyoti Pathak, S. V. M. Satyanarayana

Published Jan 1, 2026• 0 citations
Publisher

Abstract

Quantum key distribution is one of the essential developments to reduce the vulnerability in the security of the systems due to the emergence of quantum computers. As long as large-scale quantum computers emerge, all the systems will be vulnerable to attack. To secure the communication, we can use quantum key distribution protocols in the near future. In this work, I have experimentally verified the BB84 protocol with an eavesdropper. We have used a classical channel to send polarization states of light. Our source is a readily available He-Ne laser (632.8nm). To send secret Information in a secure way, we use Quantum key distribution. Sender Alice sends randomly chosen polarization states of light to Bob. The states Alice sends are |H>,|V>,|D>, and |A>, and similarly, Bob also selects some random basis and detects this Information. In this experiment, |H>,|V> states belong to the '+' basis and |D>,|A> on the 'X' basis. Detecting |H>,|D> states at the detector is considered as '1' and detecting |V>,|A> represents the '0' bit as the output. Alice and Bob can choose the basis randomly. We got these | H>,|V>,|D>, and |A> states by rotating the half-wave plate at angles respectively 0°,90°,45°, and -45°. We used a motorized rotator to rotate the two half-wave plates, one at Alice's side and one at Bob's side, to select the basis and generate these states. The motorized rotator runs on a python code. Python code is designed in such a way that it can generate random bits and can run Alice and Bob parts simultaneously. A polarized beam splitter is used just before the detector to split the beam into | H> and |V> states with 100% intensity at one detector and 0% at the other and |D> and |A> states with 50:50 intensity. Therefore we used one half-wave plate just before the PBS, which can convert |H> and |V> states into |D> and |A> states when we rotate at these particular angles. Using this, we can detect |D> and |A> states with 100% intensity at one detector and 0% at the other. Based upon the basic choices of Alice and Bob, at the receiver part, Bob will receive the bits. At the end of the process, both parties will verify the basis. When the basis is matching, they will keep those bits, and which are not matching, they will discard them. The successful bits will become the encryption key. I did this experiment by sending 1000 bits, and 452 bits among them were successful. For the security analysis of this protocol, we implemented a third-person Eve who tries to steal the Information Alice sends to Bob. Eve used one Beam splitter to take half part of the light intensity and sent another half to Bob. Eve's part has one 50:50 beam splitter, which splits the beam into two. Then, one beam goes to a PBS, then to the detectors, and the other beam goes to a setup that has HWP and PBS, then to the detectors. In this experiment, Eve is successful in stealing the Information correctly. As we are using classical light, which has a huge number of photons, anyone can take some photons and execute a photon number splitting attack; the security of this process is very low. We need a single-photon source and a single photon detector to get total security from this protocol. Right now, I have done this experiment with the available pieces of equipment I have. When the needed types of equipment are available to me, I can implement the single-photon QKD experiment also. After the experiment, we realized that the superposition of states always holds in this experiment, but states do not collapse, as we are not performing the quantum measurement. Also, I have implemented the QKD protocol in the IBM Quantum lab, where Alice sends 1000 bits to Bob, and 474 bits among them were successful. Also, Eve’s interception was detected successfully.

DOI
10.17605/osf.io/smxn9

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Quantum key distribution is one of the essential developments to reduce the vulnerability in the security of the systems due to the emergence of quantum computers. As long as large-scale quantum computers emerge, all the systems will be vulnerable to attack. To secure the communication, we can use quantum key distribution protocols in the near future. In this work, I have experimentally verified the BB84 protocol with an eavesdropper. We have used a classical channel to send polarization states of light. Our source is a readily available He-Ne laser (632.8nm). To send secret Information in a secure way, we use Quantum key distribution. Sender Alice sends randomly chosen polarization states of light to Bob. The states Alice sends are |H>,|V>,|D>, and |A>, and similarly, Bob also selects some random basis and detects this Information. In this experiment, |H>,|V> states belong to the '+' basis and |D>,|A> on the 'X' basis. Detecting |H>,|D> states at the detector is considered as '1' and detecting |V>,|A> represents the '0' bit as the output. Alice and Bob can choose the basis randomly. We got these | H>,|V>,|D>, and |A> states by rotating the half-wave plate at angles respectively 0°,90°,45°, and -45°. We used a motorized rotator to rotate the two half-wave plates, one at Alice's side and one at Bob's side, to select the basis and generate these states. The motorized rotator runs on a python code. Python code is designed in such a way that it can generate random bits and can run Alice and Bob parts simultaneously. A polarized beam splitter is used just before the detector to split the beam into | H> and |V> states with 100% intensity at one detector and 0% at the other and |D> and |A> states with 50:50 intensity. Therefore we used one half-wave plate just before the PBS, which can convert |H> and |V> states into |D> and |A> states when we rotate at these particular angles. Using this, we can detect |D> and |A> states with 100% intensity at one detector and 0% at the other. Based upon the basic choices of Alice and Bob, at the receiver part, Bob will receive the bits. At the end of the process, both parties will verify the basis. When the basis is matching, they will keep those bits, and which are not matching, they will discard them. The successful bits will become the encryption key. I did this experiment by sending 1000 bits, and 452 bits among them were successful. For the security analysis of this protocol, we implemented a third-person Eve who tries to steal the Information Alice sends to Bob. Eve used one Beam splitter to take half part of the light intensity and sent another half to Bob. Eve's part has one 50:50 beam splitter, which splits the beam into two. Then, one beam goes to a PBS, then to the detectors, and the other beam goes to a setup that has HWP and PBS, then to the detectors. In this experiment, Eve is successful in stealing the Information correctly. As we are using classical light, which has a huge number of photons, anyone can take some photons and execute a photon number splitting attack; the security of this process is very low. We need a single-photon source and a single photon detector to get total security from this protocol. Right now, I have done this experiment with the available pieces of equipment I have. When the needed types of equipment are available to me, I can implement the single-photon QKD experiment also. After the experiment, we realized that the superposition of states always holds in this experiment, but states do not collapse, as we are not performing the quantum measurement. Also, I have implemented the QKD protocol in the IBM Quantum lab, where Alice sends 1000 bits to Bob, and 474 bits among them were successful. Also, Eve’s interception was detected successfully.
As the digital front becomes our new frontier, and digital data becomes increasingly vulnerable to highly sophisticated cyber attacks, conventional encryption approaches may no longer be sufficient to withstand a quantum attack. The focus of this work is to deploy a simulation of the BB84 protocol, one of the first Quantum Key Distribution (QKD) protocols developed by Charles Bennett and Gilles Brassard in 1984. The simulation involves two communicating parties, Alice and Bob, with Bob creating a secret keys generated cryptographically and sending it reliably over to Alice using quantum bits, or qubits. By leveraging quantum mechanics, this protocol ensures that any interception can be identified, thus bolstering both the integrity and confidentiality of the key exchange through scientists' understanding of superposition and the no-cloning principle. In the simulation, the potential of quantum communication to achieve secure key distribution over an insecure channel is demonstrated. Differently from traditional encryption protocols, QKD guarantees security not on computational but on physical basis. The aim of this paper is to show the feasibility and robustness of the BB84 protocol for actual cryptographic applications. This models the protocol between Alice and Bob, which paves the way for quantum-proof encryption systems and is a relevant step towards next generation cyber security.
Quantum cryptography using the BB84 protocol is at the forefront of modern secure communication. This paper emphasizes on BB84 protocol and its role in secure key distribution utilizing the Qiskit libraries in Python to simulate Quantum Key distribution (QKD). This QKD is then applied to the One-Time Pad algorithm for message encryption and decryption. Ensuring data confidentiality and integrity and is difficult due to advanced cyber threats and the potential of quantum computing to undermine traditional cryptographic methods. Current encryption techniques are susceptible to quantum related attacks, risking the decryption of sensitive data. Alice (sender) and Bob (receiver) use classical encryption to communicate but eavesdropper Eve with quantum capabilities, can potentially decrypt their messages. This vulnerability affects critical data security in finance, healthcare, and national security, making robust cryptographic solutions essential for maintaining trust and safety in digital communications. Our work emphasis the utilization of the quantum key generated by employing the BB84 protocol with the help of Qiskit library in python as cipher text in the process of one time pad encryption and decryption. This encrypted data dispatched between the sender and receiver to ensure maximum security, confidentiality and integrity over the period of communication.
Quantum cryptography, or, more precisely, quantum key distribution (QKD) allows two distant parties, Alice and Bob, to expand a previously shared secret key by sending quantum states through a quantum channel. The goal here is for Alice and Bob to communicate securely in the presence of an eavesdropper, Eve. The most well-known QKD protocol is the Bennett-Brassard 1984 (BB84) protocol, which has been proved unconditionally secure against any attacks allowed by quantum mechanics. The main advantage of QKD over conventional cryptography is its absolute security. Thus, it is imperative to evaluate the security and performance of QKD protocols and realistic QKD systems. In this thesis, we study the security and performance aspects of QKD in four parts. In the first part, we study the Scarani-Acin-Ribordy-Gisin 2004 (SARG04) protocol. This protocol differs from the BB84 protocol only in the classical post-processing step and uses the same four quantum states as the BB84 protocol. We compared these two protocols and showed that in typical situations, the classical post-processing software for BB84 should be used in order to have a higher performance. In the second part, we prove the security of a three-state protocol. This protocol is similar to the BB84 protocol in that they share the same three qubit states. In the third part, we consider a practical Trojan horse attack on practical QKD systems implementing the BB84 protocol. The attack works by taking advantage of the finite response time of practical phase modulators to remap the states sent out by the legitimate user, Alice. We showed that if Alice and Bob are unaware of our attack, the final key shared between them can be compromised in some situations. In the fourth part, we consider another type of Trojan horse attack, which is based on mismatch between detection efficiencies of detectors. Practical detectors in QKD systems usually do not have identical efficiencies and an eavesdropper Eve may be able to exploit this efficiency mismatch to steal information about the final secret key. We analyze the security of the attack and show that it is possible for Eve to acquire some information on the final secret key if Alice and Bob are unaware of this attack.
Autonomous "Things" is becoming the future trend as the role, and responsibility of IoT keep diversifying. Its applicability and deployment need to re-stand technological advancement. The versatile security interaction between IoTs in human-to-machine and machine-to-machine must also endure mathematical and computational cryptographic attack intricacies. Quantum cryptography uses the laws of quantum mechanics to generate a secure key by manipulating light properties for secure end-to-end communication. We present a proof-of-principle via a communication architecture model and implementation to simulate these laws of nature. The model relies on the BB84 quantum key distribution (QKD) protocol with two scenarios, without and with the presence of an eavesdropper via the interception-resend attack model from a theoretical, methodological, and practical perspective. The proposed simulation initiates communication over a quantum channel for polarized photon transmission after a pre-agreed configuration over a Classic Channel with parameters. Simulation implementation results confirm that the presence of an eavesdropper is detectable during key generation due to Heisenberg's uncertainty and no-cloning principles. An eavesdropper has a 0.5 probability of guessing transmission qubit and 0.25 for the polarization state. During simulation re-iterations, a base-mismatch process discarded about 50 percent of the total initial key bits with an Error threshold of 0.11 percent.
In recent years, traditional cryptography has faced a lot of threats with advancements in quantum computing technology. The objective of the work is to analyze the suitability of the BB84 protocol for quantum key distribution. The BB84 protocol uses the principles of superposition, entanglement, and the no-cloning theorem that provide a framework enabling the secure exchange of secret keys. Qiskit, an open-source software, is used for analysis and study. An ideal quantum channel is established between the two communicating parties using Qiskit. The analysis is done in the presence of an eavesdropper, and it is found that the eavesdropper’s incorrect basis choices alter the states of the qubits, and thereby, the communicating parties will come to know about the interception.
Considering the security and efficiency of quantum communication system, one step quantum key distribution protocol based on hyperentangled Bell state is proposed. Every 6 classical bits are divided into a group, which are encoded by single particle and hyperentangled Bell state, the sender Alice sends them to receiver Bob, Bob randomly selects the position of hyperentangled Bell state to measure and detects the existence of eavesdropper Eve by comparing measurement results in his hand and transmitted by Alice. Quantum key distribution protocol based on grouping is proposed to solve the storage problem of quantum information and improve the maneuverability, a security analysis is calculated under the intercept-measure-resend attack which introduce at least an error rate of 46.875%, if Eve wants to get all the information, the probability of detection eavesdropping under the entanglement-measure attack is 93.75%, so it proves that proposed protocol does not need to store the quantum state and asymptotically secure under intercept-measure-resend attack and entanglement-measure attack.