We introduce an explicit construction for a key distribution protocol in the Quantum Computational Timelock (QCT) security model, where one assumes that computationally secure encryption may only be broken after a time much longer than the coherence time of available quantum memories.Taking advantage of the QCT assumptions, we build a key distribution protocol called HM-QCT from the Hidden Matching problem for which there exists an exponential gap in one-way communication complexity between classical and quantum strategies.We establish that the security of HM-QCT against arbitrary i.i.d. attacks can be reduced to the difficulty of solving the underlying Hidden Matching problem with classical information. Legitimate users, on the other hand, can use quantum communication, which gives them the possibility of sending multiple copies of the same quantum state while retaining an information advantage. This leads to an everlasting secure key distribution scheme over n bosonic modes. Such a level of security is unattainable with purely classical techniques. Remarkably, the scheme remains secure with up to O ( n log ( n ) ) input photons for each channel use, extending the functionalities and potentially outperforming QKD rates by several orders of magnitudes.
We introduce an explicit construction for a key distribution protocol in the Quantum Computational Timelock (QCT) security model, where one assumes that computationally secure encryption may only be broken after a time much longer than the coherence time of available quantum memories.Taking advantage of the QCT assumptions, we build a key distribution protocol called HM-QCT from the Hidden Matching problem for which there exists an exponential gap in one-way communication complexity between classical and quantum strategies.We establish that the security of HM-QCT against arbitrary i.i.d. attacks can be reduced to the difficulty of solving the underlying Hidden Matching problem with classical information. Legitimate users, on the other hand, can use quantum communication, which gives them the possibility of sending multiple copies of the same quantum state while retaining an information advantage. This leads to an everlasting secure key distribution scheme over n bosonic modes. Such a level of security is unattainable with purely classical techniques. Remarkably, the scheme remains secure with up to O ( n log ( n ) ) input photons for each channel use, extending the functionalities and potentially outperforming QKD rates by several orders of magnitudes.
Extending the functionality and overcoming the performance limitation under which QKD can operate requires either quantum repeaters or new security models. Investigating the latter option, we introduce the \textit{Quantum Computational Hybrid} (QCH) security model, where we assume that computationally secure encryption may only be broken after time much longer than the coherence time of available quantum memories. We propose an explicit d-dimensional key distribution protocol, that we call MUB-\textit{Quantum Computational Timelock} (MUB-QCT) where one bit is encoded on a qudit state chosen among d+1 mutually unbiased bases (MUBs). Short-term-secure encryption is used to share the basis information with legitimate users while keeping it unknown from Eve until after her quantum memory decoheres. This allows reducing Eve's optimal attack to an immediate measurement followed by post-measurement decoding. \par We demonstrate that MUB-QCT enables everlasting secure key distribution with input states containing up to O(d) photons. This leads to a series of important improvements when compared to QKD: on the functional side, the ability to operate securely between one sender and many receivers, whose implementation can moreover be untrusted; significant performance increase, characterized by a O(d) multiplication of key rates and an extension by 25km×log(d) of the attainable distance over fiber. Implementable with a large number of modes with current or near-term multimode photonics technologies, the MUB-QCT construction has the potential to provide a radical shift to the performance and practicality of quantum key distribution.
Security of quantum key distribution (QKD) protocols rely solely on quantum physics laws, namely, on the impossibility to distinguish between non-orthogonal quantum states with absolute certainty. Due to this, a potential eavesdropper cannot extract full information from the states stored in their quantum memory after an attack despite knowing all the information disclosed during classical post-processing stages of QKD. Here, we introduce the idea of encrypting classical communication related to error-correction in order to decrease the amount of information available to the eavesdropper and hence improve the performance of quantum key distribution protocols. We analyze the applicability of the method in the context of additional assumptions concerning the eavesdropper's quantum memory coherence time and discuss the similarity of our proposition and the quantum data locking (QDL) technique.
How could quantum cryptography help us achieve what are not achievable in classical cryptography? In this work we study the classical cryptographic problem that two parties would like to perform secure computations with long outputs. As a basic primitive and example, we first consider the following problem which we call secure function sampling with long outputs: suppose f:{0,1}n→{0,1}m is a public, efficient classical function, where m is big; Alice would like to sample x from its domain and sends f(x) to Bob; what Bob knows should be no more than f(x) even if it behaves maliciously. Classical cryptography, like FHE and succinct arguments [Gen09,Kil92,HW15], allows us to achieve this task within communication complexity O(n+m); could we achieve this task with communication complexity independent of m? In this work, we first design a quantum cryptographic protocol that achieves secure function sampling with approximate security, within O(n) communication (omitting the dependency on the security parameter and error tolerance). We also prove the classical impossibility using techniques in [HW15], which means that our protocol indeed achieves a type of quantum advantage. Building on the secure function sampling protocol, we further construct protocols for general secure two-party computations [Yao86,GB01] with approximate security, with communication complexity only depending on the input length and the targeted security. In terms of the assumptions, we construct protocols for these problems assuming only the existence of collapsing hash functions [Unr16]; what's more, we also construct a classical-channel protocol for these problems additionally assuming the existence of noisy trapdoor claw-free functions [BCMVV,BKVV].
Data protection and information security have been the essence of communication in today's digital era. Authentication and secrecy of secure communication are achieved using key-based cryptographic primitives; the security of which significantly relies upon the underlying computationally complex mathematics. Moreover, these existing cryptographic primitives are considered to be non-deterministic on the basis of the existing computational capabilities. However, the considerable advancements in the development of quantum computers have significantly enhanced parallel computations; thereby, posing a great threat to these existing encryption primitives. Thus, in the future, the physical manifestation of a large successful quantum computer is likely to break all the existing public-key encryption algorithms in no time. This has led to a remarkable surge of interest in propelling quantum mechanics into existence; subsequently, leading cryptographers to research various viable domains to offer quantum-resistant secure communications. Resultantly, quantum cryptography/quantum key distribution has emerged as a futuristic replacement for classical cryptography as it offers unconditionally secure communication along with the inherent detection of any unintended user. Thus, keeping in view the significance of this relatively newer domain of cryptography, this research focuses on presenting a consolidated review of the various Quantum Key Distribution (QKD) protocols. A comparative analysis of the working mechanism of the prominent QKD protocols is presented along with an overview of the various emerging trends that have been proposed to optimize the implementational efficiency of the BB84 protocol.
Current cryptographic systems and information security methods are largely based on the computational intractability and impracticability of reversing complex cryptographic algorithms and protocols. The foundation of secure communication and data protection strategies that we rely on a daily basis is provided by this computational difficulty. However, quantum computers with sufficient processing power could breach these basic security assumptions, making it possible to recover the cryptographic keys used to safeguard sensitive data and compromise widely used key exchange techniques. A viable strategy to counter the threat of quantum attacks and maintain standard security guarantees is hybrid systems. The software-based hybrid cryptographic framework that guarantees forward secrecy and contemporary cryptographic authentication while also integrating quantum-resilient key establishment schemes, namely, quantum key distribution simulation and a post-quantum key encapsulation mechanism, in a manner that also combines their security properties to generate a hybrid key that remains secure as long as at least one underlying component remains uncompromised is experimentally implemented in this paper. We demonstrate how this approach can safeguard both real-time secure communication and long-term data protection against current threats as well as future quantum adversaries.
Digital interaction's expansion has created a necessity for safe and efficient data transfer. Standard encryption procedures can be cracked by sophisticated hacking techniques, and moreover, they will become obsolete in the future with the emergence of quantum computers. This article introduces a hybrid cryptography that consists of a secure channel based on quantum entanglement and a lightweight encryption scheme using XOR operations. Quantum key distribution allows for a tamper-proof key exchange, and at the same time, XOR encryption provides a very simple and quick encryption and decryption process. Thus, this double-layer security system not only ensures data privacy and data integrity but also makes it difficult for the attackers to use brute force or become one of the middle parties during the transaction. Moreover, the XOR algorithm can lower the number of calculations needed for the process, so the method can be utilized in real-time secure communication without any computational overhead. Simulation experiments are used for the evaluation of security, the time for the key generation, and the efficiency of encryption. Experiments of results underline the excellent protection of information interception and low technical overhead signalled in comparison with traditional methods of cryptography. This paper exemplifies one possible way to mix quantum and classical encryption techniques to build a secure communication system that is reliable, upgradable, and less vulnerable to attacks, which could eventually lead to a post-quantum era.