Mayssaa El Rifai

Multi-photon tolerant secure quantum communication — From theory to practice

Contemporary implementations of Quantum Key Distribution are based on BB84, first proposed in 1984, and commercially implemented for limited market applications in the early 2000s. A major limitation of BB84 is that it requires no more than a single photon per time slot. But no device can reliably generate single photons with guaranteed periodicity. In this paper, we address the practical issues of realizing quantum cryptography systems. In particular, we address the major shortcomings of quantum cryptography as practiced today - the limitation of requiring a single photon to be used in communication. This not only affects the security of the practical quantum cryptography systems, but also restricts the distance over which secure keys can be sent and their rate. Our approach is not limited to a single photon per time-slot thus making it possible to send keys faster and over longer distances. The paper discusses the innate nature of multi-photon communication protocols as a surrogate for quantum communication while giving it a cryptographic strength that would closely match that of a pure quantum communication system.

An Algorithmic Approach to Securing the Three-Stage Quantum Cryptography Protocol

A recent paper has discussed the implementation of the three-stage protocol as a multi-photon tolerant protocol. In this paper, we present a powerful algorithm to further enhance the security of the three-stage protocol. Using this algorithm, the three-stage protocol will be provided with yet another layer of security by provisioning an initialization vector between the two communicating parties. The addition of this contrivance makes it theoretically impossible for any intruder to recover the plaintext except under the condition when the intruder has simultaneous real-time access to four elements in the implementation of the protocol. In this paper, it is postulated that the concept can be extended to an electronic implementation with minor enhancement.

Multi-photon quantum key distribution based on double-lock encryption

We present a quantum key distribution protocol based on the double-lock cryptography. It exploits the asymmetry in the detection strategies between the legitimate users and the eavesdropper. With coherent states, the mean photon number can be as larger as 10.

Multi-stage quantum secure communication using polarization hopping

This paper proposes a generalized multi-stage multi-photon protocol that uses arbitrary polarization states to securely communicate between a sender and a receiver. Because the polarization measurement of an arbitrarily polarized state results in altering the state in an irreversible way, any such measurement produces noise in the measured state. The proposed multi-stage protocol exploits this phenomenon to provide quantum secure communication. This paper assesses the vulnerability of the multi-stage protocol to photon number splitting attack and Trojan horse attack. In addition, it presents an upper bound on the number of photons that can be used per pulse to exchange information while maintaining quantum-level security. Determination of such a bound is important for the multi-stage protocol to operate in the multi-photon domain while maintaining a quantum level of security. Furthermore, this paper proposes a key/message expansion scheme that provides another layer of security to the multi-stage protocol. The multi-stage protocol, can potentially provide higher data rates as well as longer communication distances. Copyright

Quantum secure communication using a multi-photon tolerant protocol

This paper proposes a quantum secure communication protocol using multiple photons to represent each bit of a message to be shared. The multi-photon tolerant approach to quantum cryptography provides a quantum level security while using more than a single photon per transmission. The protocol proposed is a multi-stage protocol; an explanation of its operation and implementation are provided. The multi-stage protocol is based on the use of unitary transformations known only to Alice and Bob. This paper studies the security aspects of the multi-stage protocol by assessing its vulnerability to different attacks. It is well known that as the number of photons increases, the level of vulnerability of the multi-stage protocol increases. This paper sets a limit on the number of photons that can be used while keeping the multi-stage protocol a multi-photon tolerant quantum secure method for communication. The analysis of the number of photons to be used is based on the probability of success of a Helstrom discrimination done by an eavesdropper on the channel. Limiting the number of photons up to certain threshold per stage makes it impossible for an eavesdropper to decipher the message sent over the channel. The proposed protocol obviates the disadvantages associated with single photon implementations, such as limited data rates and distances along with the need to have no more than a single photon per time slot. The multi-stage protocol is a step toward direct quantum communication rather than quantum key distribution associated with single photon approaches.

Implementation of an m-ary three-stage quantum cryptography protocol

This paper introduces an m-ary version of the Three-stage Quantum Cryptography protocol. The three-stage protocol was first proposed in 2006 and implemented in 2012. The m-ary version of the three-stage protocol proposed in this paper results in enhanced data transfer between a sender Alice and a receiver Bob since each pulse carries more than one bit of information. An experimental realization of the m-ary three-stage protocol is also reported in this paper. The implementation has used free-space optics as the transmission medium and passive optical components controlled through LabView. Furthermore, analytical results that address the impact of the noise factor and its trade-off with data rate are presented. This analysis includes a study of the probability of errors and channel capacity variations in terms of the noise variance factor for the m-ary three-stage protocol using two, four and eight levels. Limits within which the m-ary three-stage protocol can be used with higher performance efficiency compared to its original version counterpart are set.

An Ultra-Secure Router-to-Router Key Exchange System

This chapter presents an ultra-secure router-to-router key exchange system. The key exchange process can be initiated by either router at will and can be carried out as often as required. The cryptographic strength of the proposed protocols lies in the use of multi-stage transmission where the number of variables exceeds the number of stages by one, ensuring that the number of possible measurements is one less that the number of variables. The proposed system carries out all processing in electronics and is not vulnerable to the man in the middle attack. The treatment presented in this chapter is based on the authors’ work in [1, 2].

Preliminary Security Analysis of the Multi-stage Protocol

This chapter presents a security analysis of the multi-stage protocol assessing its vulnerability to known security attacks. It shows that the multi-stage protocol can offer quantum level security under certain conditions. The material presented in this chapter is based on the authors’ work previously published in [12, 13].

The Three-Stage Protocol: Its Operation and Implementation

This chapter introduces the three-stage multi-photon protocol, its operation and implementation in a laboratory environment. The implementation uses free-space optics as the transmission medium. Parts of this chapter are based on the authors’ work previously reported in [1].

The Multi-stage Protocol

This chapter generalizes the three-stage protocol into a family of multi-stage protocols. It compares the multi-stage protocol with single-photon protocols and illustrates how a multi-photon protocol can be made secure against man-in-the-middle attack. Since a multi-photon protocol is, in general, subject to photon-siphoning attacks, the protocol introduces another variable to thwart such attacks. Parts of this chapter are based on the authors’ work previously reported in [1, 2, 3].