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International Conference on Transparent Optical Networks

Covert Communications-Based Information Reconciliation for Quantum Key Distribution Protocols

John Gariano, Ivan B. Djordjević

Published Jul 1, 2019• 2 citations
Publisher

Abstract

The rate at which a secure key can be generated in a quantum key distribution (QKD) protocol is limited by the channel loss and the quantum bit-error rate (QBER). Increases to the QBER can stem from detector noise, channel noise, or the presence of an eavesdropper, Eve. Eve is capable of obtaining information of the unsecure key by performing an attack on the quantum channel or by listening to all discussion performed via a noiseless public channel. Conventionally a QKD protocol will perform the information reconciliation over the authenticated public channel, revealing the parity bits used to correct for any quantum bit errors. In this invited paper, the possibility of limiting the information revealed to Eve during the information reconciliation is considered. Using a covert communication channel for the transmission of the parity bits, secure key rates are possible at much higher QBERs. This is demonstrated through the simulation of a polarization based QKD system implementing the BB84 protocol, showing significant improvement of the SKRs over the conventional QKD protocols.

DOI
10.1109/icton.2019.8839991

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The rate at which a secure key can be generated in a quantum key distribution (QKD) protocol is limited by the channel loss and the quantum bit-error rate (QBER). Increases to the QBER can stem from detector noise, channel noise, or the presence of an eavesdropper, Eve. Eve is capable of obtaining information of the unsecure key by performing an attack on the quantum channel or by listening to all discussion performed via a noiseless public channel. Conventionally a QKD protocol will perform the information reconciliation over the authenticated public channel, revealing the parity bits used to correct for any quantum bit errors. In this invited paper, the possibility of limiting the information revealed to Eve during the information reconciliation is considered. Using a covert communication channel for the transmission of the parity bits, secure key rates are possible at much higher QBERs. This is demonstrated through the simulation of a polarization based QKD system implementing the BB84 protocol, showing significant improvement of the SKRs over the conventional QKD protocols.
The information that is leaked to an eavesdropper during the error reconciliation phase of quantum key distribution (QKD) protocols limits the maximum bit error rate (BER) of a system. In a standard QKD protocol, parity bits are transmitted over an authenticated noiseless channel, to which Eve has access. This Letter presents the concept of using a covert classical communication channel to transmit the parity bits between Alice and Bob without Eve gaining information of the transmitted parity bits. This allows for higher secure key generation rates and operation of a QKD system in which the BER exceeds the limit of the standard protocol. This concept is then applied to a practical free-space optical system that contains multiple parallel channels, where channel loss, crosstalk, atmospheric turbulence effects, and noise are considered.
Quantum Key Distribution (QKD) is a prominent solution to achieve proven secure data transmission between legitimate users despite any assumptions about the eavesdropper's computational power (given that the laws of quantum mechanics are correct). This remains true even under attacks by quantum computers. In recent years, there has been a great research interest in developing enhanced security constructions based on QKD. This is mainly driven by the envisioned threats of quantum computers to the traditional information security infrastructure based on public key cryptography. This research lies under the wide umbrella of the so-called post-quantum cryptography. However, for any QKD protocol, an accurate estimation of the Quantum Bit Error Rate (QBER) before the information reconciliation phase is crucial for both the efficiency and security perspectives. In spite of the importance of the QBER estimation step, the state-of-the-art literature still lacks a detailed investigation of the practical aspects of this issue. Therefore, this work aims to fill this research gap. An extension of the EnQuad simulator has been used to study the effect of QBER estimation on the efficiency and security of the BB84 QKD protocol for depolarizing quantum channels and individual Intercept/Resend Eve attacks. Various parameters affecting the QBER estimation process have been carefully investigated. Our evaluation has shown the significant importance of the QBER estimation step. Indeed, an empirical formula has been derived for calculating the required size of the sifted key subset (the so-called sharing rate) needed for the QBER estimation. This is a major contribution of the presented work.
In the system of quantum key distribution (QKD), errors may occur in the initial keys due to system noise or eavesdropping during the transmission on quantum channel. The goal of information reconciliation is to remove these errors by exchanging messages on an authenticated public channel. In this paper, we discuss the problem of secrete key reconciliation (SKR) in QKD, analyze the cascade protocol used for SKR, then modify it according to our conclusion. Experiments have shown that the modified protocol is of much higher efficiency.
CASCADE protocol is an error detection and correction (EDC) method proposed firstly for use in quantum key distribution (QKD) systems. It is used to detect and correct all the errors in keys transmitted over a noisy quantum channel. This is done by sending some redundant information about the key to receiver as usual. However, just as differently, this extra information is sent over another noiseless classical channel after the quantum transmission is completely finished. Briefly, all the errors in noisy quantum communication are detected and corrected by a later noiseless classical communication using CASCADE protocol. In QKD literature, this EDC process is also called as information reconciliation (IR) or secret key reconciliation (SKR). For an IR protocol in QKD, one of the main performance measures is efficiency which depends on the amount of redundant information sent to make EDC possible. Since this extra information is transmitted over public channels, everyone can get it easily. Because this can damage the secrecy of keys that must be kept secret from third parties, more efficient, that is revealing less information about keys, IR methods are needed. In this paper, we present more efficient implementations of CASCADE protocol, using some inherent information already available in the protocol, exactly known bits and already known parities. This information is used in error detection and correction steps of the protocol to decrease the redundancy in redundant information. Our experiments have shown that the resulting protocols have higher efficiency than both all the previous CASCADE versions and several other more recently proposed IR methods.
Practical quantum key distribution (QKD) systems operate under noise, but security of most protocols have been analyzed under ideal noiseless scenarios. In this work, we investigated security performance of BB84 protocol under effect of collective rotation noise. Using theoretical quantum information frameworks, we analyzed key security parameters including quantum bit error rate (QBER), mutual information and secret key rate (SKR). Security of protocol is studied under various eavesdropping scenarios based on intercept and resend attacks. Our results show that collective rotation noise has a significant impact on the information shared between the two parties. Particularly, we extended prior treatments by suggesting a noise engineering strategy where we identified a non-zero noise range where information accessed by Eve is minimized while corresponding SKR degradation remains relatively small. This analysis provide insights into robustness of BB84 protocol under realistic noisy channels and may contribute towards development of more resilient QKD systems.
Quantum Key Distribution (QKD) is a promising field in modern cryptography where the security of key information is guaranteed by the laws of quantum mechanics. One of the key stages in QKD protocols is error estimation and reconciliation in the secret key. This procedure requires the transmission of a certain number of secret key bits over a public channel. Such transmission leads to disclosing these bits to a potential eavesdropper. The fraction of disclosed bits—the sampling rate-largely depends on the chosen approach for preliminary error estimation in the channel. This work is devoted to the optimization of the sampling rate for an LDPC code from the 5G\mathbf{5 G}5G standard. The results of our experiments show that for a QBER below 0.2 and key lengths of 264, 528, 792, and 1056 bits, it is necessary to disclose no more than 18%,11%,10%18 \%, 11 \%, 10 \%18%,11%,10%, and 7%7 \%7% of the key bits for error estimation, respectively. Furthermore, the proposed algorithm allows for similar optimization for any information reconciliation protocols and actual quantum bit error rates.