The Throughput Bottleneck of Quantum-Secure Communication Links: Analysis and Mitigation

The use of quantum key distribution (QKD) to improve security may impact the quality of service (Qos) of high rate classical data links. The key generation process with an empty buffer can be modeled as a queuing system, and data throughput limits can be determined using queueing theory to assess the impact on the QoS. The proposed key generation model is based on an on-demand paradigm. Based on the results of this study, a discrete variable (DV)-QKD-secured link could be designed using the data rate bounds to guarantee a given QoS. Furthermore, we validate the derived bounds by comparing the theoretical derivations with simulations. We show that in a one-time-pad system, the achievable throughput approaches 0.59 times the secret key rate as the key length increases. In the case of a key scheme with key reuse, the throughput is asymptotically linear with the number of key reuses, and the slope of the curve corresponds to the secret key rate multiplied by a function of the protocol and channel characteristics. The analysis is carried out on optical fiber and free-space links.

I. Introduction

Public key encryption is based on computational security, which is the assumption that the encryption system is safe from the attacks of an eavesdropper with limited computing power. As quantum computing advances, it has become apparent that some schemes considered computationally secure may be vulnerable to quantum algorithm-supported attacks. Rivest-Shamir-Adleman (RSA) cipher or Diffie-Hellman key exchange are examples of cryptographic schemes that have been proven vulnerable to quantum attacks [1]. Quantum key distribution (QKD) has been proposed as a complementary technology to traditional encryption schemes to improve the secrecy of the shared keys. The security of QKD schemes is based on the inherent randomness of quantum physical systems, and not on the computational complexity of solving a mathematical problem [2], [3], [4]. In QKD-secured communication, the source wants to establish a secure channel to communicate sensitive information to the receiver. To secure the contents of the message, an encryption scheme that uses the keys generated with QKD is used. The QKD protocol needs a quantum channel to propagate the states and an authenticated classical channel to exchange information about the measurements.