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Chinese Physics B

Fast implementation of length-adaptive privacy amplification in quantum key distribution

Chunmei Zhang, Mo Li, Jingzheng Huang, Hongwei Li, Fangyi Li, Chuan Wang, Zhen−Qiang Yin, Wei Ren Chen, Zhen-Fu Han, Patcharapong Treeviriyanupab, Keattisak Sripimanwat

Published Sep 1, 2014• 26 citations
Publisher

Abstract

Post-processing is indispensable in quantum key distribution (QKD), which is aimed at sharing secret keys between two distant parties. It mainly consists of key reconciliation and privacy amplification, which is used for sharing the same keys and for distilling unconditional secret keys. In this paper, we focus on speeding up the privacy amplification process by choosing a simple multiplicative universal class of hash functions. By constructing an optimal multiplication algorithm based on four basic multiplication algorithms, we give a fast software implementation of length-adaptive privacy amplification. "Length-adaptive" indicates that the implementation of privacy amplification automatically adapts to different lengths of input blocks. When the lengths of the input blocks are 1 Mbit and 10 Mbit, the speed of privacy amplification can be as fast as 14.86 Mbps and 10.88 Mbps, respectively. Thus, it is practical for GHz or even higher repetition frequency QKD systems.

DOI
10.1088/1674-1056/23/9/090310

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Post-processing is indispensable in quantum key distribution (QKD), which is aimed at sharing secret keys between two distant parties. It mainly consists of key reconciliation and privacy amplification, which is used for sharing the same keys and for distilling unconditional secret keys. In this paper, we focus on speeding up the privacy amplification process by choosing a simple multiplicative universal class of hash functions. By constructing an optimal multiplication algorithm based on four basic multiplication algorithms, we give a fast software implementation of length-adaptive privacy amplification. "Length-adaptive" indicates that the implementation of privacy amplification automatically adapts to different lengths of input blocks. When the lengths of the input blocks are 1 Mbit and 10 Mbit, the speed of privacy amplification can be as fast as 14.86 Mbps and 10.88 Mbps, respectively. Thus, it is practical for GHz or even higher repetition frequency QKD systems.
Privacy amplification is an indispensable step in postprocessing of continuous-variable quantum key distribution (CV-QKD), which is used to distill unconditional secure keys from identical corrected keys between two distant legal parties. The processing speed of privacy amplification has a significant effect on the secret key rate of a CV-QKD system. We report the high-speed parallel implementation of the length-compatible privacy amplification algorithm based on a graphic processing unit. The length-compatible algorithm is used to satisfy the security requirements of privacy amplification at different transmission distances when considering finite-size effect. We achieve the speed of privacy amplification over 1 Gb/s at arbitrary input length and the speed is one to two orders of magnitude faster than previous demonstrations, which supports the high-speed real-time CV-QKD system and ensures the security of privacy amplification.
In a quantum key distribution (QKD) system, privacy amplification (PA) is an essential procedure that can effectively eliminate the leaked information to an eavesdropper and distill a secret key. The processing speed of the PA algorithm inevitably affects the final key rate of the QKD system. We propose a high-speed PA algorithm based on field-programmable gate array (FPGA), where the matrix multiplications are divided into a number of rhomboid-block operations. The implementation of the PA reduces significantly the required number of FPGA Block RAMs. Meanwhile, it automatically adapts to different lengths of input and output blocks. Finally, we verified the correctness and high-speed of the algorithm when implemented in a Xilinx Virtex-7 FPGA.
Privacy amplification is an indispensable procedure to share secure secret key between legitimate parties in quantum key distribution (QKD) because a portion of bits are still leaked to eavesdropper Eve after the secret reconciliation. Here, we propose a novel privacy amplification scheme with an optimal hash function. In particular, by utilizing the linear feedback shift register (LFSR) technique, we optimize and simplify the construction of the Toeplitz matrix. In this way, the LFSR-based Toeplitz matrix is used to execute the privacy amplification algorithm. The hardware storage resources can then be drastically saved, and the time consuming will be only about half of that without using the LFSR-based Toeplitz matrix. This work breaks the bottleneck of privacy amplification in high-speed continuous-variable QKD (CVQKD), and thus contributes to the real-time performance of the whole CVQKD system.
Abstract Privacy Amplification (PA) is indispensable in Quantum Key Distribution (QKD), ensuring security against eavesdropping by eliminating information leakage. For Discrete-Variable QKD (DV-QKD) protocols, a large input block size exceeding 108 bits is preferred to achieve the secure key rate approaching the asymptotic limit. However, in state-of-the-art quantum key distribution systems operating at multi-GHz pulse rates, PA becomes a critical bottleneck due to the conflicting requirements of large input block sizes and high throughput. To address this challenge, we propose a novel PA algorithm utilizing a newly constructed universal hash family DM3H and prove its cryptographic security rigorously. Based on the PA algorithm, we design and implement an efficient PA scheme which is capable of processing input block sizes up to 10 10 bits while achieving high throughput performance. For an input block size of 1010 bits, the implementation on the i9-14900 platform demonstrates a throughput of 112 Mbps with a retention ratio of 0.33. This breakthrough significantly enhances the secure key rate and maximum transmission distance of DV-QKD systems.
Quantum key distribution protocols typically proceed in several phases: in a first phase, the honest parties exchange signals over the quantum channel. Then, there is a classical post-processing phase, where the honest parties communicate over the classical authentic channel to discard superfluous signals (sifting), estimate the error in the communication channel and the amount of eavesdropping (parameter estimation), correct the errors in their raw key (information reconciliation) and finally create a shorter but highly secure key (privacy amplification). This post-processing phase is often the limiting factor for the secure key rate of quantum key distribution implementations. Significant research effort is therefore made to find better algorithms and create better implementations. Here we propose a fast implementation of privacy amplification. The currently known algorithm with the best asymptotic time-complexity is modified Toeplitz hashing, running at O(n log n) using Fast-Fourier-Transform for fast matrix multiplication. We implement this algorithm on common GPUs using a very efficient and highly parallel CUDA algorithm. For large block sizes of approximately 10^8 bits - needed to limit the finite key effects - we achieve an input throughput of 3.7 Gbit/s with a dynamic Toeplitz seed and 5.7 Gbit/s using a fixed seed. This is several times faster than previously known implementations and can increase the total key-rate of practical quantum key distribution systems significantly.
Privacy amplification (PA) is an essential part in a quantum key distribution (QKD) system, distilling a highly secure key from a partially secure string by public negotiation between two parties. The optimization objectives of privacy amplification for QKD are large block size, high throughput and low cost. For the global optimization of these objectives, a novel privacy amplification algorithm is proposed in this paper by combining multilinear-modular-hashing and modular arithmetic hashing. This paper proves the security of this hybrid hashing PA algorithm within the framework of both information theory and composition security theory. A scheme based on this algorithm is implemented and evaluated on a CPU platform. The results on a typical CV-QKD system indicate that the throughput of this scheme (261Mbps@2.6*10^8 input block size) is twice higher than the best existing scheme (140Mbps@1*10^8 input block size). Moreover, This scheme is implemented on a mobile CPU platform instead of a desktop CPU or a server CPU, which means that this algorithm has a better performance with a much lower cost and power consumption.