# Implementation of a New Strongly-Asymmetric Algorithm and Its Optimization

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Information Science Department, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-0022, Japan

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DICII, Engineering Faculty Via del Politecnico Universitá di Roma Tor Vergata, 1, 00133 Roma, Italy

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Author to whom correspondence should be addressed.

Received: 4 June 2020 / Revised: 28 July 2020 / Accepted: 28 July 2020 / Published: 30 July 2020

(This article belongs to the Special Issue Cryptographic Protocols 2020)

A new public key agreement (PKA) algorithm, called the strongly-asymmetric algorithm (SAA-5), was introduced by Accardi et al. The main differences from the usual PKA algorithms are that Bob has some independent public keys and Alice produces her public key by using some part of the public keys from Bob. Then, the preparation and calculation processes are essentially asymmetric. This algorithms has several free parameters more than the usual symmetric PKA algorithms and the velocity of calculation is largely dependent on the parameters chosen; however, the performance of it has not yet been tested. The purpose of our study was to discuss efficient parameters to share the key with high speeds in SAA-5 and to optimize SAA-5 in terms of calculation speed. To find efficient parameters of SAA-5, we compared the calculation speed with Diffie–Hellman (D-H) while varying values of some parameters under the circumstance where the length of the secret shared key (SSK) was fixed. For optimization, we discuss a more general framework of SAA-5 to find more efficient operations. By fixing the parameters of the framework properly, a new PKA algorithm with the same security level as SAA-5 was produced. The result shows that the calculation speed of the proposed PKA algorithm is faster than D-H, especially for large key lengths. The calculation speed of the proposed PKA algorithm increases linearly as the SSK length increases, whereas D-H increases exponentially.