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Paper Abstract and Keywords
Presentation 2026-03-03 16:20
Revisited Constant-Time Modular Inversion
Tomoya Ozaki, Atsuko Miyaji (UOsaka) ICSS2025-110
Abstract (in Japanese) (See Japanese page) 
(in English) In elliptic curve cryptography, scalar multiplication on elliptic curves is composed of point addition and point doubling, and these operations rely on basic arithmetic operations over finite fields.
Among finite field operations, modular inversion is generally more complex in terms of circuit construction compared to addition and multiplication. In classical implementations, constant-time execution is required to provide resistance against side-channel attacks (SCA) for inversion operations. Particularly in timing attacks, secret key information may leak through variations in execution time; therefore, algorithms that guarantee constant execution time independent of input values are essential. Such constant-time implementation requirements contribute to increased implementation complexity.
In this study, we conduct a detailed analysis of the computational characteristics of the Bernstein-Yang divstep algorithm, which has been adopted as the de facto standard for constant-time modular inversion (CTMI), as well as related existing methods. Based on the analysis results, we propose a novel CTMI algorithm that achieves higher performance compared to existing approaches.
Keyword (in Japanese) (See Japanese page) 
(in English) elliptic curve / modular inversion / side-channel attack / / / / /  
Reference Info. IEICE Tech. Rep., vol. 125, no. 381, ICSS2025-110, pp. 177-184, March 2026.
Paper # ICSS2025-110 
Date of Issue 2026-02-24 (ICSS) 
ISSN Online edition: ISSN 2432-6380
Copyright
and
reproduction		 All rights are reserved and no part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Notwithstanding, instructors are permitted to photocopy isolated articles for noncommercial classroom use without fee. (License No.: 10GA0019/12GB0052/13GB0056/17GB0034/18GB0034)
Download PDF ICSS2025-110

Conference Information
Committee ICSS IPSJ-SPT  
Conference Date 2026-03-03 - 2026-03-04 
Place (in Japanese) (See Japanese page) 
Place (in English) Okinawa Prefectural Museum & Art Museum 
Topics (in Japanese) (See Japanese page) 
Topics (in English) Security, Trust, etc. 
Paper Information
Registration To ICSS 
Conference Code 2026-03-ICSS-SPT 
Language Japanese 
Title (in Japanese) (See Japanese page) 
Sub Title (in Japanese) (See Japanese page) 
Title (in English) Revisited Constant-Time Modular Inversion 
Sub Title (in English)  
Keyword(1) elliptic curve  
Keyword(2) modular inversion  
Keyword(3) side-channel attack  
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1st Author's Name Tomoya Ozaki  
1st Author's Affiliation The University of Osaka (UOsaka)
2nd Author's Name Atsuko Miyaji  
2nd Author's Affiliation The University of Osaka (UOsaka)
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Speaker Author-1 
Date Time 2026-03-03 16:20:00 
Presentation Time 20 minutes 
Registration for ICSS 
Paper # ICSS2025-110 
Volume (vol) vol.125 
Number (no) no.381 
Page pp.177-184 
#Pages 8 
Date of Issue 2026-02-24 (ICSS) 

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