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Paper Abstract and Keywords
Presentation 2026-03-03 10:00
Automated Security Verification of LINE Group Communication Using Tamarin-Prover
Takehiro Matsumoto, Atsushi Tanaka, Kyosuke Yamashita, Ryoma Ito, Takanori Isobe (The University of Osaka, Japan) ICSS2025-86
Abstract (in Japanese) (See Japanese page) 
(in English) In this paper, we conduct a formal security verification of LINE’s group communication protocols, Letter Sealing Version 1 and Version 2, using the Tamarin Prover. While LINE’s end-to-end encrypted (E2EE) communication has become an essential component of Japan’s social infrastructure, formal verification of its group communication protocol had not been previously explored.

This study defines two threat models: a malicious server (E2E adversary) and a malicious group member. Based on these models, we verify critical security properties, including confidentiality, authenticity, integrity, and resistance to replay attacks. Our verification results demonstrate that Version 2 provides enhanced authenticity against malicious servers through the adoption of AES-GCM. However, the analysis also reveals persistent vulnerabilities, specifically regarding internal attackers and the inherent lack of forward secrecy.
Keyword (in Japanese) (See Japanese page) 
(in English) LINE Letter Sealing / End-to-End Encryption / Formal Verification / Tamarin Prover / / / /  
Reference Info. IEICE Tech. Rep., vol. 125, no. 381, ICSS2025-86, pp. 1-8, March 2026.
Paper # ICSS2025-86 
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 ICSS2025-86

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) Automated Security Verification of LINE Group Communication Using Tamarin-Prover 
Sub Title (in English)  
Keyword(1) LINE Letter Sealing  
Keyword(2) End-to-End Encryption  
Keyword(3) Formal Verification  
Keyword(4) Tamarin Prover  
Keyword(5)  
Keyword(6)  
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1st Author's Name Takehiro Matsumoto  
1st Author's Affiliation The University of Osaka, Japan (The University of Osaka, Japan)
2nd Author's Name Atsushi Tanaka  
2nd Author's Affiliation The University of Osaka, Japan (The University of Osaka, Japan)
3rd Author's Name Kyosuke Yamashita  
3rd Author's Affiliation The University of Osaka, Japan (The University of Osaka, Japan)
4th Author's Name Ryoma Ito  
4th Author's Affiliation The University of Osaka, Japan (The University of Osaka, Japan)
5th Author's Name Takanori Isobe  
5th Author's Affiliation The University of Osaka, Japan (The University of Osaka, Japan)
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Speaker Author-1 
Date Time 2026-03-03 10:00:00 
Presentation Time 20 minutes 
Registration for ICSS 
Paper # ICSS2025-86 
Volume (vol) vol.125 
Number (no) no.381 
Page pp.1-8 
#Pages 8 
Date of Issue 2026-02-24 (ICSS) 

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