eprint.iacr.orgpaperLINE-Break: Cryptanalysis and Reverse Engineering of Letter Sealing
LINE-Break is a security analysis of Letter Sealing v2, the custom end-to-end encryption protocol in the LINE messenger. A TLS man-in-the-middle attacker or malicious server can replay, reorder and block messages undetected, and colluding users can forge message authorship in one-to-one and group chats. Stickers and URL previews leak plaintext. The attacks were verified on the real iOS app and an independent implementation.
TL;DR Shows Letter Sealing v2 in LINE lacks replay protection and origin authentication and leaks plaintext via stickers and URL previews, verified with a MITM on iOS.
Organisations named here
- ACM ASIA CCS 2026
- Diego F. Aranha
- Letter Sealing
- Letter Sealing v2
Technologies named here
- iOS
- LINE
Techniques named here
- Reverse engineering and cryptanalysis of Letter Sealing v2
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