Megolm key confusionEstablished cryptographic algorithms like Signal’s double ratchet algorithm may include guidance ...

Megolm key confusionEstablished cryptographic algorithms like Signal’s double ratchet algorithm may include guidance or cautions for application or modifications of the parameters or construction used. But what can happen if you ignore said advice?This article is a full disclosure on a low-severity key confusion vulnerability in version 3 of megolm, the latest version of megolm that is specified and used.Timeline2022-07-05: A pull request for adding a fixed version 4 of megolm was opened2022-08-05: It was merged into vodozemac2022-09-13: vodozemac 0.3.0 was released which contained the fixed versionca. 2024-08: I independently rediscover the vulnerability, but decided to not pursue this further2026-02-26: I discover the aforementioned undeployed fix2026-09-11: I publish this articleThis change, as far as I am aware, is entirely undocumented and unspecified. I decided to immediately disclose the vulnerability due to languishing for several years at this point.Overview of MegolmMegolm…