[fix] Derive symmetric key correctly

[freak4pc]

I discussed this with @Sn0wfreezeDev privately,

When deriving symmetric keys, the code was always deriving from the root symmetric key instead of deriving from the oldest relevant symmetric key.

This produced the same symmetric key over and over and over instead of deriving new rolling ones.

Thanks to @ThatFatPat for helping me debug this 🚀

[Sn0wfreezeDev]

Thanks a lot for discovering that issue. Happy to accept your PR 😊