QuiNVarium messenger
Safety numbers
Proving that nobody is sitting between you.
Every conversation has a safety number that both sides can see. If the two of you compare it — in person, or over a channel that is not this one — and it matches, then the keys in use are the keys you expect and no one is relaying between you.
When it changes#
A safety number changes when the other person reinstalls the app, switches device or restores their account. That is ordinary. It also changes if someone has taken over their account, which is not. If it changes unexpectedly, ask them why before sending anything sensitive.