http://ssd.iykpqm7jiradoeezzkhj7c4b33g4hbgfwelht2evxxeicbpjy44c7ead.onion/ps/module/deep-dive-end-end-encryption-how-do-public-key-encryption-systems-work
With OTR, every back-and-forth message is a “session.” This means that if a single key is leaked, only messages from that session are compromised, not anything before or after. If multiple messages were sent from one user in a row, one key leak would reveal all of them, but not anything before or after.