As far as i understand, a encryption system is forward secure if new session keys are generated for each session, which is also part of what wikipedia says about forward secrecy:
By generating a unique session key for every session a user initiates, the compromise of a single session key will not affect any data other than that exchanged in the specific session protected by that particular key.
So far, so good, but it is the definition that bugs me:
An encryption system has the property of forward secrecy if plain-text (decrypted) inspection of the data exchange that occurs during key agreement phase of session initiation does not reveal the key that was used to encrypt the remainder of the session.
1. In this way, shouldn't e.g. asymmetric encryption be forward secure even if we do NOT alter keys between sessions?
For asymmetric encryption, the data exchange during key agreement does NOT include the private key and also not necessarily the public key, hence a plain-text inspection of it does not reveal the key(s) that are used to encrypt the session...
If i interpret it as both keys shouldn't be send as plaintext, then an assumed asymmetric encryption that changes the private-public key pair for each session is also NOT forward secure, because the public key is always public.