Lets say you and the mIRC server is SLS secured.
So the mIRC server issuses you a Public Key when the session starts.
Then what if you talk to private message someone on the server that is not SLS secured, your conversation still encrypted?
Or when you transfer files, and the someone is also not encryted, but you and the server are, your files still encryted?
Both User's data has to pass through the server before it reaches the user, so I supposed it is still encryted? As your connection with the server is secure, but the other person is not secured, but since the server is the middlemen, the data is still encryted with the public key before reaching you?
It's SSL, not SLS.
If I'm not wrong, I don't think it's possible. Either the person sign on to the server or you sign off the server to message him. The way PKI works requires a public and private key, of which is three-way. It's not a one-way communication thing.
I won't go into the technical aspects, but since you ask, you should know why it's 3-way. Basically, it goes this way:
1. Client ask for an SSL-secured website
2. Website sends back the public key
3. Client checks the public key, if OK, continue
Secure communications data packets are encrypted, and this applies to files as well. As per usual, no one-way communication. Either both are communicating via secured communications or no.
Yes, the data is still encrypted. However, once it leaves the server, there's no guarantee that it will still be encrypted.
That means, even though you are connected securely to a server, your files are not. Once it reaches the other person, there's also no guarantee that he keeps the files encrypted as well.