I have studied how SSL/TLS works when we use HTTPS connection. After authentication stage is over, using Diffie–Hellman both client and server share secret session key which is used for encryption/decryption.
I have also read using Wireshark or Fiddler one can decrypt HTTPS traffic in case Server private key is known and when Diffie–Hellman is not used for exchange of secret session key .
I have following doubts with respect to my Linux System -
(1) In case my root/admin password is compromised or my admin becomes untrusted, will the Intruder with root permission / untrusted admin can retrieve Secret Session Key used for HTTPS communication (With Known Server private key) and still able to decrypt the HTTPS traffic?
(2) Can I say with 100% confidence that without Server private key, it is not possible to decrypt HTTPS traffic even for an root/admin user? (This is the reason HTTPS is used).
(3) Is it true, when Diffie-Hellman is used to share Secret Shared Key,the connection is 100% secure , means no tools are available to retrieve decrypted HTTPS traffic?
Any help to clear my doubts or relevant links will be highly appreciated. Thank you in advance.