True. Both the sender and receiver needed to know the same secret (the position of internal rotors) in order to communicate successfully and in secret.
A2:
False. The trusted third party maintains our public keys.
A3:
True. Diffie-Hellman is simply a means whereby individuals can agree on a shared, secret key over an insecure medium.
A4:
False. IPSec SAs are uni-directional, and utilities such as telnet and ftp will have at least two SAs: one inbound and one outbound.
A5:
False. By default, IPFilter has no rules defined, and hence all network services are enabled.