Can a hacker attach to a proprietary server port with a generic client source high port and somehow be able to utilise the other services running on that server?

telnet, rlogin, vnc, ssh and programs like them can be used to login and access a system. If they are allowed.

ssh can be used with a public key infrastructure with encryption keys that can be distributed to allow access to certain users. The high encrytion used has never been broken to my knowledge. I think it would be like picking a star from the universe.

The other login daemons are insecure and should be disabled.

Anything that is dependant on a simple password that can be broken with enough time is insecure and should not be allowed root access.

56bit = ok
57bit = 2 x ok
58bit = 4 x ok
59bit = 8 x ok
768bit = ssh