Remote Administration of Linux Systems - page 3
Introducing Remote Adnministration
Personally, I do not recommend using modem access, as described above, because of some pertinent considerations. First of all, it's not secure--all data will be transferd via phone lines without any encryption (plain-text). Second, it's not suitable--you can only open one terminal per session. If you will need to gain access to a text console via modem, I suggest you to configure mgetty in AutoPPP modem. If using a PPP connection (like a dialup connection to an ISP) you can run the TCP/IP protocol and work with that.
For very paranoid users, we can configure authentification in ssh with the help of a digital signature (RSA key), which we can keep not on a diskette, but rather loaded onto a smart card. For detailed information about ssh configuration in this mode, you will need to read the corresponding equipment manuals and HOW-TOs.