Specifications

32 Chapter 2 Connecting to Remote Computers
The following are SSH tools:
 sshd—Daemon that acts as a server to all other commands
 ssh—Primary user tool that includes a remote shell, remote command, and port-
forwarding sessions
 scp—Secure copy, a tool for automated file transfers
 sftp—Secure FTP, a replacement for FTP
Generating Key Pairs for Key-Based SSH Connections
By default, SSH supports the use of password, key, and Kerberos authentication.
The standard method of SSH authentication is to supply login credentials in the form of
a user name and password. Identity key pair authentication enables you to log in to the
server without supplying a password.
Key-based authentication is more secure than password authentication because it
requires that you have the private key file and know the password that lets you access
that key file. Password authentication can be compromised without a private key file.
This process works as follows:
1 A private and a public key are generated, each associated with a user name to establish
that user’s authenticity.
2 When you attempt to log in as that user, the user name is sent to the remote computer.
3 The remote computer looks in the user’s .ssh/ folder for the user’s public key.
This folder is created after using SSH the first time.
4 A challenge is sent to the user based on his or her public key.
5 The user verifies his or her identity by using the private portion of the key pair to
decode the challenge.
6 After the key is decoded, the user is logged in without the need for a password.
This is especially useful when automating remote scripts.
Note: If the server uses FileVault to encrypt the home folder of the user you want to
use SSH to connect as, you must be logged in on the server to use SSH. Alternatively,
you can store the keys for the user in a location that is not protected by FileVault, but
this is not secure.