Understanding SSH authentication ssh

126 ask for a password or passphrase as long as password authentication is not needed as when youre using RSA user authentication, and as long a passphrase isnt used to protect the users private key. Although this method is less secure, its useful in scripts where a user might not be around to supply input. Some security is still maintained because only the user, as the owner of her identity file, can read the private key due to file permissions.

8.3.2.3 Useful ssh parameters for our purposes

Like sshd, ssh also has a configuration file, called etcssh_config. By default, everything in the file is commented out. In addition, there are a number of command-line parameters. Well look at a few of them here: - username : A useful feature of the SSH client is the ability to change the login name youre using when logging into another machine. Like rsh, it will normally use the name that youre logged in with on the system youre connecting from. You can override that behavior with this parameter. -c cipher : This parameter lets you change the encryption technique the client is using. As weve said, its IDEA by default. The types of ciphers you can set with this parameter are idea , blowfish , des , 3des , arcfour , and none . You can also change this with the Cipher parameter in the ssh_config file. -p port : This allows you to change the default port from 22 to something else, just as in sshd. The Port parameter in ssh_config also controls this. -o option : This allows you to enter a command that includes one of the ssh_config file options for which there might not be a separate parameter. For example, including the configuration file option BatchMode yes will keep the client from asking you for a password or passphrase, which is useful in scripts. -t: This parameter tells the client to force the server to allocate a pseudo-terminal, even if the client is being used to run a command remotely. This parameter is important to our VPN setup.

8.3.2.4 ssh-keygen

The ssh-keygen utility can be used by SSH users to generate their RSA userkey pairs on their client systems, or by an administrator to create a host key pair. Its run straight from the command line, and most users wont need to include any other parameters. It generates the HOME.sshidentity file for the private key, and the HOME.sshidentity.pub file for the