openSolaris 2008 - Using Solaris Secure Shell - System Administration Guide: Security Services

Using Solaris Secure Shell

Solaris Secure Shell provides secure access between a local shell and a remote shell. For more information, see the ssh_config(4) and ssh(1) man pages.

How to Generate a Public/Private Key Pair for Use With Solaris Secure Shell

Users must generate a public/private key pair when their site implements host-based authentication or user public-key authentication. For additional options, see the ssh-keygen(1) man page.

Before You Begin

Determine from your system administrator if host-based authentication is configured.

Start the key generation program.
```
myLocalHost% ssh-keygen -t rsa
Generating public/private rsa key pair.
…
```
where -t is the type of algorithm, one of rsa, dsa, or rsa1.
Specify the path to the file that will hold the key.
By default, the file name id_rsa, which represents an RSA v2 key, appears in parentheses. You can select this file by pressing the Return key. Or, you can type an alternative file name.
```
Enter file in which to save the key (/home/jdoe/.ssh/id_rsa):<Press Return>
```
The file name of the public key is created automatically by appending the string .pub to the name of the private key file.
Type a passphrase for using your key.
This passphrase is used for encrypting your private key. A null entry is strongly discouraged. Note that the passphrase is not displayed when you type it in.
```
Enter passphrase (empty for no passphrase): <Type passphrase>
```

Retype the passphrase to confirm it.

Enter same passphrase again: <Type passphrase>
Your identification has been saved in /home/jdoe/.ssh/id_rsa.
Your public key has been saved in /home/jdoe/.ssh/id_rsa.pub.
The key fingerprint is:
0e:fb:3d:57:71:73:bf:58:b8:eb:f3:a3:aa:df:e0:d1 jdoe@myLocalHost

Check the results.
Check that the path to the key file is correct.
```
% ls ~/.ssh
id_rsa
id_rsa.pub
```
At this point, you have created a public/private key pair.
Choose the appropriate option:
- If your administrator has configured host-based authentication, you might need to copy the local host's public key to the remote host.
  You can now log in to the remote host. For details, see How to Log In to a Remote Host With Solaris Secure Shell.
  1. Type the command on one line with no backslash.
```
% cat /etc/ssh/ssh_host_dsa_key.pub | ssh RemoteHost \
'cat >> ~./ssh/known_hosts && echo "Host key copied"'
```
  2. When you are prompted, supply your login password.
```
Enter password: <Type password>
Host key copied
%
```
- If your site uses user authentication with public keys, populate your authorized_keys file on the remote host.
  1. Copy your public key to the remote host.
    Type the command on one line with no backslash.
```
myLocalHost% cat $HOME/.ssh/id_rsa.pub | ssh myRemoteHost \
'cat >> .ssh/authorized_keys && echo "Key copied"'
```
  2. When you are prompted, supply your login password.
    When the file is copied, the message “Key copied” is displayed.
```
Enter password: Type login password
Key copied
myLocalHost%
```
(Optional) Reduce the prompting for passphrases.
For a procedure, see How to Reduce Password Prompts in Solaris Secure Shell. For more information, see the ssh-agent(1) and ssh-add(1) man pages.

Example 19-2 Establishing a v1 RSA Key for a User

In the following example, the user can contact hosts that run v1 of the Solaris Secure Shell protocol. To be authenticated by v1 hosts, the user creates a v1 key, then copies the public key portion to the remote host.

myLocalHost% ssh-keygen -t rsa1 -f /home/jdoe/.ssh/identity
Generating public/private rsa key pair.
…
Enter passphrase (empty for no passphrase): <Type passphrase>
Enter same passphrase again: <Type passphrase>
Your identification has been saved in /home/jdoe/.ssh/identity.
Your public key has been saved in /home/jdoe/.ssh/identity.pub.
The key fingerprint is:
…
myLocalHost% ls ~/.ssh
id_rsa
id_rsa.pub
identity
identity.pub
myLocalHost% cat $HOME/.ssh/identity.pub | ssh myRemoteHost \
'cat >> .ssh/authorized_keys && echo "Key copied"'

How to Change the Passphrase for a Solaris Secure Shell Private Key

The following procedure does not change the private key. The procedure changes the authentication mechanism for the private key, the passphrase. For more information, see the ssh-keygen(1) man page.

Change your passphrase.

Type the ssh-keygen command with the -p option, and answer the prompts.

myLocalHost% ssh-keygen -p
Enter file which contains the private key (/home/jdoe/.ssh/id_rsa):<Press Return>
Enter passphrase (empty for no passphrase): <Type passphrase>
Enter same passphrase again:   <Type passphrase>

where -p requests changing the passphrase of a private key file.

How to Log In to a Remote Host With Solaris Secure Shell

Start a Solaris Secure Shell session.

Type the ssh command, and specify the name of the remote host.

myLocalHost% ssh myRemoteHost

A prompt questions the authenticity of the remote host:

The authenticity of host 'myRemoteHost' can't be established.
RSA key fingerprint in md5 is: 04:9f:bd:fc:3d:3e:d2:e7:49:fd:6e:18:4f:9c:26
Are you sure you want to continue connecting(yes/no)?

This prompt is normal for initial connections to remote hosts.

If prompted, verify the authenticity of the remote host key.
- If you cannot confirm the authenticity of the remote host, type no and contact your system administrator.
```
Are you sure you want to continue connecting(yes/no)? no
```
  The administrator is responsible for updating the global /etc/ssh/ssh_known_hosts file. An updated ssh_known_hosts file prevents this prompt from appearing.
- If you confirm the authenticity of the remote host, answer the prompt and continue to the next step.
```
Are you sure you want to continue connecting(yes/no)? yes
```

Authenticate yourself to Solaris Secure Shell.

When prompted, type your passphrase.

Enter passphrase for key '/home/jdoe/.ssh/id_rsa': <Type passphrase>

When prompted, type your account password.

jdoe@myRemoteHost's password: <Type password>
Last login: Fri Jul 20 14:24:10 2001 from myLocalHost
myRemoteHost%

Conduct transactions on the remote host.
The commands that you send are encrypted. Any responses that you receive are encrypted.
Close the Solaris Secure Shell connection.
When you are finished, type exit or use your usual method for exiting your shell.
```
myRemoteHost% exit
myRemoteHost% logout
Connection to myRemoteHost closed
myLocalHost%
```

How to Reduce Password Prompts in Solaris Secure Shell

If you do not want to type your passphrase and your password to use Solaris Secure Shell, you can use the agent daemon. Start the daemon at the beginning of the session. Then, store your private keys with the agent daemon by using the ssh-add command. If you have different accounts on different hosts, add the keys that you need for the session.

You can start the agent daemon manually when needed, as described in the following procedure. Or, you can set the agent daemon to run automatically at the start of every session as described in How to Set Up the ssh-agent Command to Run Automatically in CDE.

Start the agent daemon.
```
myLocalHost% ssh-agent
```

Verify that the agent daemon has been started.

myLocalHost% eval `ssh-agent`
Agent pid 9892

Add your private key to the agent daemon.

Type the ssh-add command.

myLocalHost% ssh-add
Enter passphrase for /home/jdoe/.ssh/id_rsa: <Type passphrase>
Identity added: /home/jdoe/.ssh/id_rsa(/home/jdoe/.ssh/id_rsa)
myLocalHost%

Start a Solaris Secure Shell session.
```
myLocalHost% ssh myRemoteHost
```
You are not prompted for a passphrase.

Example 19-3 Using `ssh-add` Options

In this example, jdoe adds two keys to the agent daemon. The -l option is used to list all keys that are stored in the daemon. At the end of the session, the -D option is used to remove all the keys from the agent daemon.

myLocalHost% ssh-agent
myLocalHost% ssh-add
Enter passphrase for /home/jdoe/.ssh/id_rsa: <Type passphrase>
Identity added: /home/jdoe/.ssh/id_rsa(/home/jdoe/.ssh/id_rsa)
myLocalHost% ssh-add /home/jdoe/.ssh/id_dsa
Enter passphrase for /home/jdoe/.ssh/id_dsa: <Type passphrase>
Identity added:
/home/jdoe/.ssh/id_dsa(/home/jdoe/.ssh/id_dsa)

myLocalHost% ssh-add -l
md5 1024 0e:fb:3d:53:71:77:bf:57:b8:eb:f7:a7:aa:df:e0:d1
/home/jdoe/.ssh/id_rsa(RSA)
md5 1024 c1:d3:21:5e:40:60:c5:73:d8:87:09:3a:fa:5f:32:53
/home/jdoe/.ssh/id_dsa(DSA)

User conducts Solaris Secure Shell transactions

myLocalHost% ssh-add -D
Identity removed:
/home/jdoe/.ssh/id_rsa(/home/jdoe/.ssh/id_rsa.pub)
/home/jdoe/.ssh/id_dsa(DSA)

How to Set Up the `ssh-agent` Command to Run Automatically in CDE

If you use CDE, you can avoid providing your passphrase and password whenever you use Solaris Secure Shell by automatically starting an agent daemon, ssh-agent. You can start the agent daemon from the .dtprofile script. To add your passphrase and password to the agent daemon, see Example 19-3.

Caution - If you use the Sun Java^TM Desktop System (Java DS), do not set up the ssh-agent command to run automatically. Because the killing of the ssh-agent process is controlled by a CDE interface, when you exit the Java DS, the daemon continues to run. For example, if you start the daemon in a CDE session, move to a Java DS session, and then log out, the daemon continues to run.

A running daemon uses system resources. Although no known issues are associated with leaving the ssh-agent daemon running, the daemon contains a password, which could create a security risk.

Start the agent daemon automatically in a user startup script.
Add the following lines to the end of the $HOME/.dtprofile script:
```
if [ "$SSH_AUTH_SOCK" = "" -a -x /usr/bin/ssh-agent ]; then
                eval `/usr/bin/ssh-agent`
fi
```
Terminate the agent daemon when you exit the CDE session.
Add the following lines to the $HOME/.dt/sessions/sessionexit script:
```
if [ "$SSH_AGENT_PID" != "" -a -x /usr/bin/ssh-agent ]; then
                /usr/bin/ssh-agent -k
fi
```
This entry ensures that no one can use the Solaris Secure Shell agent after a CDE session is terminated. Because the script uses a CDE-specific interface, sessionexit, this procedure does not terminate the agent daemon in a Sun Java Desktop System session.

How to Use Port Forwarding in Solaris Secure Shell

You can specify that a local port be forwarded to a remote host. Effectively, a socket is allocated to listen to the port on the local side. The connection from this port is made over a secure channel to the remote host. For example, you might specify port 143 to obtain email remotely with IMAP4. Similarly, a port can be specified on the remote side.

Before You Begin

To use port forwarding, the administrator must have enabled port forwarding on the remote Solaris Secure Shell server. For details, see How to Configure Port Forwarding in Solaris Secure Shell.

To use secure port forwarding, choose one of the following options:
- To set a local port to receive secure communication from a remote port, specify both ports.
  Specify the local port that listens for remote communication. Also, specify the remote host and the remote port that forward the communication.
```
myLocalHost% ssh -L localPort:remoteHost:remotePort 
```
- To set a remote port to receive a secure connection from a local port, specify both ports.
  Specify the remote port that listens for remote communication. Also, specify the local host and the local port that forward the communication.
```
myLocalHost% ssh -R remotePort:localhost:localPort
```

Example 19-4 Using Local Port Forwarding to Receive Mail

The following example demonstrates how you can use local port forwarding to receive mail securely from a remote server.

myLocalHost% ssh -L 9143:myRemoteHost:143 myRemoteHost

This command forwards connections from port 9143 on myLocalHost to port 143. Port 143 is the IMAP v2 server port on myRemoteHost. When the user launches a mail application, the user needs to specify the local port number, as shown in the following dialog box.

Dialog box titled Mailer - Login. The IMAP Server field shows the server name followed by a colon and the port number.

Do not confuse localhost in the dialog box with myLocalHost. myLocalHost is a hypothetical host name. localhost is a keyword that identifies your local system.

Example 19-5 Using Remote Port Forwarding to Communicate Outside of a Firewall

This example demonstrates how a user in an enterprise environment can forward connections from a host on an external network to a host inside a corporate firewall.

myLocalHost% ssh -R 9022:myLocalHost:22 myOutsideHost

This command forwards connections from port 9022 on myOutsideHost to port 22, the sshd server, on the local host.

myOutsideHost% ssh -p 9022 localhost
myLocalHost%

How to Copy Files With Solaris Secure Shell

The following procedure shows how to use the scp command to copy encrypted files between hosts. You can copy encrypted files either between a local host and a remote host, or between two remote hosts. The command operates similarly to the rcp command, except that the scp command prompts for authentication. For more information, see the scp(1) man page.

You can also use the sftp, a more secure form of the ftp command. For more information, see the sftp(1) man page. For an example, see Example 19-6.

Start the secure copy program.
Specify the source file, the user name at the remote destination, and the destination directory.
```
myLocalHost% scp myfile.1 jdoe@myRemoteHost:~
```
Supply your passphrase when prompted.
```
Enter passphrase for key '/home/jdoe/.ssh/id_rsa': <Type passphrase>
myfile.1       25% |*******                      |    640 KB  0:20 ETA 
myfile.1 
```
After you type the passphrase, a progress meter is displayed. See the second line in the preceding output. The progress meter displays:
- The file name
- The percentage of the file that has been transferred
- A series of asterisks that indicate the percentage of the file that has been transferred
- The quantity of data transferred
- The estimated time of arrival, or ETA, of the complete file (that is, the remaining amount of time)

Example 19-6 Specifying a Port When Using the `sftp` Command

In this example, the user wants the sftp command to use a specific port. The user uses the -o option to specify the port.

% sftp -o port=2222 guest@RemoteFileServer

How to Set Up Default Connections to Hosts Outside a Firewall

You can use Solaris Secure Shell to make a connection from a host inside a firewall to a host outside the firewall. This task is done by specifying a proxy command for ssh either in a configuration file or as an option on the command line. For the command-line option, see Example 19-7.

In general, you can customize your ssh interactions through a configuration file.

You can customize either your own personal file in ~/.ssh/config.
Or, you can use the settings in the administrative configuration file, /etc/ssh/ssh_config.

The files can be customized with two types of proxy commands. One proxy command is for HTTP connections. The other proxy command is for SOCKS5 connections. For more information, see the ssh_config(4) man page.

Specify the proxy commands and hosts in a configuration file.
Use the following syntax to add as many lines as you need:
```
[Host outside-host]
ProxyCommand proxy-command [-h proxy-server] \
[-p proxy-port] outside-host|%h outside-port|%p
```
Host outside-host

Limits the proxy command specification to instances when a remote host name is specified on the command line. If you use a wildcard for outside-host, you apply the proxy command specification to a set of hosts.

proxy-command
Specifies the proxy command.
The command can be either of the following:
- /usr/lib/ssh/ssh-http-proxy-connect for HTTP connections
- /usr/lib/ssh/ssh-socks5-proxy-connect for SOCKS5 connections
-h proxy-server and -p proxy-port

These options specify a proxy server and a proxy port, respectively. If present, the proxies override any environment variables that specify proxy servers and proxy ports, such as HTTPPROXY, HTTPPROXYPORT, SOCKS5_PORT, SOCKS5_SERVER, and http_proxy. The http_proxy variable specifies a URL. If the options are not used, then the relevant environment variables must be set. For more information, see the ssh-socks5-proxy-connect(1) and ssh-http-proxy-connect(1) man pages.

outside-host

Designates a specific host to connect to. Use the %h substitution argument to specify the host on the command line.

outside-port

Designates a specific port to connect to. Use the %p substitution argument to specify the port on the command line. By specifying %h and %p without using the Host outside-host option, the proxy command is applied to the host argument whenever the ssh command is invoked.
Run Solaris Secure Shell, specifying the outside host.
For example, type the following:
```
myLocalHost% ssh myOutsideHost
```
This command looks for a proxy command specification for myOutsideHost in your personal configuration file. If the specification is not found, then the command looks in the system-wide configuration file, /etc/ssh/ssh_config. The proxy command is substituted for the ssh command.

Example 19-7 Connecting to Hosts Outside a Firewall From the Command Line

How to Set Up Default Connections to Hosts Outside a Firewall explains how to specify a proxy command in a configuration file. In this example, a proxy command is specified on the ssh command line.

% ssh -o'Proxycommand=/usr/lib/ssh/ssh-http-proxy-connect \
-h myProxyServer -p 8080 myOutsideHost 22' myOutsideHost

The -o option to the ssh command provides a command-line method of specifying a proxy command. This example command does the following:

Substitutes the HTTP proxy command for ssh
Uses port 8080 and myProxyServer as the proxy server
Connects to port 22 on myOutsideHost

Using Solaris Secure Shell

How to Generate a Public/Private Key Pair for Use With Solaris Secure Shell

Before You Begin

Example 19-2 Establishing a v1 RSA Key for a User

How to Change the Passphrase for a Solaris Secure Shell Private Key

How to Log In to a Remote Host With Solaris Secure Shell

How to Reduce Password Prompts in Solaris Secure Shell

Example 19-3 Using ssh-add Options

How to Set Up the ssh-agent Command to Run Automatically in CDE

How to Use Port Forwarding in Solaris Secure Shell

Before You Begin

Example 19-4 Using Local Port Forwarding to Receive Mail

Example 19-5 Using Remote Port Forwarding to Communicate Outside of a Firewall

How to Copy Files With Solaris Secure Shell

Example 19-6 Specifying a Port When Using the sftp Command

How to Set Up Default Connections to Hosts Outside a Firewall

Example 19-7 Connecting to Hosts Outside a Firewall From the Command Line

Example 19-3 Using `ssh-add` Options

How to Set Up the `ssh-agent` Command to Run Automatically in CDE

Example 19-6 Specifying a Port When Using the `sftp` Command