More Than A Secure Shell - Red Hat LINUX 7.2 Reference Manual

Section 10.5:More Than a Secure Shell
• ssh_host_rsa_key.pub — The RSA public key used by sshd for version 2 of the SSH
protocol.
User-specific SSH configuration information is stored in the user's home directory within the .ssh
subdirectory:
• authorized_keys2 — The file that holds a list of "authorized" public keys. If a connecting
user can prove that they know the private key which corresponds to any of these, then they are
authenticated. Note, this is only an optional authentication method.
• id_dsa — Contains the DSA authentication identity of the user.
• id_dsa.pub — The DSA public key of the user.
• id_rsa — The RSA public key used by sshd for version 2 of the SSH protocol.
• identity — The RSA private key used by sshd for version 1 of the SSH protocol.
• known_hosts2 — Stores the DSA host keys of the servers a user logs into via SSH when the
user elects to record them. If a server has its host keys legitimately altered, perhaps on a re-instal-
lation of Red Hat Linux, the user will be notified that the host key stored in the known_hosts2
file that corresponds with this host does not match. Then, the user must delete that host's key in
known_hosts in order to store the new host key for that system. The known_hosts2 file
is very important for ensuring that the client is connecting the correct server. If a host's key has
changed, and you are not absolutely certain why it has changed, then you should contact the host's
system administrator to make sure that the host has not be compromised.
See the man pages for ssh and sshd for information concerning the various directives available in
the SSH configuration files.

10.5 More Than a Secure Shell

A secure command line interface is just the beginning of the many ways SSH can be used. Given
the proper amount of bandwidth, X11 sessions can be directed over an SSH channel. Or, by using
TCP/IP forwarding, previously insecure port connections between systems can be mapped to specific
SSH channels.
10.5.1 X11 Forwarding
Opening an X11 session over an established SSH connection is as easy as running an X program while
already running an X client on your host. When an X program is run from the secure shell prompt,
the SSH client and server create a new secure channel within the current SSH connection, and the X
program data is sent over that channel to your client machine as if you were connected to the X server
via a local terminal.
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