===================================================================
RCS file: /cvsrepo/anoncvs/cvs/src/usr.bin/ssh/sshd.8,v
retrieving revision 1.206
retrieving revision 1.206.2.2
diff -u -r1.206 -r1.206.2.2
--- src/usr.bin/ssh/sshd.8	2005/03/01 14:59:49	1.206
+++ src/usr.bin/ssh/sshd.8	2006/02/03 02:53:45	1.206.2.2
@@ -34,7 +34,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: sshd.8,v 1.206 2005/03/01 14:59:49 jmc Exp $
+.\" $OpenBSD: sshd.8,v 1.206.2.2 2006/02/03 02:53:45 brad Exp $
 .Dd September 25, 1999
 .Dt SSHD 8
 .Os
@@ -56,16 +56,14 @@
 .Ek
 .Sh DESCRIPTION
 .Nm
-(SSH Daemon) is the daemon program for
+(OpenSSH Daemon) is the daemon program for
 .Xr ssh 1 .
 Together these programs replace rlogin and rsh, and
 provide secure encrypted communications between two untrusted hosts
 over an insecure network.
-The programs are intended to be as easy to
-install and use as possible.
 .Pp
 .Nm
-is the daemon that listens for connections from clients.
+listens for connections from clients.
 It is normally started at boot from
 .Pa /etc/rc .
 It forks a new
@@ -73,97 +71,13 @@
 The forked daemons handle
 key exchange, encryption, authentication, command execution,
 and data exchange.
-This implementation of
-.Nm
-supports both SSH protocol version 1 and 2 simultaneously.
-.Nm
-works as follows:
-.Ss SSH protocol version 1
-Each host has a host-specific RSA key
-(normally 1024 bits) used to identify the host.
-Additionally, when
-the daemon starts, it generates a server RSA key (normally 768 bits).
-This key is normally regenerated every hour if it has been used, and
-is never stored on disk.
 .Pp
-Whenever a client connects, the daemon responds with its public
-host and server keys.
-The client compares the
-RSA host key against its own database to verify that it has not changed.
-The client then generates a 256-bit random number.
-It encrypts this
-random number using both the host key and the server key, and sends
-the encrypted number to the server.
-Both sides then use this
-random number as a session key which is used to encrypt all further
-communications in the session.
-The rest of the session is encrypted
-using a conventional cipher, currently Blowfish or 3DES, with 3DES
-being used by default.
-The client selects the encryption algorithm
-to use from those offered by the server.
-.Pp
-Next, the server and the client enter an authentication dialog.
-The client tries to authenticate itself using
-.Em rhosts
-authentication combined with RSA host
-authentication, RSA challenge-response authentication, or password
-based authentication.
-.Pp
-System security is not improved unless
-.Nm rshd ,
-.Nm rlogind ,
-and
-.Nm rexecd
-are disabled (thus completely disabling
-.Xr rlogin
-and
-.Xr rsh
-into the machine).
-.Ss SSH protocol version 2
-Version 2 works similarly:
-Each host has a host-specific key (RSA or DSA) used to identify the host.
-However, when the daemon starts, it does not generate a server key.
-Forward security is provided through a Diffie-Hellman key agreement.
-This key agreement results in a shared session key.
-.Pp
-The rest of the session is encrypted using a symmetric cipher, currently
-128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES.
-The client selects the encryption algorithm
-to use from those offered by the server.
-Additionally, session integrity is provided
-through a cryptographic message authentication code
-(hmac-sha1 or hmac-md5).
-.Pp
-Protocol version 2 provides a public key based
-user (PubkeyAuthentication) or
-client host (HostbasedAuthentication) authentication method,
-conventional password authentication and challenge response based methods.
-.Ss Command execution and data forwarding
-If the client successfully authenticates itself, a dialog for
-preparing the session is entered.
-At this time the client may request
-things like allocating a pseudo-tty, forwarding X11 connections,
-forwarding TCP/IP connections, or forwarding the authentication agent
-connection over the secure channel.
-.Pp
-Finally, the client either requests a shell or execution of a command.
-The sides then enter session mode.
-In this mode, either side may send
-data at any time, and such data is forwarded to/from the shell or
-command on the server side, and the user terminal in the client side.
-.Pp
-When the user program terminates and all forwarded X11 and other
-connections have been closed, the server sends command exit status to
-the client, and both sides exit.
-.Pp
 .Nm
 can be configured using command-line options or a configuration file
 (by default
-.Xr sshd_config 5 ) .
-Command-line options override values specified in the
+.Xr sshd_config 5 ) ;
+command-line options override values specified in the
 configuration file.
-.Pp
 .Nm
 rereads its configuration file when it receives a hangup signal,
 .Dv SIGHUP ,
@@ -263,8 +177,12 @@
 Specifies the port on which the server listens for connections
 (default 22).
 Multiple port options are permitted.
-Ports specified in the configuration file are ignored when a
-command-line port is specified.
+Ports specified in the configuration file with the
+.Cm Port
+option are ignored when a command-line port is specified.
+Ports specified using the
+.Cm ListenAddress
+option override command-line ports.
 .It Fl q
 Quiet mode.
 Nothing is sent to the system log.
@@ -299,7 +217,7 @@
 mechanism or configuration requires it.
 Authentication mechanisms that may require DNS include
 .Cm RhostsRSAAuthentication ,
-.Cm HostbasedAuthentication
+.Cm HostbasedAuthentication ,
 and using a
 .Cm from="pattern-list"
 option in a key file.
@@ -309,15 +227,88 @@
 or
 .Cm DenyUsers .
 .El
-.Sh CONFIGURATION FILE
-.Nm
-reads configuration data from
-.Pa /etc/ssh/sshd_config
-(or the file specified with
-.Fl f
-on the command line).
-The file format and configuration options are described in
+.Sh AUTHENTICATION
+The OpenSSH SSH daemon supports SSH protocols 1 and 2.
+Both protocols are supported by default,
+though this can be changed via the
+.Cm Protocol
+option in
 .Xr sshd_config 5 .
+Protocol 2 supports both RSA and DSA keys;
+protocol 1 only supports RSA keys.
+For both protocols,
+each host has a host-specific key,
+normally 2048 bits,
+used to identify the host.
+.Pp
+Forward security for protocol 1 is provided through
+an additional server key,
+normally 768 bits,
+generated when the server starts.
+This key is normally regenerated every hour if it has been used, and
+is never stored on disk.
+Whenever a client connects, the daemon responds with its public
+host and server keys.
+The client compares the
+RSA host key against its own database to verify that it has not changed.
+The client then generates a 256-bit random number.
+It encrypts this
+random number using both the host key and the server key, and sends
+the encrypted number to the server.
+Both sides then use this
+random number as a session key which is used to encrypt all further
+communications in the session.
+The rest of the session is encrypted
+using a conventional cipher, currently Blowfish or 3DES, with 3DES
+being used by default.
+The client selects the encryption algorithm
+to use from those offered by the server.
+.Pp
+For protocol 2,
+forward security is provided through a Diffie-Hellman key agreement.
+This key agreement results in a shared session key.
+The rest of the session is encrypted using a symmetric cipher, currently
+128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES.
+The client selects the encryption algorithm
+to use from those offered by the server.
+Additionally, session integrity is provided
+through a cryptographic message authentication code
+(hmac-sha1 or hmac-md5).
+.Pp
+Finally, the server and the client enter an authentication dialog.
+The client tries to authenticate itself using
+host-based authentication,
+public key authentication,
+challenge-response authentication,
+or password authentication.
+.Pp
+System security is not improved unless
+.Nm rshd ,
+.Nm rlogind ,
+and
+.Nm rexecd
+are disabled (thus completely disabling
+.Xr rlogin
+and
+.Xr rsh
+into the machine).
+.Sh COMMAND EXECUTION AND DATA FORWARDING
+If the client successfully authenticates itself, a dialog for
+preparing the session is entered.
+At this time the client may request
+things like allocating a pseudo-tty, forwarding X11 connections,
+forwarding TCP connections, or forwarding the authentication agent
+connection over the secure channel.
+.Pp
+Finally, the client either requests a shell or execution of a command.
+The sides then enter session mode.
+In this mode, either side may send
+data at any time, and such data is forwarded to/from the shell or
+command on the server side, and the user terminal in the client side.
+.Pp
+When the user program terminates and all forwarded X11 and other
+connections have been closed, the server sends command exit status to
+the client, and both sides exit.
 .Sh LOGIN PROCESS
 When a user successfully logs in,
 .Nm
@@ -328,7 +319,7 @@
 prints last login time and
 .Pa /etc/motd
 (unless prevented in the configuration file or by
-.Pa $HOME/.hushlogin ;
+.Pa ~/.hushlogin ;
 see the
 .Sx FILES
 section).
@@ -345,7 +336,7 @@
 Sets up basic environment.
 .It
 Reads the file
-.Pa $HOME/.ssh/environment ,
+.Pa ~/.ssh/environment ,
 if it exists, and users are allowed to change their environment.
 See the
 .Cm PermitUserEnvironment
@@ -355,7 +346,7 @@
 Changes to user's home directory.
 .It
 If
-.Pa $HOME/.ssh/rc
+.Pa ~/.ssh/rc
 exists, runs it; else if
 .Pa /etc/ssh/sshrc
 exists, runs
@@ -368,7 +359,7 @@
 Runs user's shell or command.
 .El
 .Sh AUTHORIZED_KEYS FILE FORMAT
-.Pa $HOME/.ssh/authorized_keys
+.Pa ~/.ssh/authorized_keys
 is the default file that lists the public keys that are
 permitted for RSA authentication in protocol version 1
 and for public key authentication (PubkeyAuthentication)
@@ -451,7 +442,7 @@
 This option might be useful
 to restrict certain public keys to perform just a specific operation.
 An example might be a key that permits remote backups but nothing else.
-Note that the client may specify TCP/IP and/or X11
+Note that the client may specify TCP and/or X11
 forwarding unless they are explicitly prohibited.
 Note that this option applies to shell, command or subsystem execution.
 .It Cm environment="NAME=value"
@@ -468,7 +459,7 @@
 .Cm UseLogin
 is enabled.
 .It Cm no-port-forwarding
-Forbids TCP/IP forwarding when this key is used for authentication.
+Forbids TCP forwarding when this key is used for authentication.
 Any port forward requests by the client will return an error.
 This might be used, e.g., in connection with the
 .Cm command
@@ -493,6 +484,12 @@
 options may be applied separated by commas.
 No pattern matching is performed on the specified hostnames,
 they must be literal domains or addresses.
+.It Cm tunnel="n"
+Force a
+.Xr tun 4
+device on the server.
+Without this option, the next available device will be used if
+the client requests a tunnel.
 .El
 .Ss Examples
 1024 33 12121...312314325 ylo@foo.bar
@@ -502,11 +499,13 @@
 command="dump /home",no-pty,no-port-forwarding 1024 33 23...2323 backup.hut.fi
 .Pp
 permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23...2323
+.Pp
+tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...== reyk@openbsd.org
 .Sh SSH_KNOWN_HOSTS FILE FORMAT
 The
 .Pa /etc/ssh/ssh_known_hosts
 and
-.Pa $HOME/.ssh/known_hosts
+.Pa ~/.ssh/known_hosts
 files contain host public keys for all known hosts.
 The global file should
 be prepared by the administrator (optional), and the per-user file is
@@ -617,7 +616,7 @@
 concurrently for different ports, this contains the process ID of the one
 started last).
 The content of this file is not sensitive; it can be world-readable.
-.It Pa $HOME/.ssh/authorized_keys
+.It Pa ~/.ssh/authorized_keys
 Lists the public keys (RSA or DSA) that can be used to log into the user's account.
 This file must be readable by root (which may on some machines imply
 it being world-readable if the user's home directory resides on an NFS
@@ -631,7 +630,7 @@
 .Pa id_rsa.pub
 files into this file, as described in
 .Xr ssh-keygen 1 .
-.It Pa "/etc/ssh/ssh_known_hosts", "$HOME/.ssh/known_hosts"
+.It Pa "/etc/ssh/ssh_known_hosts", "~/.ssh/known_hosts"
 These files are consulted when using rhosts with RSA host
 authentication or protocol version 2 hostbased authentication
 to check the public key of the host.
@@ -641,12 +640,12 @@
 These files should be writable only by root/the owner.
 .Pa /etc/ssh/ssh_known_hosts
 should be world-readable, and
-.Pa $HOME/.ssh/known_hosts
+.Pa ~/.ssh/known_hosts
 can, but need not be, world-readable.
 .It Pa /etc/motd
 See
 .Xr motd 5 .
-.It Pa $HOME/.hushlogin
+.It Pa ~/.hushlogin
 This file is used to suppress printing the last login time and
 .Pa /etc/motd ,
 if
@@ -669,7 +668,7 @@
 Access controls that should be enforced by tcp-wrappers are defined here.
 Further details are described in
 .Xr hosts_access 5 .
-.It Pa $HOME/.rhosts
+.It Pa ~/.rhosts
 This file is used during
 .Cm RhostsRSAAuthentication
 and
@@ -687,7 +686,7 @@
 Either host or user
 name may be of the form +@groupname to specify all hosts or all users
 in the group.
-.It Pa $HOME/.shosts
+.It Pa ~/.shosts
 For ssh,
 this file is exactly the same as for
 .Pa .rhosts .
@@ -736,7 +735,7 @@
 .Pa /etc/hosts.equiv .
 However, this file may be useful in environments that want to run both
 rsh/rlogin and ssh.
-.It Pa $HOME/.ssh/environment
+.It Pa ~/.ssh/environment
 This file is read into the environment at login (if it exists).
 It can only contain empty lines, comment lines (that start with
 .Ql # ) ,
@@ -747,7 +746,7 @@
 controlled via the
 .Cm PermitUserEnvironment
 option.
-.It Pa $HOME/.ssh/rc
+.It Pa ~/.ssh/rc
 If this file exists, it is run with
 .Pa /bin/sh
 after reading the
@@ -792,7 +791,7 @@
 readable by anyone else.
 .It Pa /etc/ssh/sshrc
 Like
-.Pa $HOME/.ssh/rc .
+.Pa ~/.ssh/rc .
 This can be used to specify
 machine-specific login-time initializations globally.
 This file should be writable only by root, and should be world-readable.