import openssh-4.3p2-gsskex-20060223.patch

1 files changed, 447 insertions, 384 deletions

diff --git a/ssh.0 b/ssh.0
index 274fab8b5..83c4b94eb 100644
--- a/ssh.0
+++ b/ssh.0
@@ -5,208 +5,26 @@ NAME
 
 SYNOPSIS
      ssh [-1246AaCfgkMNnqsTtVvXxY] [-b bind_address] [-c cipher_spec]
-         [-D port] [-e escape_char] [-F configfile] [-i identity_file]
-         [-L [bind_address:]port:host:hostport] [-l login_name] [-m mac_spec]
-         [-O ctl_cmd] [-o option] [-p port]
-         [-R [bind_address:]port:host:hostport] [-S ctl_path] [user@]hostname
-         [command]
+         [-D [bind_address:]port] [-e escape_char] [-F configfile]
+         [-i identity_file] [-L [bind_address:]port:host:hostport]
+         [-l login_name] [-m mac_spec] [-O ctl_cmd] [-o option] [-p port]
+         [-R [bind_address:]port:host:hostport] [-S ctl_path]
+         [-w tunnel:tunnel] [user@]hostname [command]
 
 DESCRIPTION
      ssh (SSH client) is a program for logging into a remote machine and for
      executing commands on a remote machine.  It is intended to replace rlogin
      and rsh, and provide secure encrypted communications between two untrust-
-     ed hosts over an insecure network.  X11 connections and arbitrary TCP/IP
+     ed hosts over an insecure network.  X11 connections and arbitrary TCP
      ports can also be forwarded over the secure channel.
 
      ssh connects and logs into the specified hostname (with optional user
      name).  The user must prove his/her identity to the remote machine using
-     one of several methods depending on the protocol version used.
+     one of several methods depending on the protocol version used (see be-
+     low).
 
-     If command is specified, command is executed on the remote host instead
-     of a login shell.
-
-   SSH protocol version 1
-     The first authentication method is the rhosts or hosts.equiv method com-
-     bined with RSA-based host authentication.  If the machine the user logs
-     in from is listed in /etc/hosts.equiv or /etc/shosts.equiv on the remote
-     machine, and the user names are the same on both sides, or if the files
-     ~/.rhosts or ~/.shosts exist in the user's home directory on the remote
-     machine and contain a line containing the name of the client machine and
-     the name of the user on that machine, the user is considered for log in.
-     Additionally, if the server can verify the client's host key (see
-     /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts in the FILES section),
-     only then is login permitted.  This authentication method closes security
-     holes due to IP spoofing, DNS spoofing and routing spoofing.  [Note to
-     the administrator: /etc/hosts.equiv, ~/.rhosts, and the rlogin/rsh proto-
-     col in general, are inherently insecure and should be disabled if securi-
-     ty is desired.]
-
-     As a second authentication method, ssh supports RSA based authentication.
-     The scheme is based on public-key cryptography: there are cryptosystems
-     where encryption and decryption are done using separate keys, and it is
-     not possible to derive the decryption key from the encryption key.  RSA
-     is one such system.  The idea is that each user creates a public/private
-     key pair for authentication purposes.  The server knows the public key,
-     and only the user knows the private key.
-
-     The file ~/.ssh/authorized_keys lists the public keys that are permitted
-     for logging in.  When the user logs in, the ssh program tells the server
-     which key pair it would like to use for authentication.  The server
-     checks if this key is permitted, and if so, sends the user (actually the
-     ssh program running on behalf of the user) a challenge, a random number,
-     encrypted by the user's public key.  The challenge can only be decrypted
-     using the proper private key.  The user's client then decrypts the chal-
-     lenge using the private key, proving that he/she knows the private key
-     but without disclosing it to the server.
-
-     ssh implements the RSA authentication protocol automatically.  The user
-     creates his/her RSA key pair by running ssh-keygen(1).  This stores the
-     private key in ~/.ssh/identity and stores the public key in
-     ~/.ssh/identity.pub in the user's home directory.  The user should then
-     copy the identity.pub to ~/.ssh/authorized_keys in his/her home directory
-     on the remote machine (the authorized_keys file corresponds to the con-
-     ventional ~/.rhosts file, and has one key per line, though the lines can
-     be very long).  After this, the user can log in without giving the pass-
-     word.
-
-     The most convenient way to use RSA authentication may be with an authen-
-     tication agent.  See ssh-agent(1) for more information.
-
-     If other authentication methods fail, ssh prompts the user for a pass-
-     word.  The password is sent to the remote host for checking; however,
-     since all communications are encrypted, the password cannot be seen by
-     someone listening on the network.
-
-   SSH protocol version 2
-     When a user connects using protocol version 2, similar authentication
-     methods are available.  Using the default values for
-     PreferredAuthentications, the client will try to authenticate first using
-     the hostbased method; if this method fails, public key authentication is
-     attempted, and finally if this method fails, keyboard-interactive and
-     password authentication are tried.
-
-     The public key method is similar to RSA authentication described in the
-     previous section and allows the RSA or DSA algorithm to be used: The
-     client uses his private key, ~/.ssh/id_dsa or ~/.ssh/id_rsa, to sign the
-     session identifier and sends the result to the server.  The server checks
-     whether the matching public key is listed in ~/.ssh/authorized_keys and
-     grants access if both the key is found and the signature is correct.  The
-     session identifier is derived from a shared Diffie-Hellman value and is
-     only known to the client and the server.
-
-     If public key authentication fails or is not available, a password can be
-     sent encrypted to the remote host to prove the user's identity.
-
-     Additionally, ssh supports hostbased or challenge response authentica-
-     tion.
-
-     Protocol 2 provides additional mechanisms for confidentiality (the traf-
-     fic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour) and in-
-     tegrity (hmac-md5, hmac-sha1, hmac-ripemd160).  Note that protocol 1
-     lacks a strong mechanism for ensuring the integrity of the connection.
-
-   Login session and remote execution
-     When the user's identity has been accepted by the server, the server ei-
-     ther executes the given command, or logs into the machine and gives the
-     user a normal shell on the remote machine.  All communication with the
-     remote command or shell will be automatically encrypted.
-
-     If a pseudo-terminal has been allocated (normal login session), the user
-     may use the escape characters noted below.
-
-     If no pseudo-tty has been allocated, the session is transparent and can
-     be used to reliably transfer binary data.  On most systems, setting the
-     escape character to ``none'' will also make the session transparent even
-     if a tty is used.
-
-     The session terminates when the command or shell on the remote machine
-     exits and all X11 and TCP/IP connections have been closed.  The exit sta-
-     tus of the remote program is returned as the exit status of ssh.
-
-   Escape Characters
-     When a pseudo-terminal has been requested, ssh supports a number of func-
-     tions through the use of an escape character.
-
-     A single tilde character can be sent as ~~ or by following the tilde by a
-     character other than those described below.  The escape character must
-     always follow a newline to be interpreted as special.  The escape charac-
-     ter can be changed in configuration files using the EscapeChar configura-
-     tion directive or on the command line by the -e option.
-
-     The supported escapes (assuming the default `~') are:
-
-     ~.      Disconnect.
-
-     ~^Z     Background ssh.
-
-     ~#      List forwarded connections.
-
-     ~&      Background ssh at logout when waiting for forwarded connection /
-             X11 sessions to terminate.
-
-     ~?      Display a list of escape characters.
-
-     ~B      Send a BREAK to the remote system (only useful for SSH protocol
-             version 2 and if the peer supports it).
-
-     ~C      Open command line.  Currently this allows the addition of port
-             forwardings using the -L and -R options (see below).  It also al-
-             lows the cancellation of existing remote port-forwardings using
-             -KR hostport.  Basic help is available, using the -h option.
-
-     ~R      Request rekeying of the connection (only useful for SSH protocol
-             version 2 and if the peer supports it).
-
-   X11 and TCP forwarding
-     If the ForwardX11 variable is set to ``yes'' (or see the description of
-     the -X and -x options described later) and the user is using X11 (the
-     DISPLAY environment variable is set), the connection to the X11 display
-     is automatically forwarded to the remote side in such a way that any X11
-     programs started from the shell (or command) will go through the encrypt-
-     ed channel, and the connection to the real X server will be made from the
-     local machine.  The user should not manually set DISPLAY.  Forwarding of
-     X11 connections can be configured on the command line or in configuration
-     files.
-
-     The DISPLAY value set by ssh will point to the server machine, but with a
-     display number greater than zero.  This is normal, and happens because
-     ssh creates a ``proxy'' X server on the server machine for forwarding the
-     connections over the encrypted channel.
-
-     ssh will also automatically set up Xauthority data on the server machine.
-     For this purpose, it will generate a random authorization cookie, store
-     it in Xauthority on the server, and verify that any forwarded connections
-     carry this cookie and replace it by the real cookie when the connection
-     is opened.  The real authentication cookie is never sent to the server
-     machine (and no cookies are sent in the plain).
-
-     If the ForwardAgent variable is set to ``yes'' (or see the description of
-     the -A and -a options described later) and the user is using an authenti-
-     cation agent, the connection to the agent is automatically forwarded to
-     the remote side.
-
-     Forwarding of arbitrary TCP/IP connections over the secure channel can be
-     specified either on the command line or in a configuration file.  One
-     possible application of TCP/IP forwarding is a secure connection to an
-     electronic purse; another is going through firewalls.
-
-   Server authentication
-     ssh automatically maintains and checks a database containing identifica-
-     tions for all hosts it has ever been used with.  Host keys are stored in
-     ~/.ssh/known_hosts in the user's home directory.  Additionally, the file
-     /etc/ssh/ssh_known_hosts is automatically checked for known hosts.  Any
-     new hosts are automatically added to the user's file.  If a host's iden-
-     tification ever changes, ssh warns about this and disables password au-
-     thentication to prevent a trojan horse from getting the user's password.
-     Another purpose of this mechanism is to prevent man-in-the-middle attacks
-     which could otherwise be used to circumvent the encryption.  The
-     StrictHostKeyChecking option can be used to prevent logins to machines
-     whose host key is not known or has changed.
-
-     ssh can be configured to verify host identification using fingerprint re-
-     source records (SSHFP) published in DNS.  The VerifyHostKeyDNS option can
-     be used to control how DNS lookups are performed.  SSHFP resource records
-     can be generated using ssh-keygen(1).
+     If command is specified, it is executed on the remote host instead of a
+     login shell.
 
      The options are as follows:
 
@@ -238,7 +56,7 @@ DESCRIPTION
              dress.
 
      -C      Requests compression of all data (including stdin, stdout,
-             stderr, and data for forwarded X11 and TCP/IP connections).  The
+             stderr, and data for forwarded X11 and TCP connections).  The
              compression algorithm is the same used by gzip(1), and the
              ``level'' can be controlled by the CompressionLevel option for
              protocol version 1.  Compression is desirable on modem lines and
@@ -250,7 +68,7 @@ DESCRIPTION
              Selects the cipher specification for encrypting the session.
 
              Protocol version 1 allows specification of a single cipher.  The
-             suported values are ``3des'', ``blowfish'' and ``des''.  3des
+             supported values are ``3des'', ``blowfish'', and ``des''.  3des
              (triple-des) is an encrypt-decrypt-encrypt triple with three dif-
              ferent keys.  It is believed to be secure.  blowfish is a fast
              block cipher; it appears very secure and is much faster than
@@ -259,29 +77,39 @@ DESCRIPTION
              the 3des cipher.  Its use is strongly discouraged due to crypto-
              graphic weaknesses.  The default is ``3des''.
 
-             For protocol version 2 cipher_spec is a comma-separated list of
-             ciphers listed in order of preference.  The supported ciphers are
-             ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'',
-             ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'', ``arcfour128'',
-             ``arcfour256'', ``arcfour'', ``blowfish-cbc'', and
-             ``cast128-cbc''.  The default is
+             For protocol version 2, cipher_spec is a comma-separated list of
+             ciphers listed in order of preference.  The supported ciphers
+             are: 3des-cbc, aes128-cbc, aes192-cbc, aes256-cbc, aes128-ctr,
+             aes192-ctr, aes256-ctr, arcfour128, arcfour256, arcfour, blow-
+             fish-cbc, and cast128-cbc.  The default is:
 
-               ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
-                 arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
-                 aes192-ctr,aes256-ctr''
+                   aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
+                   arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
+                   aes192-ctr,aes256-ctr
 
-     -D port
+     -D [bind_address:]port
              Specifies a local ``dynamic'' application-level port forwarding.
              This works by allocating a socket to listen to port on the local
-             side, and whenever a connection is made to this port, the connec-
-             tion is forwarded over the secure channel, and the application
-             protocol is then used to determine where to connect to from the
-             remote machine.  Currently the SOCKS4 and SOCKS5 protocols are
-             supported, and ssh will act as a SOCKS server.  Only root can
-             forward privileged ports.  Dynamic port forwardings can also be
-             specified in the configuration file.
-
-     -e ch | ^ch | none
+             side, optionally bound to the specified bind_address.  Whenever a
+             connection is made to this port, the connection is forwarded over
+             the secure channel, and the application protocol is then used to
+             determine where to connect to from the remote machine.  Currently
+             the SOCKS4 and SOCKS5 protocols are supported, and ssh will act
+             as a SOCKS server.  Only root can forward privileged ports.  Dy-
+             namic port forwardings can also be specified in the configuration
+             file.
+
+             IPv6 addresses can be specified with an alternative syntax:
+             [bind_address/]port or by enclosing the address in square brack-
+             ets.  Only the superuser can forward privileged ports.  By de-
+             fault, the local port is bound in accordance with the
+             GatewayPorts setting.  However, an explicit bind_address may be
+             used to bind the connection to a specific address.  The
+             bind_address of ``localhost'' indicates that the listening port
+             be bound for local use only, while an empty address or `*' indi-
+             cates that the port should be available from all interfaces.
+
+     -e escape_char
              Sets the escape character for sessions with a pty (default: `~').
              The escape character is only recognized at the beginning of a
              line.  The escape character followed by a dot (`.') closes the
@@ -305,9 +133,10 @@ DESCRIPTION
      -g      Allows remote hosts to connect to local forwarded ports.
 
      -I smartcard_device
-             Specifies which smartcard device to use.  The argument is the de-
-             vice ssh should use to communicate with a smartcard used for
-             storing the user's private RSA key.
+             Specify the device ssh should use to communicate with a smartcard
+             used for storing the user's private RSA key.  This option is only
+             available if support for smartcard devices is compiled in (de-
+             fault is no support).
 
      -i identity_file
              Selects a file from which the identity (private key) for RSA or
@@ -345,8 +174,10 @@ DESCRIPTION
              may be specified on a per-host basis in the configuration file.
 
      -M      Places the ssh client into ``master'' mode for connection shar-
-             ing.  Refer to the description of ControlMaster in ssh_config(5)
-             for details.
+             ing.  Multiple -M options places ssh into ``master'' mode with
+             confirmation required before slave connections are accepted.  Re-
+             fer to the description of ControlMaster in ssh_config(5) for de-
+             tails.
 
      -m mac_spec
              Additionally, for protocol version 2 a comma-separated list of
@@ -410,17 +241,20 @@ DESCRIPTION
                    IdentityFile
                    IdentitiesOnly
                    KbdInteractiveDevices
+                   LocalCommand
                    LocalForward
                    LogLevel
                    MACs
                    NoHostAuthenticationForLocalhost
                    NumberOfPasswordPrompts
                    PasswordAuthentication
+                   PermitLocalCommand
                    Port
                    PreferredAuthentications
                    Protocol
                    ProxyCommand
                    PubkeyAuthentication
+                   RekeyLimit
                    RemoteForward
                    RhostsRSAAuthentication
                    RSAAuthentication
@@ -430,6 +264,8 @@ DESCRIPTION
                    SmartcardDevice
                    StrictHostKeyChecking
                    TCPKeepAlive
+                   Tunnel
+                   TunnelDevice
                    UsePrivilegedPort
                    User
                    UserKnownHostsFile
@@ -489,6 +325,12 @@ DESCRIPTION
              tion, and configuration problems.  Multiple -v options increase
              the verbosity.  The maximum is 3.
 
+     -w tunnel:tunnel
+             Requests a tun(4) device on the client (first tunnel arg) and
+             server (second tunnel arg).  The devices may be specified by nu-
+             merical ID or the keyword ``any'', which uses the next available
+             tunnel device.  See also the Tunnel directive in ssh_config(5).
+
      -X      Enables X11 forwarding.  This can also be specified on a per-host
              basis in a configuration file.
 
@@ -508,100 +350,358 @@ DESCRIPTION
      -Y      Enables trusted X11 forwarding.  Trusted X11 forwardings are not
              subjected to the X11 SECURITY extension controls.
 
-CONFIGURATION FILES
      ssh may additionally obtain configuration data from a per-user configura-
      tion file and a system-wide configuration file.  The file format and con-
      figuration options are described in ssh_config(5).
 
-ENVIRONMENT
-     ssh will normally set the following environment variables:
+     ssh exits with the exit status of the remote command or with 255 if an
+     error occurred.
+
+AUTHENTICATION
+     The OpenSSH SSH client supports SSH protocols 1 and 2.  Protocol 2 is the
+     default, with ssh falling back to protocol 1 if it detects protocol 2 is
+     unsupported.  These settings may be altered using the Protocol option in
+     ssh_config(5), or enforced using the -1 and -2 options (see above).  Both
+     protocols support similar authentication methods, but protocol 2 is pre-
+     ferred since it provides additional mechanisms for confidentiality (the
+     traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) and
+     integrity (hmac-md5, hmac-sha1, hmac-ripemd160).  Protocol 1 lacks a
+     strong mechanism for ensuring the integrity of the connection.
+
+     The methods available for authentication are: host-based authentication,
+     public key authentication, challenge-response authentication, and pass-
+     word authentication.  Authentication methods are tried in the order spec-
+     ified above, though protocol 2 has a configuration option to change the
+     default order: PreferredAuthentications.
+
+     Host-based authentication works as follows: If the machine the user logs
+     in from is listed in /etc/hosts.equiv or /etc/shosts.equiv on the remote
+     machine, and the user names are the same on both sides, or if the files
+     ~/.rhosts or ~/.shosts exist in the user's home directory on the remote
+     machine and contain a line containing the name of the client machine and
+     the name of the user on that machine, the user is considered for login.
+     Additionally, the server must be able to verify the client's host key
+     (see the description of /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts,
+     below) for login to be permitted.  This authentication method closes se-
+     curity holes due to IP spoofing, DNS spoofing, and routing spoofing.
+     [Note to the administrator: /etc/hosts.equiv, ~/.rhosts, and the
+     rlogin/rsh protocol in general, are inherently insecure and should be
+     disabled if security is desired.]
+
+     Public key authentication works as follows: The scheme is based on pub-
+     lic-key cryptography, using cryptosystems where encryption and decryption
+     are done using separate keys, and it is unfeasible to derive the decryp-
+     tion key from the encryption key.  The idea is that each user creates a
+     public/private key pair for authentication purposes.  The server knows
+     the public key, and only the user knows the private key.  ssh implements
+     public key authentication protocol automatically, using either the RSA or
+     DSA algorithms.  Protocol 1 is restricted to using only RSA keys, but
+     protocol 2 may use either.  The HISTORY section of ssl(8) contains a
+     brief discussion of the two algorithms.
+
+     The file ~/.ssh/authorized_keys lists the public keys that are permitted
+     for logging in.  When the user logs in, the ssh program tells the server
+     which key pair it would like to use for authentication.  The client
+     proves that it has access to the private key and the server checks that
+     the corresponding public key is authorized to accept the account.
+
+     The user creates his/her key pair by running ssh-keygen(1).  This stores
+     the private key in ~/.ssh/identity (protocol 1), ~/.ssh/id_dsa (protocol
+     2 DSA), or ~/.ssh/id_rsa (protocol 2 RSA) and stores the public key in
+     ~/.ssh/identity.pub (protocol 1), ~/.ssh/id_dsa.pub (protocol 2 DSA), or
+     ~/.ssh/id_rsa.pub (protocol 2 RSA) in the user's home directory.  The us-
+     er should then copy the public key to ~/.ssh/authorized_keys in his/her
+     home directory on the remote machine.  The authorized_keys file corre-
+     sponds to the conventional ~/.rhosts file, and has one key per line,
+     though the lines can be very long.  After this, the user can log in with-
+     out giving the password.
+
+     The most convenient way to use public key authentication may be with an
+     authentication agent.  See ssh-agent(1) for more information.
+
+     Challenge-response authentication works as follows: The server sends an
+     arbitrary "challenge" text, and prompts for a response.  Protocol 2 al-
+     lows multiple challenges and responses; protocol 1 is restricted to just
+     one challenge/response.  Examples of challenge-response authentication
+     include BSD Authentication (see login.conf(5)) and PAM (some non-OpenBSD
+     systems).
+
+     Finally, if other authentication methods fail, ssh prompts the user for a
+     password.  The password is sent to the remote host for checking; however,
+     since all communications are encrypted, the password cannot be seen by
+     someone listening on the network.
+
+     ssh automatically maintains and checks a database containing identifica-
+     tion for all hosts it has ever been used with.  Host keys are stored in
+     ~/.ssh/known_hosts in the user's home directory.  Additionally, the file
+     /etc/ssh/ssh_known_hosts is automatically checked for known hosts.  Any
+     new hosts are automatically added to the user's file.  If a host's iden-
+     tification ever changes, ssh warns about this and disables password au-
+     thentication to prevent server spoofing or man-in-the-middle attacks,
+     which could otherwise be used to circumvent the encryption.  The
+     StrictHostKeyChecking option can be used to control logins to machines
+     whose host key is not known or has changed.
+
+     When the user's identity has been accepted by the server, the server ei-
+     ther executes the given command, or logs into the machine and gives the
+     user a normal shell on the remote machine.  All communication with the
+     remote command or shell will be automatically encrypted.
+
+     If a pseudo-terminal has been allocated (normal login session), the user
+     may use the escape characters noted below.
+
+     If no pseudo-tty has been allocated, the session is transparent and can
+     be used to reliably transfer binary data.  On most systems, setting the
+     escape character to ``none'' will also make the session transparent even
+     if a tty is used.
+
+     The session terminates when the command or shell on the remote machine
+     exits and all X11 and TCP connections have been closed.
+
+ESCAPE CHARACTERS
+     When a pseudo-terminal has been requested, ssh supports a number of func-
+     tions through the use of an escape character.
+
+     A single tilde character can be sent as ~~ or by following the tilde by a
+     character other than those described below.  The escape character must
+     always follow a newline to be interpreted as special.  The escape charac-
+     ter can be changed in configuration files using the EscapeChar configura-
+     tion directive or on the command line by the -e option.
+
+     The supported escapes (assuming the default `~') are:
+
+     ~.      Disconnect.
+
+     ~^Z     Background ssh.
+
+     ~#      List forwarded connections.
+
+     ~&      Background ssh at logout when waiting for forwarded connection /
+             X11 sessions to terminate.
+
+     ~?      Display a list of escape characters.
+
+     ~B      Send a BREAK to the remote system (only useful for SSH protocol
+             version 2 and if the peer supports it).
+
+     ~C      Open command line.  Currently this allows the addition of port
+             forwardings using the -L and -R options (see above).  It also al-
+             lows the cancellation of existing remote port-forwardings using
+             -KR hostport.  !command allows the user to execute a local com-
+             mand if the PermitLocalCommand option is enabled in
+             ssh_config(5).  Basic help is available, using the -h option.
+
+     ~R      Request rekeying of the connection (only useful for SSH protocol
+             version 2 and if the peer supports it).
+
+TCP FORWARDING
+     Forwarding of arbitrary TCP connections over the secure channel can be
+     specified either on the command line or in a configuration file.  One
+     possible application of TCP forwarding is a secure connection to a mail
+     server; another is going through firewalls.
+
+     In the example below, we look at encrypting communication between an IRC
+     client and server, even though the IRC server does not directly support
+     encrypted communications.  This works as follows: the user connects to
+     the remote host using ssh, specifying a port to be used to forward con-
+     nections to the remote server.  After that it is possible to start the
+     service which is to be encrypted on the client machine, connecting to the
+     same local port, and ssh will encrypt and forward the connection.
+
+     The following example tunnels an IRC session from client machine
+     ``127.0.0.1'' (localhost) to remote server ``server.example.com'':
+
+         $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
+         $ irc -c '#users' -p 1234 pinky 127.0.0.1
+
+     This tunnels a connection to IRC server ``server.example.com'', joining
+     channel ``#users'', nickname ``pinky'', using port 1234.  It doesn't mat-
+     ter which port is used, as long as it's greater than 1023 (remember, only
+     root can open sockets on privileged ports) and doesn't conflict with any
+     ports already in use.  The connection is forwarded to port 6667 on the
+     remote server, since that's the standard port for IRC services.
+
+     The -f option backgrounds ssh and the remote command ``sleep 10'' is
+     specified to allow an amount of time (10 seconds, in the example) to
+     start the service which is to be tunnelled.  If no connections are made
+     within the time specified, ssh will exit.
+
+X11 FORWARDING
+     If the ForwardX11 variable is set to ``yes'' (or see the description of
+     the -X, -x, and -Y options above) and the user is using X11 (the DISPLAY
+     environment variable is set), the connection to the X11 display is auto-
+     matically forwarded to the remote side in such a way that any X11 pro-
+     grams started from the shell (or command) will go through the encrypted
+     channel, and the connection to the real X server will be made from the
+     local machine.  The user should not manually set DISPLAY.  Forwarding of
+     X11 connections can be configured on the command line or in configuration
+     files.
+
+     The DISPLAY value set by ssh will point to the server machine, but with a
+     display number greater than zero.  This is normal, and happens because
+     ssh creates a ``proxy'' X server on the server machine for forwarding the
+     connections over the encrypted channel.
+
+     ssh will also automatically set up Xauthority data on the server machine.
+     For this purpose, it will generate a random authorization cookie, store
+     it in Xauthority on the server, and verify that any forwarded connections
+     carry this cookie and replace it by the real cookie when the connection
+     is opened.  The real authentication cookie is never sent to the server
+     machine (and no cookies are sent in the plain).
+
+     If the ForwardAgent variable is set to ``yes'' (or see the description of
+     the -A and -a options above) and the user is using an authentication
+     agent, the connection to the agent is automatically forwarded to the re-
+     mote side.
+
+VERIFYING HOST KEYS
+     When connecting to a server for the first time, a fingerprint of the
+     server's public key is presented to the user (unless the option
+     StrictHostKeyChecking has been disabled).  Fingerprints can be determined
+     using ssh-keygen(1):
+
+           $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
+
+     If the fingerprint is already known, it can be matched and verified, and
+     the key can be accepted.  If the fingerprint is unknown, an alternative
+     method of verification is available: SSH fingerprints verified by DNS.
+     An additional resource record (RR), SSHFP, is added to a zonefile and the
+     connecting client is able to match the fingerprint with that of the key
+     presented.
+
+     In this example, we are connecting a client to a server,
+     ``host.example.com''.  The SSHFP resource records should first be added
+     to the zonefile for host.example.com:
 
-     DISPLAY  The DISPLAY variable indicates the location of the X11 server.
-              It is automatically set by ssh to point to a value of the form
-              ``hostname:n'' where hostname indicates the host where the shell
-              runs, and n is an integer >= 1.  ssh uses this special value to
-              forward X11 connections over the secure channel.  The user
-              should normally not set DISPLAY explicitly, as that will render
-              the X11 connection insecure (and will require the user to manu-
-              ally copy any required authorization cookies).
+           $ ssh-keygen -f /etc/ssh/ssh_host_rsa_key.pub -r host.example.com.
+           $ ssh-keygen -f /etc/ssh/ssh_host_dsa_key.pub -r host.example.com.
 
-     HOME     Set to the path of the user's home directory.
+     The output lines will have to be added to the zonefile.  To check that
+     the zone is answering fingerprint queries:
 
-     LOGNAME  Synonym for USER; set for compatibility with systems that use
-              this variable.
+           $ dig -t SSHFP host.example.com
 
-     MAIL     Set to the path of the user's mailbox.
+     Finally the client connects:
 
-     PATH     Set to the default PATH, as specified when compiling ssh.
+           $ ssh -o "VerifyHostKeyDNS ask" host.example.com
+           [...]
+           Matching host key fingerprint found in DNS.
+           Are you sure you want to continue connecting (yes/no)?
 
-     SSH_ASKPASS
-              If ssh needs a passphrase, it will read the passphrase from the
-              current terminal if it was run from a terminal.  If ssh does not
-              have a terminal associated with it but DISPLAY and SSH_ASKPASS
-              are set, it will execute the program specified by SSH_ASKPASS
-              and open an X11 window to read the passphrase.  This is particu-
-              larly useful when calling ssh from a .xsession or related
-              script.  (Note that on some machines it may be necessary to
-              redirect the input from /dev/null to make this work.)
+     See the VerifyHostKeyDNS option in ssh_config(5) for more information.
 
-     SSH_AUTH_SOCK
-              Identifies the path of a unix-domain socket used to communicate
-              with the agent.
+SSH-BASED VIRTUAL PRIVATE NETWORKS
+     ssh contains support for Virtual Private Network (VPN) tunnelling using
+     the tun(4) network pseudo-device, allowing two networks to be joined se-
+     curely.  The sshd_config(5) configuration option PermitTunnel controls
+     whether the server supports this, and at what level (layer 2 or 3 traf-
+     fic).
 
-     SSH_CONNECTION
-              Identifies the client and server ends of the connection.  The
-              variable contains four space-separated values: client ip-ad-
-              dress, client port number, server ip-address and server port
-              number.
+     The following example would connect client network 10.0.50.0/24 with re-
+     mote network 10.0.99.0/24, provided that the SSH server running on the
+     gateway to the remote network, at 192.168.1.15, allows it:
 
-     SSH_ORIGINAL_COMMAND
-              The variable contains the original command line if a forced com-
-              mand is executed.  It can be used to extract the original argu-
-              ments.
+           # ssh -f -w 0:1 192.168.1.15 true
+           # ifconfig tun0 10.0.50.1 10.0.99.1 netmask 255.255.255.252
 
-     SSH_TTY  This is set to the name of the tty (path to the device) associ-
-              ated with the current shell or command.  If the current session
-              has no tty, this variable is not set.
+     Client access may be more finely tuned via the /root/.ssh/authorized_keys
+     file (see below) and the PermitRootLogin server option.  The following
+     entry would permit connections on the first tun(4) device from user
+     ``jane'' and on the second device from user ``john'', if PermitRootLogin
+     is set to ``forced-commands-only'':
 
-     TZ       The timezone variable is set to indicate the present timezone if
-              it was set when the daemon was started (i.e., the daemon passes
-              the value on to new connections).
+       tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
+       tunnel="2",command="sh /etc/netstart tun1" ssh-rsa ... john
 
-     USER     Set to the name of the user logging in.
+     Since a SSH-based setup entails a fair amount of overhead, it may be more
+     suited to temporary setups, such as for wireless VPNs.  More permanent
+     VPNs are better provided by tools such as ipsecctl(8) and isakmpd(8).
+
+ENVIRONMENT
+     ssh will normally set the following environment variables:
+
+     DISPLAY               The DISPLAY variable indicates the location of the
+                           X11 server.  It is automatically set by ssh to
+                           point to a value of the form ``hostname:n'', where
+                           ``hostname'' indicates the host where the shell
+                           runs, and `n' is an integer >= 1.  ssh uses this
+                           special value to forward X11 connections over the
+                           secure channel.  The user should normally not set
+                           DISPLAY explicitly, as that will render the X11
+                           connection insecure (and will require the user to
+                           manually copy any required authorization cookies).
+
+     HOME                  Set to the path of the user's home directory.
+
+     LOGNAME               Synonym for USER; set for compatibility with sys-
+                           tems that use this variable.
+
+     MAIL                  Set to the path of the user's mailbox.
+
+     PATH                  Set to the default PATH, as specified when compil-
+                           ing ssh.
+
+     SSH_ASKPASS           If ssh needs a passphrase, it will read the
+                           passphrase from the current terminal if it was run
+                           from a terminal.  If ssh does not have a terminal
+                           associated with it but DISPLAY and SSH_ASKPASS are
+                           set, it will execute the program specified by
+                           SSH_ASKPASS and open an X11 window to read the
+                           passphrase.  This is particularly useful when call-
+                           ing ssh from a .xsession or related script.  (Note
+                           that on some machines it may be necessary to redi-
+                           rect the input from /dev/null to make this work.)
+
+     SSH_AUTH_SOCK         Identifies the path of a UNIX-domain socket used to
+                           communicate with the agent.
+
+     SSH_CONNECTION        Identifies the client and server ends of the con-
+                           nection.  The variable contains four space-separat-
+                           ed values: client IP address, client port number,
+                           server IP address, and server port number.
+
+     SSH_ORIGINAL_COMMAND  This variable contains the original command line if
+                           a forced command is executed.  It can be used to
+                           extract the original arguments.
+
+     SSH_TTY               This is set to the name of the tty (path to the de-
+                           vice) associated with the current shell or command.
+                           If the current session has no tty, this variable is
+                           not set.
+
+     TZ                    This variable is set to indicate the present time
+                           zone if it was set when the daemon was started
+                           (i.e., the daemon passes the value on to new con-
+                           nections).
+
+     USER                  Set to the name of the user logging in.
 
      Additionally, ssh reads ~/.ssh/environment, and adds lines of the format
-     ``VARNAME=value'' to the environment if the file exists and if users are
-     allowed to change their environment.  For more information, see the
+     ``VARNAME=value'' to the environment if the file exists and users are al-
+     lowed to change their environment.  For more information, see the
      PermitUserEnvironment option in sshd_config(5).
 
 FILES
-     ~/.ssh/known_hosts
-             Records host keys for all hosts the user has logged into that are
-             not in /etc/ssh/ssh_known_hosts.  See sshd(8).
-
-     ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
-             Contains the authentication identity of the user.  They are for
-             protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
-             These files contain sensitive data and should be readable by the
-             user but not accessible by others (read/write/execute).  Note
-             that ssh ignores a private key file if it is accessible by oth-
-             ers.  It is possible to specify a passphrase when generating the
-             key; the passphrase will be used to encrypt the sensitive part of
-             this file using 3DES.
-
-     ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
-             Contains the public key for authentication (public part of the
-             identity file in human-readable form).  The contents of the
-             ~/.ssh/identity.pub file should be added to the file
-             ~/.ssh/authorized_keys on all machines where the user wishes to
-             log in using protocol version 1 RSA authentication.  The contents
-             of the ~/.ssh/id_dsa.pub and ~/.ssh/id_rsa.pub file should be
-             added to ~/.ssh/authorized_keys on all machines where the user
-             wishes to log in using protocol version 2 DSA/RSA authentication.
-             These files are not sensitive and can (but need not) be readable
-             by anyone.  These files are never used automatically and are not
-             necessary; they are only provided for the convenience of the us-
-             er.
+     ~/.rhosts
+             This file is used for host-based authentication (see above).  On
+             some machines this file may need to be world-readable if the us-
+             er's home directory is on an NFS partition, because sshd(8) reads
+             it as root.  Additionally, this file must be owned by the user,
+             and must not have write permissions for anyone else.  The recom-
+             mended permission for most machines is read/write for the user,
+             and not accessible by others.
+
+     ~/.shosts
+             This file is used in exactly the same way as .rhosts, but allows
+             host-based authentication without permitting login with
+             rlogin/rsh.
+
+     ~/.ssh/authorized_keys
+             Lists the public keys (RSA/DSA) that can be used for logging in
+             as this user.  The format of this file is described in the
+             sshd(8) manual page.  This file is not highly sensitive, but the
+             recommended permissions are read/write for the user, and not ac-
+             cessible by others.
 
      ~/.ssh/config
              This is the per-user configuration file.  The file format and
@@ -609,112 +709,75 @@ FILES
              the potential for abuse, this file must have strict permissions:
              read/write for the user, and not accessible by others.
 
-     ~/.ssh/authorized_keys
-             Lists the public keys (RSA/DSA) that can be used for logging in
-             as this user.  The format of this file is described in the
-             sshd(8) manual page.  In the simplest form the format is the same
-             as the .pub identity files.  This file is not highly sensitive,
-             but the recommended permissions are read/write for the user, and
-             not accessible by others.
+     ~/.ssh/environment
+             Contains additional definitions for environment variables; see
+             ENVIRONMENT, above.
+
+     ~/.ssh/identity
+     ~/.ssh/id_dsa
+     ~/.ssh/id_rsa
+             Contains the private key for authentication.  These files contain
+             sensitive data and should be readable by the user but not acces-
+             sible by others (read/write/execute).  ssh will simply ignore a
+             private key file if it is accessible by others.  It is possible
+             to specify a passphrase when generating the key which will be
+             used to encrypt the sensitive part of this file using 3DES.
+
+     ~/.ssh/identity.pub
+     ~/.ssh/id_dsa.pub
+     ~/.ssh/id_rsa.pub
+             Contains the public key for authentication.  These files are not
+             sensitive and can (but need not) be readable by anyone.
 
-     /etc/ssh/ssh_known_hosts
-             Systemwide list of known host keys.  This file should be prepared
-             by the system administrator to contain the public host keys of
-             all machines in the organization.  This file should be world-
-             readable.  This file contains public keys, one per line, in the
-             following format (fields separated by spaces): system name, pub-
-             lic key and optional comment field.  When different names are
-             used for the same machine, all such names should be listed, sepa-
-             rated by commas.  The format is described in the sshd(8) manual
-             page.
-
-             The canonical system name (as returned by name servers) is used
-             by sshd(8) to verify the client host when logging in; other names
-             are needed because ssh does not convert the user-supplied name to
-             a canonical name before checking the key, because someone with
-             access to the name servers would then be able to fool host au-
-             thentication.
+     ~/.ssh/known_hosts
+             Contains a list of host keys for all hosts the user has logged
+             into that are not already in the systemwide list of known host
+             keys.  See sshd(8) for further details of the format of this
+             file.
+
+     ~/.ssh/rc
+             Commands in this file are executed by ssh when the user logs in,
+             just before the user's shell (or command) is started.  See the
+             sshd(8) manual page for more information.
+
+     /etc/hosts.equiv
+             This file is for host-based authentication (see above).  It
+             should only be writable by root.
+
+     /etc/shosts.equiv
+             This file is used in exactly the same way as hosts.equiv, but al-
+             lows host-based authentication without permitting login with
+             rlogin/rsh.
 
      /etc/ssh/ssh_config
              Systemwide configuration file.  The file format and configuration
              options are described in ssh_config(5).
 
-     /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key,
-             /etc/ssh/ssh_host_rsa_key
+     /etc/ssh/ssh_host_key
+     /etc/ssh/ssh_host_dsa_key
+     /etc/ssh/ssh_host_rsa_key
              These three files contain the private parts of the host keys and
-             are used for RhostsRSAAuthentication and HostbasedAuthentication.
-             If the protocol version 1 RhostsRSAAuthentication method is used,
-             ssh must be setuid root, since the host key is readable only by
-             root.  For protocol version 2, ssh uses ssh-keysign(8) to access
-             the host keys for HostbasedAuthentication.  This eliminates the
-             requirement that ssh be setuid root when that authentication
-             method is used.  By default ssh is not setuid root.
+             are used for host-based authentication.  If protocol version 1 is
+             used, ssh must be setuid root, since the host key is readable on-
+             ly by root.  For protocol version 2, ssh uses ssh-keysign(8) to
+             access the host keys, eliminating the requirement that ssh be se-
+             tuid root when host-based authentication is used.  By default ssh
+             is not setuid root.
 
-     ~/.rhosts
-             This file is used in RhostsRSAAuthentication and
-             HostbasedAuthentication authentication to list the host/user
-             pairs that are permitted to log in.  (Note that this file is also
-             used by rlogin and rsh, which makes using this file insecure.)
-             Each line of the file contains a host name (in the canonical form
-             returned by name servers), and then a user name on that host,
-             separated by a space.  On some machines this file may need to be
-             world-readable if the user's home directory is on a NFS parti-
-             tion, because sshd(8) reads it as root.  Additionally, this file
-             must be owned by the user, and must not have write permissions
-             for anyone else.  The recommended permission for most machines is
-             read/write for the user, and not accessible by others.
-
-             Note that sshd(8) allows authentication only in combination with
-             client host key authentication before permitting log in.  If the
-             server machine does not have the client's host key in
-             /etc/ssh/ssh_known_hosts, it can be stored in ~/.ssh/known_hosts.
-             The easiest way to do this is to connect back to the client from
-             the server machine using ssh; this will automatically add the
-             host key to ~/.ssh/known_hosts.
-
-     ~/.shosts
-             This file is used exactly the same way as .rhosts.  The purpose
-             for having this file is to be able to use RhostsRSAAuthentication
-             and HostbasedAuthentication authentication without permitting lo-
-             gin with rlogin or rsh(1).
-
-     /etc/hosts.equiv
-             This file is used during RhostsRSAAuthentication and
-             HostbasedAuthentication authentication.  It contains canonical
-             hosts names, one per line (the full format is described in the
-             sshd(8) manual page).  If the client host is found in this file,
-             login is automatically permitted provided client and server user
-             names are the same.  Additionally, successful client host key au-
-             thentication is required.  This file should only be writable by
-             root.
-
-     /etc/shosts.equiv
-             This file is processed exactly as /etc/hosts.equiv.  This file
-             may be useful to permit logins using ssh but not using
-             rsh/rlogin.
+     /etc/ssh/ssh_known_hosts
+             Systemwide list of known host keys.  This file should be prepared
+             by the system administrator to contain the public host keys of
+             all machines in the organization.  It should be world-readable.
+             See sshd(8) for further details of the format of this file.
 
      /etc/ssh/sshrc
-             Commands in this file are executed by ssh when the user logs in
-             just before the user's shell (or command) is started.  See the
-             sshd(8) manual page for more information.
-
-     ~/.ssh/rc
-             Commands in this file are executed by ssh when the user logs in
+             Commands in this file are executed by ssh when the user logs in,
              just before the user's shell (or command) is started.  See the
              sshd(8) manual page for more information.
 
-     ~/.ssh/environment
-             Contains additional definitions for environment variables, see
-             section ENVIRONMENT above.
-
-DIAGNOSTICS
-     ssh exits with the exit status of the remote command or with 255 if an
-     error occurred.
-
 SEE ALSO
-     gzip(1), rsh(1), scp(1), sftp(1), ssh-add(1), ssh-agent(1),
-     ssh-keygen(1), telnet(1), hosts.equiv(5), ssh_config(5), ssh-keysign(8),
-     sshd(8)
+     scp(1), sftp(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), ssh-keyscan(1),
+     tun(4), hosts.equiv(5), ssh_config(5), ssh-keysign(8), sshd(8)
 
      T. Ylonen, T. Kivinen, M. Saarinen, T. Rinne, and S. Lehtinen, SSH
      Protocol Architecture, draft-ietf-secsh-architecture-12.txt, January
@@ -727,4 +790,4 @@ AUTHORS
      created OpenSSH.  Markus Friedl contributed the support for SSH protocol
      versions 1.5 and 2.0.
 
-OpenBSD 3.8                   September 25, 1999                            12
+OpenBSD 3.9                   September 25, 1999                            12