diff options
Diffstat (limited to 'ssh.1')
| -rw-r--r-- | ssh.1 | 498 |
1 files changed, 316 insertions, 182 deletions
@@ -33,17 +33,17 @@ .\" (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: ssh.1,v 1.356 2015/03/03 06:48:58 djm Exp $ -.Dd $Mdocdate: March 3 2015 $ +.\" $OpenBSD: ssh.1,v 1.412 2020/04/17 03:34:42 djm Exp $ +.Dd $Mdocdate: April 17 2020 $ .Dt SSH 1 .Os .Sh NAME .Nm ssh -.Nd OpenSSH SSH client (remote login program) +.Nd OpenSSH remote login client .Sh SYNOPSIS .Nm ssh -.Bk -words -.Op Fl 1246AaCfGgKkMNnqsTtVvXxYy +.Op Fl 46AaCfGgKkMNnqsTtVvXxYy +.Op Fl B Ar bind_interface .Op Fl b Ar bind_address .Op Fl c Ar cipher_spec .Op Fl D Oo Ar bind_address : Oc Ns Ar port @@ -52,26 +52,25 @@ .Op Fl F Ar configfile .Op Fl I Ar pkcs11 .Op Fl i Ar identity_file -.Op Fl L Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport +.Op Fl J Ar destination +.Op Fl L Ar address .Op Fl l Ar login_name .Op Fl m Ar mac_spec .Op Fl O Ar ctl_cmd .Op Fl o Ar option .Op Fl p Ar port -.Op Fl Q Cm cipher | cipher-auth | mac | kex | key | protocol-version -.Op Fl R Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport +.Op Fl Q Ar query_option +.Op Fl R Ar address .Op Fl S Ar ctl_path .Op Fl W Ar host : Ns Ar port .Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun -.Oo Ar user Ns @ Oc Ns Ar hostname +.Ar destination .Op Ar command -.Ek .Sh DESCRIPTION .Nm (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 +It is intended to provide secure encrypted communications between two untrusted hosts over an insecure network. X11 connections, arbitrary TCP ports and .Ux Ns -domain @@ -79,39 +78,40 @@ sockets can also be forwarded over the secure channel. .Pp .Nm connects and logs into the specified -.Ar hostname -(with optional -.Ar user -name). +.Ar destination , +which may be specified as either +.Sm off +.Oo user @ Oc hostname +.Sm on +or a URI of the form +.Sm off +.No ssh:// Oo user @ Oc hostname Op : port . +.Sm on The user must prove his/her identity to the remote machine using one of several methods -depending on the protocol version used (see below). +(see below). .Pp -If +If a .Ar command is specified, it is executed on the remote host instead of a login shell. .Pp The options are as follows: -.Bl -tag -width Ds -.It Fl 1 -Forces -.Nm -to try protocol version 1 only. -.It Fl 2 -Forces -.Nm -to try protocol version 2 only. +.Pp +.Bl -tag -width Ds -compact .It Fl 4 Forces .Nm to use IPv4 addresses only. +.Pp .It Fl 6 Forces .Nm to use IPv6 addresses only. +.Pp .It Fl A -Enables forwarding of the authentication agent connection. +Enables forwarding of connections from an authentication agent such as +.Xr ssh-agent 1 . This can also be specified on a per-host basis in a configuration file. .Pp Agent forwarding should be enabled with caution. @@ -122,42 +122,42 @@ socket) can access the local agent through the forwarded connection. An attacker cannot obtain key material from the agent, however they can perform operations on the keys that enable them to authenticate using the identities loaded into the agent. +A safer alternative may be to use a jump host +(see +.Fl J ) . +.Pp .It Fl a Disables forwarding of the authentication agent connection. +.Pp +.It Fl B Ar bind_interface +Bind to the address of +.Ar bind_interface +before attempting to connect to the destination host. +This is only useful on systems with more than one address. +.Pp .It Fl b Ar bind_address Use .Ar bind_address on the local machine as the source address of the connection. Only useful on systems with more than one address. +.Pp .It Fl C Requests compression of all data (including stdin, stdout, stderr, and data for forwarded X11, TCP and .Ux Ns -domain connections). The compression algorithm is the same used by -.Xr gzip 1 , -and the -.Dq level -can be controlled by the -.Cm CompressionLevel -option for protocol version 1. +.Xr gzip 1 . Compression is desirable on modem lines and other slow connections, but will only slow down things on fast networks. The default value can be set on a host-by-host basis in the configuration files; see the .Cm Compression option. +.Pp .It Fl c Ar cipher_spec Selects the cipher specification for encrypting the session. -.Pp -Protocol version 1 allows specification of a single cipher. -The supported values are -.Dq 3des , -.Dq blowfish , -and -.Dq des . -For protocol version 2, .Ar cipher_spec is a comma-separated list of ciphers listed in order of preference. @@ -166,6 +166,7 @@ See the keyword in .Xr ssh_config 5 for more information. +.Pp .It Fl D Xo .Sm off .Oo Ar bind_address : Oc @@ -205,10 +206,12 @@ indicates that the listening port be bound for local use only, while an empty address or .Sq * indicates that the port should be available from all interfaces. +.Pp .It Fl E Ar log_file Append debug logs to .Ar log_file instead of standard error. +.Pp .It Fl e Ar escape_char Sets the escape character for sessions with a pty (default: .Ql ~ ) . @@ -221,6 +224,7 @@ and followed by itself sends the escape character once. Setting the character to .Dq none disables any escapes and makes the session fully transparent. +.Pp .It Fl F Ar configfile Specifies an alternative per-user configuration file. If a configuration file is given on the command line, @@ -229,6 +233,10 @@ the system-wide configuration file will be ignored. The default for the per-user configuration file is .Pa ~/.ssh/config . +If set to +.Dq none , +no configuration files will be read. +.Pp .It Fl f Requests .Nm @@ -251,6 +259,7 @@ then a client started with .Fl f will wait for all remote port forwards to be successfully established before placing itself in the background. +.Pp .It Fl G Causes .Nm @@ -259,65 +268,112 @@ to print its configuration after evaluating and .Cm Match blocks and exit. +.Pp .It Fl g Allows remote hosts to connect to local forwarded ports. If used on a multiplexed connection, then this option must be specified on the master process. +.Pp .It Fl I Ar pkcs11 Specify the PKCS#11 shared library .Nm -should use to communicate with a PKCS#11 token providing the user's -private RSA key. +should use to communicate with a PKCS#11 token providing keys for user +authentication. +.Pp .It Fl i Ar identity_file Selects a file from which the identity (private key) for public key authentication is read. The default is -.Pa ~/.ssh/identity -for protocol version 1, and .Pa ~/.ssh/id_dsa , .Pa ~/.ssh/id_ecdsa , -.Pa ~/.ssh/id_ed25519 +.Pa ~/.ssh/id_ecdsa_sk , +.Pa ~/.ssh/id_ed25519 , +.Pa ~/.ssh/id_ed25519_sk and -.Pa ~/.ssh/id_rsa -for protocol version 2. +.Pa ~/.ssh/id_rsa . Identity files may also be specified on a per-host basis in the configuration file. It is possible to have multiple .Fl i options (and multiple identities specified in configuration files). +If no certificates have been explicitly specified by the +.Cm CertificateFile +directive, .Nm will also try to load certificate information from the filename obtained by appending .Pa -cert.pub to identity filenames. +.Pp +.It Fl J Ar destination +Connect to the target host by first making a +.Nm +connection to the jump host described by +.Ar destination +and then establishing a TCP forwarding to the ultimate destination from +there. +Multiple jump hops may be specified separated by comma characters. +This is a shortcut to specify a +.Cm ProxyJump +configuration directive. +Note that configuration directives supplied on the command-line generally +apply to the destination host and not any specified jump hosts. +Use +.Pa ~/.ssh/config +to specify configuration for jump hosts. +.Pp .It Fl K Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI credentials to the server. +.Pp .It Fl k Disables forwarding (delegation) of GSSAPI credentials to the server. +.Pp .It Fl L Xo .Sm off .Oo Ar bind_address : Oc .Ar port : host : hostport .Sm on .Xc -Specifies that the given port on the local (client) host is to be -forwarded to the given host and port on the remote side. -This works by allocating a socket to listen to +.It Fl L Xo +.Sm off +.Oo Ar bind_address : Oc +.Ar port : remote_socket +.Sm on +.Xc +.It Fl L Xo +.Sm off +.Ar local_socket : host : hostport +.Sm on +.Xc +.It Fl L Xo +.Sm off +.Ar local_socket : remote_socket +.Sm on +.Xc +Specifies that connections to the given TCP port or Unix socket on the local +(client) host are to be forwarded to the given host and port, or Unix socket, +on the remote side. +This works by allocating a socket to listen to either a TCP .Ar port on the local side, optionally bound to the specified -.Ar bind_address . -Whenever a connection is made to this port, the +.Ar bind_address , +or to a Unix socket. +Whenever a connection is made to the local port or socket, the connection is forwarded over the secure channel, and a connection is -made to +made to either .Ar host port -.Ar hostport +.Ar hostport , +or the Unix socket +.Ar remote_socket , from the remote machine. +.Pp Port forwardings can also be specified in the configuration file. -IPv6 addresses can be specified by enclosing the address in square brackets. Only the superuser can forward privileged ports. +IPv6 addresses can be specified by enclosing the address in square brackets. +.Pp By default, the local port is bound in accordance with the .Cm GatewayPorts setting. @@ -332,9 +388,11 @@ indicates that the listening port be bound for local use only, while an empty address or .Sq * indicates that the port should be available from all interfaces. +.Pp .It Fl l Ar login_name Specifies the user to log in as on the remote machine. This also may be specified on a per-host basis in the configuration file. +.Pp .It Fl M Places the .Nm @@ -347,23 +405,27 @@ options places .Nm into .Dq master -mode with confirmation required before slave connections are accepted. +mode but with confirmation required using +.Xr ssh-askpass 1 +before each operation that changes the multiplexing state +(e.g. opening a new session). Refer to the description of .Cm ControlMaster in .Xr ssh_config 5 for details. +.Pp .It Fl m Ar mac_spec -Additionally, for protocol version 2 a comma-separated list of MAC -(message authentication code) algorithms can -be specified in order of preference. +A comma-separated list of MAC (message authentication code) algorithms, +specified in order of preference. See the .Cm MACs keyword for more information. +.Pp .It Fl N Do not execute a remote command. -This is useful for just forwarding ports -(protocol version 2 only). +This is useful for just forwarding ports. +.Pp .It Fl n Redirects stdin from .Pa /dev/null @@ -384,6 +446,7 @@ program will be put in the background. needs to ask for a password or passphrase; see also the .Fl f option.) +.Pp .It Fl O Ar ctl_cmd Control an active connection multiplexing master process. When the @@ -402,6 +465,7 @@ Valid commands are: (request the master to exit), and .Dq stop (request the master to stop accepting further multiplexing requests). +.Pp .It Fl o Ar option Can be used to give options in the format used in the configuration file. This is useful for specifying options for which there is no separate @@ -410,6 +474,7 @@ For full details of the options listed below, and their possible values, see .Xr ssh_config 5 . .Pp .Bl -tag -width Ds -offset indent -compact +.It AddKeysToAgent .It AddressFamily .It BatchMode .It BindAddress @@ -418,13 +483,13 @@ For full details of the options listed below, and their possible values, see .It CanonicalizeHostname .It CanonicalizeMaxDots .It CanonicalizePermittedCNAMEs +.It CASignatureAlgorithms +.It CertificateFile .It ChallengeResponseAuthentication .It CheckHostIP -.It Cipher .It Ciphers .It ClearAllForwardings .It Compression -.It CompressionLevel .It ConnectionAttempts .It ConnectTimeout .It ControlMaster @@ -448,9 +513,10 @@ For full details of the options listed below, and their possible values, see .It HostbasedKeyTypes .It HostKeyAlgorithms .It HostKeyAlias -.It HostName -.It IdentityFile +.It Hostname .It IdentitiesOnly +.It IdentityAgent +.It IdentityFile .It IPQoS .It KbdInteractiveAuthentication .It KbdInteractiveDevices @@ -467,18 +533,19 @@ For full details of the options listed below, and their possible values, see .It PKCS11Provider .It Port .It PreferredAuthentications -.It Protocol .It ProxyCommand +.It ProxyJump .It ProxyUseFdpass +.It PubkeyAcceptedKeyTypes .It PubkeyAuthentication .It RekeyLimit +.It RemoteCommand .It RemoteForward .It RequestTTY -.It RhostsRSAAuthentication -.It RSAAuthentication .It SendEnv .It ServerAliveInterval .It ServerAliveCountMax +.It SetEnv .It StreamLocalBindMask .It StreamLocalBindUnlink .It StrictHostKeyChecking @@ -486,18 +553,19 @@ For full details of the options listed below, and their possible values, see .It Tunnel .It TunnelDevice .It UpdateHostKeys -.It UsePrivilegedPort .It User .It UserKnownHostsFile .It VerifyHostKeyDNS .It VisualHostKey .It XAuthLocation .El +.Pp .It Fl p Ar port Port to connect to on the remote host. This can be specified on a per-host basis in the configuration file. -.It Fl Q Cm cipher | cipher-auth | mac | kex | key | protocol-version +.Pp +.It Fl Q Ar query_option Queries .Nm for the algorithms supported for the specified version 2. @@ -506,41 +574,90 @@ The available features are: (supported symmetric ciphers), .Ar cipher-auth (supported symmetric ciphers that support authenticated encryption), +.Ar help +(supported query terms for use with the +.Fl Q +flag), .Ar mac (supported message integrity codes), .Ar kex (key exchange algorithms), .Ar key -(key types) and +(key types), +.Ar key-cert +(certificate key types), +.Ar key-plain +(non-certificate key types), +.Ar key-sig +(all key types and signature algorithms), .Ar protocol-version -(supported SSH protocol versions). +(supported SSH protocol versions), and +.Ar sig +(supported signature algorithms). +Alternatively, any keyword from +.Xr ssh_config 5 +or +.Xr sshd_config 5 +that takes an algorithm list may be used as an alias for the corresponding +query_option. +.Pp .It Fl q Quiet mode. Causes most warning and diagnostic messages to be suppressed. +.Pp .It Fl R Xo .Sm off .Oo Ar bind_address : Oc .Ar port : host : hostport .Sm on .Xc -Specifies that the given port on the remote (server) host is to be -forwarded to the given host and port on the local side. -This works by allocating a socket to listen to +.It Fl R Xo +.Sm off +.Oo Ar bind_address : Oc +.Ar port : local_socket +.Sm on +.Xc +.It Fl R Xo +.Sm off +.Ar remote_socket : host : hostport +.Sm on +.Xc +.It Fl R Xo +.Sm off +.Ar remote_socket : local_socket +.Sm on +.Xc +.It Fl R Xo +.Sm off +.Oo Ar bind_address : Oc .Ar port -on the remote side, and whenever a connection is made to this port, the -connection is forwarded over the secure channel, and a connection is -made to +.Sm on +.Xc +Specifies that connections to the given TCP port or Unix socket on the remote +(server) host are to be forwarded to the local side. +.Pp +This works by allocating a socket to listen to either a TCP +.Ar port +or to a Unix socket on the remote side. +Whenever a connection is made to this port or Unix socket, the +connection is forwarded over the secure channel, and a connection +is made from the local machine to either an explicit destination specified by .Ar host port -.Ar hostport -from the local machine. +.Ar hostport , +or +.Ar local_socket , +or, if no explicit destination was specified, +.Nm +will act as a SOCKS 4/5 proxy and forward connections to the destinations +requested by the remote SOCKS client. .Pp Port forwardings can also be specified in the configuration file. Privileged ports can be forwarded only when logging in as root on the remote machine. IPv6 addresses can be specified by enclosing the address in square brackets. .Pp -By default, the listening socket on the server will be bound to the loopback +By default, TCP listening sockets on the server will be bound to the loopback interface only. This may be overridden by specifying a .Ar bind_address . @@ -565,6 +682,7 @@ to the client at run time. When used together with .Ic -O forward the allocated port will be printed to the standard output. +.Pp .It Fl S Ar ctl_path Specifies the location of a control socket for connection sharing, or the string @@ -577,16 +695,19 @@ and in .Xr ssh_config 5 for details. +.Pp .It Fl s May be used to request invocation of a subsystem on the remote system. -Subsystems are a feature of the SSH2 protocol which facilitate the use -of SSH as a secure transport for other applications (eg.\& +Subsystems facilitate the use of SSH +as a secure transport for other applications (e.g.\& .Xr sftp 1 ) . The subsystem is specified as the remote command. +.Pp .It Fl T -Disable pseudo-tty allocation. +Disable pseudo-terminal allocation. +.Pp .It Fl t -Force pseudo-tty allocation. +Force pseudo-terminal allocation. This can be used to execute arbitrary screen-based programs on a remote machine, which can be very useful, e.g. when implementing menu services. @@ -595,8 +716,10 @@ Multiple options force tty allocation, even if .Nm has no local tty. +.Pp .It Fl V Display the version number and exit. +.Pp .It Fl v Verbose mode. Causes @@ -608,6 +731,7 @@ Multiple .Fl v options increase the verbosity. The maximum is 3. +.Pp .It Fl W Ar host : Ns Ar port Requests that standard input and output on the client be forwarded to .Ar host @@ -619,8 +743,11 @@ Implies .Fl T , .Cm ExitOnForwardFailure and -.Cm ClearAllForwardings . -Works with Protocol version 2 only. +.Cm ClearAllForwardings , +though these can be overridden in the configuration file or using +.Fl o +command line options. +.Pp .It Fl w Xo .Ar local_tun Ns Op : Ns Ar remote_tun .Xc @@ -646,10 +773,16 @@ and .Cm TunnelDevice directives in .Xr ssh_config 5 . +.Pp If the .Cm Tunnel -directive is unset, it is set to the default tunnel mode, which is +directive is unset, it will be set to the default tunnel mode, which is .Dq point-to-point . +If a different +.Cm Tunnel +forwarding mode it desired, then it should be specified before +.Fl w . +.Pp .It Fl X Enables X11 forwarding. This can also be specified on a per-host basis in a configuration file. @@ -670,12 +803,15 @@ option and the directive in .Xr ssh_config 5 for more information. +.Pp .It Fl x Disables X11 forwarding. +.Pp .It Fl Y Enables trusted X11 forwarding. Trusted X11 forwardings are not subjected to the X11 SECURITY extension controls. +.Pp .It Fl y Send log information using the .Xr syslog 3 @@ -689,26 +825,7 @@ a per-user configuration file and a system-wide configuration file. The file format and configuration options are described in .Xr ssh_config 5 . .Sh AUTHENTICATION -The OpenSSH SSH client supports SSH protocols 1 and 2. -The default is to use protocol 2 only, -though this can be changed via the -.Cm Protocol -option in -.Xr ssh_config 5 -or the -.Fl 1 -and -.Fl 2 -options (see above). -Both protocols support similar authentication methods, -but protocol 2 is the default 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-sha2-256, hmac-sha2-512, -umac-64, umac-128, hmac-ripemd160). -Protocol 1 lacks a strong mechanism for ensuring the -integrity of the connection. +The OpenSSH SSH client supports SSH protocol 2. .Pp The methods available for authentication are: GSSAPI-based authentication, @@ -717,15 +834,16 @@ public key authentication, challenge-response authentication, and password authentication. Authentication methods are tried in the order specified above, -though protocol 2 has a configuration option to change the default order: -.Cm PreferredAuthentications . +though +.Cm PreferredAuthentications +can be used to change the default order. .Pp Host-based authentication works as follows: If the machine the user logs in from is listed in .Pa /etc/hosts.equiv or .Pa /etc/shosts.equiv -on the remote machine, and the user names are +on the remote machine, the user is non-root and the user names are the same on both sides, or if the files .Pa ~/.rhosts or @@ -762,8 +880,6 @@ The server knows the public key, and only the user knows the private key. .Nm implements public key authentication protocol automatically, using one of the DSA, ECDSA, Ed25519 or RSA algorithms. -Protocol 1 is restricted to using only RSA keys, -but protocol 2 may use any. The HISTORY section of .Xr ssl 8 contains a brief discussion of the DSA and RSA algorithms. @@ -779,32 +895,47 @@ 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. .Pp +The server may inform the client of errors that prevented public key +authentication from succeeding after authentication completes using a +different method. +These may be viewed by increasing the +.Cm LogLevel +to +.Cm DEBUG +or higher (e.g. by using the +.Fl v +flag). +.Pp The user creates his/her key pair by running .Xr ssh-keygen 1 . This stores the private key in -.Pa ~/.ssh/identity -(protocol 1), .Pa ~/.ssh/id_dsa -(protocol 2 DSA), +(DSA), .Pa ~/.ssh/id_ecdsa -(protocol 2 ECDSA), +(ECDSA), +.Pa ~/.ssh/id_ecdsa_sk +(authenticator-hosted ECDSA), .Pa ~/.ssh/id_ed25519 -(protocol 2 Ed25519), +(Ed25519), +.Pa ~/.ssh/id_ed25519_sk +(authenticator-hosted Ed25519), or .Pa ~/.ssh/id_rsa -(protocol 2 RSA) +(RSA) and stores the public key in -.Pa ~/.ssh/identity.pub -(protocol 1), .Pa ~/.ssh/id_dsa.pub -(protocol 2 DSA), +(DSA), .Pa ~/.ssh/id_ecdsa.pub -(protocol 2 ECDSA), +(ECDSA), +.Pa ~/.ssh/id_ecdsa_sk.pub +(authenticator-hosted ECDSA), .Pa ~/.ssh/id_ed25519.pub -(protocol 2 Ed25519), +(Ed25519), +.Pa ~/.ssh/id_ed25519_sk.pub +(authenticator-hosted Ed25519), or .Pa ~/.ssh/id_rsa.pub -(protocol 2 RSA) +(RSA) in the user's home directory. The user should then copy the public key to @@ -832,14 +963,16 @@ The most convenient way to use public key or certificate authentication may be with an authentication agent. See .Xr ssh-agent 1 +and (optionally) the +.Cm AddKeysToAgent +directive in +.Xr ssh_config 5 for more information. .Pp Challenge-response authentication works as follows: The server sends an arbitrary .Qq challenge text, and prompts for a response. -Protocol 2 allows multiple challenges and responses; -protocol 1 is restricted to just one challenge/response. Examples of challenge-response authentication include .Bx Authentication (see @@ -876,15 +1009,26 @@ option can be used to control logins to machines whose host key is not known or has changed. .Pp When the user's identity has been accepted by the server, the server -either executes the given command, or logs into the machine and gives -the user a normal shell on the remote machine. +either executes the given command in a non-interactive session or, +if no command has been specified, logs into the machine and gives +the user a normal shell as an interactive session. All communication with the remote command or shell will be automatically encrypted. .Pp -If a pseudo-terminal has been allocated (normal login session), the +If an interactive session is requested +.Nm +by default will only request a pseudo-terminal (pty) for interactive +sessions when the client has one. +The flags +.Fl T +and +.Fl t +can be used to override this behaviour. +.Pp +If a pseudo-terminal has been allocated the user may use the escape characters noted below. .Pp -If no pseudo-tty has been allocated, +If no pseudo-terminal has been allocated, the session is transparent and can be used to reliably transfer binary data. On most systems, setting the escape character to .Dq none @@ -927,7 +1071,7 @@ at logout when waiting for forwarded connection / X11 sessions to terminate. Display a list of escape characters. .It Cm ~B Send a BREAK to the remote system -(only useful for SSH protocol version 2 and if the peer supports it). +(only useful if the peer supports it). .It Cm ~C Open command line. Currently this allows the addition of port forwardings using the @@ -960,7 +1104,7 @@ Basic help is available, using the option. .It Cm ~R Request rekeying of the connection -(only useful for SSH protocol version 2 and if the peer supports it). +(only useful if the peer supports it). .It Cm ~V Decrease the verbosity .Pq Ic LogLevel @@ -971,49 +1115,35 @@ Increase the verbosity when errors are being written to stderr. .El .Sh TCP FORWARDING -Forwarding of arbitrary TCP connections over the secure channel can -be specified either on the command line or in a configuration file. +Forwarding of arbitrary TCP connections over a 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. .Pp -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. +In the example below, we look at encrypting communication for an IRC client, +even though the IRC server it connects to does not directly +support encrypted communication. This works as follows: the user connects to the remote host using .Nm , -specifying a port to be used to forward connections -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, +specifying the ports to be used to forward the connection. +After that it is possible to start the program locally, and .Nm -will encrypt and forward the connection. +will encrypt and forward the connection to the remote server. .Pp -The following example tunnels an IRC session from client machine -.Dq 127.0.0.1 -(localhost) -to remote server -.Dq server.example.com : -.Bd -literal -offset 4n -$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 -$ irc -c '#users' -p 1234 pinky 127.0.0.1 -.Ed -.Pp -This tunnels a connection to IRC server +The following example tunnels an IRC session from the client +to an IRC server at .Dq server.example.com , joining channel .Dq #users , nickname .Dq pinky , -using port 1234. -It doesn't matter 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. +using the standard IRC port, 6667: +.Bd -literal -offset 4n +$ ssh -f -L 6667:localhost:6667 server.example.com sleep 10 +$ irc -c '#users' pinky IRC/127.0.0.1 +.Ed .Pp The .Fl f @@ -1023,7 +1153,7 @@ and the remote command .Dq sleep 10 is specified to allow an amount of time (10 seconds, in the example) -to start the service which is to be tunnelled. +to start the program which is going to use the tunnel. If no connections are made within the time specified, .Nm will exit. @@ -1095,6 +1225,11 @@ Fingerprints can be determined using .Pp If the fingerprint is already known, it can be matched and the key can be accepted or rejected. +If only legacy (MD5) fingerprints for the server are available, the +.Xr ssh-keygen 1 +.Fl E +option may be used to downgrade the fingerprint algorithm to match. +.Pp Because of the difficulty of comparing host keys just by looking at fingerprint strings, there is also support to compare host keys visually, @@ -1292,6 +1427,17 @@ This is set to the name of the tty (path to the device) associated with the current shell or command. If the current session has no tty, this variable is not set. +.It Ev SSH_TUNNEL +Optionally set by +.Xr sshd 8 +to contain the interface names assigned if tunnel forwarding was +requested by the client. +.It Ev SSH_USER_AUTH +Optionally set by +.Xr sshd 8 , +this variable may contain a pathname to a file that lists the authentication +methods successfully used when the session was established, including any +public keys that were used. .It Ev 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 @@ -1361,10 +1507,11 @@ Contains additional definitions for environment variables; see .Sx ENVIRONMENT , above. .Pp -.It Pa ~/.ssh/identity .It Pa ~/.ssh/id_dsa .It Pa ~/.ssh/id_ecdsa +.It Pa ~/.ssh/id_ecdsa_sk .It Pa ~/.ssh/id_ed25519 +.It Pa ~/.ssh/id_ed25519_sk .It Pa ~/.ssh/id_rsa Contains the private key for authentication. These files @@ -1374,12 +1521,13 @@ accessible by others (read/write/execute). 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. +sensitive part of this file using AES-128. .Pp -.It Pa ~/.ssh/identity.pub .It Pa ~/.ssh/id_dsa.pub .It Pa ~/.ssh/id_ecdsa.pub +.It Pa ~/.ssh/id_ecdsa_sk.pub .It Pa ~/.ssh/id_ed25519.pub +.It Pa ~/.ssh/id_ed25519_sk.pub .It Pa ~/.ssh/id_rsa.pub Contains the public key for authentication. These files are not @@ -1423,20 +1571,6 @@ The file format and configuration options are described in .It Pa /etc/ssh/ssh_host_rsa_key These files contain the private parts of the host keys and are used for host-based authentication. -If protocol version 1 is used, -.Nm -must be setuid root, since the host key is readable only by root. -For protocol version 2, -.Nm -uses -.Xr ssh-keysign 8 -to access the host keys, -eliminating the requirement that -.Nm -be setuid root when host-based authentication is used. -By default -.Nm -is not setuid root. .Pp .It Pa /etc/ssh/ssh_known_hosts Systemwide list of known host keys. |