Annotation of src/usr.bin/ssh/ssh.1, Revision 1.432
1.1 deraadt 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
1.59 deraadt 6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
1.93 deraadt 12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
1.59 deraadt 15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
18: .\" are met:
19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
1.1 deraadt 24: .\"
1.59 deraadt 25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
34: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.1 deraadt 35: .\"
1.432 ! djm 36: .\" $OpenBSD: ssh.1,v 1.431 2022/05/28 05:57:56 jmc Exp $
! 37: .Dd $Mdocdate: May 28 2022 $
1.2 deraadt 38: .Dt SSH 1
39: .Os
40: .Sh NAME
41: .Nm ssh
1.408 jmc 42: .Nd OpenSSH remote login client
1.2 deraadt 43: .Sh SYNOPSIS
44: .Nm ssh
1.377 djm 45: .Op Fl 46AaCfGgKkMNnqsTtVvXxYy
1.390 djm 46: .Op Fl B Ar bind_interface
1.108 markus 47: .Op Fl b Ar bind_address
1.51 markus 48: .Op Fl c Ar cipher_spec
1.306 jmc 49: .Op Fl D Oo Ar bind_address : Oc Ns Ar port
1.331 dtucker 50: .Op Fl E Ar log_file
1.2 deraadt 51: .Op Fl e Ar escape_char
1.176 jmc 52: .Op Fl F Ar configfile
1.292 jmc 53: .Op Fl I Ar pkcs11
1.2 deraadt 54: .Op Fl i Ar identity_file
1.386 millert 55: .Op Fl J Ar destination
1.360 millert 56: .Op Fl L Ar address
1.176 jmc 57: .Op Fl l Ar login_name
58: .Op Fl m Ar mac_spec
1.198 djm 59: .Op Fl O Ar ctl_cmd
1.176 jmc 60: .Op Fl o Ar option
61: .Op Fl p Ar port
1.362 djm 62: .Op Fl Q Ar query_option
1.360 millert 63: .Op Fl R Ar address
1.198 djm 64: .Op Fl S Ar ctl_path
1.290 dtucker 65: .Op Fl W Ar host : Ns Ar port
1.306 jmc 66: .Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun
1.386 millert 67: .Ar destination
1.427 dtucker 68: .Op Ar command Op Ar argument ...
1.44 aaron 69: .Sh DESCRIPTION
1.2 deraadt 70: .Nm
1.96 deraadt 71: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 72: executing commands on a remote machine.
1.365 mmcc 73: It is intended to provide secure encrypted communications between
1.40 aaron 74: two untrusted hosts over an insecure network.
1.348 millert 75: X11 connections, arbitrary TCP ports and
76: .Ux Ns -domain
77: sockets can also be forwarded over the secure channel.
1.2 deraadt 78: .Pp
79: .Nm
1.44 aaron 80: connects and logs into the specified
1.388 jmc 81: .Ar destination ,
1.386 millert 82: which may be specified as either
1.388 jmc 83: .Sm off
84: .Oo user @ Oc hostname
85: .Sm on
86: or a URI of the form
87: .Sm off
88: .No ssh:// Oo user @ Oc hostname Op : port .
89: .Sm on
1.1 deraadt 90: The user must prove
1.420 dtucker 91: their identity to the remote machine using one of several methods
1.365 mmcc 92: (see below).
1.49 markus 93: .Pp
1.386 millert 94: If a
1.176 jmc 95: .Ar command
96: is specified,
1.427 dtucker 97: it will be executed on the remote host instead of a login shell.
98: A complete command line may be specified as
99: .Ar command ,
100: or it may have additional arguments.
101: If supplied, the arguments will be appended to the command, separated by
102: spaces, before it is sent to the server to be executed.
1.2 deraadt 103: .Pp
1.218 jmc 104: The options are as follows:
1.361 millert 105: .Pp
1.360 millert 106: .Bl -tag -width Ds -compact
1.218 jmc 107: .It Fl 4
108: Forces
1.2 deraadt 109: .Nm
1.218 jmc 110: to use IPv4 addresses only.
1.360 millert 111: .Pp
1.218 jmc 112: .It Fl 6
113: Forces
1.2 deraadt 114: .Nm
1.218 jmc 115: to use IPv6 addresses only.
1.360 millert 116: .Pp
1.218 jmc 117: .It Fl A
1.407 jmc 118: Enables forwarding of connections from an authentication agent such as
119: .Xr ssh-agent 1 .
1.218 jmc 120: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 121: .Pp
1.218 jmc 122: Agent forwarding should be enabled with caution.
123: Users with the ability to bypass file permissions on the remote host
1.285 sobrado 124: (for the agent's
1.286 sobrado 125: .Ux Ns -domain
126: socket) can access the local agent through the forwarded connection.
1.218 jmc 127: An attacker cannot obtain key material from the agent,
128: however they can perform operations on the keys that enable them to
129: authenticate using the identities loaded into the agent.
1.407 jmc 130: A safer alternative may be to use a jump host
131: (see
132: .Fl J ) .
1.360 millert 133: .Pp
1.218 jmc 134: .It Fl a
135: Disables forwarding of the authentication agent connection.
1.390 djm 136: .Pp
1.391 jmc 137: .It Fl B Ar bind_interface
1.390 djm 138: Bind to the address of
1.391 jmc 139: .Ar bind_interface
1.390 djm 140: before attempting to connect to the destination host.
141: This is only useful on systems with more than one address.
1.360 millert 142: .Pp
1.218 jmc 143: .It Fl b Ar bind_address
144: Use
145: .Ar bind_address
146: on the local machine as the source address
147: of the connection.
148: Only useful on systems with more than one address.
1.360 millert 149: .Pp
1.218 jmc 150: .It Fl C
151: Requests compression of all data (including stdin, stdout, stderr, and
1.348 millert 152: data for forwarded X11, TCP and
153: .Ux Ns -domain
154: connections).
1.218 jmc 155: The compression algorithm is the same used by
1.377 djm 156: .Xr gzip 1 .
1.218 jmc 157: Compression is desirable on modem lines and other
158: slow connections, but will only slow down things on fast networks.
159: The default value can be set on a host-by-host basis in the
160: configuration files; see the
161: .Cm Compression
1.431 jmc 162: option in
163: .Xr ssh_config 5 .
1.360 millert 164: .Pp
1.218 jmc 165: .It Fl c Ar cipher_spec
166: Selects the cipher specification for encrypting the session.
167: .Ar cipher_spec
168: is a comma-separated list of ciphers
169: listed in order of preference.
1.283 jmc 170: See the
171: .Cm Ciphers
1.307 dtucker 172: keyword in
173: .Xr ssh_config 5
174: for more information.
1.360 millert 175: .Pp
1.218 jmc 176: .It Fl D Xo
177: .Sm off
178: .Oo Ar bind_address : Oc
179: .Ar port
180: .Sm on
181: .Xc
182: Specifies a local
183: .Dq dynamic
184: application-level port forwarding.
185: This works by allocating a socket to listen to
186: .Ar port
187: on the local side, optionally bound to the specified
188: .Ar bind_address .
189: Whenever a connection is made to this port, the
190: connection is forwarded over the secure channel, and the application
191: protocol is then used to determine where to connect to from the
192: remote machine.
193: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.107 markus 194: .Nm
1.218 jmc 195: will act as a SOCKS server.
196: Only root can forward privileged ports.
197: Dynamic port forwardings can also be specified in the configuration file.
1.49 markus 198: .Pp
1.308 djm 199: IPv6 addresses can be specified by enclosing the address in square brackets.
1.218 jmc 200: Only the superuser can forward privileged ports.
201: By default, the local port is bound in accordance with the
202: .Cm GatewayPorts
203: setting.
204: However, an explicit
205: .Ar bind_address
206: may be used to bind the connection to a specific address.
207: The
208: .Ar bind_address
209: of
210: .Dq localhost
211: indicates that the listening port be bound for local use only, while an
212: empty address or
213: .Sq *
214: indicates that the port should be available from all interfaces.
1.360 millert 215: .Pp
1.331 dtucker 216: .It Fl E Ar log_file
217: Append debug logs to
218: .Ar log_file
219: instead of standard error.
1.360 millert 220: .Pp
1.229 jmc 221: .It Fl e Ar escape_char
1.218 jmc 222: Sets the escape character for sessions with a pty (default:
223: .Ql ~ ) .
224: The escape character is only recognized at the beginning of a line.
225: The escape character followed by a dot
226: .Pq Ql \&.
227: closes the connection;
228: followed by control-Z suspends the connection;
229: and followed by itself sends the escape character once.
230: Setting the character to
1.2 deraadt 231: .Dq none
1.218 jmc 232: disables any escapes and makes the session fully transparent.
1.360 millert 233: .Pp
1.218 jmc 234: .It Fl F Ar configfile
235: Specifies an alternative per-user configuration file.
236: If a configuration file is given on the command line,
237: the system-wide configuration file
238: .Pq Pa /etc/ssh/ssh_config
239: will be ignored.
240: The default for the per-user configuration file is
241: .Pa ~/.ssh/config .
1.411 naddy 242: If set to
243: .Dq none ,
244: no configuration files will be read.
1.360 millert 245: .Pp
1.218 jmc 246: .It Fl f
247: Requests
248: .Nm
249: to go to background just before command execution.
250: This is useful if
1.176 jmc 251: .Nm
1.218 jmc 252: is going to ask for passwords or passphrases, but the user
253: wants it in the background.
254: This implies
255: .Fl n .
256: The recommended way to start X11 programs at a remote site is with
257: something like
258: .Ic ssh -f host xterm .
1.277 djm 259: .Pp
260: If the
261: .Cm ExitOnForwardFailure
262: configuration option is set to
263: .Dq yes ,
264: then a client started with
265: .Fl f
266: will wait for all remote port forwards to be successfully established
267: before placing itself in the background.
1.424 djm 268: Refer to the description of
269: .Cm ForkAfterAuthentication
270: in
271: .Xr ssh_config 5
272: for details.
1.360 millert 273: .Pp
1.350 djm 274: .It Fl G
275: Causes
276: .Nm
277: to print its configuration after evaluating
278: .Cm Host
279: and
280: .Cm Match
281: blocks and exit.
1.360 millert 282: .Pp
1.218 jmc 283: .It Fl g
284: Allows remote hosts to connect to local forwarded ports.
1.346 djm 285: If used on a multiplexed connection, then this option must be specified
286: on the master process.
1.360 millert 287: .Pp
1.291 markus 288: .It Fl I Ar pkcs11
1.294 jmc 289: Specify the PKCS#11 shared library
1.176 jmc 290: .Nm
1.401 naddy 291: should use to communicate with a PKCS#11 token providing keys for user
292: authentication.
1.360 millert 293: .Pp
1.218 jmc 294: .It Fl i Ar identity_file
295: Selects a file from which the identity (private key) for
1.310 djm 296: public key authentication is read.
1.426 dtucker 297: You can also specify a public key file to use the corresponding
298: private key that is loaded in
299: .Xr ssh-agent 1
300: when the private key file is not present locally.
1.218 jmc 301: The default is
1.428 dtucker 302: .Pa ~/.ssh/id_rsa ,
1.343 naddy 303: .Pa ~/.ssh/id_ecdsa ,
1.404 naddy 304: .Pa ~/.ssh/id_ecdsa_sk ,
1.406 naddy 305: .Pa ~/.ssh/id_ed25519 ,
306: .Pa ~/.ssh/id_ed25519_sk
1.310 djm 307: and
1.428 dtucker 308: .Pa ~/.ssh/id_dsa .
1.218 jmc 309: Identity files may also be specified on
310: a per-host basis in the configuration file.
311: It is possible to have multiple
312: .Fl i
313: options (and multiple identities specified in
314: configuration files).
1.364 jmc 315: If no certificates have been explicitly specified by the
1.363 djm 316: .Cm CertificateFile
317: directive,
1.302 djm 318: .Nm
319: will also try to load certificate information from the filename obtained
320: by appending
321: .Pa -cert.pub
322: to identity filenames.
1.360 millert 323: .Pp
1.386 millert 324: .It Fl J Ar destination
1.375 djm 325: Connect to the target host by first making a
326: .Nm
1.386 millert 327: connection to the jump host described by
328: .Ar destination
1.376 jmc 329: and then establishing a TCP forwarding to the ultimate destination from
1.375 djm 330: there.
331: Multiple jump hops may be specified separated by comma characters.
332: This is a shortcut to specify a
333: .Cm ProxyJump
334: configuration directive.
1.400 djm 335: Note that configuration directives supplied on the command-line generally
336: apply to the destination host and not any specified jump hosts.
337: Use
338: .Pa ~/.ssh/config
339: to specify configuration for jump hosts.
1.375 djm 340: .Pp
1.269 djm 341: .It Fl K
342: Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
343: credentials to the server.
1.360 millert 344: .Pp
1.218 jmc 345: .It Fl k
346: Disables forwarding (delegation) of GSSAPI credentials to the server.
1.360 millert 347: .Pp
1.218 jmc 348: .It Fl L Xo
349: .Sm off
350: .Oo Ar bind_address : Oc
351: .Ar port : host : hostport
352: .Sm on
353: .Xc
1.360 millert 354: .It Fl L Xo
355: .Sm off
356: .Oo Ar bind_address : Oc
357: .Ar port : remote_socket
358: .Sm on
359: .Xc
360: .It Fl L Xo
361: .Sm off
362: .Ar local_socket : host : hostport
363: .Sm on
364: .Xc
365: .It Fl L Xo
366: .Sm off
367: .Ar local_socket : remote_socket
368: .Sm on
369: .Xc
370: Specifies that connections to the given TCP port or Unix socket on the local
371: (client) host are to be forwarded to the given host and port, or Unix socket,
372: on the remote side.
373: This works by allocating a socket to listen to either a TCP
1.218 jmc 374: .Ar port
375: on the local side, optionally bound to the specified
1.360 millert 376: .Ar bind_address ,
377: or to a Unix socket.
378: Whenever a connection is made to the local port or socket, the
1.218 jmc 379: connection is forwarded over the secure channel, and a connection is
1.360 millert 380: made to either
1.218 jmc 381: .Ar host
382: port
1.360 millert 383: .Ar hostport ,
384: or the Unix socket
385: .Ar remote_socket ,
1.218 jmc 386: from the remote machine.
1.360 millert 387: .Pp
1.218 jmc 388: Port forwardings can also be specified in the configuration file.
1.360 millert 389: Only the superuser can forward privileged ports.
1.308 djm 390: IPv6 addresses can be specified by enclosing the address in square brackets.
1.360 millert 391: .Pp
1.218 jmc 392: By default, the local port is bound in accordance with the
393: .Cm GatewayPorts
394: setting.
395: However, an explicit
396: .Ar bind_address
397: may be used to bind the connection to a specific address.
1.2 deraadt 398: The
1.218 jmc 399: .Ar bind_address
400: of
401: .Dq localhost
402: indicates that the listening port be bound for local use only, while an
403: empty address or
404: .Sq *
405: indicates that the port should be available from all interfaces.
1.360 millert 406: .Pp
1.218 jmc 407: .It Fl l Ar login_name
408: Specifies the user to log in as on the remote machine.
409: This also may be specified on a per-host basis in the configuration file.
1.360 millert 410: .Pp
1.218 jmc 411: .It Fl M
412: Places the
413: .Nm
414: client into
415: .Dq master
416: mode for connection sharing.
1.231 stevesk 417: Multiple
418: .Fl M
419: options places
420: .Nm
421: into
422: .Dq master
1.397 djm 423: mode but with confirmation required using
424: .Xr ssh-askpass 1
425: before each operation that changes the multiplexing state
426: (e.g. opening a new session).
1.218 jmc 427: Refer to the description of
428: .Cm ControlMaster
429: in
430: .Xr ssh_config 5
431: for details.
1.360 millert 432: .Pp
1.218 jmc 433: .It Fl m Ar mac_spec
1.369 jmc 434: A comma-separated list of MAC (message authentication code) algorithms,
435: specified in order of preference.
1.218 jmc 436: See the
437: .Cm MACs
1.431 jmc 438: keyword in
439: .Xr ssh_config 5
440: for more information.
1.360 millert 441: .Pp
1.218 jmc 442: .It Fl N
443: Do not execute a remote command.
1.369 jmc 444: This is useful for just forwarding ports.
1.422 djm 445: Refer to the description of
446: .Cm SessionType
447: in
448: .Xr ssh_config 5
449: for details.
1.360 millert 450: .Pp
1.218 jmc 451: .It Fl n
452: Redirects stdin from
453: .Pa /dev/null
454: (actually, prevents reading from stdin).
455: This must be used when
1.2 deraadt 456: .Nm
1.218 jmc 457: is run in the background.
458: A common trick is to use this to run X11 programs on a remote machine.
459: For example,
460: .Ic ssh -n shadows.cs.hut.fi emacs &
461: will start an emacs on shadows.cs.hut.fi, and the X11
462: connection will be automatically forwarded over an encrypted channel.
463: The
1.2 deraadt 464: .Nm
1.218 jmc 465: program will be put in the background.
466: (This does not work if
1.2 deraadt 467: .Nm
1.218 jmc 468: needs to ask for a password or passphrase; see also the
469: .Fl f
470: option.)
1.423 djm 471: Refer to the description of
472: .Cm StdinNull
473: in
474: .Xr ssh_config 5
475: for details.
1.360 millert 476: .Pp
1.218 jmc 477: .It Fl O Ar ctl_cmd
478: Control an active connection multiplexing master process.
479: When the
480: .Fl O
481: option is specified, the
482: .Ar ctl_cmd
483: argument is interpreted and passed to the master process.
484: Valid commands are:
485: .Dq check
1.305 markus 486: (check that the master process is running),
487: .Dq forward
1.318 jmc 488: (request forwardings without command execution),
1.323 okan 489: .Dq cancel
490: (cancel forwardings),
1.218 jmc 491: .Dq exit
1.318 jmc 492: (request the master to exit), and
1.317 djm 493: .Dq stop
494: (request the master to stop accepting further multiplexing requests).
1.360 millert 495: .Pp
1.218 jmc 496: .It Fl o Ar option
497: Can be used to give options in the format used in the configuration file.
498: This is useful for specifying options for which there is no separate
499: command-line flag.
500: For full details of the options listed below, and their possible values, see
501: .Xr ssh_config 5 .
1.2 deraadt 502: .Pp
1.218 jmc 503: .Bl -tag -width Ds -offset indent -compact
1.366 jcs 504: .It AddKeysToAgent
1.218 jmc 505: .It AddressFamily
506: .It BatchMode
507: .It BindAddress
1.338 djm 508: .It CanonicalDomains
1.339 djm 509: .It CanonicalizeFallbackLocal
510: .It CanonicalizeHostname
511: .It CanonicalizeMaxDots
512: .It CanonicalizePermittedCNAMEs
1.399 jmc 513: .It CASignatureAlgorithms
1.363 djm 514: .It CertificateFile
1.218 jmc 515: .It CheckHostIP
516: .It Ciphers
517: .It ClearAllForwardings
518: .It Compression
1.380 naddy 519: .It ConnectionAttempts
1.218 jmc 520: .It ConnectTimeout
521: .It ControlMaster
522: .It ControlPath
1.321 djm 523: .It ControlPersist
1.218 jmc 524: .It DynamicForward
525: .It EscapeChar
1.263 markus 526: .It ExitOnForwardFailure
1.353 jmc 527: .It FingerprintHash
1.424 djm 528: .It ForkAfterAuthentication
1.218 jmc 529: .It ForwardAgent
530: .It ForwardX11
1.321 djm 531: .It ForwardX11Timeout
1.218 jmc 532: .It ForwardX11Trusted
533: .It GatewayPorts
534: .It GlobalKnownHostsFile
535: .It GSSAPIAuthentication
536: .It GSSAPIDelegateCredentials
537: .It HashKnownHosts
538: .It Host
1.418 naddy 539: .It HostbasedAcceptedAlgorithms
1.218 jmc 540: .It HostbasedAuthentication
541: .It HostKeyAlgorithms
542: .It HostKeyAlias
1.403 jmc 543: .It Hostname
1.374 jmc 544: .It IdentitiesOnly
1.371 markus 545: .It IdentityAgent
1.218 jmc 546: .It IdentityFile
1.316 jmc 547: .It IPQoS
1.321 djm 548: .It KbdInteractiveAuthentication
1.218 jmc 549: .It KbdInteractiveDevices
1.314 jmc 550: .It KexAlgorithms
1.415 djm 551: .It KnownHostsCommand
1.218 jmc 552: .It LocalCommand
553: .It LocalForward
554: .It LogLevel
555: .It MACs
1.337 jmc 556: .It Match
1.218 jmc 557: .It NoHostAuthenticationForLocalhost
558: .It NumberOfPasswordPrompts
559: .It PasswordAuthentication
560: .It PermitLocalCommand
1.419 markus 561: .It PermitRemoteOpen
1.291 markus 562: .It PKCS11Provider
1.218 jmc 563: .It Port
564: .It PreferredAuthentications
565: .It ProxyCommand
1.375 djm 566: .It ProxyJump
1.336 jmc 567: .It ProxyUseFdpass
1.416 dtucker 568: .It PubkeyAcceptedAlgorithms
1.218 jmc 569: .It PubkeyAuthentication
1.251 dtucker 570: .It RekeyLimit
1.382 bluhm 571: .It RemoteCommand
1.218 jmc 572: .It RemoteForward
1.319 jmc 573: .It RequestTTY
1.432 ! djm 574: .It RequiredRSASize
1.218 jmc 575: .It SendEnv
576: .It ServerAliveInterval
577: .It ServerAliveCountMax
1.422 djm 578: .It SessionType
1.395 jmc 579: .It SetEnv
1.423 djm 580: .It StdinNull
1.347 jmc 581: .It StreamLocalBindMask
582: .It StreamLocalBindUnlink
1.218 jmc 583: .It StrictHostKeyChecking
584: .It TCPKeepAlive
585: .It Tunnel
586: .It TunnelDevice
1.354 djm 587: .It UpdateHostKeys
1.218 jmc 588: .It User
589: .It UserKnownHostsFile
590: .It VerifyHostKeyDNS
1.276 jmc 591: .It VisualHostKey
1.218 jmc 592: .It XAuthLocation
593: .El
1.360 millert 594: .Pp
1.218 jmc 595: .It Fl p Ar port
596: Port to connect to on the remote host.
597: This can be specified on a
598: per-host basis in the configuration file.
1.360 millert 599: .Pp
1.362 djm 600: .It Fl Q Ar query_option
1.425 jmc 601: Queries for the algorithms supported by one of the following features:
1.341 deraadt 602: .Ar cipher
1.332 djm 603: (supported symmetric ciphers),
1.341 deraadt 604: .Ar cipher-auth
1.340 djm 605: (supported symmetric ciphers that support authenticated encryption),
1.398 djm 606: .Ar help
607: (supported query terms for use with the
608: .Fl Q
609: flag),
1.341 deraadt 610: .Ar mac
1.332 djm 611: (supported message integrity codes),
1.341 deraadt 612: .Ar kex
1.332 djm 613: (key exchange algorithms),
1.341 deraadt 614: .Ar key
1.362 djm 615: (key types),
616: .Ar key-cert
617: (certificate key types),
618: .Ar key-plain
1.398 djm 619: (non-certificate key types),
1.410 dtucker 620: .Ar key-sig
621: (all key types and signature algorithms),
1.356 djm 622: .Ar protocol-version
1.398 djm 623: (supported SSH protocol versions), and
624: .Ar sig
625: (supported signature algorithms).
1.410 dtucker 626: Alternatively, any keyword from
627: .Xr ssh_config 5
628: or
629: .Xr sshd_config 5
630: that takes an algorithm list may be used as an alias for the corresponding
631: query_option.
1.360 millert 632: .Pp
1.218 jmc 633: .It Fl q
634: Quiet mode.
1.271 djm 635: Causes most warning and diagnostic messages to be suppressed.
1.360 millert 636: .Pp
1.218 jmc 637: .It Fl R Xo
638: .Sm off
639: .Oo Ar bind_address : Oc
640: .Ar port : host : hostport
641: .Sm on
642: .Xc
1.360 millert 643: .It Fl R Xo
644: .Sm off
645: .Oo Ar bind_address : Oc
646: .Ar port : local_socket
647: .Sm on
648: .Xc
649: .It Fl R Xo
650: .Sm off
651: .Ar remote_socket : host : hostport
652: .Sm on
653: .Xc
654: .It Fl R Xo
655: .Sm off
656: .Ar remote_socket : local_socket
657: .Sm on
658: .Xc
1.384 markus 659: .It Fl R Xo
660: .Sm off
661: .Oo Ar bind_address : Oc
662: .Ar port
663: .Sm on
664: .Xc
1.360 millert 665: Specifies that connections to the given TCP port or Unix socket on the remote
1.384 markus 666: (server) host are to be forwarded to the local side.
667: .Pp
1.360 millert 668: This works by allocating a socket to listen to either a TCP
1.218 jmc 669: .Ar port
1.360 millert 670: or to a Unix socket on the remote side.
671: Whenever a connection is made to this port or Unix socket, the
672: connection is forwarded over the secure channel, and a connection
1.384 markus 673: is made from the local machine to either an explicit destination specified by
1.218 jmc 674: .Ar host
675: port
1.360 millert 676: .Ar hostport ,
677: or
678: .Ar local_socket ,
1.384 markus 679: or, if no explicit destination was specified,
680: .Nm
681: will act as a SOCKS 4/5 proxy and forward connections to the destinations
682: requested by the remote SOCKS client.
1.2 deraadt 683: .Pp
1.218 jmc 684: Port forwardings can also be specified in the configuration file.
685: Privileged ports can be forwarded only when
686: logging in as root on the remote machine.
1.324 jmc 687: IPv6 addresses can be specified by enclosing the address in square brackets.
1.194 jakob 688: .Pp
1.360 millert 689: By default, TCP listening sockets on the server will be bound to the loopback
1.218 jmc 690: interface only.
1.280 tobias 691: This may be overridden by specifying a
1.218 jmc 692: .Ar bind_address .
693: An empty
694: .Ar bind_address ,
695: or the address
696: .Ql * ,
697: indicates that the remote socket should listen on all interfaces.
698: Specifying a remote
699: .Ar bind_address
700: will only succeed if the server's
701: .Cm GatewayPorts
702: option is enabled (see
703: .Xr sshd_config 5 ) .
1.281 djm 704: .Pp
705: If the
706: .Ar port
707: argument is
1.282 djm 708: .Ql 0 ,
1.281 djm 709: the listen port will be dynamically allocated on the server and reported
710: to the client at run time.
1.305 markus 711: When used together with
1.430 naddy 712: .Ic -O forward ,
1.305 markus 713: the allocated port will be printed to the standard output.
1.360 millert 714: .Pp
1.218 jmc 715: .It Fl S Ar ctl_path
1.304 jmc 716: Specifies the location of a control socket for connection sharing,
1.303 djm 717: or the string
718: .Dq none
719: to disable connection sharing.
1.218 jmc 720: Refer to the description of
721: .Cm ControlPath
722: and
723: .Cm ControlMaster
724: in
725: .Xr ssh_config 5
726: for details.
1.360 millert 727: .Pp
1.218 jmc 728: .It Fl s
729: May be used to request invocation of a subsystem on the remote system.
1.369 jmc 730: Subsystems facilitate the use of SSH
731: as a secure transport for other applications (e.g.\&
1.218 jmc 732: .Xr sftp 1 ) .
733: The subsystem is specified as the remote command.
1.422 djm 734: Refer to the description of
735: .Cm SessionType
736: in
737: .Xr ssh_config 5
738: for details.
1.360 millert 739: .Pp
1.218 jmc 740: .It Fl T
1.357 dtucker 741: Disable pseudo-terminal allocation.
1.360 millert 742: .Pp
1.218 jmc 743: .It Fl t
1.357 dtucker 744: Force pseudo-terminal allocation.
1.218 jmc 745: This can be used to execute arbitrary
746: screen-based programs on a remote machine, which can be very useful,
1.257 jmc 747: e.g. when implementing menu services.
1.218 jmc 748: Multiple
749: .Fl t
750: options force tty allocation, even if
1.194 jakob 751: .Nm
1.218 jmc 752: has no local tty.
1.360 millert 753: .Pp
1.218 jmc 754: .It Fl V
755: Display the version number and exit.
1.360 millert 756: .Pp
1.218 jmc 757: .It Fl v
758: Verbose mode.
759: Causes
1.176 jmc 760: .Nm
1.218 jmc 761: to print debugging messages about its progress.
762: This is helpful in
763: debugging connection, authentication, and configuration problems.
764: Multiple
765: .Fl v
766: options increase the verbosity.
767: The maximum is 3.
1.360 millert 768: .Pp
1.290 dtucker 769: .It Fl W Ar host : Ns Ar port
770: Requests that standard input and output on the client be forwarded to
771: .Ar host
772: on
773: .Ar port
774: over the secure channel.
775: Implies
776: .Fl N ,
777: .Fl T ,
778: .Cm ExitOnForwardFailure
779: and
1.373 jmc 780: .Cm ClearAllForwardings ,
781: though these can be overridden in the configuration file or using
1.372 dtucker 782: .Fl o
783: command line options.
1.360 millert 784: .Pp
1.261 stevesk 785: .It Fl w Xo
786: .Ar local_tun Ns Op : Ns Ar remote_tun
787: .Xc
788: Requests
789: tunnel
790: device forwarding with the specified
1.218 jmc 791: .Xr tun 4
1.261 stevesk 792: devices between the client
793: .Pq Ar local_tun
794: and the server
795: .Pq Ar remote_tun .
796: .Pp
1.228 jmc 797: The devices may be specified by numerical ID or the keyword
798: .Dq any ,
799: which uses the next available tunnel device.
1.261 stevesk 800: If
801: .Ar remote_tun
802: is not specified, it defaults to
803: .Dq any .
1.228 jmc 804: See also the
1.218 jmc 805: .Cm Tunnel
1.261 stevesk 806: and
807: .Cm TunnelDevice
808: directives in
1.218 jmc 809: .Xr ssh_config 5 .
1.393 djm 810: .Pp
1.261 stevesk 811: If the
812: .Cm Tunnel
1.393 djm 813: directive is unset, it will be set to the default tunnel mode, which is
1.261 stevesk 814: .Dq point-to-point .
1.393 djm 815: If a different
816: .Cm Tunnel
817: forwarding mode it desired, then it should be specified before
818: .Fl w .
1.360 millert 819: .Pp
1.218 jmc 820: .It Fl X
821: Enables X11 forwarding.
1.54 markus 822: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 823: .Pp
1.218 jmc 824: X11 forwarding should be enabled with caution.
1.168 jmc 825: Users with the ability to bypass file permissions on the remote host
1.218 jmc 826: (for the user's X authorization database)
827: can access the local X11 display through the forwarded connection.
828: An attacker may then be able to perform activities such as keystroke monitoring.
829: .Pp
830: For this reason, X11 forwarding is subjected to X11 SECURITY extension
831: restrictions by default.
1.429 jsg 832: Refer to the
1.218 jmc 833: .Nm
834: .Fl Y
835: option and the
836: .Cm ForwardX11Trusted
837: directive in
838: .Xr ssh_config 5
839: for more information.
1.360 millert 840: .Pp
1.218 jmc 841: .It Fl x
842: Disables X11 forwarding.
1.360 millert 843: .Pp
1.218 jmc 844: .It Fl Y
845: Enables trusted X11 forwarding.
846: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
847: controls.
1.360 millert 848: .Pp
1.278 djm 849: .It Fl y
850: Send log information using the
851: .Xr syslog 3
852: system module.
853: By default this information is sent to stderr.
1.218 jmc 854: .El
1.224 jmc 855: .Pp
856: .Nm
857: may additionally obtain configuration data from
858: a per-user configuration file and a system-wide configuration file.
859: The file format and configuration options are described in
860: .Xr ssh_config 5 .
1.222 jmc 861: .Sh AUTHENTICATION
1.377 djm 862: The OpenSSH SSH client supports SSH protocol 2.
1.222 jmc 863: .Pp
864: The methods available for authentication are:
1.260 jmc 865: GSSAPI-based authentication,
1.222 jmc 866: host-based authentication,
867: public key authentication,
1.421 dtucker 868: keyboard-interactive authentication,
1.222 jmc 869: and password authentication.
870: Authentication methods are tried in the order specified above,
1.369 jmc 871: though
872: .Cm PreferredAuthentications
873: can be used to change the default order.
1.222 jmc 874: .Pp
875: Host-based authentication works as follows:
1.218 jmc 876: If the machine the user logs in from is listed in
877: .Pa /etc/hosts.equiv
878: or
879: .Pa /etc/shosts.equiv
1.412 djm 880: on the remote machine, the user is non-root and the user names are
1.218 jmc 881: the same on both sides, or if the files
882: .Pa ~/.rhosts
883: or
884: .Pa ~/.shosts
885: exist in the user's home directory on the
886: remote machine and contain a line containing the name of the client
887: machine and the name of the user on that machine, the user is
1.222 jmc 888: considered for login.
889: Additionally, the server
890: .Em must
891: be able to verify the client's
892: host key (see the description of
1.218 jmc 893: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 894: and
1.222 jmc 895: .Pa ~/.ssh/known_hosts ,
896: below)
897: for login to be permitted.
1.218 jmc 898: This authentication method closes security holes due to IP
1.222 jmc 899: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 900: [Note to the administrator:
901: .Pa /etc/hosts.equiv ,
902: .Pa ~/.rhosts ,
903: and the rlogin/rsh protocol in general, are inherently insecure and should be
904: disabled if security is desired.]
1.189 dtucker 905: .Pp
1.222 jmc 906: Public key authentication works as follows:
907: The scheme is based on public-key cryptography,
908: using cryptosystems
909: where encryption and decryption are done using separate keys,
910: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 911: The idea is that each user creates a public/private
912: key pair for authentication purposes.
913: The server knows the public key, and only the user knows the private key.
1.222 jmc 914: .Nm
915: implements public key authentication protocol automatically,
1.349 sobrado 916: using one of the DSA, ECDSA, Ed25519 or RSA algorithms.
1.333 jmc 917: The HISTORY section of
1.222 jmc 918: .Xr ssl 8
1.311 jmc 919: contains a brief discussion of the DSA and RSA algorithms.
1.210 djm 920: .Pp
1.218 jmc 921: The file
922: .Pa ~/.ssh/authorized_keys
923: lists the public keys that are permitted for logging in.
924: When the user logs in, the
1.2 deraadt 925: .Nm
1.218 jmc 926: program tells the server which key pair it would like to use for
927: authentication.
1.222 jmc 928: The client proves that it has access to the private key
929: and the server checks that the corresponding public key
930: is authorized to accept the account.
1.383 djm 931: .Pp
932: The server may inform the client of errors that prevented public key
933: authentication from succeeding after authentication completes using a
934: different method.
935: These may be viewed by increasing the
936: .Cm LogLevel
937: to
938: .Cm DEBUG
939: or higher (e.g. by using the
940: .Fl v
941: flag).
1.218 jmc 942: .Pp
1.420 dtucker 943: The user creates their key pair by running
1.218 jmc 944: .Xr ssh-keygen 1 .
945: This stores the private key in
1.222 jmc 946: .Pa ~/.ssh/id_dsa
1.369 jmc 947: (DSA),
1.310 djm 948: .Pa ~/.ssh/id_ecdsa
1.369 jmc 949: (ECDSA),
1.404 naddy 950: .Pa ~/.ssh/id_ecdsa_sk
1.409 naddy 951: (authenticator-hosted ECDSA),
1.343 naddy 952: .Pa ~/.ssh/id_ed25519
1.369 jmc 953: (Ed25519),
1.406 naddy 954: .Pa ~/.ssh/id_ed25519_sk
1.409 naddy 955: (authenticator-hosted Ed25519),
1.222 jmc 956: or
957: .Pa ~/.ssh/id_rsa
1.369 jmc 958: (RSA)
1.218 jmc 959: and stores the public key in
1.222 jmc 960: .Pa ~/.ssh/id_dsa.pub
1.369 jmc 961: (DSA),
1.310 djm 962: .Pa ~/.ssh/id_ecdsa.pub
1.369 jmc 963: (ECDSA),
1.404 naddy 964: .Pa ~/.ssh/id_ecdsa_sk.pub
1.409 naddy 965: (authenticator-hosted ECDSA),
1.343 naddy 966: .Pa ~/.ssh/id_ed25519.pub
1.369 jmc 967: (Ed25519),
1.406 naddy 968: .Pa ~/.ssh/id_ed25519_sk.pub
1.409 naddy 969: (authenticator-hosted Ed25519),
1.222 jmc 970: or
971: .Pa ~/.ssh/id_rsa.pub
1.369 jmc 972: (RSA)
1.218 jmc 973: in the user's home directory.
1.222 jmc 974: The user should then copy the public key
1.218 jmc 975: to
976: .Pa ~/.ssh/authorized_keys
1.420 dtucker 977: in their home directory on the remote machine.
1.222 jmc 978: The
1.218 jmc 979: .Pa authorized_keys
980: file corresponds to the conventional
981: .Pa ~/.rhosts
982: file, and has one key
1.222 jmc 983: per line, though the lines can be very long.
1.218 jmc 984: After this, the user can log in without giving the password.
985: .Pp
1.301 jmc 986: A variation on public key authentication
987: is available in the form of certificate authentication:
988: instead of a set of public/private keys,
989: signed certificates are used.
990: This has the advantage that a single trusted certification authority
991: can be used in place of many public/private keys.
1.333 jmc 992: See the CERTIFICATES section of
1.301 jmc 993: .Xr ssh-keygen 1
994: for more information.
995: .Pp
996: The most convenient way to use public key or certificate authentication
997: may be with an authentication agent.
1.218 jmc 998: See
999: .Xr ssh-agent 1
1.366 jcs 1000: and (optionally) the
1001: .Cm AddKeysToAgent
1002: directive in
1003: .Xr ssh_config 5
1.218 jmc 1004: for more information.
1005: .Pp
1.421 dtucker 1006: Keyboard-interactive authentication works as follows:
1.222 jmc 1007: The server sends an arbitrary
1008: .Qq challenge
1.421 dtucker 1009: text and prompts for a response, possibly multiple times.
1010: Examples of keyboard-interactive authentication include
1.335 jmc 1011: .Bx
1012: Authentication (see
1.222 jmc 1013: .Xr login.conf 5 )
1.335 jmc 1014: and PAM (some
1015: .Pf non- Ox
1016: systems).
1.222 jmc 1017: .Pp
1018: Finally, if other authentication methods fail,
1.218 jmc 1019: .Nm
1020: prompts the user for a password.
1021: The password is sent to the remote
1022: host for checking; however, since all communications are encrypted,
1023: the password cannot be seen by someone listening on the network.
1.232 jmc 1024: .Pp
1025: .Nm
1026: automatically maintains and checks a database containing
1027: identification for all hosts it has ever been used with.
1028: Host keys are stored in
1029: .Pa ~/.ssh/known_hosts
1030: in the user's home directory.
1031: Additionally, the file
1032: .Pa /etc/ssh/ssh_known_hosts
1033: is automatically checked for known hosts.
1034: Any new hosts are automatically added to the user's file.
1035: If a host's identification ever changes,
1036: .Nm
1037: warns about this and disables password authentication to prevent
1038: server spoofing or man-in-the-middle attacks,
1039: which could otherwise be used to circumvent the encryption.
1040: The
1041: .Cm StrictHostKeyChecking
1042: option can be used to control logins to machines whose
1043: host key is not known or has changed.
1044: .Pp
1.218 jmc 1045: When the user's identity has been accepted by the server, the server
1.357 dtucker 1046: either executes the given command in a non-interactive session or,
1047: if no command has been specified, logs into the machine and gives
1048: the user a normal shell as an interactive session.
1.218 jmc 1049: All communication with
1050: the remote command or shell will be automatically encrypted.
1051: .Pp
1.430 naddy 1052: If an interactive session is requested,
1.357 dtucker 1053: .Nm
1054: by default will only request a pseudo-terminal (pty) for interactive
1055: sessions when the client has one.
1056: The flags
1057: .Fl T
1058: and
1059: .Fl t
1060: can be used to override this behaviour.
1061: .Pp
1.430 naddy 1062: If a pseudo-terminal has been allocated, the
1.218 jmc 1063: user may use the escape characters noted below.
1064: .Pp
1.357 dtucker 1065: If no pseudo-terminal has been allocated,
1.218 jmc 1066: the session is transparent and can be used to reliably transfer binary data.
1067: On most systems, setting the escape character to
1068: .Dq none
1069: will also make the session transparent even if a tty is used.
1070: .Pp
1071: The session terminates when the command or shell on the remote
1.247 jmc 1072: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 1073: .Sh ESCAPE CHARACTERS
1.218 jmc 1074: When a pseudo-terminal has been requested,
1.2 deraadt 1075: .Nm
1.218 jmc 1076: supports a number of functions through the use of an escape character.
1077: .Pp
1078: A single tilde character can be sent as
1079: .Ic ~~
1080: or by following the tilde by a character other than those described below.
1081: The escape character must always follow a newline to be interpreted as
1082: special.
1083: The escape character can be changed in configuration files using the
1084: .Cm EscapeChar
1085: configuration directive or on the command line by the
1086: .Fl e
1087: option.
1088: .Pp
1089: The supported escapes (assuming the default
1090: .Ql ~ )
1091: are:
1092: .Bl -tag -width Ds
1093: .It Cm ~.
1094: Disconnect.
1095: .It Cm ~^Z
1096: Background
1.234 jmc 1097: .Nm .
1.218 jmc 1098: .It Cm ~#
1099: List forwarded connections.
1100: .It Cm ~&
1101: Background
1.2 deraadt 1102: .Nm
1.218 jmc 1103: at logout when waiting for forwarded connection / X11 sessions to terminate.
1104: .It Cm ~?
1105: Display a list of escape characters.
1106: .It Cm ~B
1107: Send a BREAK to the remote system
1.369 jmc 1108: (only useful if the peer supports it).
1.218 jmc 1109: .It Cm ~C
1110: Open command line.
1111: Currently this allows the addition of port forwardings using the
1.279 stevesk 1112: .Fl L ,
1113: .Fl R
1.218 jmc 1114: and
1.279 stevesk 1115: .Fl D
1.225 jmc 1116: options (see above).
1.322 markus 1117: It also allows the cancellation of existing port-forwardings
1118: with
1.262 stevesk 1119: .Sm off
1.322 markus 1120: .Fl KL Oo Ar bind_address : Oc Ar port
1.262 stevesk 1121: .Sm on
1.322 markus 1122: for local,
1123: .Sm off
1124: .Fl KR Oo Ar bind_address : Oc Ar port
1125: .Sm on
1126: for remote and
1127: .Sm off
1128: .Fl KD Oo Ar bind_address : Oc Ar port
1129: .Sm on
1130: for dynamic port-forwardings.
1.218 jmc 1131: .Ic !\& Ns Ar command
1132: allows the user to execute a local command if the
1133: .Ic PermitLocalCommand
1134: option is enabled in
1.176 jmc 1135: .Xr ssh_config 5 .
1.218 jmc 1136: Basic help is available, using the
1137: .Fl h
1138: option.
1139: .It Cm ~R
1140: Request rekeying of the connection
1.369 jmc 1141: (only useful if the peer supports it).
1.327 dtucker 1142: .It Cm ~V
1143: Decrease the verbosity
1144: .Pq Ic LogLevel
1145: when errors are being written to stderr.
1146: .It Cm ~v
1.328 jmc 1147: Increase the verbosity
1.327 dtucker 1148: .Pq Ic LogLevel
1149: when errors are being written to stderr.
1.176 jmc 1150: .El
1.246 jmc 1151: .Sh TCP FORWARDING
1.402 jmc 1152: Forwarding of arbitrary TCP connections over a secure channel
1153: can be specified either on the command line or in a configuration file.
1.246 jmc 1154: One possible application of TCP forwarding is a secure connection to a
1155: mail server; another is going through firewalls.
1156: .Pp
1.402 jmc 1157: In the example below, we look at encrypting communication for an IRC client,
1158: even though the IRC server it connects to does not directly
1159: support encrypted communication.
1.246 jmc 1160: This works as follows:
1161: the user connects to the remote host using
1162: .Nm ,
1.402 jmc 1163: specifying the ports to be used to forward the connection.
1164: After that it is possible to start the program locally,
1.246 jmc 1165: and
1166: .Nm
1.402 jmc 1167: will encrypt and forward the connection to the remote server.
1.246 jmc 1168: .Pp
1.402 jmc 1169: The following example tunnels an IRC session from the client
1170: to an IRC server at
1.246 jmc 1171: .Dq server.example.com ,
1172: joining channel
1173: .Dq #users ,
1174: nickname
1175: .Dq pinky ,
1.402 jmc 1176: using the standard IRC port, 6667:
1177: .Bd -literal -offset 4n
1178: $ ssh -f -L 6667:localhost:6667 server.example.com sleep 10
1179: $ irc -c '#users' pinky IRC/127.0.0.1
1180: .Ed
1.246 jmc 1181: .Pp
1182: The
1183: .Fl f
1184: option backgrounds
1185: .Nm
1186: and the remote command
1187: .Dq sleep 10
1188: is specified to allow an amount of time
1189: (10 seconds, in the example)
1.402 jmc 1190: to start the program which is going to use the tunnel.
1.246 jmc 1191: If no connections are made within the time specified,
1192: .Nm
1193: will exit.
1194: .Sh X11 FORWARDING
1.218 jmc 1195: If the
1196: .Cm ForwardX11
1197: variable is set to
1198: .Dq yes
1199: (or see the description of the
1.227 jmc 1200: .Fl X ,
1201: .Fl x ,
1.218 jmc 1202: and
1.227 jmc 1203: .Fl Y
1.226 jmc 1204: options above)
1.218 jmc 1205: and the user is using X11 (the
1206: .Ev DISPLAY
1207: environment variable is set), the connection to the X11 display is
1208: automatically forwarded to the remote side in such a way that any X11
1209: programs started from the shell (or command) will go through the
1210: encrypted channel, and the connection to the real X server will be made
1.176 jmc 1211: from the local machine.
1.218 jmc 1212: The user should not manually set
1213: .Ev DISPLAY .
1214: Forwarding of X11 connections can be
1215: configured on the command line or in configuration files.
1216: .Pp
1217: The
1218: .Ev DISPLAY
1219: value set by
1220: .Nm
1221: will point to the server machine, but with a display number greater than zero.
1222: This is normal, and happens because
1223: .Nm
1224: creates a
1225: .Dq proxy
1226: X server on the server machine for forwarding the
1227: connections over the encrypted channel.
1.200 djm 1228: .Pp
1.218 jmc 1229: .Nm
1230: will also automatically set up Xauthority data on the server machine.
1231: For this purpose, it will generate a random authorization cookie,
1232: store it in Xauthority on the server, and verify that any forwarded
1233: connections carry this cookie and replace it by the real cookie when
1234: the connection is opened.
1235: The real authentication cookie is never
1236: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1237: .Pp
1.218 jmc 1238: If the
1239: .Cm ForwardAgent
1240: variable is set to
1241: .Dq yes
1242: (or see the description of the
1243: .Fl A
1.191 djm 1244: and
1.218 jmc 1245: .Fl a
1.226 jmc 1246: options above) and
1.218 jmc 1247: the user is using an authentication agent, the connection to the agent
1248: is automatically forwarded to the remote side.
1.252 jmc 1249: .Sh VERIFYING HOST KEYS
1250: When connecting to a server for the first time,
1251: a fingerprint of the server's public key is presented to the user
1252: (unless the option
1253: .Cm StrictHostKeyChecking
1254: has been disabled).
1255: Fingerprints can be determined using
1256: .Xr ssh-keygen 1 :
1257: .Pp
1258: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1259: .Pp
1.274 grunk 1260: If the fingerprint is already known, it can be matched
1261: and the key can be accepted or rejected.
1.358 djm 1262: If only legacy (MD5) fingerprints for the server are available, the
1263: .Xr ssh-keygen 1
1264: .Fl E
1265: option may be used to downgrade the fingerprint algorithm to match.
1266: .Pp
1.274 grunk 1267: Because of the difficulty of comparing host keys
1.352 djm 1268: just by looking at fingerprint strings,
1.274 grunk 1269: there is also support to compare host keys visually,
1270: using
1271: .Em random art .
1272: By setting the
1.275 grunk 1273: .Cm VisualHostKey
1.274 grunk 1274: option to
1.275 grunk 1275: .Dq yes ,
1.274 grunk 1276: a small ASCII graphic gets displayed on every login to a server, no matter
1277: if the session itself is interactive or not.
1278: By learning the pattern a known server produces, a user can easily
1279: find out that the host key has changed when a completely different pattern
1280: is displayed.
1281: Because these patterns are not unambiguous however, a pattern that looks
1282: similar to the pattern remembered only gives a good probability that the
1283: host key is the same, not guaranteed proof.
1284: .Pp
1285: To get a listing of the fingerprints along with their random art for
1286: all known hosts, the following command line can be used:
1287: .Pp
1288: .Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1289: .Pp
1.252 jmc 1290: If the fingerprint is unknown,
1291: an alternative method of verification is available:
1292: SSH fingerprints verified by DNS.
1293: An additional resource record (RR),
1294: SSHFP,
1295: is added to a zonefile
1296: and the connecting client is able to match the fingerprint
1297: with that of the key presented.
1298: .Pp
1299: In this example, we are connecting a client to a server,
1300: .Dq host.example.com .
1301: The SSHFP resource records should first be added to the zonefile for
1302: host.example.com:
1303: .Bd -literal -offset indent
1.259 jakob 1304: $ ssh-keygen -r host.example.com.
1.252 jmc 1305: .Ed
1306: .Pp
1307: The output lines will have to be added to the zonefile.
1308: To check that the zone is answering fingerprint queries:
1309: .Pp
1310: .Dl $ dig -t SSHFP host.example.com
1311: .Pp
1312: Finally the client connects:
1313: .Bd -literal -offset indent
1314: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1315: [...]
1316: Matching host key fingerprint found in DNS.
1317: Are you sure you want to continue connecting (yes/no)?
1318: .Ed
1319: .Pp
1320: See the
1321: .Cm VerifyHostKeyDNS
1322: option in
1323: .Xr ssh_config 5
1324: for more information.
1.250 jmc 1325: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1326: .Nm
1327: contains support for Virtual Private Network (VPN) tunnelling
1328: using the
1329: .Xr tun 4
1330: network pseudo-device,
1331: allowing two networks to be joined securely.
1332: The
1333: .Xr sshd_config 5
1334: configuration option
1335: .Cm PermitTunnel
1336: controls whether the server supports this,
1337: and at what level (layer 2 or 3 traffic).
1338: .Pp
1339: The following example would connect client network 10.0.50.0/24
1.265 otto 1340: with remote network 10.0.99.0/24 using a point-to-point connection
1341: from 10.1.1.1 to 10.1.1.2,
1342: provided that the SSH server running on the gateway to the remote network,
1343: at 192.168.1.15, allows it.
1344: .Pp
1345: On the client:
1.250 jmc 1346: .Bd -literal -offset indent
1347: # ssh -f -w 0:1 192.168.1.15 true
1.265 otto 1348: # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1349: # route add 10.0.99.0/24 10.1.1.2
1350: .Ed
1351: .Pp
1352: On the server:
1353: .Bd -literal -offset indent
1354: # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1355: # route add 10.0.50.0/24 10.1.1.1
1.250 jmc 1356: .Ed
1357: .Pp
1358: Client access may be more finely tuned via the
1359: .Pa /root/.ssh/authorized_keys
1360: file (see below) and the
1361: .Cm PermitRootLogin
1362: server option.
1.255 jmc 1363: The following entry would permit connections on
1.250 jmc 1364: .Xr tun 4
1.255 jmc 1365: device 1 from user
1.250 jmc 1366: .Dq jane
1.255 jmc 1367: and on tun device 2 from user
1.250 jmc 1368: .Dq john ,
1369: if
1370: .Cm PermitRootLogin
1371: is set to
1372: .Dq forced-commands-only :
1373: .Bd -literal -offset 2n
1374: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1375: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1376: .Ed
1377: .Pp
1.264 ray 1378: Since an SSH-based setup entails a fair amount of overhead,
1.250 jmc 1379: it may be more suited to temporary setups,
1380: such as for wireless VPNs.
1381: More permanent VPNs are better provided by tools such as
1382: .Xr ipsecctl 8
1383: and
1384: .Xr isakmpd 8 .
1.2 deraadt 1385: .Sh ENVIRONMENT
1386: .Nm
1.1 deraadt 1387: will normally set the following environment variables:
1.237 jmc 1388: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1389: .It Ev DISPLAY
1390: The
1391: .Ev DISPLAY
1.40 aaron 1392: variable indicates the location of the X11 server.
1.44 aaron 1393: It is automatically set by
1.2 deraadt 1394: .Nm
1395: to point to a value of the form
1.233 jmc 1396: .Dq hostname:n ,
1397: where
1398: .Dq hostname
1399: indicates the host where the shell runs, and
1400: .Sq n
1401: is an integer \*(Ge 1.
1.40 aaron 1402: .Nm
1403: uses this special value to forward X11 connections over the secure
1404: channel.
1.107 markus 1405: The user should normally not set
1406: .Ev DISPLAY
1407: explicitly, as that
1.1 deraadt 1408: will render the X11 connection insecure (and will require the user to
1409: manually copy any required authorization cookies).
1.2 deraadt 1410: .It Ev HOME
1.1 deraadt 1411: Set to the path of the user's home directory.
1.2 deraadt 1412: .It Ev LOGNAME
1413: Synonym for
1.12 aaron 1414: .Ev USER ;
1415: set for compatibility with systems that use this variable.
1.2 deraadt 1416: .It Ev MAIL
1.129 stevesk 1417: Set to the path of the user's mailbox.
1.40 aaron 1418: .It Ev PATH
1.2 deraadt 1419: Set to the default
1420: .Ev PATH ,
1421: as specified when compiling
1.234 jmc 1422: .Nm .
1.118 markus 1423: .It Ev SSH_ASKPASS
1424: If
1425: .Nm
1426: needs a passphrase, it will read the passphrase from the current
1427: terminal if it was run from a terminal.
1428: If
1429: .Nm
1430: does not have a terminal associated with it but
1431: .Ev DISPLAY
1432: and
1433: .Ev SSH_ASKPASS
1434: are set, it will execute the program specified by
1435: .Ev SSH_ASKPASS
1436: and open an X11 window to read the passphrase.
1437: This is particularly useful when calling
1438: .Nm
1439: from a
1.196 jmc 1440: .Pa .xsession
1.118 markus 1441: or related script.
1442: (Note that on some machines it
1443: may be necessary to redirect the input from
1444: .Pa /dev/null
1445: to make this work.)
1.413 djm 1446: .It Ev SSH_ASKPASS_REQUIRE
1.414 jmc 1447: Allows further control over the use of an askpass program.
1.413 djm 1448: If this variable is set to
1449: .Dq never
1450: then
1451: .Nm
1452: will never attempt to use one.
1453: If it is set to
1454: .Dq prefer ,
1455: then
1456: .Nm
1457: will prefer to use the askpass program instead of the TTY when requesting
1458: passwords.
1459: Finally, if the variable is set to
1460: .Dq force ,
1461: then the askpass program will be used for all passphrase input regardless
1462: of whether
1463: .Ev DISPLAY
1464: is set.
1.18 markus 1465: .It Ev SSH_AUTH_SOCK
1.233 jmc 1466: Identifies the path of a
1467: .Ux Ns -domain
1468: socket used to communicate with the agent.
1.166 stevesk 1469: .It Ev SSH_CONNECTION
1470: Identifies the client and server ends of the connection.
1.40 aaron 1471: The variable contains
1.233 jmc 1472: four space-separated values: client IP address, client port number,
1473: server IP address, and server port number.
1.73 markus 1474: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1475: This variable contains the original command line if a forced command
1.73 markus 1476: is executed.
1477: It can be used to extract the original arguments.
1.2 deraadt 1478: .It Ev SSH_TTY
1.1 deraadt 1479: This is set to the name of the tty (path to the device) associated
1.40 aaron 1480: with the current shell or command.
1481: If the current session has no tty,
1.1 deraadt 1482: this variable is not set.
1.387 djm 1483: .It Ev SSH_TUNNEL
1484: Optionally set by
1485: .Xr sshd 8
1486: to contain the interface names assigned if tunnel forwarding was
1487: requested by the client.
1.385 djm 1488: .It Ev SSH_USER_AUTH
1489: Optionally set by
1490: .Xr sshd 8 ,
1491: this variable may contain a pathname to a file that lists the authentication
1492: methods successfully used when the session was established, including any
1493: public keys that were used.
1.2 deraadt 1494: .It Ev TZ
1.214 jmc 1495: This variable is set to indicate the present time zone if it
1.257 jmc 1496: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1497: on to new connections).
1.2 deraadt 1498: .It Ev USER
1.1 deraadt 1499: Set to the name of the user logging in.
1.2 deraadt 1500: .El
1501: .Pp
1.44 aaron 1502: Additionally,
1.2 deraadt 1503: .Nm
1.44 aaron 1504: reads
1.207 djm 1505: .Pa ~/.ssh/environment ,
1.2 deraadt 1506: and adds lines of the format
1507: .Dq VARNAME=value
1.233 jmc 1508: to the environment if the file exists and users are allowed to
1.161 marc 1509: change their environment.
1.176 jmc 1510: For more information, see the
1.161 marc 1511: .Cm PermitUserEnvironment
1.162 stevesk 1512: option in
1.161 marc 1513: .Xr sshd_config 5 .
1.2 deraadt 1514: .Sh FILES
1.236 jmc 1515: .Bl -tag -width Ds -compact
1.309 jmc 1516: .It Pa ~/.rhosts
1.240 jmc 1517: This file is used for host-based authentication (see above).
1.92 markus 1518: On some machines this file may need to be
1.240 jmc 1519: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1520: because
1.2 deraadt 1521: .Xr sshd 8
1.40 aaron 1522: reads it as root.
1523: Additionally, this file must be owned by the user,
1524: and must not have write permissions for anyone else.
1525: The recommended
1.1 deraadt 1526: permission for most machines is read/write for the user, and not
1527: accessible by others.
1.2 deraadt 1528: .Pp
1.309 jmc 1529: .It Pa ~/.shosts
1.240 jmc 1530: This file is used in exactly the same way as
1531: .Pa .rhosts ,
1532: but allows host-based authentication without permitting login with
1533: rlogin/rsh.
1.272 mcbride 1534: .Pp
1.309 jmc 1535: .It Pa ~/.ssh/
1.272 mcbride 1536: This directory is the default location for all user-specific configuration
1537: and authentication information.
1538: There is no general requirement to keep the entire contents of this directory
1539: secret, but the recommended permissions are read/write/execute for the user,
1540: and not accessible by others.
1.236 jmc 1541: .Pp
1.309 jmc 1542: .It Pa ~/.ssh/authorized_keys
1.349 sobrado 1543: Lists the public keys (DSA, ECDSA, Ed25519, RSA)
1.343 naddy 1544: that can be used for logging in as this user.
1.238 jmc 1545: The format of this file is described in the
1546: .Xr sshd 8
1547: manual page.
1548: This file is not highly sensitive, but the recommended
1549: permissions are read/write for the user, and not accessible by others.
1550: .Pp
1.309 jmc 1551: .It Pa ~/.ssh/config
1.238 jmc 1552: This is the per-user configuration file.
1553: The file format and configuration options are described in
1554: .Xr ssh_config 5 .
1555: Because of the potential for abuse, this file must have strict permissions:
1.334 djm 1556: read/write for the user, and not writable by others.
1.238 jmc 1557: .Pp
1.309 jmc 1558: .It Pa ~/.ssh/environment
1.239 jmc 1559: Contains additional definitions for environment variables; see
1560: .Sx ENVIRONMENT ,
1.238 jmc 1561: above.
1562: .Pp
1.309 jmc 1563: .It Pa ~/.ssh/id_dsa
1.310 djm 1564: .It Pa ~/.ssh/id_ecdsa
1.404 naddy 1565: .It Pa ~/.ssh/id_ecdsa_sk
1.343 naddy 1566: .It Pa ~/.ssh/id_ed25519
1.406 naddy 1567: .It Pa ~/.ssh/id_ed25519_sk
1.309 jmc 1568: .It Pa ~/.ssh/id_rsa
1.238 jmc 1569: Contains the private key for authentication.
1570: These files
1571: contain sensitive data and should be readable by the user but not
1572: accessible by others (read/write/execute).
1573: .Nm
1574: will simply ignore a private key file if it is accessible by others.
1575: It is possible to specify a passphrase when
1576: generating the key which will be used to encrypt the
1.389 djm 1577: sensitive part of this file using AES-128.
1.238 jmc 1578: .Pp
1.309 jmc 1579: .It Pa ~/.ssh/id_dsa.pub
1.310 djm 1580: .It Pa ~/.ssh/id_ecdsa.pub
1.404 naddy 1581: .It Pa ~/.ssh/id_ecdsa_sk.pub
1.343 naddy 1582: .It Pa ~/.ssh/id_ed25519.pub
1.406 naddy 1583: .It Pa ~/.ssh/id_ed25519_sk.pub
1.309 jmc 1584: .It Pa ~/.ssh/id_rsa.pub
1.238 jmc 1585: Contains the public key for authentication.
1586: These files are not
1587: sensitive and can (but need not) be readable by anyone.
1588: .Pp
1.309 jmc 1589: .It Pa ~/.ssh/known_hosts
1.244 jmc 1590: Contains a list of host keys for all hosts the user has logged into
1591: that are not already in the systemwide list of known host keys.
1.238 jmc 1592: See
1.244 jmc 1593: .Xr sshd 8
1594: for further details of the format of this file.
1.238 jmc 1595: .Pp
1.309 jmc 1596: .It Pa ~/.ssh/rc
1.238 jmc 1597: Commands in this file are executed by
1598: .Nm
1.245 jmc 1599: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1600: started.
1601: See the
1602: .Xr sshd 8
1603: manual page for more information.
1604: .Pp
1.309 jmc 1605: .It Pa /etc/hosts.equiv
1.240 jmc 1606: This file is for host-based authentication (see above).
1607: It should only be writable by root.
1.236 jmc 1608: .Pp
1.309 jmc 1609: .It Pa /etc/shosts.equiv
1.240 jmc 1610: This file is used in exactly the same way as
1611: .Pa hosts.equiv ,
1612: but allows host-based authentication without permitting login with
1613: rlogin/rsh.
1.236 jmc 1614: .Pp
1.238 jmc 1615: .It Pa /etc/ssh/ssh_config
1616: Systemwide configuration file.
1617: The file format and configuration options are described in
1618: .Xr ssh_config 5 .
1619: .Pp
1.309 jmc 1620: .It Pa /etc/ssh/ssh_host_key
1621: .It Pa /etc/ssh/ssh_host_dsa_key
1.310 djm 1622: .It Pa /etc/ssh/ssh_host_ecdsa_key
1.343 naddy 1623: .It Pa /etc/ssh/ssh_host_ed25519_key
1.309 jmc 1624: .It Pa /etc/ssh/ssh_host_rsa_key
1.325 dtucker 1625: These files contain the private parts of the host keys
1.245 jmc 1626: and are used for host-based authentication.
1.238 jmc 1627: .Pp
1.309 jmc 1628: .It Pa /etc/ssh/ssh_known_hosts
1.238 jmc 1629: Systemwide list of known host keys.
1630: This file should be prepared by the
1631: system administrator to contain the public host keys of all machines in the
1632: organization.
1.244 jmc 1633: It should be world-readable.
1634: See
1.238 jmc 1635: .Xr sshd 8
1.244 jmc 1636: for further details of the format of this file.
1.236 jmc 1637: .Pp
1.309 jmc 1638: .It Pa /etc/ssh/sshrc
1.1 deraadt 1639: Commands in this file are executed by
1.2 deraadt 1640: .Nm
1.245 jmc 1641: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1642: See the
1.2 deraadt 1643: .Xr sshd 8
1.1 deraadt 1644: manual page for more information.
1.58 itojun 1645: .El
1.312 jmc 1646: .Sh EXIT STATUS
1647: .Nm
1648: exits with the exit status of the remote command or with 255
1649: if an error occurred.
1.2 deraadt 1650: .Sh SEE ALSO
1651: .Xr scp 1 ,
1.83 djm 1652: .Xr sftp 1 ,
1.2 deraadt 1653: .Xr ssh-add 1 ,
1654: .Xr ssh-agent 1 ,
1655: .Xr ssh-keygen 1 ,
1.242 jmc 1656: .Xr ssh-keyscan 1 ,
1.250 jmc 1657: .Xr tun 4 ,
1.159 stevesk 1658: .Xr ssh_config 5 ,
1.160 naddy 1659: .Xr ssh-keysign 8 ,
1.87 itojun 1660: .Xr sshd 8
1.329 jmc 1661: .Sh STANDARDS
1.106 markus 1662: .Rs
1.329 jmc 1663: .%A S. Lehtinen
1664: .%A C. Lonvick
1665: .%D January 2006
1.256 jmc 1666: .%R RFC 4250
1.329 jmc 1667: .%T The Secure Shell (SSH) Protocol Assigned Numbers
1.256 jmc 1668: .Re
1.329 jmc 1669: .Pp
1.256 jmc 1670: .Rs
1.329 jmc 1671: .%A T. Ylonen
1672: .%A C. Lonvick
1673: .%D January 2006
1.256 jmc 1674: .%R RFC 4251
1.329 jmc 1675: .%T The Secure Shell (SSH) Protocol Architecture
1.256 jmc 1676: .Re
1.329 jmc 1677: .Pp
1.256 jmc 1678: .Rs
1.329 jmc 1679: .%A T. Ylonen
1680: .%A C. Lonvick
1681: .%D January 2006
1.256 jmc 1682: .%R RFC 4252
1.329 jmc 1683: .%T The Secure Shell (SSH) Authentication Protocol
1.256 jmc 1684: .Re
1.329 jmc 1685: .Pp
1.256 jmc 1686: .Rs
1.329 jmc 1687: .%A T. Ylonen
1688: .%A C. Lonvick
1689: .%D January 2006
1.256 jmc 1690: .%R RFC 4253
1.329 jmc 1691: .%T The Secure Shell (SSH) Transport Layer Protocol
1.256 jmc 1692: .Re
1.329 jmc 1693: .Pp
1.256 jmc 1694: .Rs
1.329 jmc 1695: .%A T. Ylonen
1696: .%A C. Lonvick
1697: .%D January 2006
1.256 jmc 1698: .%R RFC 4254
1.329 jmc 1699: .%T The Secure Shell (SSH) Connection Protocol
1.256 jmc 1700: .Re
1.329 jmc 1701: .Pp
1.256 jmc 1702: .Rs
1.329 jmc 1703: .%A J. Schlyter
1704: .%A W. Griffin
1705: .%D January 2006
1.256 jmc 1706: .%R RFC 4255
1.329 jmc 1707: .%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
1.256 jmc 1708: .Re
1.329 jmc 1709: .Pp
1.256 jmc 1710: .Rs
1.329 jmc 1711: .%A F. Cusack
1712: .%A M. Forssen
1713: .%D January 2006
1.256 jmc 1714: .%R RFC 4256
1.329 jmc 1715: .%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)
1.256 jmc 1716: .Re
1.329 jmc 1717: .Pp
1.256 jmc 1718: .Rs
1.329 jmc 1719: .%A J. Galbraith
1720: .%A P. Remaker
1721: .%D January 2006
1.256 jmc 1722: .%R RFC 4335
1.329 jmc 1723: .%T The Secure Shell (SSH) Session Channel Break Extension
1.256 jmc 1724: .Re
1.329 jmc 1725: .Pp
1.256 jmc 1726: .Rs
1.329 jmc 1727: .%A M. Bellare
1728: .%A T. Kohno
1729: .%A C. Namprempre
1730: .%D January 2006
1.256 jmc 1731: .%R RFC 4344
1.329 jmc 1732: .%T The Secure Shell (SSH) Transport Layer Encryption Modes
1.256 jmc 1733: .Re
1.329 jmc 1734: .Pp
1.256 jmc 1735: .Rs
1.329 jmc 1736: .%A B. Harris
1737: .%D January 2006
1.256 jmc 1738: .%R RFC 4345
1.329 jmc 1739: .%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol
1.258 djm 1740: .Re
1.329 jmc 1741: .Pp
1.258 djm 1742: .Rs
1.329 jmc 1743: .%A M. Friedl
1744: .%A N. Provos
1745: .%A W. Simpson
1746: .%D March 2006
1.258 djm 1747: .%R RFC 4419
1.329 jmc 1748: .%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
1.266 markus 1749: .Re
1.329 jmc 1750: .Pp
1.266 markus 1751: .Rs
1.329 jmc 1752: .%A J. Galbraith
1753: .%A R. Thayer
1754: .%D November 2006
1.266 markus 1755: .%R RFC 4716
1.329 jmc 1756: .%T The Secure Shell (SSH) Public Key File Format
1.313 djm 1757: .Re
1.329 jmc 1758: .Pp
1.313 djm 1759: .Rs
1.329 jmc 1760: .%A D. Stebila
1761: .%A J. Green
1762: .%D December 2009
1.313 djm 1763: .%R RFC 5656
1.329 jmc 1764: .%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
1.274 grunk 1765: .Re
1.329 jmc 1766: .Pp
1.274 grunk 1767: .Rs
1768: .%A A. Perrig
1769: .%A D. Song
1770: .%D 1999
1.329 jmc 1771: .%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
1772: .%T Hash Visualization: a New Technique to improve Real-World Security
1.106 markus 1773: .Re
1.173 jmc 1774: .Sh AUTHORS
1775: OpenSSH is a derivative of the original and free
1776: ssh 1.2.12 release by Tatu Ylonen.
1777: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1778: Theo de Raadt and Dug Song
1779: removed many bugs, re-added newer features and
1780: created OpenSSH.
1781: Markus Friedl contributed the support for SSH
1782: protocol versions 1.5 and 2.0.
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