Annotation of src/usr.bin/ssh/ssh.1, Revision 1.431
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: .\"
1.431 ! jmc 36: .\" $OpenBSD: ssh.1,v 1.430 2022/03/31 17:27:27 naddy Exp $
! 37: .Dd $Mdocdate: March 31 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
1.218 jmc 574: .It SendEnv
575: .It ServerAliveInterval
576: .It ServerAliveCountMax
1.422 djm 577: .It SessionType
1.395 jmc 578: .It SetEnv
1.423 djm 579: .It StdinNull
1.347 jmc 580: .It StreamLocalBindMask
581: .It StreamLocalBindUnlink
1.218 jmc 582: .It StrictHostKeyChecking
583: .It TCPKeepAlive
584: .It Tunnel
585: .It TunnelDevice
1.354 djm 586: .It UpdateHostKeys
1.218 jmc 587: .It User
588: .It UserKnownHostsFile
589: .It VerifyHostKeyDNS
1.276 jmc 590: .It VisualHostKey
1.218 jmc 591: .It XAuthLocation
592: .El
1.360 millert 593: .Pp
1.218 jmc 594: .It Fl p Ar port
595: Port to connect to on the remote host.
596: This can be specified on a
597: per-host basis in the configuration file.
1.360 millert 598: .Pp
1.362 djm 599: .It Fl Q Ar query_option
1.425 jmc 600: Queries for the algorithms supported by one of the following features:
1.341 deraadt 601: .Ar cipher
1.332 djm 602: (supported symmetric ciphers),
1.341 deraadt 603: .Ar cipher-auth
1.340 djm 604: (supported symmetric ciphers that support authenticated encryption),
1.398 djm 605: .Ar help
606: (supported query terms for use with the
607: .Fl Q
608: flag),
1.341 deraadt 609: .Ar mac
1.332 djm 610: (supported message integrity codes),
1.341 deraadt 611: .Ar kex
1.332 djm 612: (key exchange algorithms),
1.341 deraadt 613: .Ar key
1.362 djm 614: (key types),
615: .Ar key-cert
616: (certificate key types),
617: .Ar key-plain
1.398 djm 618: (non-certificate key types),
1.410 dtucker 619: .Ar key-sig
620: (all key types and signature algorithms),
1.356 djm 621: .Ar protocol-version
1.398 djm 622: (supported SSH protocol versions), and
623: .Ar sig
624: (supported signature algorithms).
1.410 dtucker 625: Alternatively, any keyword from
626: .Xr ssh_config 5
627: or
628: .Xr sshd_config 5
629: that takes an algorithm list may be used as an alias for the corresponding
630: query_option.
1.360 millert 631: .Pp
1.218 jmc 632: .It Fl q
633: Quiet mode.
1.271 djm 634: Causes most warning and diagnostic messages to be suppressed.
1.360 millert 635: .Pp
1.218 jmc 636: .It Fl R Xo
637: .Sm off
638: .Oo Ar bind_address : Oc
639: .Ar port : host : hostport
640: .Sm on
641: .Xc
1.360 millert 642: .It Fl R Xo
643: .Sm off
644: .Oo Ar bind_address : Oc
645: .Ar port : local_socket
646: .Sm on
647: .Xc
648: .It Fl R Xo
649: .Sm off
650: .Ar remote_socket : host : hostport
651: .Sm on
652: .Xc
653: .It Fl R Xo
654: .Sm off
655: .Ar remote_socket : local_socket
656: .Sm on
657: .Xc
1.384 markus 658: .It Fl R Xo
659: .Sm off
660: .Oo Ar bind_address : Oc
661: .Ar port
662: .Sm on
663: .Xc
1.360 millert 664: Specifies that connections to the given TCP port or Unix socket on the remote
1.384 markus 665: (server) host are to be forwarded to the local side.
666: .Pp
1.360 millert 667: This works by allocating a socket to listen to either a TCP
1.218 jmc 668: .Ar port
1.360 millert 669: or to a Unix socket on the remote side.
670: Whenever a connection is made to this port or Unix socket, the
671: connection is forwarded over the secure channel, and a connection
1.384 markus 672: is made from the local machine to either an explicit destination specified by
1.218 jmc 673: .Ar host
674: port
1.360 millert 675: .Ar hostport ,
676: or
677: .Ar local_socket ,
1.384 markus 678: or, if no explicit destination was specified,
679: .Nm
680: will act as a SOCKS 4/5 proxy and forward connections to the destinations
681: requested by the remote SOCKS client.
1.2 deraadt 682: .Pp
1.218 jmc 683: Port forwardings can also be specified in the configuration file.
684: Privileged ports can be forwarded only when
685: logging in as root on the remote machine.
1.324 jmc 686: IPv6 addresses can be specified by enclosing the address in square brackets.
1.194 jakob 687: .Pp
1.360 millert 688: By default, TCP listening sockets on the server will be bound to the loopback
1.218 jmc 689: interface only.
1.280 tobias 690: This may be overridden by specifying a
1.218 jmc 691: .Ar bind_address .
692: An empty
693: .Ar bind_address ,
694: or the address
695: .Ql * ,
696: indicates that the remote socket should listen on all interfaces.
697: Specifying a remote
698: .Ar bind_address
699: will only succeed if the server's
700: .Cm GatewayPorts
701: option is enabled (see
702: .Xr sshd_config 5 ) .
1.281 djm 703: .Pp
704: If the
705: .Ar port
706: argument is
1.282 djm 707: .Ql 0 ,
1.281 djm 708: the listen port will be dynamically allocated on the server and reported
709: to the client at run time.
1.305 markus 710: When used together with
1.430 naddy 711: .Ic -O forward ,
1.305 markus 712: the allocated port will be printed to the standard output.
1.360 millert 713: .Pp
1.218 jmc 714: .It Fl S Ar ctl_path
1.304 jmc 715: Specifies the location of a control socket for connection sharing,
1.303 djm 716: or the string
717: .Dq none
718: to disable connection sharing.
1.218 jmc 719: Refer to the description of
720: .Cm ControlPath
721: and
722: .Cm ControlMaster
723: in
724: .Xr ssh_config 5
725: for details.
1.360 millert 726: .Pp
1.218 jmc 727: .It Fl s
728: May be used to request invocation of a subsystem on the remote system.
1.369 jmc 729: Subsystems facilitate the use of SSH
730: as a secure transport for other applications (e.g.\&
1.218 jmc 731: .Xr sftp 1 ) .
732: The subsystem is specified as the remote command.
1.422 djm 733: Refer to the description of
734: .Cm SessionType
735: in
736: .Xr ssh_config 5
737: for details.
1.360 millert 738: .Pp
1.218 jmc 739: .It Fl T
1.357 dtucker 740: Disable pseudo-terminal allocation.
1.360 millert 741: .Pp
1.218 jmc 742: .It Fl t
1.357 dtucker 743: Force pseudo-terminal allocation.
1.218 jmc 744: This can be used to execute arbitrary
745: screen-based programs on a remote machine, which can be very useful,
1.257 jmc 746: e.g. when implementing menu services.
1.218 jmc 747: Multiple
748: .Fl t
749: options force tty allocation, even if
1.194 jakob 750: .Nm
1.218 jmc 751: has no local tty.
1.360 millert 752: .Pp
1.218 jmc 753: .It Fl V
754: Display the version number and exit.
1.360 millert 755: .Pp
1.218 jmc 756: .It Fl v
757: Verbose mode.
758: Causes
1.176 jmc 759: .Nm
1.218 jmc 760: to print debugging messages about its progress.
761: This is helpful in
762: debugging connection, authentication, and configuration problems.
763: Multiple
764: .Fl v
765: options increase the verbosity.
766: The maximum is 3.
1.360 millert 767: .Pp
1.290 dtucker 768: .It Fl W Ar host : Ns Ar port
769: Requests that standard input and output on the client be forwarded to
770: .Ar host
771: on
772: .Ar port
773: over the secure channel.
774: Implies
775: .Fl N ,
776: .Fl T ,
777: .Cm ExitOnForwardFailure
778: and
1.373 jmc 779: .Cm ClearAllForwardings ,
780: though these can be overridden in the configuration file or using
1.372 dtucker 781: .Fl o
782: command line options.
1.360 millert 783: .Pp
1.261 stevesk 784: .It Fl w Xo
785: .Ar local_tun Ns Op : Ns Ar remote_tun
786: .Xc
787: Requests
788: tunnel
789: device forwarding with the specified
1.218 jmc 790: .Xr tun 4
1.261 stevesk 791: devices between the client
792: .Pq Ar local_tun
793: and the server
794: .Pq Ar remote_tun .
795: .Pp
1.228 jmc 796: The devices may be specified by numerical ID or the keyword
797: .Dq any ,
798: which uses the next available tunnel device.
1.261 stevesk 799: If
800: .Ar remote_tun
801: is not specified, it defaults to
802: .Dq any .
1.228 jmc 803: See also the
1.218 jmc 804: .Cm Tunnel
1.261 stevesk 805: and
806: .Cm TunnelDevice
807: directives in
1.218 jmc 808: .Xr ssh_config 5 .
1.393 djm 809: .Pp
1.261 stevesk 810: If the
811: .Cm Tunnel
1.393 djm 812: directive is unset, it will be set to the default tunnel mode, which is
1.261 stevesk 813: .Dq point-to-point .
1.393 djm 814: If a different
815: .Cm Tunnel
816: forwarding mode it desired, then it should be specified before
817: .Fl w .
1.360 millert 818: .Pp
1.218 jmc 819: .It Fl X
820: Enables X11 forwarding.
1.54 markus 821: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 822: .Pp
1.218 jmc 823: X11 forwarding should be enabled with caution.
1.168 jmc 824: Users with the ability to bypass file permissions on the remote host
1.218 jmc 825: (for the user's X authorization database)
826: can access the local X11 display through the forwarded connection.
827: An attacker may then be able to perform activities such as keystroke monitoring.
828: .Pp
829: For this reason, X11 forwarding is subjected to X11 SECURITY extension
830: restrictions by default.
1.429 jsg 831: Refer to the
1.218 jmc 832: .Nm
833: .Fl Y
834: option and the
835: .Cm ForwardX11Trusted
836: directive in
837: .Xr ssh_config 5
838: for more information.
1.360 millert 839: .Pp
1.218 jmc 840: .It Fl x
841: Disables X11 forwarding.
1.360 millert 842: .Pp
1.218 jmc 843: .It Fl Y
844: Enables trusted X11 forwarding.
845: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
846: controls.
1.360 millert 847: .Pp
1.278 djm 848: .It Fl y
849: Send log information using the
850: .Xr syslog 3
851: system module.
852: By default this information is sent to stderr.
1.218 jmc 853: .El
1.224 jmc 854: .Pp
855: .Nm
856: may additionally obtain configuration data from
857: a per-user configuration file and a system-wide configuration file.
858: The file format and configuration options are described in
859: .Xr ssh_config 5 .
1.222 jmc 860: .Sh AUTHENTICATION
1.377 djm 861: The OpenSSH SSH client supports SSH protocol 2.
1.222 jmc 862: .Pp
863: The methods available for authentication are:
1.260 jmc 864: GSSAPI-based authentication,
1.222 jmc 865: host-based authentication,
866: public key authentication,
1.421 dtucker 867: keyboard-interactive authentication,
1.222 jmc 868: and password authentication.
869: Authentication methods are tried in the order specified above,
1.369 jmc 870: though
871: .Cm PreferredAuthentications
872: can be used to change the default order.
1.222 jmc 873: .Pp
874: Host-based authentication works as follows:
1.218 jmc 875: If the machine the user logs in from is listed in
876: .Pa /etc/hosts.equiv
877: or
878: .Pa /etc/shosts.equiv
1.412 djm 879: on the remote machine, the user is non-root and the user names are
1.218 jmc 880: the same on both sides, or if the files
881: .Pa ~/.rhosts
882: or
883: .Pa ~/.shosts
884: exist in the user's home directory on the
885: remote machine and contain a line containing the name of the client
886: machine and the name of the user on that machine, the user is
1.222 jmc 887: considered for login.
888: Additionally, the server
889: .Em must
890: be able to verify the client's
891: host key (see the description of
1.218 jmc 892: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 893: and
1.222 jmc 894: .Pa ~/.ssh/known_hosts ,
895: below)
896: for login to be permitted.
1.218 jmc 897: This authentication method closes security holes due to IP
1.222 jmc 898: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 899: [Note to the administrator:
900: .Pa /etc/hosts.equiv ,
901: .Pa ~/.rhosts ,
902: and the rlogin/rsh protocol in general, are inherently insecure and should be
903: disabled if security is desired.]
1.189 dtucker 904: .Pp
1.222 jmc 905: Public key authentication works as follows:
906: The scheme is based on public-key cryptography,
907: using cryptosystems
908: where encryption and decryption are done using separate keys,
909: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 910: The idea is that each user creates a public/private
911: key pair for authentication purposes.
912: The server knows the public key, and only the user knows the private key.
1.222 jmc 913: .Nm
914: implements public key authentication protocol automatically,
1.349 sobrado 915: using one of the DSA, ECDSA, Ed25519 or RSA algorithms.
1.333 jmc 916: The HISTORY section of
1.222 jmc 917: .Xr ssl 8
1.311 jmc 918: contains a brief discussion of the DSA and RSA algorithms.
1.210 djm 919: .Pp
1.218 jmc 920: The file
921: .Pa ~/.ssh/authorized_keys
922: lists the public keys that are permitted for logging in.
923: When the user logs in, the
1.2 deraadt 924: .Nm
1.218 jmc 925: program tells the server which key pair it would like to use for
926: authentication.
1.222 jmc 927: The client proves that it has access to the private key
928: and the server checks that the corresponding public key
929: is authorized to accept the account.
1.383 djm 930: .Pp
931: The server may inform the client of errors that prevented public key
932: authentication from succeeding after authentication completes using a
933: different method.
934: These may be viewed by increasing the
935: .Cm LogLevel
936: to
937: .Cm DEBUG
938: or higher (e.g. by using the
939: .Fl v
940: flag).
1.218 jmc 941: .Pp
1.420 dtucker 942: The user creates their key pair by running
1.218 jmc 943: .Xr ssh-keygen 1 .
944: This stores the private key in
1.222 jmc 945: .Pa ~/.ssh/id_dsa
1.369 jmc 946: (DSA),
1.310 djm 947: .Pa ~/.ssh/id_ecdsa
1.369 jmc 948: (ECDSA),
1.404 naddy 949: .Pa ~/.ssh/id_ecdsa_sk
1.409 naddy 950: (authenticator-hosted ECDSA),
1.343 naddy 951: .Pa ~/.ssh/id_ed25519
1.369 jmc 952: (Ed25519),
1.406 naddy 953: .Pa ~/.ssh/id_ed25519_sk
1.409 naddy 954: (authenticator-hosted Ed25519),
1.222 jmc 955: or
956: .Pa ~/.ssh/id_rsa
1.369 jmc 957: (RSA)
1.218 jmc 958: and stores the public key in
1.222 jmc 959: .Pa ~/.ssh/id_dsa.pub
1.369 jmc 960: (DSA),
1.310 djm 961: .Pa ~/.ssh/id_ecdsa.pub
1.369 jmc 962: (ECDSA),
1.404 naddy 963: .Pa ~/.ssh/id_ecdsa_sk.pub
1.409 naddy 964: (authenticator-hosted ECDSA),
1.343 naddy 965: .Pa ~/.ssh/id_ed25519.pub
1.369 jmc 966: (Ed25519),
1.406 naddy 967: .Pa ~/.ssh/id_ed25519_sk.pub
1.409 naddy 968: (authenticator-hosted Ed25519),
1.222 jmc 969: or
970: .Pa ~/.ssh/id_rsa.pub
1.369 jmc 971: (RSA)
1.218 jmc 972: in the user's home directory.
1.222 jmc 973: The user should then copy the public key
1.218 jmc 974: to
975: .Pa ~/.ssh/authorized_keys
1.420 dtucker 976: in their home directory on the remote machine.
1.222 jmc 977: The
1.218 jmc 978: .Pa authorized_keys
979: file corresponds to the conventional
980: .Pa ~/.rhosts
981: file, and has one key
1.222 jmc 982: per line, though the lines can be very long.
1.218 jmc 983: After this, the user can log in without giving the password.
984: .Pp
1.301 jmc 985: A variation on public key authentication
986: is available in the form of certificate authentication:
987: instead of a set of public/private keys,
988: signed certificates are used.
989: This has the advantage that a single trusted certification authority
990: can be used in place of many public/private keys.
1.333 jmc 991: See the CERTIFICATES section of
1.301 jmc 992: .Xr ssh-keygen 1
993: for more information.
994: .Pp
995: The most convenient way to use public key or certificate authentication
996: may be with an authentication agent.
1.218 jmc 997: See
998: .Xr ssh-agent 1
1.366 jcs 999: and (optionally) the
1000: .Cm AddKeysToAgent
1001: directive in
1002: .Xr ssh_config 5
1.218 jmc 1003: for more information.
1004: .Pp
1.421 dtucker 1005: Keyboard-interactive authentication works as follows:
1.222 jmc 1006: The server sends an arbitrary
1007: .Qq challenge
1.421 dtucker 1008: text and prompts for a response, possibly multiple times.
1009: Examples of keyboard-interactive authentication include
1.335 jmc 1010: .Bx
1011: Authentication (see
1.222 jmc 1012: .Xr login.conf 5 )
1.335 jmc 1013: and PAM (some
1014: .Pf non- Ox
1015: systems).
1.222 jmc 1016: .Pp
1017: Finally, if other authentication methods fail,
1.218 jmc 1018: .Nm
1019: prompts the user for a password.
1020: The password is sent to the remote
1021: host for checking; however, since all communications are encrypted,
1022: the password cannot be seen by someone listening on the network.
1.232 jmc 1023: .Pp
1024: .Nm
1025: automatically maintains and checks a database containing
1026: identification for all hosts it has ever been used with.
1027: Host keys are stored in
1028: .Pa ~/.ssh/known_hosts
1029: in the user's home directory.
1030: Additionally, the file
1031: .Pa /etc/ssh/ssh_known_hosts
1032: is automatically checked for known hosts.
1033: Any new hosts are automatically added to the user's file.
1034: If a host's identification ever changes,
1035: .Nm
1036: warns about this and disables password authentication to prevent
1037: server spoofing or man-in-the-middle attacks,
1038: which could otherwise be used to circumvent the encryption.
1039: The
1040: .Cm StrictHostKeyChecking
1041: option can be used to control logins to machines whose
1042: host key is not known or has changed.
1043: .Pp
1.218 jmc 1044: When the user's identity has been accepted by the server, the server
1.357 dtucker 1045: either executes the given command in a non-interactive session or,
1046: if no command has been specified, logs into the machine and gives
1047: the user a normal shell as an interactive session.
1.218 jmc 1048: All communication with
1049: the remote command or shell will be automatically encrypted.
1050: .Pp
1.430 naddy 1051: If an interactive session is requested,
1.357 dtucker 1052: .Nm
1053: by default will only request a pseudo-terminal (pty) for interactive
1054: sessions when the client has one.
1055: The flags
1056: .Fl T
1057: and
1058: .Fl t
1059: can be used to override this behaviour.
1060: .Pp
1.430 naddy 1061: If a pseudo-terminal has been allocated, the
1.218 jmc 1062: user may use the escape characters noted below.
1063: .Pp
1.357 dtucker 1064: If no pseudo-terminal has been allocated,
1.218 jmc 1065: the session is transparent and can be used to reliably transfer binary data.
1066: On most systems, setting the escape character to
1067: .Dq none
1068: will also make the session transparent even if a tty is used.
1069: .Pp
1070: The session terminates when the command or shell on the remote
1.247 jmc 1071: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 1072: .Sh ESCAPE CHARACTERS
1.218 jmc 1073: When a pseudo-terminal has been requested,
1.2 deraadt 1074: .Nm
1.218 jmc 1075: supports a number of functions through the use of an escape character.
1076: .Pp
1077: A single tilde character can be sent as
1078: .Ic ~~
1079: or by following the tilde by a character other than those described below.
1080: The escape character must always follow a newline to be interpreted as
1081: special.
1082: The escape character can be changed in configuration files using the
1083: .Cm EscapeChar
1084: configuration directive or on the command line by the
1085: .Fl e
1086: option.
1087: .Pp
1088: The supported escapes (assuming the default
1089: .Ql ~ )
1090: are:
1091: .Bl -tag -width Ds
1092: .It Cm ~.
1093: Disconnect.
1094: .It Cm ~^Z
1095: Background
1.234 jmc 1096: .Nm .
1.218 jmc 1097: .It Cm ~#
1098: List forwarded connections.
1099: .It Cm ~&
1100: Background
1.2 deraadt 1101: .Nm
1.218 jmc 1102: at logout when waiting for forwarded connection / X11 sessions to terminate.
1103: .It Cm ~?
1104: Display a list of escape characters.
1105: .It Cm ~B
1106: Send a BREAK to the remote system
1.369 jmc 1107: (only useful if the peer supports it).
1.218 jmc 1108: .It Cm ~C
1109: Open command line.
1110: Currently this allows the addition of port forwardings using the
1.279 stevesk 1111: .Fl L ,
1112: .Fl R
1.218 jmc 1113: and
1.279 stevesk 1114: .Fl D
1.225 jmc 1115: options (see above).
1.322 markus 1116: It also allows the cancellation of existing port-forwardings
1117: with
1.262 stevesk 1118: .Sm off
1.322 markus 1119: .Fl KL Oo Ar bind_address : Oc Ar port
1.262 stevesk 1120: .Sm on
1.322 markus 1121: for local,
1122: .Sm off
1123: .Fl KR Oo Ar bind_address : Oc Ar port
1124: .Sm on
1125: for remote and
1126: .Sm off
1127: .Fl KD Oo Ar bind_address : Oc Ar port
1128: .Sm on
1129: for dynamic port-forwardings.
1.218 jmc 1130: .Ic !\& Ns Ar command
1131: allows the user to execute a local command if the
1132: .Ic PermitLocalCommand
1133: option is enabled in
1.176 jmc 1134: .Xr ssh_config 5 .
1.218 jmc 1135: Basic help is available, using the
1136: .Fl h
1137: option.
1138: .It Cm ~R
1139: Request rekeying of the connection
1.369 jmc 1140: (only useful if the peer supports it).
1.327 dtucker 1141: .It Cm ~V
1142: Decrease the verbosity
1143: .Pq Ic LogLevel
1144: when errors are being written to stderr.
1145: .It Cm ~v
1.328 jmc 1146: Increase the verbosity
1.327 dtucker 1147: .Pq Ic LogLevel
1148: when errors are being written to stderr.
1.176 jmc 1149: .El
1.246 jmc 1150: .Sh TCP FORWARDING
1.402 jmc 1151: Forwarding of arbitrary TCP connections over a secure channel
1152: can be specified either on the command line or in a configuration file.
1.246 jmc 1153: One possible application of TCP forwarding is a secure connection to a
1154: mail server; another is going through firewalls.
1155: .Pp
1.402 jmc 1156: In the example below, we look at encrypting communication for an IRC client,
1157: even though the IRC server it connects to does not directly
1158: support encrypted communication.
1.246 jmc 1159: This works as follows:
1160: the user connects to the remote host using
1161: .Nm ,
1.402 jmc 1162: specifying the ports to be used to forward the connection.
1163: After that it is possible to start the program locally,
1.246 jmc 1164: and
1165: .Nm
1.402 jmc 1166: will encrypt and forward the connection to the remote server.
1.246 jmc 1167: .Pp
1.402 jmc 1168: The following example tunnels an IRC session from the client
1169: to an IRC server at
1.246 jmc 1170: .Dq server.example.com ,
1171: joining channel
1172: .Dq #users ,
1173: nickname
1174: .Dq pinky ,
1.402 jmc 1175: using the standard IRC port, 6667:
1176: .Bd -literal -offset 4n
1177: $ ssh -f -L 6667:localhost:6667 server.example.com sleep 10
1178: $ irc -c '#users' pinky IRC/127.0.0.1
1179: .Ed
1.246 jmc 1180: .Pp
1181: The
1182: .Fl f
1183: option backgrounds
1184: .Nm
1185: and the remote command
1186: .Dq sleep 10
1187: is specified to allow an amount of time
1188: (10 seconds, in the example)
1.402 jmc 1189: to start the program which is going to use the tunnel.
1.246 jmc 1190: If no connections are made within the time specified,
1191: .Nm
1192: will exit.
1193: .Sh X11 FORWARDING
1.218 jmc 1194: If the
1195: .Cm ForwardX11
1196: variable is set to
1197: .Dq yes
1198: (or see the description of the
1.227 jmc 1199: .Fl X ,
1200: .Fl x ,
1.218 jmc 1201: and
1.227 jmc 1202: .Fl Y
1.226 jmc 1203: options above)
1.218 jmc 1204: and the user is using X11 (the
1205: .Ev DISPLAY
1206: environment variable is set), the connection to the X11 display is
1207: automatically forwarded to the remote side in such a way that any X11
1208: programs started from the shell (or command) will go through the
1209: encrypted channel, and the connection to the real X server will be made
1.176 jmc 1210: from the local machine.
1.218 jmc 1211: The user should not manually set
1212: .Ev DISPLAY .
1213: Forwarding of X11 connections can be
1214: configured on the command line or in configuration files.
1215: .Pp
1216: The
1217: .Ev DISPLAY
1218: value set by
1219: .Nm
1220: will point to the server machine, but with a display number greater than zero.
1221: This is normal, and happens because
1222: .Nm
1223: creates a
1224: .Dq proxy
1225: X server on the server machine for forwarding the
1226: connections over the encrypted channel.
1.200 djm 1227: .Pp
1.218 jmc 1228: .Nm
1229: will also automatically set up Xauthority data on the server machine.
1230: For this purpose, it will generate a random authorization cookie,
1231: store it in Xauthority on the server, and verify that any forwarded
1232: connections carry this cookie and replace it by the real cookie when
1233: the connection is opened.
1234: The real authentication cookie is never
1235: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1236: .Pp
1.218 jmc 1237: If the
1238: .Cm ForwardAgent
1239: variable is set to
1240: .Dq yes
1241: (or see the description of the
1242: .Fl A
1.191 djm 1243: and
1.218 jmc 1244: .Fl a
1.226 jmc 1245: options above) and
1.218 jmc 1246: the user is using an authentication agent, the connection to the agent
1247: is automatically forwarded to the remote side.
1.252 jmc 1248: .Sh VERIFYING HOST KEYS
1249: When connecting to a server for the first time,
1250: a fingerprint of the server's public key is presented to the user
1251: (unless the option
1252: .Cm StrictHostKeyChecking
1253: has been disabled).
1254: Fingerprints can be determined using
1255: .Xr ssh-keygen 1 :
1256: .Pp
1257: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1258: .Pp
1.274 grunk 1259: If the fingerprint is already known, it can be matched
1260: and the key can be accepted or rejected.
1.358 djm 1261: If only legacy (MD5) fingerprints for the server are available, the
1262: .Xr ssh-keygen 1
1263: .Fl E
1264: option may be used to downgrade the fingerprint algorithm to match.
1265: .Pp
1.274 grunk 1266: Because of the difficulty of comparing host keys
1.352 djm 1267: just by looking at fingerprint strings,
1.274 grunk 1268: there is also support to compare host keys visually,
1269: using
1270: .Em random art .
1271: By setting the
1.275 grunk 1272: .Cm VisualHostKey
1.274 grunk 1273: option to
1.275 grunk 1274: .Dq yes ,
1.274 grunk 1275: a small ASCII graphic gets displayed on every login to a server, no matter
1276: if the session itself is interactive or not.
1277: By learning the pattern a known server produces, a user can easily
1278: find out that the host key has changed when a completely different pattern
1279: is displayed.
1280: Because these patterns are not unambiguous however, a pattern that looks
1281: similar to the pattern remembered only gives a good probability that the
1282: host key is the same, not guaranteed proof.
1283: .Pp
1284: To get a listing of the fingerprints along with their random art for
1285: all known hosts, the following command line can be used:
1286: .Pp
1287: .Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1288: .Pp
1.252 jmc 1289: If the fingerprint is unknown,
1290: an alternative method of verification is available:
1291: SSH fingerprints verified by DNS.
1292: An additional resource record (RR),
1293: SSHFP,
1294: is added to a zonefile
1295: and the connecting client is able to match the fingerprint
1296: with that of the key presented.
1297: .Pp
1298: In this example, we are connecting a client to a server,
1299: .Dq host.example.com .
1300: The SSHFP resource records should first be added to the zonefile for
1301: host.example.com:
1302: .Bd -literal -offset indent
1.259 jakob 1303: $ ssh-keygen -r host.example.com.
1.252 jmc 1304: .Ed
1305: .Pp
1306: The output lines will have to be added to the zonefile.
1307: To check that the zone is answering fingerprint queries:
1308: .Pp
1309: .Dl $ dig -t SSHFP host.example.com
1310: .Pp
1311: Finally the client connects:
1312: .Bd -literal -offset indent
1313: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1314: [...]
1315: Matching host key fingerprint found in DNS.
1316: Are you sure you want to continue connecting (yes/no)?
1317: .Ed
1318: .Pp
1319: See the
1320: .Cm VerifyHostKeyDNS
1321: option in
1322: .Xr ssh_config 5
1323: for more information.
1.250 jmc 1324: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1325: .Nm
1326: contains support for Virtual Private Network (VPN) tunnelling
1327: using the
1328: .Xr tun 4
1329: network pseudo-device,
1330: allowing two networks to be joined securely.
1331: The
1332: .Xr sshd_config 5
1333: configuration option
1334: .Cm PermitTunnel
1335: controls whether the server supports this,
1336: and at what level (layer 2 or 3 traffic).
1337: .Pp
1338: The following example would connect client network 10.0.50.0/24
1.265 otto 1339: with remote network 10.0.99.0/24 using a point-to-point connection
1340: from 10.1.1.1 to 10.1.1.2,
1341: provided that the SSH server running on the gateway to the remote network,
1342: at 192.168.1.15, allows it.
1343: .Pp
1344: On the client:
1.250 jmc 1345: .Bd -literal -offset indent
1346: # ssh -f -w 0:1 192.168.1.15 true
1.265 otto 1347: # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1348: # route add 10.0.99.0/24 10.1.1.2
1349: .Ed
1350: .Pp
1351: On the server:
1352: .Bd -literal -offset indent
1353: # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1354: # route add 10.0.50.0/24 10.1.1.1
1.250 jmc 1355: .Ed
1356: .Pp
1357: Client access may be more finely tuned via the
1358: .Pa /root/.ssh/authorized_keys
1359: file (see below) and the
1360: .Cm PermitRootLogin
1361: server option.
1.255 jmc 1362: The following entry would permit connections on
1.250 jmc 1363: .Xr tun 4
1.255 jmc 1364: device 1 from user
1.250 jmc 1365: .Dq jane
1.255 jmc 1366: and on tun device 2 from user
1.250 jmc 1367: .Dq john ,
1368: if
1369: .Cm PermitRootLogin
1370: is set to
1371: .Dq forced-commands-only :
1372: .Bd -literal -offset 2n
1373: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1374: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1375: .Ed
1376: .Pp
1.264 ray 1377: Since an SSH-based setup entails a fair amount of overhead,
1.250 jmc 1378: it may be more suited to temporary setups,
1379: such as for wireless VPNs.
1380: More permanent VPNs are better provided by tools such as
1381: .Xr ipsecctl 8
1382: and
1383: .Xr isakmpd 8 .
1.2 deraadt 1384: .Sh ENVIRONMENT
1385: .Nm
1.1 deraadt 1386: will normally set the following environment variables:
1.237 jmc 1387: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1388: .It Ev DISPLAY
1389: The
1390: .Ev DISPLAY
1.40 aaron 1391: variable indicates the location of the X11 server.
1.44 aaron 1392: It is automatically set by
1.2 deraadt 1393: .Nm
1394: to point to a value of the form
1.233 jmc 1395: .Dq hostname:n ,
1396: where
1397: .Dq hostname
1398: indicates the host where the shell runs, and
1399: .Sq n
1400: is an integer \*(Ge 1.
1.40 aaron 1401: .Nm
1402: uses this special value to forward X11 connections over the secure
1403: channel.
1.107 markus 1404: The user should normally not set
1405: .Ev DISPLAY
1406: explicitly, as that
1.1 deraadt 1407: will render the X11 connection insecure (and will require the user to
1408: manually copy any required authorization cookies).
1.2 deraadt 1409: .It Ev HOME
1.1 deraadt 1410: Set to the path of the user's home directory.
1.2 deraadt 1411: .It Ev LOGNAME
1412: Synonym for
1.12 aaron 1413: .Ev USER ;
1414: set for compatibility with systems that use this variable.
1.2 deraadt 1415: .It Ev MAIL
1.129 stevesk 1416: Set to the path of the user's mailbox.
1.40 aaron 1417: .It Ev PATH
1.2 deraadt 1418: Set to the default
1419: .Ev PATH ,
1420: as specified when compiling
1.234 jmc 1421: .Nm .
1.118 markus 1422: .It Ev SSH_ASKPASS
1423: If
1424: .Nm
1425: needs a passphrase, it will read the passphrase from the current
1426: terminal if it was run from a terminal.
1427: If
1428: .Nm
1429: does not have a terminal associated with it but
1430: .Ev DISPLAY
1431: and
1432: .Ev SSH_ASKPASS
1433: are set, it will execute the program specified by
1434: .Ev SSH_ASKPASS
1435: and open an X11 window to read the passphrase.
1436: This is particularly useful when calling
1437: .Nm
1438: from a
1.196 jmc 1439: .Pa .xsession
1.118 markus 1440: or related script.
1441: (Note that on some machines it
1442: may be necessary to redirect the input from
1443: .Pa /dev/null
1444: to make this work.)
1.413 djm 1445: .It Ev SSH_ASKPASS_REQUIRE
1.414 jmc 1446: Allows further control over the use of an askpass program.
1.413 djm 1447: If this variable is set to
1448: .Dq never
1449: then
1450: .Nm
1451: will never attempt to use one.
1452: If it is set to
1453: .Dq prefer ,
1454: then
1455: .Nm
1456: will prefer to use the askpass program instead of the TTY when requesting
1457: passwords.
1458: Finally, if the variable is set to
1459: .Dq force ,
1460: then the askpass program will be used for all passphrase input regardless
1461: of whether
1462: .Ev DISPLAY
1463: is set.
1.18 markus 1464: .It Ev SSH_AUTH_SOCK
1.233 jmc 1465: Identifies the path of a
1466: .Ux Ns -domain
1467: socket used to communicate with the agent.
1.166 stevesk 1468: .It Ev SSH_CONNECTION
1469: Identifies the client and server ends of the connection.
1.40 aaron 1470: The variable contains
1.233 jmc 1471: four space-separated values: client IP address, client port number,
1472: server IP address, and server port number.
1.73 markus 1473: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1474: This variable contains the original command line if a forced command
1.73 markus 1475: is executed.
1476: It can be used to extract the original arguments.
1.2 deraadt 1477: .It Ev SSH_TTY
1.1 deraadt 1478: This is set to the name of the tty (path to the device) associated
1.40 aaron 1479: with the current shell or command.
1480: If the current session has no tty,
1.1 deraadt 1481: this variable is not set.
1.387 djm 1482: .It Ev SSH_TUNNEL
1483: Optionally set by
1484: .Xr sshd 8
1485: to contain the interface names assigned if tunnel forwarding was
1486: requested by the client.
1.385 djm 1487: .It Ev SSH_USER_AUTH
1488: Optionally set by
1489: .Xr sshd 8 ,
1490: this variable may contain a pathname to a file that lists the authentication
1491: methods successfully used when the session was established, including any
1492: public keys that were used.
1.2 deraadt 1493: .It Ev TZ
1.214 jmc 1494: This variable is set to indicate the present time zone if it
1.257 jmc 1495: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1496: on to new connections).
1.2 deraadt 1497: .It Ev USER
1.1 deraadt 1498: Set to the name of the user logging in.
1.2 deraadt 1499: .El
1500: .Pp
1.44 aaron 1501: Additionally,
1.2 deraadt 1502: .Nm
1.44 aaron 1503: reads
1.207 djm 1504: .Pa ~/.ssh/environment ,
1.2 deraadt 1505: and adds lines of the format
1506: .Dq VARNAME=value
1.233 jmc 1507: to the environment if the file exists and users are allowed to
1.161 marc 1508: change their environment.
1.176 jmc 1509: For more information, see the
1.161 marc 1510: .Cm PermitUserEnvironment
1.162 stevesk 1511: option in
1.161 marc 1512: .Xr sshd_config 5 .
1.2 deraadt 1513: .Sh FILES
1.236 jmc 1514: .Bl -tag -width Ds -compact
1.309 jmc 1515: .It Pa ~/.rhosts
1.240 jmc 1516: This file is used for host-based authentication (see above).
1.92 markus 1517: On some machines this file may need to be
1.240 jmc 1518: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1519: because
1.2 deraadt 1520: .Xr sshd 8
1.40 aaron 1521: reads it as root.
1522: Additionally, this file must be owned by the user,
1523: and must not have write permissions for anyone else.
1524: The recommended
1.1 deraadt 1525: permission for most machines is read/write for the user, and not
1526: accessible by others.
1.2 deraadt 1527: .Pp
1.309 jmc 1528: .It Pa ~/.shosts
1.240 jmc 1529: This file is used in exactly the same way as
1530: .Pa .rhosts ,
1531: but allows host-based authentication without permitting login with
1532: rlogin/rsh.
1.272 mcbride 1533: .Pp
1.309 jmc 1534: .It Pa ~/.ssh/
1.272 mcbride 1535: This directory is the default location for all user-specific configuration
1536: and authentication information.
1537: There is no general requirement to keep the entire contents of this directory
1538: secret, but the recommended permissions are read/write/execute for the user,
1539: and not accessible by others.
1.236 jmc 1540: .Pp
1.309 jmc 1541: .It Pa ~/.ssh/authorized_keys
1.349 sobrado 1542: Lists the public keys (DSA, ECDSA, Ed25519, RSA)
1.343 naddy 1543: that can be used for logging in as this user.
1.238 jmc 1544: The format of this file is described in the
1545: .Xr sshd 8
1546: manual page.
1547: This file is not highly sensitive, but the recommended
1548: permissions are read/write for the user, and not accessible by others.
1549: .Pp
1.309 jmc 1550: .It Pa ~/.ssh/config
1.238 jmc 1551: This is the per-user configuration file.
1552: The file format and configuration options are described in
1553: .Xr ssh_config 5 .
1554: Because of the potential for abuse, this file must have strict permissions:
1.334 djm 1555: read/write for the user, and not writable by others.
1.238 jmc 1556: .Pp
1.309 jmc 1557: .It Pa ~/.ssh/environment
1.239 jmc 1558: Contains additional definitions for environment variables; see
1559: .Sx ENVIRONMENT ,
1.238 jmc 1560: above.
1561: .Pp
1.309 jmc 1562: .It Pa ~/.ssh/id_dsa
1.310 djm 1563: .It Pa ~/.ssh/id_ecdsa
1.404 naddy 1564: .It Pa ~/.ssh/id_ecdsa_sk
1.343 naddy 1565: .It Pa ~/.ssh/id_ed25519
1.406 naddy 1566: .It Pa ~/.ssh/id_ed25519_sk
1.309 jmc 1567: .It Pa ~/.ssh/id_rsa
1.238 jmc 1568: Contains the private key for authentication.
1569: These files
1570: contain sensitive data and should be readable by the user but not
1571: accessible by others (read/write/execute).
1572: .Nm
1573: will simply ignore a private key file if it is accessible by others.
1574: It is possible to specify a passphrase when
1575: generating the key which will be used to encrypt the
1.389 djm 1576: sensitive part of this file using AES-128.
1.238 jmc 1577: .Pp
1.309 jmc 1578: .It Pa ~/.ssh/id_dsa.pub
1.310 djm 1579: .It Pa ~/.ssh/id_ecdsa.pub
1.404 naddy 1580: .It Pa ~/.ssh/id_ecdsa_sk.pub
1.343 naddy 1581: .It Pa ~/.ssh/id_ed25519.pub
1.406 naddy 1582: .It Pa ~/.ssh/id_ed25519_sk.pub
1.309 jmc 1583: .It Pa ~/.ssh/id_rsa.pub
1.238 jmc 1584: Contains the public key for authentication.
1585: These files are not
1586: sensitive and can (but need not) be readable by anyone.
1587: .Pp
1.309 jmc 1588: .It Pa ~/.ssh/known_hosts
1.244 jmc 1589: Contains a list of host keys for all hosts the user has logged into
1590: that are not already in the systemwide list of known host keys.
1.238 jmc 1591: See
1.244 jmc 1592: .Xr sshd 8
1593: for further details of the format of this file.
1.238 jmc 1594: .Pp
1.309 jmc 1595: .It Pa ~/.ssh/rc
1.238 jmc 1596: Commands in this file are executed by
1597: .Nm
1.245 jmc 1598: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1599: started.
1600: See the
1601: .Xr sshd 8
1602: manual page for more information.
1603: .Pp
1.309 jmc 1604: .It Pa /etc/hosts.equiv
1.240 jmc 1605: This file is for host-based authentication (see above).
1606: It should only be writable by root.
1.236 jmc 1607: .Pp
1.309 jmc 1608: .It Pa /etc/shosts.equiv
1.240 jmc 1609: This file is used in exactly the same way as
1610: .Pa hosts.equiv ,
1611: but allows host-based authentication without permitting login with
1612: rlogin/rsh.
1.236 jmc 1613: .Pp
1.238 jmc 1614: .It Pa /etc/ssh/ssh_config
1615: Systemwide configuration file.
1616: The file format and configuration options are described in
1617: .Xr ssh_config 5 .
1618: .Pp
1.309 jmc 1619: .It Pa /etc/ssh/ssh_host_key
1620: .It Pa /etc/ssh/ssh_host_dsa_key
1.310 djm 1621: .It Pa /etc/ssh/ssh_host_ecdsa_key
1.343 naddy 1622: .It Pa /etc/ssh/ssh_host_ed25519_key
1.309 jmc 1623: .It Pa /etc/ssh/ssh_host_rsa_key
1.325 dtucker 1624: These files contain the private parts of the host keys
1.245 jmc 1625: and are used for host-based authentication.
1.238 jmc 1626: .Pp
1.309 jmc 1627: .It Pa /etc/ssh/ssh_known_hosts
1.238 jmc 1628: Systemwide list of known host keys.
1629: This file should be prepared by the
1630: system administrator to contain the public host keys of all machines in the
1631: organization.
1.244 jmc 1632: It should be world-readable.
1633: See
1.238 jmc 1634: .Xr sshd 8
1.244 jmc 1635: for further details of the format of this file.
1.236 jmc 1636: .Pp
1.309 jmc 1637: .It Pa /etc/ssh/sshrc
1.1 deraadt 1638: Commands in this file are executed by
1.2 deraadt 1639: .Nm
1.245 jmc 1640: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1641: See the
1.2 deraadt 1642: .Xr sshd 8
1.1 deraadt 1643: manual page for more information.
1.58 itojun 1644: .El
1.312 jmc 1645: .Sh EXIT STATUS
1646: .Nm
1647: exits with the exit status of the remote command or with 255
1648: if an error occurred.
1.2 deraadt 1649: .Sh SEE ALSO
1650: .Xr scp 1 ,
1.83 djm 1651: .Xr sftp 1 ,
1.2 deraadt 1652: .Xr ssh-add 1 ,
1653: .Xr ssh-agent 1 ,
1654: .Xr ssh-keygen 1 ,
1.242 jmc 1655: .Xr ssh-keyscan 1 ,
1.250 jmc 1656: .Xr tun 4 ,
1.159 stevesk 1657: .Xr ssh_config 5 ,
1.160 naddy 1658: .Xr ssh-keysign 8 ,
1.87 itojun 1659: .Xr sshd 8
1.329 jmc 1660: .Sh STANDARDS
1.106 markus 1661: .Rs
1.329 jmc 1662: .%A S. Lehtinen
1663: .%A C. Lonvick
1664: .%D January 2006
1.256 jmc 1665: .%R RFC 4250
1.329 jmc 1666: .%T The Secure Shell (SSH) Protocol Assigned Numbers
1.256 jmc 1667: .Re
1.329 jmc 1668: .Pp
1.256 jmc 1669: .Rs
1.329 jmc 1670: .%A T. Ylonen
1671: .%A C. Lonvick
1672: .%D January 2006
1.256 jmc 1673: .%R RFC 4251
1.329 jmc 1674: .%T The Secure Shell (SSH) Protocol Architecture
1.256 jmc 1675: .Re
1.329 jmc 1676: .Pp
1.256 jmc 1677: .Rs
1.329 jmc 1678: .%A T. Ylonen
1679: .%A C. Lonvick
1680: .%D January 2006
1.256 jmc 1681: .%R RFC 4252
1.329 jmc 1682: .%T The Secure Shell (SSH) Authentication Protocol
1.256 jmc 1683: .Re
1.329 jmc 1684: .Pp
1.256 jmc 1685: .Rs
1.329 jmc 1686: .%A T. Ylonen
1687: .%A C. Lonvick
1688: .%D January 2006
1.256 jmc 1689: .%R RFC 4253
1.329 jmc 1690: .%T The Secure Shell (SSH) Transport Layer Protocol
1.256 jmc 1691: .Re
1.329 jmc 1692: .Pp
1.256 jmc 1693: .Rs
1.329 jmc 1694: .%A T. Ylonen
1695: .%A C. Lonvick
1696: .%D January 2006
1.256 jmc 1697: .%R RFC 4254
1.329 jmc 1698: .%T The Secure Shell (SSH) Connection Protocol
1.256 jmc 1699: .Re
1.329 jmc 1700: .Pp
1.256 jmc 1701: .Rs
1.329 jmc 1702: .%A J. Schlyter
1703: .%A W. Griffin
1704: .%D January 2006
1.256 jmc 1705: .%R RFC 4255
1.329 jmc 1706: .%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
1.256 jmc 1707: .Re
1.329 jmc 1708: .Pp
1.256 jmc 1709: .Rs
1.329 jmc 1710: .%A F. Cusack
1711: .%A M. Forssen
1712: .%D January 2006
1.256 jmc 1713: .%R RFC 4256
1.329 jmc 1714: .%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)
1.256 jmc 1715: .Re
1.329 jmc 1716: .Pp
1.256 jmc 1717: .Rs
1.329 jmc 1718: .%A J. Galbraith
1719: .%A P. Remaker
1720: .%D January 2006
1.256 jmc 1721: .%R RFC 4335
1.329 jmc 1722: .%T The Secure Shell (SSH) Session Channel Break Extension
1.256 jmc 1723: .Re
1.329 jmc 1724: .Pp
1.256 jmc 1725: .Rs
1.329 jmc 1726: .%A M. Bellare
1727: .%A T. Kohno
1728: .%A C. Namprempre
1729: .%D January 2006
1.256 jmc 1730: .%R RFC 4344
1.329 jmc 1731: .%T The Secure Shell (SSH) Transport Layer Encryption Modes
1.256 jmc 1732: .Re
1.329 jmc 1733: .Pp
1.256 jmc 1734: .Rs
1.329 jmc 1735: .%A B. Harris
1736: .%D January 2006
1.256 jmc 1737: .%R RFC 4345
1.329 jmc 1738: .%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol
1.258 djm 1739: .Re
1.329 jmc 1740: .Pp
1.258 djm 1741: .Rs
1.329 jmc 1742: .%A M. Friedl
1743: .%A N. Provos
1744: .%A W. Simpson
1745: .%D March 2006
1.258 djm 1746: .%R RFC 4419
1.329 jmc 1747: .%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
1.266 markus 1748: .Re
1.329 jmc 1749: .Pp
1.266 markus 1750: .Rs
1.329 jmc 1751: .%A J. Galbraith
1752: .%A R. Thayer
1753: .%D November 2006
1.266 markus 1754: .%R RFC 4716
1.329 jmc 1755: .%T The Secure Shell (SSH) Public Key File Format
1.313 djm 1756: .Re
1.329 jmc 1757: .Pp
1.313 djm 1758: .Rs
1.329 jmc 1759: .%A D. Stebila
1760: .%A J. Green
1761: .%D December 2009
1.313 djm 1762: .%R RFC 5656
1.329 jmc 1763: .%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
1.274 grunk 1764: .Re
1.329 jmc 1765: .Pp
1.274 grunk 1766: .Rs
1767: .%A A. Perrig
1768: .%A D. Song
1769: .%D 1999
1.329 jmc 1770: .%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
1771: .%T Hash Visualization: a New Technique to improve Real-World Security
1.106 markus 1772: .Re
1.173 jmc 1773: .Sh AUTHORS
1774: OpenSSH is a derivative of the original and free
1775: ssh 1.2.12 release by Tatu Ylonen.
1776: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1777: Theo de Raadt and Dug Song
1778: removed many bugs, re-added newer features and
1779: created OpenSSH.
1780: Markus Friedl contributed the support for SSH
1781: protocol versions 1.5 and 2.0.
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