Annotation of src/usr.bin/ssh/ssh.1, Revision 1.430
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: .\"
1.430 ! naddy 36: .\" $OpenBSD: ssh.1,v 1.429 2022/02/06 00:29:03 jsg Exp $
! 37: .Dd $Mdocdate: February 6 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
162: option.
1.360 millert 163: .Pp
1.218 jmc 164: .It Fl c Ar cipher_spec
165: Selects the cipher specification for encrypting the session.
166: .Ar cipher_spec
167: is a comma-separated list of ciphers
168: listed in order of preference.
1.283 jmc 169: See the
170: .Cm Ciphers
1.307 dtucker 171: keyword in
172: .Xr ssh_config 5
173: for more information.
1.360 millert 174: .Pp
1.218 jmc 175: .It Fl D Xo
176: .Sm off
177: .Oo Ar bind_address : Oc
178: .Ar port
179: .Sm on
180: .Xc
181: Specifies a local
182: .Dq dynamic
183: application-level port forwarding.
184: This works by allocating a socket to listen to
185: .Ar port
186: on the local side, optionally bound to the specified
187: .Ar bind_address .
188: Whenever a connection is made to this port, the
189: connection is forwarded over the secure channel, and the application
190: protocol is then used to determine where to connect to from the
191: remote machine.
192: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.107 markus 193: .Nm
1.218 jmc 194: will act as a SOCKS server.
195: Only root can forward privileged ports.
196: Dynamic port forwardings can also be specified in the configuration file.
1.49 markus 197: .Pp
1.308 djm 198: IPv6 addresses can be specified by enclosing the address in square brackets.
1.218 jmc 199: Only the superuser can forward privileged ports.
200: By default, the local port is bound in accordance with the
201: .Cm GatewayPorts
202: setting.
203: However, an explicit
204: .Ar bind_address
205: may be used to bind the connection to a specific address.
206: The
207: .Ar bind_address
208: of
209: .Dq localhost
210: indicates that the listening port be bound for local use only, while an
211: empty address or
212: .Sq *
213: indicates that the port should be available from all interfaces.
1.360 millert 214: .Pp
1.331 dtucker 215: .It Fl E Ar log_file
216: Append debug logs to
217: .Ar log_file
218: instead of standard error.
1.360 millert 219: .Pp
1.229 jmc 220: .It Fl e Ar escape_char
1.218 jmc 221: Sets the escape character for sessions with a pty (default:
222: .Ql ~ ) .
223: The escape character is only recognized at the beginning of a line.
224: The escape character followed by a dot
225: .Pq Ql \&.
226: closes the connection;
227: followed by control-Z suspends the connection;
228: and followed by itself sends the escape character once.
229: Setting the character to
1.2 deraadt 230: .Dq none
1.218 jmc 231: disables any escapes and makes the session fully transparent.
1.360 millert 232: .Pp
1.218 jmc 233: .It Fl F Ar configfile
234: Specifies an alternative per-user configuration file.
235: If a configuration file is given on the command line,
236: the system-wide configuration file
237: .Pq Pa /etc/ssh/ssh_config
238: will be ignored.
239: The default for the per-user configuration file is
240: .Pa ~/.ssh/config .
1.411 naddy 241: If set to
242: .Dq none ,
243: no configuration files will be read.
1.360 millert 244: .Pp
1.218 jmc 245: .It Fl f
246: Requests
247: .Nm
248: to go to background just before command execution.
249: This is useful if
1.176 jmc 250: .Nm
1.218 jmc 251: is going to ask for passwords or passphrases, but the user
252: wants it in the background.
253: This implies
254: .Fl n .
255: The recommended way to start X11 programs at a remote site is with
256: something like
257: .Ic ssh -f host xterm .
1.277 djm 258: .Pp
259: If the
260: .Cm ExitOnForwardFailure
261: configuration option is set to
262: .Dq yes ,
263: then a client started with
264: .Fl f
265: will wait for all remote port forwards to be successfully established
266: before placing itself in the background.
1.424 djm 267: Refer to the description of
268: .Cm ForkAfterAuthentication
269: in
270: .Xr ssh_config 5
271: for details.
1.360 millert 272: .Pp
1.350 djm 273: .It Fl G
274: Causes
275: .Nm
276: to print its configuration after evaluating
277: .Cm Host
278: and
279: .Cm Match
280: blocks and exit.
1.360 millert 281: .Pp
1.218 jmc 282: .It Fl g
283: Allows remote hosts to connect to local forwarded ports.
1.346 djm 284: If used on a multiplexed connection, then this option must be specified
285: on the master process.
1.360 millert 286: .Pp
1.291 markus 287: .It Fl I Ar pkcs11
1.294 jmc 288: Specify the PKCS#11 shared library
1.176 jmc 289: .Nm
1.401 naddy 290: should use to communicate with a PKCS#11 token providing keys for user
291: authentication.
1.360 millert 292: .Pp
1.218 jmc 293: .It Fl i Ar identity_file
294: Selects a file from which the identity (private key) for
1.310 djm 295: public key authentication is read.
1.426 dtucker 296: You can also specify a public key file to use the corresponding
297: private key that is loaded in
298: .Xr ssh-agent 1
299: when the private key file is not present locally.
1.218 jmc 300: The default is
1.428 dtucker 301: .Pa ~/.ssh/id_rsa ,
1.343 naddy 302: .Pa ~/.ssh/id_ecdsa ,
1.404 naddy 303: .Pa ~/.ssh/id_ecdsa_sk ,
1.406 naddy 304: .Pa ~/.ssh/id_ed25519 ,
305: .Pa ~/.ssh/id_ed25519_sk
1.310 djm 306: and
1.428 dtucker 307: .Pa ~/.ssh/id_dsa .
1.218 jmc 308: Identity files may also be specified on
309: a per-host basis in the configuration file.
310: It is possible to have multiple
311: .Fl i
312: options (and multiple identities specified in
313: configuration files).
1.364 jmc 314: If no certificates have been explicitly specified by the
1.363 djm 315: .Cm CertificateFile
316: directive,
1.302 djm 317: .Nm
318: will also try to load certificate information from the filename obtained
319: by appending
320: .Pa -cert.pub
321: to identity filenames.
1.360 millert 322: .Pp
1.386 millert 323: .It Fl J Ar destination
1.375 djm 324: Connect to the target host by first making a
325: .Nm
1.386 millert 326: connection to the jump host described by
327: .Ar destination
1.376 jmc 328: and then establishing a TCP forwarding to the ultimate destination from
1.375 djm 329: there.
330: Multiple jump hops may be specified separated by comma characters.
331: This is a shortcut to specify a
332: .Cm ProxyJump
333: configuration directive.
1.400 djm 334: Note that configuration directives supplied on the command-line generally
335: apply to the destination host and not any specified jump hosts.
336: Use
337: .Pa ~/.ssh/config
338: to specify configuration for jump hosts.
1.375 djm 339: .Pp
1.269 djm 340: .It Fl K
341: Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
342: credentials to the server.
1.360 millert 343: .Pp
1.218 jmc 344: .It Fl k
345: Disables forwarding (delegation) of GSSAPI credentials to the server.
1.360 millert 346: .Pp
1.218 jmc 347: .It Fl L Xo
348: .Sm off
349: .Oo Ar bind_address : Oc
350: .Ar port : host : hostport
351: .Sm on
352: .Xc
1.360 millert 353: .It Fl L Xo
354: .Sm off
355: .Oo Ar bind_address : Oc
356: .Ar port : remote_socket
357: .Sm on
358: .Xc
359: .It Fl L Xo
360: .Sm off
361: .Ar local_socket : host : hostport
362: .Sm on
363: .Xc
364: .It Fl L Xo
365: .Sm off
366: .Ar local_socket : remote_socket
367: .Sm on
368: .Xc
369: Specifies that connections to the given TCP port or Unix socket on the local
370: (client) host are to be forwarded to the given host and port, or Unix socket,
371: on the remote side.
372: This works by allocating a socket to listen to either a TCP
1.218 jmc 373: .Ar port
374: on the local side, optionally bound to the specified
1.360 millert 375: .Ar bind_address ,
376: or to a Unix socket.
377: Whenever a connection is made to the local port or socket, the
1.218 jmc 378: connection is forwarded over the secure channel, and a connection is
1.360 millert 379: made to either
1.218 jmc 380: .Ar host
381: port
1.360 millert 382: .Ar hostport ,
383: or the Unix socket
384: .Ar remote_socket ,
1.218 jmc 385: from the remote machine.
1.360 millert 386: .Pp
1.218 jmc 387: Port forwardings can also be specified in the configuration file.
1.360 millert 388: Only the superuser can forward privileged ports.
1.308 djm 389: IPv6 addresses can be specified by enclosing the address in square brackets.
1.360 millert 390: .Pp
1.218 jmc 391: By default, the local port is bound in accordance with the
392: .Cm GatewayPorts
393: setting.
394: However, an explicit
395: .Ar bind_address
396: may be used to bind the connection to a specific address.
1.2 deraadt 397: The
1.218 jmc 398: .Ar bind_address
399: of
400: .Dq localhost
401: indicates that the listening port be bound for local use only, while an
402: empty address or
403: .Sq *
404: indicates that the port should be available from all interfaces.
1.360 millert 405: .Pp
1.218 jmc 406: .It Fl l Ar login_name
407: Specifies the user to log in as on the remote machine.
408: This also may be specified on a per-host basis in the configuration file.
1.360 millert 409: .Pp
1.218 jmc 410: .It Fl M
411: Places the
412: .Nm
413: client into
414: .Dq master
415: mode for connection sharing.
1.231 stevesk 416: Multiple
417: .Fl M
418: options places
419: .Nm
420: into
421: .Dq master
1.397 djm 422: mode but with confirmation required using
423: .Xr ssh-askpass 1
424: before each operation that changes the multiplexing state
425: (e.g. opening a new session).
1.218 jmc 426: Refer to the description of
427: .Cm ControlMaster
428: in
429: .Xr ssh_config 5
430: for details.
1.360 millert 431: .Pp
1.218 jmc 432: .It Fl m Ar mac_spec
1.369 jmc 433: A comma-separated list of MAC (message authentication code) algorithms,
434: specified in order of preference.
1.218 jmc 435: See the
436: .Cm MACs
437: keyword for more information.
1.360 millert 438: .Pp
1.218 jmc 439: .It Fl N
440: Do not execute a remote command.
1.369 jmc 441: This is useful for just forwarding ports.
1.422 djm 442: Refer to the description of
443: .Cm SessionType
444: in
445: .Xr ssh_config 5
446: for details.
1.360 millert 447: .Pp
1.218 jmc 448: .It Fl n
449: Redirects stdin from
450: .Pa /dev/null
451: (actually, prevents reading from stdin).
452: This must be used when
1.2 deraadt 453: .Nm
1.218 jmc 454: is run in the background.
455: A common trick is to use this to run X11 programs on a remote machine.
456: For example,
457: .Ic ssh -n shadows.cs.hut.fi emacs &
458: will start an emacs on shadows.cs.hut.fi, and the X11
459: connection will be automatically forwarded over an encrypted channel.
460: The
1.2 deraadt 461: .Nm
1.218 jmc 462: program will be put in the background.
463: (This does not work if
1.2 deraadt 464: .Nm
1.218 jmc 465: needs to ask for a password or passphrase; see also the
466: .Fl f
467: option.)
1.423 djm 468: Refer to the description of
469: .Cm StdinNull
470: in
471: .Xr ssh_config 5
472: for details.
1.360 millert 473: .Pp
1.218 jmc 474: .It Fl O Ar ctl_cmd
475: Control an active connection multiplexing master process.
476: When the
477: .Fl O
478: option is specified, the
479: .Ar ctl_cmd
480: argument is interpreted and passed to the master process.
481: Valid commands are:
482: .Dq check
1.305 markus 483: (check that the master process is running),
484: .Dq forward
1.318 jmc 485: (request forwardings without command execution),
1.323 okan 486: .Dq cancel
487: (cancel forwardings),
1.218 jmc 488: .Dq exit
1.318 jmc 489: (request the master to exit), and
1.317 djm 490: .Dq stop
491: (request the master to stop accepting further multiplexing requests).
1.360 millert 492: .Pp
1.218 jmc 493: .It Fl o Ar option
494: Can be used to give options in the format used in the configuration file.
495: This is useful for specifying options for which there is no separate
496: command-line flag.
497: For full details of the options listed below, and their possible values, see
498: .Xr ssh_config 5 .
1.2 deraadt 499: .Pp
1.218 jmc 500: .Bl -tag -width Ds -offset indent -compact
1.366 jcs 501: .It AddKeysToAgent
1.218 jmc 502: .It AddressFamily
503: .It BatchMode
504: .It BindAddress
1.338 djm 505: .It CanonicalDomains
1.339 djm 506: .It CanonicalizeFallbackLocal
507: .It CanonicalizeHostname
508: .It CanonicalizeMaxDots
509: .It CanonicalizePermittedCNAMEs
1.399 jmc 510: .It CASignatureAlgorithms
1.363 djm 511: .It CertificateFile
1.218 jmc 512: .It CheckHostIP
513: .It Ciphers
514: .It ClearAllForwardings
515: .It Compression
1.380 naddy 516: .It ConnectionAttempts
1.218 jmc 517: .It ConnectTimeout
518: .It ControlMaster
519: .It ControlPath
1.321 djm 520: .It ControlPersist
1.218 jmc 521: .It DynamicForward
522: .It EscapeChar
1.263 markus 523: .It ExitOnForwardFailure
1.353 jmc 524: .It FingerprintHash
1.424 djm 525: .It ForkAfterAuthentication
1.218 jmc 526: .It ForwardAgent
527: .It ForwardX11
1.321 djm 528: .It ForwardX11Timeout
1.218 jmc 529: .It ForwardX11Trusted
530: .It GatewayPorts
531: .It GlobalKnownHostsFile
532: .It GSSAPIAuthentication
533: .It GSSAPIDelegateCredentials
534: .It HashKnownHosts
535: .It Host
1.418 naddy 536: .It HostbasedAcceptedAlgorithms
1.218 jmc 537: .It HostbasedAuthentication
538: .It HostKeyAlgorithms
539: .It HostKeyAlias
1.403 jmc 540: .It Hostname
1.374 jmc 541: .It IdentitiesOnly
1.371 markus 542: .It IdentityAgent
1.218 jmc 543: .It IdentityFile
1.316 jmc 544: .It IPQoS
1.321 djm 545: .It KbdInteractiveAuthentication
1.218 jmc 546: .It KbdInteractiveDevices
1.314 jmc 547: .It KexAlgorithms
1.415 djm 548: .It KnownHostsCommand
1.218 jmc 549: .It LocalCommand
550: .It LocalForward
551: .It LogLevel
552: .It MACs
1.337 jmc 553: .It Match
1.218 jmc 554: .It NoHostAuthenticationForLocalhost
555: .It NumberOfPasswordPrompts
556: .It PasswordAuthentication
557: .It PermitLocalCommand
1.419 markus 558: .It PermitRemoteOpen
1.291 markus 559: .It PKCS11Provider
1.218 jmc 560: .It Port
561: .It PreferredAuthentications
562: .It ProxyCommand
1.375 djm 563: .It ProxyJump
1.336 jmc 564: .It ProxyUseFdpass
1.416 dtucker 565: .It PubkeyAcceptedAlgorithms
1.218 jmc 566: .It PubkeyAuthentication
1.251 dtucker 567: .It RekeyLimit
1.382 bluhm 568: .It RemoteCommand
1.218 jmc 569: .It RemoteForward
1.319 jmc 570: .It RequestTTY
1.218 jmc 571: .It SendEnv
572: .It ServerAliveInterval
573: .It ServerAliveCountMax
1.422 djm 574: .It SessionType
1.395 jmc 575: .It SetEnv
1.423 djm 576: .It StdinNull
1.347 jmc 577: .It StreamLocalBindMask
578: .It StreamLocalBindUnlink
1.218 jmc 579: .It StrictHostKeyChecking
580: .It TCPKeepAlive
581: .It Tunnel
582: .It TunnelDevice
1.354 djm 583: .It UpdateHostKeys
1.218 jmc 584: .It User
585: .It UserKnownHostsFile
586: .It VerifyHostKeyDNS
1.276 jmc 587: .It VisualHostKey
1.218 jmc 588: .It XAuthLocation
589: .El
1.360 millert 590: .Pp
1.218 jmc 591: .It Fl p Ar port
592: Port to connect to on the remote host.
593: This can be specified on a
594: per-host basis in the configuration file.
1.360 millert 595: .Pp
1.362 djm 596: .It Fl Q Ar query_option
1.425 jmc 597: Queries for the algorithms supported by one of the following features:
1.341 deraadt 598: .Ar cipher
1.332 djm 599: (supported symmetric ciphers),
1.341 deraadt 600: .Ar cipher-auth
1.340 djm 601: (supported symmetric ciphers that support authenticated encryption),
1.398 djm 602: .Ar help
603: (supported query terms for use with the
604: .Fl Q
605: flag),
1.341 deraadt 606: .Ar mac
1.332 djm 607: (supported message integrity codes),
1.341 deraadt 608: .Ar kex
1.332 djm 609: (key exchange algorithms),
1.341 deraadt 610: .Ar key
1.362 djm 611: (key types),
612: .Ar key-cert
613: (certificate key types),
614: .Ar key-plain
1.398 djm 615: (non-certificate key types),
1.410 dtucker 616: .Ar key-sig
617: (all key types and signature algorithms),
1.356 djm 618: .Ar protocol-version
1.398 djm 619: (supported SSH protocol versions), and
620: .Ar sig
621: (supported signature algorithms).
1.410 dtucker 622: Alternatively, any keyword from
623: .Xr ssh_config 5
624: or
625: .Xr sshd_config 5
626: that takes an algorithm list may be used as an alias for the corresponding
627: query_option.
1.360 millert 628: .Pp
1.218 jmc 629: .It Fl q
630: Quiet mode.
1.271 djm 631: Causes most warning and diagnostic messages to be suppressed.
1.360 millert 632: .Pp
1.218 jmc 633: .It Fl R Xo
634: .Sm off
635: .Oo Ar bind_address : Oc
636: .Ar port : host : hostport
637: .Sm on
638: .Xc
1.360 millert 639: .It Fl R Xo
640: .Sm off
641: .Oo Ar bind_address : Oc
642: .Ar port : local_socket
643: .Sm on
644: .Xc
645: .It Fl R Xo
646: .Sm off
647: .Ar remote_socket : host : hostport
648: .Sm on
649: .Xc
650: .It Fl R Xo
651: .Sm off
652: .Ar remote_socket : local_socket
653: .Sm on
654: .Xc
1.384 markus 655: .It Fl R Xo
656: .Sm off
657: .Oo Ar bind_address : Oc
658: .Ar port
659: .Sm on
660: .Xc
1.360 millert 661: Specifies that connections to the given TCP port or Unix socket on the remote
1.384 markus 662: (server) host are to be forwarded to the local side.
663: .Pp
1.360 millert 664: This works by allocating a socket to listen to either a TCP
1.218 jmc 665: .Ar port
1.360 millert 666: or to a Unix socket on the remote side.
667: Whenever a connection is made to this port or Unix socket, the
668: connection is forwarded over the secure channel, and a connection
1.384 markus 669: is made from the local machine to either an explicit destination specified by
1.218 jmc 670: .Ar host
671: port
1.360 millert 672: .Ar hostport ,
673: or
674: .Ar local_socket ,
1.384 markus 675: or, if no explicit destination was specified,
676: .Nm
677: will act as a SOCKS 4/5 proxy and forward connections to the destinations
678: requested by the remote SOCKS client.
1.2 deraadt 679: .Pp
1.218 jmc 680: Port forwardings can also be specified in the configuration file.
681: Privileged ports can be forwarded only when
682: logging in as root on the remote machine.
1.324 jmc 683: IPv6 addresses can be specified by enclosing the address in square brackets.
1.194 jakob 684: .Pp
1.360 millert 685: By default, TCP listening sockets on the server will be bound to the loopback
1.218 jmc 686: interface only.
1.280 tobias 687: This may be overridden by specifying a
1.218 jmc 688: .Ar bind_address .
689: An empty
690: .Ar bind_address ,
691: or the address
692: .Ql * ,
693: indicates that the remote socket should listen on all interfaces.
694: Specifying a remote
695: .Ar bind_address
696: will only succeed if the server's
697: .Cm GatewayPorts
698: option is enabled (see
699: .Xr sshd_config 5 ) .
1.281 djm 700: .Pp
701: If the
702: .Ar port
703: argument is
1.282 djm 704: .Ql 0 ,
1.281 djm 705: the listen port will be dynamically allocated on the server and reported
706: to the client at run time.
1.305 markus 707: When used together with
1.430 ! naddy 708: .Ic -O forward ,
1.305 markus 709: the allocated port will be printed to the standard output.
1.360 millert 710: .Pp
1.218 jmc 711: .It Fl S Ar ctl_path
1.304 jmc 712: Specifies the location of a control socket for connection sharing,
1.303 djm 713: or the string
714: .Dq none
715: to disable connection sharing.
1.218 jmc 716: Refer to the description of
717: .Cm ControlPath
718: and
719: .Cm ControlMaster
720: in
721: .Xr ssh_config 5
722: for details.
1.360 millert 723: .Pp
1.218 jmc 724: .It Fl s
725: May be used to request invocation of a subsystem on the remote system.
1.369 jmc 726: Subsystems facilitate the use of SSH
727: as a secure transport for other applications (e.g.\&
1.218 jmc 728: .Xr sftp 1 ) .
729: The subsystem is specified as the remote command.
1.422 djm 730: Refer to the description of
731: .Cm SessionType
732: in
733: .Xr ssh_config 5
734: for details.
1.360 millert 735: .Pp
1.218 jmc 736: .It Fl T
1.357 dtucker 737: Disable pseudo-terminal allocation.
1.360 millert 738: .Pp
1.218 jmc 739: .It Fl t
1.357 dtucker 740: Force pseudo-terminal allocation.
1.218 jmc 741: This can be used to execute arbitrary
742: screen-based programs on a remote machine, which can be very useful,
1.257 jmc 743: e.g. when implementing menu services.
1.218 jmc 744: Multiple
745: .Fl t
746: options force tty allocation, even if
1.194 jakob 747: .Nm
1.218 jmc 748: has no local tty.
1.360 millert 749: .Pp
1.218 jmc 750: .It Fl V
751: Display the version number and exit.
1.360 millert 752: .Pp
1.218 jmc 753: .It Fl v
754: Verbose mode.
755: Causes
1.176 jmc 756: .Nm
1.218 jmc 757: to print debugging messages about its progress.
758: This is helpful in
759: debugging connection, authentication, and configuration problems.
760: Multiple
761: .Fl v
762: options increase the verbosity.
763: The maximum is 3.
1.360 millert 764: .Pp
1.290 dtucker 765: .It Fl W Ar host : Ns Ar port
766: Requests that standard input and output on the client be forwarded to
767: .Ar host
768: on
769: .Ar port
770: over the secure channel.
771: Implies
772: .Fl N ,
773: .Fl T ,
774: .Cm ExitOnForwardFailure
775: and
1.373 jmc 776: .Cm ClearAllForwardings ,
777: though these can be overridden in the configuration file or using
1.372 dtucker 778: .Fl o
779: command line options.
1.360 millert 780: .Pp
1.261 stevesk 781: .It Fl w Xo
782: .Ar local_tun Ns Op : Ns Ar remote_tun
783: .Xc
784: Requests
785: tunnel
786: device forwarding with the specified
1.218 jmc 787: .Xr tun 4
1.261 stevesk 788: devices between the client
789: .Pq Ar local_tun
790: and the server
791: .Pq Ar remote_tun .
792: .Pp
1.228 jmc 793: The devices may be specified by numerical ID or the keyword
794: .Dq any ,
795: which uses the next available tunnel device.
1.261 stevesk 796: If
797: .Ar remote_tun
798: is not specified, it defaults to
799: .Dq any .
1.228 jmc 800: See also the
1.218 jmc 801: .Cm Tunnel
1.261 stevesk 802: and
803: .Cm TunnelDevice
804: directives in
1.218 jmc 805: .Xr ssh_config 5 .
1.393 djm 806: .Pp
1.261 stevesk 807: If the
808: .Cm Tunnel
1.393 djm 809: directive is unset, it will be set to the default tunnel mode, which is
1.261 stevesk 810: .Dq point-to-point .
1.393 djm 811: If a different
812: .Cm Tunnel
813: forwarding mode it desired, then it should be specified before
814: .Fl w .
1.360 millert 815: .Pp
1.218 jmc 816: .It Fl X
817: Enables X11 forwarding.
1.54 markus 818: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 819: .Pp
1.218 jmc 820: X11 forwarding should be enabled with caution.
1.168 jmc 821: Users with the ability to bypass file permissions on the remote host
1.218 jmc 822: (for the user's X authorization database)
823: can access the local X11 display through the forwarded connection.
824: An attacker may then be able to perform activities such as keystroke monitoring.
825: .Pp
826: For this reason, X11 forwarding is subjected to X11 SECURITY extension
827: restrictions by default.
1.429 jsg 828: Refer to the
1.218 jmc 829: .Nm
830: .Fl Y
831: option and the
832: .Cm ForwardX11Trusted
833: directive in
834: .Xr ssh_config 5
835: for more information.
1.360 millert 836: .Pp
1.218 jmc 837: .It Fl x
838: Disables X11 forwarding.
1.360 millert 839: .Pp
1.218 jmc 840: .It Fl Y
841: Enables trusted X11 forwarding.
842: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
843: controls.
1.360 millert 844: .Pp
1.278 djm 845: .It Fl y
846: Send log information using the
847: .Xr syslog 3
848: system module.
849: By default this information is sent to stderr.
1.218 jmc 850: .El
1.224 jmc 851: .Pp
852: .Nm
853: may additionally obtain configuration data from
854: a per-user configuration file and a system-wide configuration file.
855: The file format and configuration options are described in
856: .Xr ssh_config 5 .
1.222 jmc 857: .Sh AUTHENTICATION
1.377 djm 858: The OpenSSH SSH client supports SSH protocol 2.
1.222 jmc 859: .Pp
860: The methods available for authentication are:
1.260 jmc 861: GSSAPI-based authentication,
1.222 jmc 862: host-based authentication,
863: public key authentication,
1.421 dtucker 864: keyboard-interactive authentication,
1.222 jmc 865: and password authentication.
866: Authentication methods are tried in the order specified above,
1.369 jmc 867: though
868: .Cm PreferredAuthentications
869: can be used to change the default order.
1.222 jmc 870: .Pp
871: Host-based authentication works as follows:
1.218 jmc 872: If the machine the user logs in from is listed in
873: .Pa /etc/hosts.equiv
874: or
875: .Pa /etc/shosts.equiv
1.412 djm 876: on the remote machine, the user is non-root and the user names are
1.218 jmc 877: the same on both sides, or if the files
878: .Pa ~/.rhosts
879: or
880: .Pa ~/.shosts
881: exist in the user's home directory on the
882: remote machine and contain a line containing the name of the client
883: machine and the name of the user on that machine, the user is
1.222 jmc 884: considered for login.
885: Additionally, the server
886: .Em must
887: be able to verify the client's
888: host key (see the description of
1.218 jmc 889: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 890: and
1.222 jmc 891: .Pa ~/.ssh/known_hosts ,
892: below)
893: for login to be permitted.
1.218 jmc 894: This authentication method closes security holes due to IP
1.222 jmc 895: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 896: [Note to the administrator:
897: .Pa /etc/hosts.equiv ,
898: .Pa ~/.rhosts ,
899: and the rlogin/rsh protocol in general, are inherently insecure and should be
900: disabled if security is desired.]
1.189 dtucker 901: .Pp
1.222 jmc 902: Public key authentication works as follows:
903: The scheme is based on public-key cryptography,
904: using cryptosystems
905: where encryption and decryption are done using separate keys,
906: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 907: The idea is that each user creates a public/private
908: key pair for authentication purposes.
909: The server knows the public key, and only the user knows the private key.
1.222 jmc 910: .Nm
911: implements public key authentication protocol automatically,
1.349 sobrado 912: using one of the DSA, ECDSA, Ed25519 or RSA algorithms.
1.333 jmc 913: The HISTORY section of
1.222 jmc 914: .Xr ssl 8
1.311 jmc 915: contains a brief discussion of the DSA and RSA algorithms.
1.210 djm 916: .Pp
1.218 jmc 917: The file
918: .Pa ~/.ssh/authorized_keys
919: lists the public keys that are permitted for logging in.
920: When the user logs in, the
1.2 deraadt 921: .Nm
1.218 jmc 922: program tells the server which key pair it would like to use for
923: authentication.
1.222 jmc 924: The client proves that it has access to the private key
925: and the server checks that the corresponding public key
926: is authorized to accept the account.
1.383 djm 927: .Pp
928: The server may inform the client of errors that prevented public key
929: authentication from succeeding after authentication completes using a
930: different method.
931: These may be viewed by increasing the
932: .Cm LogLevel
933: to
934: .Cm DEBUG
935: or higher (e.g. by using the
936: .Fl v
937: flag).
1.218 jmc 938: .Pp
1.420 dtucker 939: The user creates their key pair by running
1.218 jmc 940: .Xr ssh-keygen 1 .
941: This stores the private key in
1.222 jmc 942: .Pa ~/.ssh/id_dsa
1.369 jmc 943: (DSA),
1.310 djm 944: .Pa ~/.ssh/id_ecdsa
1.369 jmc 945: (ECDSA),
1.404 naddy 946: .Pa ~/.ssh/id_ecdsa_sk
1.409 naddy 947: (authenticator-hosted ECDSA),
1.343 naddy 948: .Pa ~/.ssh/id_ed25519
1.369 jmc 949: (Ed25519),
1.406 naddy 950: .Pa ~/.ssh/id_ed25519_sk
1.409 naddy 951: (authenticator-hosted Ed25519),
1.222 jmc 952: or
953: .Pa ~/.ssh/id_rsa
1.369 jmc 954: (RSA)
1.218 jmc 955: and stores the public key in
1.222 jmc 956: .Pa ~/.ssh/id_dsa.pub
1.369 jmc 957: (DSA),
1.310 djm 958: .Pa ~/.ssh/id_ecdsa.pub
1.369 jmc 959: (ECDSA),
1.404 naddy 960: .Pa ~/.ssh/id_ecdsa_sk.pub
1.409 naddy 961: (authenticator-hosted ECDSA),
1.343 naddy 962: .Pa ~/.ssh/id_ed25519.pub
1.369 jmc 963: (Ed25519),
1.406 naddy 964: .Pa ~/.ssh/id_ed25519_sk.pub
1.409 naddy 965: (authenticator-hosted Ed25519),
1.222 jmc 966: or
967: .Pa ~/.ssh/id_rsa.pub
1.369 jmc 968: (RSA)
1.218 jmc 969: in the user's home directory.
1.222 jmc 970: The user should then copy the public key
1.218 jmc 971: to
972: .Pa ~/.ssh/authorized_keys
1.420 dtucker 973: in their home directory on the remote machine.
1.222 jmc 974: The
1.218 jmc 975: .Pa authorized_keys
976: file corresponds to the conventional
977: .Pa ~/.rhosts
978: file, and has one key
1.222 jmc 979: per line, though the lines can be very long.
1.218 jmc 980: After this, the user can log in without giving the password.
981: .Pp
1.301 jmc 982: A variation on public key authentication
983: is available in the form of certificate authentication:
984: instead of a set of public/private keys,
985: signed certificates are used.
986: This has the advantage that a single trusted certification authority
987: can be used in place of many public/private keys.
1.333 jmc 988: See the CERTIFICATES section of
1.301 jmc 989: .Xr ssh-keygen 1
990: for more information.
991: .Pp
992: The most convenient way to use public key or certificate authentication
993: may be with an authentication agent.
1.218 jmc 994: See
995: .Xr ssh-agent 1
1.366 jcs 996: and (optionally) the
997: .Cm AddKeysToAgent
998: directive in
999: .Xr ssh_config 5
1.218 jmc 1000: for more information.
1001: .Pp
1.421 dtucker 1002: Keyboard-interactive authentication works as follows:
1.222 jmc 1003: The server sends an arbitrary
1004: .Qq challenge
1.421 dtucker 1005: text and prompts for a response, possibly multiple times.
1006: Examples of keyboard-interactive authentication include
1.335 jmc 1007: .Bx
1008: Authentication (see
1.222 jmc 1009: .Xr login.conf 5 )
1.335 jmc 1010: and PAM (some
1011: .Pf non- Ox
1012: systems).
1.222 jmc 1013: .Pp
1014: Finally, if other authentication methods fail,
1.218 jmc 1015: .Nm
1016: prompts the user for a password.
1017: The password is sent to the remote
1018: host for checking; however, since all communications are encrypted,
1019: the password cannot be seen by someone listening on the network.
1.232 jmc 1020: .Pp
1021: .Nm
1022: automatically maintains and checks a database containing
1023: identification for all hosts it has ever been used with.
1024: Host keys are stored in
1025: .Pa ~/.ssh/known_hosts
1026: in the user's home directory.
1027: Additionally, the file
1028: .Pa /etc/ssh/ssh_known_hosts
1029: is automatically checked for known hosts.
1030: Any new hosts are automatically added to the user's file.
1031: If a host's identification ever changes,
1032: .Nm
1033: warns about this and disables password authentication to prevent
1034: server spoofing or man-in-the-middle attacks,
1035: which could otherwise be used to circumvent the encryption.
1036: The
1037: .Cm StrictHostKeyChecking
1038: option can be used to control logins to machines whose
1039: host key is not known or has changed.
1040: .Pp
1.218 jmc 1041: When the user's identity has been accepted by the server, the server
1.357 dtucker 1042: either executes the given command in a non-interactive session or,
1043: if no command has been specified, logs into the machine and gives
1044: the user a normal shell as an interactive session.
1.218 jmc 1045: All communication with
1046: the remote command or shell will be automatically encrypted.
1047: .Pp
1.430 ! naddy 1048: If an interactive session is requested,
1.357 dtucker 1049: .Nm
1050: by default will only request a pseudo-terminal (pty) for interactive
1051: sessions when the client has one.
1052: The flags
1053: .Fl T
1054: and
1055: .Fl t
1056: can be used to override this behaviour.
1057: .Pp
1.430 ! naddy 1058: If a pseudo-terminal has been allocated, the
1.218 jmc 1059: user may use the escape characters noted below.
1060: .Pp
1.357 dtucker 1061: If no pseudo-terminal has been allocated,
1.218 jmc 1062: the session is transparent and can be used to reliably transfer binary data.
1063: On most systems, setting the escape character to
1064: .Dq none
1065: will also make the session transparent even if a tty is used.
1066: .Pp
1067: The session terminates when the command or shell on the remote
1.247 jmc 1068: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 1069: .Sh ESCAPE CHARACTERS
1.218 jmc 1070: When a pseudo-terminal has been requested,
1.2 deraadt 1071: .Nm
1.218 jmc 1072: supports a number of functions through the use of an escape character.
1073: .Pp
1074: A single tilde character can be sent as
1075: .Ic ~~
1076: or by following the tilde by a character other than those described below.
1077: The escape character must always follow a newline to be interpreted as
1078: special.
1079: The escape character can be changed in configuration files using the
1080: .Cm EscapeChar
1081: configuration directive or on the command line by the
1082: .Fl e
1083: option.
1084: .Pp
1085: The supported escapes (assuming the default
1086: .Ql ~ )
1087: are:
1088: .Bl -tag -width Ds
1089: .It Cm ~.
1090: Disconnect.
1091: .It Cm ~^Z
1092: Background
1.234 jmc 1093: .Nm .
1.218 jmc 1094: .It Cm ~#
1095: List forwarded connections.
1096: .It Cm ~&
1097: Background
1.2 deraadt 1098: .Nm
1.218 jmc 1099: at logout when waiting for forwarded connection / X11 sessions to terminate.
1100: .It Cm ~?
1101: Display a list of escape characters.
1102: .It Cm ~B
1103: Send a BREAK to the remote system
1.369 jmc 1104: (only useful if the peer supports it).
1.218 jmc 1105: .It Cm ~C
1106: Open command line.
1107: Currently this allows the addition of port forwardings using the
1.279 stevesk 1108: .Fl L ,
1109: .Fl R
1.218 jmc 1110: and
1.279 stevesk 1111: .Fl D
1.225 jmc 1112: options (see above).
1.322 markus 1113: It also allows the cancellation of existing port-forwardings
1114: with
1.262 stevesk 1115: .Sm off
1.322 markus 1116: .Fl KL Oo Ar bind_address : Oc Ar port
1.262 stevesk 1117: .Sm on
1.322 markus 1118: for local,
1119: .Sm off
1120: .Fl KR Oo Ar bind_address : Oc Ar port
1121: .Sm on
1122: for remote and
1123: .Sm off
1124: .Fl KD Oo Ar bind_address : Oc Ar port
1125: .Sm on
1126: for dynamic port-forwardings.
1.218 jmc 1127: .Ic !\& Ns Ar command
1128: allows the user to execute a local command if the
1129: .Ic PermitLocalCommand
1130: option is enabled in
1.176 jmc 1131: .Xr ssh_config 5 .
1.218 jmc 1132: Basic help is available, using the
1133: .Fl h
1134: option.
1135: .It Cm ~R
1136: Request rekeying of the connection
1.369 jmc 1137: (only useful if the peer supports it).
1.327 dtucker 1138: .It Cm ~V
1139: Decrease the verbosity
1140: .Pq Ic LogLevel
1141: when errors are being written to stderr.
1142: .It Cm ~v
1.328 jmc 1143: Increase the verbosity
1.327 dtucker 1144: .Pq Ic LogLevel
1145: when errors are being written to stderr.
1.176 jmc 1146: .El
1.246 jmc 1147: .Sh TCP FORWARDING
1.402 jmc 1148: Forwarding of arbitrary TCP connections over a secure channel
1149: can be specified either on the command line or in a configuration file.
1.246 jmc 1150: One possible application of TCP forwarding is a secure connection to a
1151: mail server; another is going through firewalls.
1152: .Pp
1.402 jmc 1153: In the example below, we look at encrypting communication for an IRC client,
1154: even though the IRC server it connects to does not directly
1155: support encrypted communication.
1.246 jmc 1156: This works as follows:
1157: the user connects to the remote host using
1158: .Nm ,
1.402 jmc 1159: specifying the ports to be used to forward the connection.
1160: After that it is possible to start the program locally,
1.246 jmc 1161: and
1162: .Nm
1.402 jmc 1163: will encrypt and forward the connection to the remote server.
1.246 jmc 1164: .Pp
1.402 jmc 1165: The following example tunnels an IRC session from the client
1166: to an IRC server at
1.246 jmc 1167: .Dq server.example.com ,
1168: joining channel
1169: .Dq #users ,
1170: nickname
1171: .Dq pinky ,
1.402 jmc 1172: using the standard IRC port, 6667:
1173: .Bd -literal -offset 4n
1174: $ ssh -f -L 6667:localhost:6667 server.example.com sleep 10
1175: $ irc -c '#users' pinky IRC/127.0.0.1
1176: .Ed
1.246 jmc 1177: .Pp
1178: The
1179: .Fl f
1180: option backgrounds
1181: .Nm
1182: and the remote command
1183: .Dq sleep 10
1184: is specified to allow an amount of time
1185: (10 seconds, in the example)
1.402 jmc 1186: to start the program which is going to use the tunnel.
1.246 jmc 1187: If no connections are made within the time specified,
1188: .Nm
1189: will exit.
1190: .Sh X11 FORWARDING
1.218 jmc 1191: If the
1192: .Cm ForwardX11
1193: variable is set to
1194: .Dq yes
1195: (or see the description of the
1.227 jmc 1196: .Fl X ,
1197: .Fl x ,
1.218 jmc 1198: and
1.227 jmc 1199: .Fl Y
1.226 jmc 1200: options above)
1.218 jmc 1201: and the user is using X11 (the
1202: .Ev DISPLAY
1203: environment variable is set), the connection to the X11 display is
1204: automatically forwarded to the remote side in such a way that any X11
1205: programs started from the shell (or command) will go through the
1206: encrypted channel, and the connection to the real X server will be made
1.176 jmc 1207: from the local machine.
1.218 jmc 1208: The user should not manually set
1209: .Ev DISPLAY .
1210: Forwarding of X11 connections can be
1211: configured on the command line or in configuration files.
1212: .Pp
1213: The
1214: .Ev DISPLAY
1215: value set by
1216: .Nm
1217: will point to the server machine, but with a display number greater than zero.
1218: This is normal, and happens because
1219: .Nm
1220: creates a
1221: .Dq proxy
1222: X server on the server machine for forwarding the
1223: connections over the encrypted channel.
1.200 djm 1224: .Pp
1.218 jmc 1225: .Nm
1226: will also automatically set up Xauthority data on the server machine.
1227: For this purpose, it will generate a random authorization cookie,
1228: store it in Xauthority on the server, and verify that any forwarded
1229: connections carry this cookie and replace it by the real cookie when
1230: the connection is opened.
1231: The real authentication cookie is never
1232: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1233: .Pp
1.218 jmc 1234: If the
1235: .Cm ForwardAgent
1236: variable is set to
1237: .Dq yes
1238: (or see the description of the
1239: .Fl A
1.191 djm 1240: and
1.218 jmc 1241: .Fl a
1.226 jmc 1242: options above) and
1.218 jmc 1243: the user is using an authentication agent, the connection to the agent
1244: is automatically forwarded to the remote side.
1.252 jmc 1245: .Sh VERIFYING HOST KEYS
1246: When connecting to a server for the first time,
1247: a fingerprint of the server's public key is presented to the user
1248: (unless the option
1249: .Cm StrictHostKeyChecking
1250: has been disabled).
1251: Fingerprints can be determined using
1252: .Xr ssh-keygen 1 :
1253: .Pp
1254: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1255: .Pp
1.274 grunk 1256: If the fingerprint is already known, it can be matched
1257: and the key can be accepted or rejected.
1.358 djm 1258: If only legacy (MD5) fingerprints for the server are available, the
1259: .Xr ssh-keygen 1
1260: .Fl E
1261: option may be used to downgrade the fingerprint algorithm to match.
1262: .Pp
1.274 grunk 1263: Because of the difficulty of comparing host keys
1.352 djm 1264: just by looking at fingerprint strings,
1.274 grunk 1265: there is also support to compare host keys visually,
1266: using
1267: .Em random art .
1268: By setting the
1.275 grunk 1269: .Cm VisualHostKey
1.274 grunk 1270: option to
1.275 grunk 1271: .Dq yes ,
1.274 grunk 1272: a small ASCII graphic gets displayed on every login to a server, no matter
1273: if the session itself is interactive or not.
1274: By learning the pattern a known server produces, a user can easily
1275: find out that the host key has changed when a completely different pattern
1276: is displayed.
1277: Because these patterns are not unambiguous however, a pattern that looks
1278: similar to the pattern remembered only gives a good probability that the
1279: host key is the same, not guaranteed proof.
1280: .Pp
1281: To get a listing of the fingerprints along with their random art for
1282: all known hosts, the following command line can be used:
1283: .Pp
1284: .Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1285: .Pp
1.252 jmc 1286: If the fingerprint is unknown,
1287: an alternative method of verification is available:
1288: SSH fingerprints verified by DNS.
1289: An additional resource record (RR),
1290: SSHFP,
1291: is added to a zonefile
1292: and the connecting client is able to match the fingerprint
1293: with that of the key presented.
1294: .Pp
1295: In this example, we are connecting a client to a server,
1296: .Dq host.example.com .
1297: The SSHFP resource records should first be added to the zonefile for
1298: host.example.com:
1299: .Bd -literal -offset indent
1.259 jakob 1300: $ ssh-keygen -r host.example.com.
1.252 jmc 1301: .Ed
1302: .Pp
1303: The output lines will have to be added to the zonefile.
1304: To check that the zone is answering fingerprint queries:
1305: .Pp
1306: .Dl $ dig -t SSHFP host.example.com
1307: .Pp
1308: Finally the client connects:
1309: .Bd -literal -offset indent
1310: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1311: [...]
1312: Matching host key fingerprint found in DNS.
1313: Are you sure you want to continue connecting (yes/no)?
1314: .Ed
1315: .Pp
1316: See the
1317: .Cm VerifyHostKeyDNS
1318: option in
1319: .Xr ssh_config 5
1320: for more information.
1.250 jmc 1321: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1322: .Nm
1323: contains support for Virtual Private Network (VPN) tunnelling
1324: using the
1325: .Xr tun 4
1326: network pseudo-device,
1327: allowing two networks to be joined securely.
1328: The
1329: .Xr sshd_config 5
1330: configuration option
1331: .Cm PermitTunnel
1332: controls whether the server supports this,
1333: and at what level (layer 2 or 3 traffic).
1334: .Pp
1335: The following example would connect client network 10.0.50.0/24
1.265 otto 1336: with remote network 10.0.99.0/24 using a point-to-point connection
1337: from 10.1.1.1 to 10.1.1.2,
1338: provided that the SSH server running on the gateway to the remote network,
1339: at 192.168.1.15, allows it.
1340: .Pp
1341: On the client:
1.250 jmc 1342: .Bd -literal -offset indent
1343: # ssh -f -w 0:1 192.168.1.15 true
1.265 otto 1344: # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1345: # route add 10.0.99.0/24 10.1.1.2
1346: .Ed
1347: .Pp
1348: On the server:
1349: .Bd -literal -offset indent
1350: # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1351: # route add 10.0.50.0/24 10.1.1.1
1.250 jmc 1352: .Ed
1353: .Pp
1354: Client access may be more finely tuned via the
1355: .Pa /root/.ssh/authorized_keys
1356: file (see below) and the
1357: .Cm PermitRootLogin
1358: server option.
1.255 jmc 1359: The following entry would permit connections on
1.250 jmc 1360: .Xr tun 4
1.255 jmc 1361: device 1 from user
1.250 jmc 1362: .Dq jane
1.255 jmc 1363: and on tun device 2 from user
1.250 jmc 1364: .Dq john ,
1365: if
1366: .Cm PermitRootLogin
1367: is set to
1368: .Dq forced-commands-only :
1369: .Bd -literal -offset 2n
1370: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1371: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1372: .Ed
1373: .Pp
1.264 ray 1374: Since an SSH-based setup entails a fair amount of overhead,
1.250 jmc 1375: it may be more suited to temporary setups,
1376: such as for wireless VPNs.
1377: More permanent VPNs are better provided by tools such as
1378: .Xr ipsecctl 8
1379: and
1380: .Xr isakmpd 8 .
1.2 deraadt 1381: .Sh ENVIRONMENT
1382: .Nm
1.1 deraadt 1383: will normally set the following environment variables:
1.237 jmc 1384: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1385: .It Ev DISPLAY
1386: The
1387: .Ev DISPLAY
1.40 aaron 1388: variable indicates the location of the X11 server.
1.44 aaron 1389: It is automatically set by
1.2 deraadt 1390: .Nm
1391: to point to a value of the form
1.233 jmc 1392: .Dq hostname:n ,
1393: where
1394: .Dq hostname
1395: indicates the host where the shell runs, and
1396: .Sq n
1397: is an integer \*(Ge 1.
1.40 aaron 1398: .Nm
1399: uses this special value to forward X11 connections over the secure
1400: channel.
1.107 markus 1401: The user should normally not set
1402: .Ev DISPLAY
1403: explicitly, as that
1.1 deraadt 1404: will render the X11 connection insecure (and will require the user to
1405: manually copy any required authorization cookies).
1.2 deraadt 1406: .It Ev HOME
1.1 deraadt 1407: Set to the path of the user's home directory.
1.2 deraadt 1408: .It Ev LOGNAME
1409: Synonym for
1.12 aaron 1410: .Ev USER ;
1411: set for compatibility with systems that use this variable.
1.2 deraadt 1412: .It Ev MAIL
1.129 stevesk 1413: Set to the path of the user's mailbox.
1.40 aaron 1414: .It Ev PATH
1.2 deraadt 1415: Set to the default
1416: .Ev PATH ,
1417: as specified when compiling
1.234 jmc 1418: .Nm .
1.118 markus 1419: .It Ev SSH_ASKPASS
1420: If
1421: .Nm
1422: needs a passphrase, it will read the passphrase from the current
1423: terminal if it was run from a terminal.
1424: If
1425: .Nm
1426: does not have a terminal associated with it but
1427: .Ev DISPLAY
1428: and
1429: .Ev SSH_ASKPASS
1430: are set, it will execute the program specified by
1431: .Ev SSH_ASKPASS
1432: and open an X11 window to read the passphrase.
1433: This is particularly useful when calling
1434: .Nm
1435: from a
1.196 jmc 1436: .Pa .xsession
1.118 markus 1437: or related script.
1438: (Note that on some machines it
1439: may be necessary to redirect the input from
1440: .Pa /dev/null
1441: to make this work.)
1.413 djm 1442: .It Ev SSH_ASKPASS_REQUIRE
1.414 jmc 1443: Allows further control over the use of an askpass program.
1.413 djm 1444: If this variable is set to
1445: .Dq never
1446: then
1447: .Nm
1448: will never attempt to use one.
1449: If it is set to
1450: .Dq prefer ,
1451: then
1452: .Nm
1453: will prefer to use the askpass program instead of the TTY when requesting
1454: passwords.
1455: Finally, if the variable is set to
1456: .Dq force ,
1457: then the askpass program will be used for all passphrase input regardless
1458: of whether
1459: .Ev DISPLAY
1460: is set.
1.18 markus 1461: .It Ev SSH_AUTH_SOCK
1.233 jmc 1462: Identifies the path of a
1463: .Ux Ns -domain
1464: socket used to communicate with the agent.
1.166 stevesk 1465: .It Ev SSH_CONNECTION
1466: Identifies the client and server ends of the connection.
1.40 aaron 1467: The variable contains
1.233 jmc 1468: four space-separated values: client IP address, client port number,
1469: server IP address, and server port number.
1.73 markus 1470: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1471: This variable contains the original command line if a forced command
1.73 markus 1472: is executed.
1473: It can be used to extract the original arguments.
1.2 deraadt 1474: .It Ev SSH_TTY
1.1 deraadt 1475: This is set to the name of the tty (path to the device) associated
1.40 aaron 1476: with the current shell or command.
1477: If the current session has no tty,
1.1 deraadt 1478: this variable is not set.
1.387 djm 1479: .It Ev SSH_TUNNEL
1480: Optionally set by
1481: .Xr sshd 8
1482: to contain the interface names assigned if tunnel forwarding was
1483: requested by the client.
1.385 djm 1484: .It Ev SSH_USER_AUTH
1485: Optionally set by
1486: .Xr sshd 8 ,
1487: this variable may contain a pathname to a file that lists the authentication
1488: methods successfully used when the session was established, including any
1489: public keys that were used.
1.2 deraadt 1490: .It Ev TZ
1.214 jmc 1491: This variable is set to indicate the present time zone if it
1.257 jmc 1492: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1493: on to new connections).
1.2 deraadt 1494: .It Ev USER
1.1 deraadt 1495: Set to the name of the user logging in.
1.2 deraadt 1496: .El
1497: .Pp
1.44 aaron 1498: Additionally,
1.2 deraadt 1499: .Nm
1.44 aaron 1500: reads
1.207 djm 1501: .Pa ~/.ssh/environment ,
1.2 deraadt 1502: and adds lines of the format
1503: .Dq VARNAME=value
1.233 jmc 1504: to the environment if the file exists and users are allowed to
1.161 marc 1505: change their environment.
1.176 jmc 1506: For more information, see the
1.161 marc 1507: .Cm PermitUserEnvironment
1.162 stevesk 1508: option in
1.161 marc 1509: .Xr sshd_config 5 .
1.2 deraadt 1510: .Sh FILES
1.236 jmc 1511: .Bl -tag -width Ds -compact
1.309 jmc 1512: .It Pa ~/.rhosts
1.240 jmc 1513: This file is used for host-based authentication (see above).
1.92 markus 1514: On some machines this file may need to be
1.240 jmc 1515: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1516: because
1.2 deraadt 1517: .Xr sshd 8
1.40 aaron 1518: reads it as root.
1519: Additionally, this file must be owned by the user,
1520: and must not have write permissions for anyone else.
1521: The recommended
1.1 deraadt 1522: permission for most machines is read/write for the user, and not
1523: accessible by others.
1.2 deraadt 1524: .Pp
1.309 jmc 1525: .It Pa ~/.shosts
1.240 jmc 1526: This file is used in exactly the same way as
1527: .Pa .rhosts ,
1528: but allows host-based authentication without permitting login with
1529: rlogin/rsh.
1.272 mcbride 1530: .Pp
1.309 jmc 1531: .It Pa ~/.ssh/
1.272 mcbride 1532: This directory is the default location for all user-specific configuration
1533: and authentication information.
1534: There is no general requirement to keep the entire contents of this directory
1535: secret, but the recommended permissions are read/write/execute for the user,
1536: and not accessible by others.
1.236 jmc 1537: .Pp
1.309 jmc 1538: .It Pa ~/.ssh/authorized_keys
1.349 sobrado 1539: Lists the public keys (DSA, ECDSA, Ed25519, RSA)
1.343 naddy 1540: that can be used for logging in as this user.
1.238 jmc 1541: The format of this file is described in the
1542: .Xr sshd 8
1543: manual page.
1544: This file is not highly sensitive, but the recommended
1545: permissions are read/write for the user, and not accessible by others.
1546: .Pp
1.309 jmc 1547: .It Pa ~/.ssh/config
1.238 jmc 1548: This is the per-user configuration file.
1549: The file format and configuration options are described in
1550: .Xr ssh_config 5 .
1551: Because of the potential for abuse, this file must have strict permissions:
1.334 djm 1552: read/write for the user, and not writable by others.
1.238 jmc 1553: .Pp
1.309 jmc 1554: .It Pa ~/.ssh/environment
1.239 jmc 1555: Contains additional definitions for environment variables; see
1556: .Sx ENVIRONMENT ,
1.238 jmc 1557: above.
1558: .Pp
1.309 jmc 1559: .It Pa ~/.ssh/id_dsa
1.310 djm 1560: .It Pa ~/.ssh/id_ecdsa
1.404 naddy 1561: .It Pa ~/.ssh/id_ecdsa_sk
1.343 naddy 1562: .It Pa ~/.ssh/id_ed25519
1.406 naddy 1563: .It Pa ~/.ssh/id_ed25519_sk
1.309 jmc 1564: .It Pa ~/.ssh/id_rsa
1.238 jmc 1565: Contains the private key for authentication.
1566: These files
1567: contain sensitive data and should be readable by the user but not
1568: accessible by others (read/write/execute).
1569: .Nm
1570: will simply ignore a private key file if it is accessible by others.
1571: It is possible to specify a passphrase when
1572: generating the key which will be used to encrypt the
1.389 djm 1573: sensitive part of this file using AES-128.
1.238 jmc 1574: .Pp
1.309 jmc 1575: .It Pa ~/.ssh/id_dsa.pub
1.310 djm 1576: .It Pa ~/.ssh/id_ecdsa.pub
1.404 naddy 1577: .It Pa ~/.ssh/id_ecdsa_sk.pub
1.343 naddy 1578: .It Pa ~/.ssh/id_ed25519.pub
1.406 naddy 1579: .It Pa ~/.ssh/id_ed25519_sk.pub
1.309 jmc 1580: .It Pa ~/.ssh/id_rsa.pub
1.238 jmc 1581: Contains the public key for authentication.
1582: These files are not
1583: sensitive and can (but need not) be readable by anyone.
1584: .Pp
1.309 jmc 1585: .It Pa ~/.ssh/known_hosts
1.244 jmc 1586: Contains a list of host keys for all hosts the user has logged into
1587: that are not already in the systemwide list of known host keys.
1.238 jmc 1588: See
1.244 jmc 1589: .Xr sshd 8
1590: for further details of the format of this file.
1.238 jmc 1591: .Pp
1.309 jmc 1592: .It Pa ~/.ssh/rc
1.238 jmc 1593: Commands in this file are executed by
1594: .Nm
1.245 jmc 1595: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1596: started.
1597: See the
1598: .Xr sshd 8
1599: manual page for more information.
1600: .Pp
1.309 jmc 1601: .It Pa /etc/hosts.equiv
1.240 jmc 1602: This file is for host-based authentication (see above).
1603: It should only be writable by root.
1.236 jmc 1604: .Pp
1.309 jmc 1605: .It Pa /etc/shosts.equiv
1.240 jmc 1606: This file is used in exactly the same way as
1607: .Pa hosts.equiv ,
1608: but allows host-based authentication without permitting login with
1609: rlogin/rsh.
1.236 jmc 1610: .Pp
1.238 jmc 1611: .It Pa /etc/ssh/ssh_config
1612: Systemwide configuration file.
1613: The file format and configuration options are described in
1614: .Xr ssh_config 5 .
1615: .Pp
1.309 jmc 1616: .It Pa /etc/ssh/ssh_host_key
1617: .It Pa /etc/ssh/ssh_host_dsa_key
1.310 djm 1618: .It Pa /etc/ssh/ssh_host_ecdsa_key
1.343 naddy 1619: .It Pa /etc/ssh/ssh_host_ed25519_key
1.309 jmc 1620: .It Pa /etc/ssh/ssh_host_rsa_key
1.325 dtucker 1621: These files contain the private parts of the host keys
1.245 jmc 1622: and are used for host-based authentication.
1.238 jmc 1623: .Pp
1.309 jmc 1624: .It Pa /etc/ssh/ssh_known_hosts
1.238 jmc 1625: Systemwide list of known host keys.
1626: This file should be prepared by the
1627: system administrator to contain the public host keys of all machines in the
1628: organization.
1.244 jmc 1629: It should be world-readable.
1630: See
1.238 jmc 1631: .Xr sshd 8
1.244 jmc 1632: for further details of the format of this file.
1.236 jmc 1633: .Pp
1.309 jmc 1634: .It Pa /etc/ssh/sshrc
1.1 deraadt 1635: Commands in this file are executed by
1.2 deraadt 1636: .Nm
1.245 jmc 1637: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1638: See the
1.2 deraadt 1639: .Xr sshd 8
1.1 deraadt 1640: manual page for more information.
1.58 itojun 1641: .El
1.312 jmc 1642: .Sh EXIT STATUS
1643: .Nm
1644: exits with the exit status of the remote command or with 255
1645: if an error occurred.
1.2 deraadt 1646: .Sh SEE ALSO
1647: .Xr scp 1 ,
1.83 djm 1648: .Xr sftp 1 ,
1.2 deraadt 1649: .Xr ssh-add 1 ,
1650: .Xr ssh-agent 1 ,
1651: .Xr ssh-keygen 1 ,
1.242 jmc 1652: .Xr ssh-keyscan 1 ,
1.250 jmc 1653: .Xr tun 4 ,
1.159 stevesk 1654: .Xr ssh_config 5 ,
1.160 naddy 1655: .Xr ssh-keysign 8 ,
1.87 itojun 1656: .Xr sshd 8
1.329 jmc 1657: .Sh STANDARDS
1.106 markus 1658: .Rs
1.329 jmc 1659: .%A S. Lehtinen
1660: .%A C. Lonvick
1661: .%D January 2006
1.256 jmc 1662: .%R RFC 4250
1.329 jmc 1663: .%T The Secure Shell (SSH) Protocol Assigned Numbers
1.256 jmc 1664: .Re
1.329 jmc 1665: .Pp
1.256 jmc 1666: .Rs
1.329 jmc 1667: .%A T. Ylonen
1668: .%A C. Lonvick
1669: .%D January 2006
1.256 jmc 1670: .%R RFC 4251
1.329 jmc 1671: .%T The Secure Shell (SSH) Protocol Architecture
1.256 jmc 1672: .Re
1.329 jmc 1673: .Pp
1.256 jmc 1674: .Rs
1.329 jmc 1675: .%A T. Ylonen
1676: .%A C. Lonvick
1677: .%D January 2006
1.256 jmc 1678: .%R RFC 4252
1.329 jmc 1679: .%T The Secure Shell (SSH) Authentication Protocol
1.256 jmc 1680: .Re
1.329 jmc 1681: .Pp
1.256 jmc 1682: .Rs
1.329 jmc 1683: .%A T. Ylonen
1684: .%A C. Lonvick
1685: .%D January 2006
1.256 jmc 1686: .%R RFC 4253
1.329 jmc 1687: .%T The Secure Shell (SSH) Transport Layer Protocol
1.256 jmc 1688: .Re
1.329 jmc 1689: .Pp
1.256 jmc 1690: .Rs
1.329 jmc 1691: .%A T. Ylonen
1692: .%A C. Lonvick
1693: .%D January 2006
1.256 jmc 1694: .%R RFC 4254
1.329 jmc 1695: .%T The Secure Shell (SSH) Connection Protocol
1.256 jmc 1696: .Re
1.329 jmc 1697: .Pp
1.256 jmc 1698: .Rs
1.329 jmc 1699: .%A J. Schlyter
1700: .%A W. Griffin
1701: .%D January 2006
1.256 jmc 1702: .%R RFC 4255
1.329 jmc 1703: .%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
1.256 jmc 1704: .Re
1.329 jmc 1705: .Pp
1.256 jmc 1706: .Rs
1.329 jmc 1707: .%A F. Cusack
1708: .%A M. Forssen
1709: .%D January 2006
1.256 jmc 1710: .%R RFC 4256
1.329 jmc 1711: .%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)
1.256 jmc 1712: .Re
1.329 jmc 1713: .Pp
1.256 jmc 1714: .Rs
1.329 jmc 1715: .%A J. Galbraith
1716: .%A P. Remaker
1717: .%D January 2006
1.256 jmc 1718: .%R RFC 4335
1.329 jmc 1719: .%T The Secure Shell (SSH) Session Channel Break Extension
1.256 jmc 1720: .Re
1.329 jmc 1721: .Pp
1.256 jmc 1722: .Rs
1.329 jmc 1723: .%A M. Bellare
1724: .%A T. Kohno
1725: .%A C. Namprempre
1726: .%D January 2006
1.256 jmc 1727: .%R RFC 4344
1.329 jmc 1728: .%T The Secure Shell (SSH) Transport Layer Encryption Modes
1.256 jmc 1729: .Re
1.329 jmc 1730: .Pp
1.256 jmc 1731: .Rs
1.329 jmc 1732: .%A B. Harris
1733: .%D January 2006
1.256 jmc 1734: .%R RFC 4345
1.329 jmc 1735: .%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol
1.258 djm 1736: .Re
1.329 jmc 1737: .Pp
1.258 djm 1738: .Rs
1.329 jmc 1739: .%A M. Friedl
1740: .%A N. Provos
1741: .%A W. Simpson
1742: .%D March 2006
1.258 djm 1743: .%R RFC 4419
1.329 jmc 1744: .%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
1.266 markus 1745: .Re
1.329 jmc 1746: .Pp
1.266 markus 1747: .Rs
1.329 jmc 1748: .%A J. Galbraith
1749: .%A R. Thayer
1750: .%D November 2006
1.266 markus 1751: .%R RFC 4716
1.329 jmc 1752: .%T The Secure Shell (SSH) Public Key File Format
1.313 djm 1753: .Re
1.329 jmc 1754: .Pp
1.313 djm 1755: .Rs
1.329 jmc 1756: .%A D. Stebila
1757: .%A J. Green
1758: .%D December 2009
1.313 djm 1759: .%R RFC 5656
1.329 jmc 1760: .%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
1.274 grunk 1761: .Re
1.329 jmc 1762: .Pp
1.274 grunk 1763: .Rs
1764: .%A A. Perrig
1765: .%A D. Song
1766: .%D 1999
1.329 jmc 1767: .%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
1768: .%T Hash Visualization: a New Technique to improve Real-World Security
1.106 markus 1769: .Re
1.173 jmc 1770: .Sh AUTHORS
1771: OpenSSH is a derivative of the original and free
1772: ssh 1.2.12 release by Tatu Ylonen.
1773: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1774: Theo de Raadt and Dug Song
1775: removed many bugs, re-added newer features and
1776: created OpenSSH.
1777: Markus Friedl contributed the support for SSH
1778: protocol versions 1.5 and 2.0.
![[BACK]](/icons/back.gif){kind=icon}
Return to ssh.1 CVS log ![[TXT]](/icons/text.gif){kind=icon}
![[DIR]](/icons/dir.gif){kind=icon}
Up to [local] / src / usr.bin / ssh