Annotation of src/usr.bin/ssh/ssh.1, Revision 1.437
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: .\"
1.437 ! naddy 36: .\" $OpenBSD: ssh.1,v 1.436 2023/07/17 05:38:10 jmc Exp $
1.436 jmc 37: .Dd $Mdocdate: July 17 2023 $
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
1.436 jmc 61: .Op Fl P Ar tag
1.176 jmc 62: .Op Fl p Ar port
1.362 djm 63: .Op Fl Q Ar query_option
1.360 millert 64: .Op Fl R Ar address
1.198 djm 65: .Op Fl S Ar ctl_path
1.290 dtucker 66: .Op Fl W Ar host : Ns Ar port
1.306 jmc 67: .Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun
1.386 millert 68: .Ar destination
1.427 dtucker 69: .Op Ar command Op Ar argument ...
1.44 aaron 70: .Sh DESCRIPTION
1.2 deraadt 71: .Nm
1.96 deraadt 72: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 73: executing commands on a remote machine.
1.365 mmcc 74: It is intended to provide secure encrypted communications between
1.40 aaron 75: two untrusted hosts over an insecure network.
1.348 millert 76: X11 connections, arbitrary TCP ports and
77: .Ux Ns -domain
78: sockets can also be forwarded over the secure channel.
1.2 deraadt 79: .Pp
80: .Nm
1.44 aaron 81: connects and logs into the specified
1.388 jmc 82: .Ar destination ,
1.386 millert 83: which may be specified as either
1.388 jmc 84: .Sm off
85: .Oo user @ Oc hostname
86: .Sm on
87: or a URI of the form
88: .Sm off
89: .No ssh:// Oo user @ Oc hostname Op : port .
90: .Sm on
1.1 deraadt 91: The user must prove
1.420 dtucker 92: their identity to the remote machine using one of several methods
1.365 mmcc 93: (see below).
1.49 markus 94: .Pp
1.386 millert 95: If a
1.176 jmc 96: .Ar command
97: is specified,
1.427 dtucker 98: it will be executed on the remote host instead of a login shell.
99: A complete command line may be specified as
100: .Ar command ,
101: or it may have additional arguments.
102: If supplied, the arguments will be appended to the command, separated by
103: spaces, before it is sent to the server to be executed.
1.2 deraadt 104: .Pp
1.218 jmc 105: The options are as follows:
1.361 millert 106: .Pp
1.360 millert 107: .Bl -tag -width Ds -compact
1.218 jmc 108: .It Fl 4
109: Forces
1.2 deraadt 110: .Nm
1.218 jmc 111: to use IPv4 addresses only.
1.360 millert 112: .Pp
1.218 jmc 113: .It Fl 6
114: Forces
1.2 deraadt 115: .Nm
1.218 jmc 116: to use IPv6 addresses only.
1.360 millert 117: .Pp
1.218 jmc 118: .It Fl A
1.407 jmc 119: Enables forwarding of connections from an authentication agent such as
120: .Xr ssh-agent 1 .
1.218 jmc 121: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 122: .Pp
1.218 jmc 123: Agent forwarding should be enabled with caution.
124: Users with the ability to bypass file permissions on the remote host
1.285 sobrado 125: (for the agent's
1.286 sobrado 126: .Ux Ns -domain
127: socket) can access the local agent through the forwarded connection.
1.218 jmc 128: An attacker cannot obtain key material from the agent,
129: however they can perform operations on the keys that enable them to
130: authenticate using the identities loaded into the agent.
1.407 jmc 131: A safer alternative may be to use a jump host
132: (see
133: .Fl J ) .
1.360 millert 134: .Pp
1.218 jmc 135: .It Fl a
136: Disables forwarding of the authentication agent connection.
1.390 djm 137: .Pp
1.391 jmc 138: .It Fl B Ar bind_interface
1.390 djm 139: Bind to the address of
1.391 jmc 140: .Ar bind_interface
1.390 djm 141: before attempting to connect to the destination host.
142: This is only useful on systems with more than one address.
1.360 millert 143: .Pp
1.218 jmc 144: .It Fl b Ar bind_address
145: Use
146: .Ar bind_address
147: on the local machine as the source address
148: of the connection.
149: Only useful on systems with more than one address.
1.360 millert 150: .Pp
1.218 jmc 151: .It Fl C
152: Requests compression of all data (including stdin, stdout, stderr, and
1.348 millert 153: data for forwarded X11, TCP and
154: .Ux Ns -domain
155: connections).
1.218 jmc 156: The compression algorithm is the same used by
1.377 djm 157: .Xr gzip 1 .
1.218 jmc 158: Compression is desirable on modem lines and other
159: slow connections, but will only slow down things on fast networks.
160: The default value can be set on a host-by-host basis in the
161: configuration files; see the
162: .Cm Compression
1.431 jmc 163: option in
164: .Xr ssh_config 5 .
1.360 millert 165: .Pp
1.218 jmc 166: .It Fl c Ar cipher_spec
167: Selects the cipher specification for encrypting the session.
168: .Ar cipher_spec
169: is a comma-separated list of ciphers
170: listed in order of preference.
1.283 jmc 171: See the
172: .Cm Ciphers
1.307 dtucker 173: keyword in
174: .Xr ssh_config 5
175: for more information.
1.360 millert 176: .Pp
1.218 jmc 177: .It Fl D Xo
178: .Sm off
179: .Oo Ar bind_address : Oc
180: .Ar port
181: .Sm on
182: .Xc
183: Specifies a local
184: .Dq dynamic
185: application-level port forwarding.
186: This works by allocating a socket to listen to
187: .Ar port
188: on the local side, optionally bound to the specified
189: .Ar bind_address .
190: Whenever a connection is made to this port, the
191: connection is forwarded over the secure channel, and the application
192: protocol is then used to determine where to connect to from the
193: remote machine.
194: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.107 markus 195: .Nm
1.218 jmc 196: will act as a SOCKS server.
197: Only root can forward privileged ports.
198: Dynamic port forwardings can also be specified in the configuration file.
1.49 markus 199: .Pp
1.308 djm 200: IPv6 addresses can be specified by enclosing the address in square brackets.
1.218 jmc 201: Only the superuser can forward privileged ports.
202: By default, the local port is bound in accordance with the
203: .Cm GatewayPorts
204: setting.
205: However, an explicit
206: .Ar bind_address
207: may be used to bind the connection to a specific address.
208: The
209: .Ar bind_address
210: of
211: .Dq localhost
212: indicates that the listening port be bound for local use only, while an
213: empty address or
214: .Sq *
215: indicates that the port should be available from all interfaces.
1.360 millert 216: .Pp
1.331 dtucker 217: .It Fl E Ar log_file
218: Append debug logs to
219: .Ar log_file
220: instead of standard error.
1.360 millert 221: .Pp
1.229 jmc 222: .It Fl e Ar escape_char
1.218 jmc 223: Sets the escape character for sessions with a pty (default:
224: .Ql ~ ) .
225: The escape character is only recognized at the beginning of a line.
226: The escape character followed by a dot
227: .Pq Ql \&.
228: closes the connection;
229: followed by control-Z suspends the connection;
230: and followed by itself sends the escape character once.
231: Setting the character to
1.2 deraadt 232: .Dq none
1.218 jmc 233: disables any escapes and makes the session fully transparent.
1.360 millert 234: .Pp
1.218 jmc 235: .It Fl F Ar configfile
236: Specifies an alternative per-user configuration file.
237: If a configuration file is given on the command line,
238: the system-wide configuration file
239: .Pq Pa /etc/ssh/ssh_config
240: will be ignored.
241: The default for the per-user configuration file is
242: .Pa ~/.ssh/config .
1.411 naddy 243: If set to
244: .Dq none ,
245: no configuration files will be read.
1.360 millert 246: .Pp
1.218 jmc 247: .It Fl f
248: Requests
249: .Nm
250: to go to background just before command execution.
251: This is useful if
1.176 jmc 252: .Nm
1.218 jmc 253: is going to ask for passwords or passphrases, but the user
254: wants it in the background.
255: This implies
256: .Fl n .
257: The recommended way to start X11 programs at a remote site is with
258: something like
259: .Ic ssh -f host xterm .
1.277 djm 260: .Pp
261: If the
262: .Cm ExitOnForwardFailure
263: configuration option is set to
264: .Dq yes ,
265: then a client started with
266: .Fl f
267: will wait for all remote port forwards to be successfully established
268: before placing itself in the background.
1.424 djm 269: Refer to the description of
270: .Cm ForkAfterAuthentication
271: in
272: .Xr ssh_config 5
273: for details.
1.360 millert 274: .Pp
1.350 djm 275: .It Fl G
276: Causes
277: .Nm
278: to print its configuration after evaluating
279: .Cm Host
280: and
281: .Cm Match
282: blocks and exit.
1.360 millert 283: .Pp
1.218 jmc 284: .It Fl g
285: Allows remote hosts to connect to local forwarded ports.
1.346 djm 286: If used on a multiplexed connection, then this option must be specified
287: on the master process.
1.360 millert 288: .Pp
1.291 markus 289: .It Fl I Ar pkcs11
1.294 jmc 290: Specify the PKCS#11 shared library
1.176 jmc 291: .Nm
1.401 naddy 292: should use to communicate with a PKCS#11 token providing keys for user
293: authentication.
1.360 millert 294: .Pp
1.218 jmc 295: .It Fl i Ar identity_file
296: Selects a file from which the identity (private key) for
1.310 djm 297: public key authentication is read.
1.426 dtucker 298: You can also specify a public key file to use the corresponding
299: private key that is loaded in
300: .Xr ssh-agent 1
301: when the private key file is not present locally.
1.218 jmc 302: The default is
1.428 dtucker 303: .Pa ~/.ssh/id_rsa ,
1.343 naddy 304: .Pa ~/.ssh/id_ecdsa ,
1.404 naddy 305: .Pa ~/.ssh/id_ecdsa_sk ,
1.406 naddy 306: .Pa ~/.ssh/id_ed25519 ,
307: .Pa ~/.ssh/id_ed25519_sk
1.310 djm 308: and
1.428 dtucker 309: .Pa ~/.ssh/id_dsa .
1.218 jmc 310: Identity files may also be specified on
311: a per-host basis in the configuration file.
312: It is possible to have multiple
313: .Fl i
314: options (and multiple identities specified in
315: configuration files).
1.364 jmc 316: If no certificates have been explicitly specified by the
1.363 djm 317: .Cm CertificateFile
318: directive,
1.302 djm 319: .Nm
320: will also try to load certificate information from the filename obtained
321: by appending
322: .Pa -cert.pub
323: to identity filenames.
1.360 millert 324: .Pp
1.386 millert 325: .It Fl J Ar destination
1.437 ! naddy 326: Connect to the target host by first making an
1.375 djm 327: .Nm
1.386 millert 328: connection to the jump host described by
329: .Ar destination
1.376 jmc 330: and then establishing a TCP forwarding to the ultimate destination from
1.375 djm 331: there.
332: Multiple jump hops may be specified separated by comma characters.
333: This is a shortcut to specify a
334: .Cm ProxyJump
335: configuration directive.
1.400 djm 336: Note that configuration directives supplied on the command-line generally
337: apply to the destination host and not any specified jump hosts.
338: Use
339: .Pa ~/.ssh/config
340: to specify configuration for jump hosts.
1.375 djm 341: .Pp
1.269 djm 342: .It Fl K
343: Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
344: credentials to the server.
1.360 millert 345: .Pp
1.218 jmc 346: .It Fl k
347: Disables forwarding (delegation) of GSSAPI credentials to the server.
1.360 millert 348: .Pp
1.218 jmc 349: .It Fl L Xo
350: .Sm off
351: .Oo Ar bind_address : Oc
352: .Ar port : host : hostport
353: .Sm on
354: .Xc
1.360 millert 355: .It Fl L Xo
356: .Sm off
357: .Oo Ar bind_address : Oc
358: .Ar port : remote_socket
359: .Sm on
360: .Xc
361: .It Fl L Xo
362: .Sm off
363: .Ar local_socket : host : hostport
364: .Sm on
365: .Xc
366: .It Fl L Xo
367: .Sm off
368: .Ar local_socket : remote_socket
369: .Sm on
370: .Xc
371: Specifies that connections to the given TCP port or Unix socket on the local
372: (client) host are to be forwarded to the given host and port, or Unix socket,
373: on the remote side.
374: This works by allocating a socket to listen to either a TCP
1.218 jmc 375: .Ar port
376: on the local side, optionally bound to the specified
1.360 millert 377: .Ar bind_address ,
378: or to a Unix socket.
379: Whenever a connection is made to the local port or socket, the
1.218 jmc 380: connection is forwarded over the secure channel, and a connection is
1.360 millert 381: made to either
1.218 jmc 382: .Ar host
383: port
1.360 millert 384: .Ar hostport ,
385: or the Unix socket
386: .Ar remote_socket ,
1.218 jmc 387: from the remote machine.
1.360 millert 388: .Pp
1.218 jmc 389: Port forwardings can also be specified in the configuration file.
1.360 millert 390: Only the superuser can forward privileged ports.
1.308 djm 391: IPv6 addresses can be specified by enclosing the address in square brackets.
1.360 millert 392: .Pp
1.218 jmc 393: By default, the local port is bound in accordance with the
394: .Cm GatewayPorts
395: setting.
396: However, an explicit
397: .Ar bind_address
398: may be used to bind the connection to a specific address.
1.2 deraadt 399: The
1.218 jmc 400: .Ar bind_address
401: of
402: .Dq localhost
403: indicates that the listening port be bound for local use only, while an
404: empty address or
405: .Sq *
406: indicates that the port should be available from all interfaces.
1.360 millert 407: .Pp
1.218 jmc 408: .It Fl l Ar login_name
409: Specifies the user to log in as on the remote machine.
410: This also may be specified on a per-host basis in the configuration file.
1.360 millert 411: .Pp
1.218 jmc 412: .It Fl M
413: Places the
414: .Nm
415: client into
416: .Dq master
417: mode for connection sharing.
1.231 stevesk 418: Multiple
419: .Fl M
420: options places
421: .Nm
422: into
423: .Dq master
1.397 djm 424: mode but with confirmation required using
425: .Xr ssh-askpass 1
426: before each operation that changes the multiplexing state
427: (e.g. opening a new session).
1.218 jmc 428: Refer to the description of
429: .Cm ControlMaster
430: in
431: .Xr ssh_config 5
432: for details.
1.360 millert 433: .Pp
1.218 jmc 434: .It Fl m Ar mac_spec
1.369 jmc 435: A comma-separated list of MAC (message authentication code) algorithms,
436: specified in order of preference.
1.218 jmc 437: See the
438: .Cm MACs
1.431 jmc 439: keyword in
440: .Xr ssh_config 5
441: for more information.
1.360 millert 442: .Pp
1.218 jmc 443: .It Fl N
444: Do not execute a remote command.
1.369 jmc 445: This is useful for just forwarding ports.
1.422 djm 446: Refer to the description of
447: .Cm SessionType
448: in
449: .Xr ssh_config 5
450: for details.
1.360 millert 451: .Pp
1.218 jmc 452: .It Fl n
453: Redirects stdin from
454: .Pa /dev/null
455: (actually, prevents reading from stdin).
456: This must be used when
1.2 deraadt 457: .Nm
1.218 jmc 458: is run in the background.
459: A common trick is to use this to run X11 programs on a remote machine.
460: For example,
461: .Ic ssh -n shadows.cs.hut.fi emacs &
462: will start an emacs on shadows.cs.hut.fi, and the X11
463: connection will be automatically forwarded over an encrypted channel.
464: The
1.2 deraadt 465: .Nm
1.218 jmc 466: program will be put in the background.
467: (This does not work if
1.2 deraadt 468: .Nm
1.218 jmc 469: needs to ask for a password or passphrase; see also the
470: .Fl f
471: option.)
1.423 djm 472: Refer to the description of
473: .Cm StdinNull
474: in
475: .Xr ssh_config 5
476: for details.
1.360 millert 477: .Pp
1.218 jmc 478: .It Fl O Ar ctl_cmd
479: Control an active connection multiplexing master process.
480: When the
481: .Fl O
482: option is specified, the
483: .Ar ctl_cmd
484: argument is interpreted and passed to the master process.
485: Valid commands are:
486: .Dq check
1.305 markus 487: (check that the master process is running),
488: .Dq forward
1.318 jmc 489: (request forwardings without command execution),
1.323 okan 490: .Dq cancel
491: (cancel forwardings),
1.218 jmc 492: .Dq exit
1.318 jmc 493: (request the master to exit), and
1.317 djm 494: .Dq stop
495: (request the master to stop accepting further multiplexing requests).
1.360 millert 496: .Pp
1.218 jmc 497: .It Fl o Ar option
498: Can be used to give options in the format used in the configuration file.
499: This is useful for specifying options for which there is no separate
500: command-line flag.
501: For full details of the options listed below, and their possible values, see
502: .Xr ssh_config 5 .
1.2 deraadt 503: .Pp
1.218 jmc 504: .Bl -tag -width Ds -offset indent -compact
1.366 jcs 505: .It AddKeysToAgent
1.218 jmc 506: .It AddressFamily
507: .It BatchMode
508: .It BindAddress
1.338 djm 509: .It CanonicalDomains
1.339 djm 510: .It CanonicalizeFallbackLocal
511: .It CanonicalizeHostname
512: .It CanonicalizeMaxDots
513: .It CanonicalizePermittedCNAMEs
1.399 jmc 514: .It CASignatureAlgorithms
1.363 djm 515: .It CertificateFile
1.218 jmc 516: .It CheckHostIP
517: .It Ciphers
518: .It ClearAllForwardings
519: .It Compression
1.380 naddy 520: .It ConnectionAttempts
1.218 jmc 521: .It ConnectTimeout
522: .It ControlMaster
523: .It ControlPath
1.321 djm 524: .It ControlPersist
1.218 jmc 525: .It DynamicForward
1.433 djm 526: .It EnableEscapeCommandline
1.218 jmc 527: .It EscapeChar
1.263 markus 528: .It ExitOnForwardFailure
1.353 jmc 529: .It FingerprintHash
1.424 djm 530: .It ForkAfterAuthentication
1.218 jmc 531: .It ForwardAgent
532: .It ForwardX11
1.321 djm 533: .It ForwardX11Timeout
1.218 jmc 534: .It ForwardX11Trusted
535: .It GatewayPorts
536: .It GlobalKnownHostsFile
537: .It GSSAPIAuthentication
538: .It GSSAPIDelegateCredentials
539: .It HashKnownHosts
540: .It Host
1.418 naddy 541: .It HostbasedAcceptedAlgorithms
1.218 jmc 542: .It HostbasedAuthentication
543: .It HostKeyAlgorithms
544: .It HostKeyAlias
1.403 jmc 545: .It Hostname
1.374 jmc 546: .It IdentitiesOnly
1.371 markus 547: .It IdentityAgent
1.218 jmc 548: .It IdentityFile
1.316 jmc 549: .It IPQoS
1.321 djm 550: .It KbdInteractiveAuthentication
1.218 jmc 551: .It KbdInteractiveDevices
1.314 jmc 552: .It KexAlgorithms
1.415 djm 553: .It KnownHostsCommand
1.218 jmc 554: .It LocalCommand
555: .It LocalForward
556: .It LogLevel
557: .It MACs
1.337 jmc 558: .It Match
1.218 jmc 559: .It NoHostAuthenticationForLocalhost
560: .It NumberOfPasswordPrompts
561: .It PasswordAuthentication
562: .It PermitLocalCommand
1.419 markus 563: .It PermitRemoteOpen
1.291 markus 564: .It PKCS11Provider
1.218 jmc 565: .It Port
566: .It PreferredAuthentications
567: .It ProxyCommand
1.375 djm 568: .It ProxyJump
1.336 jmc 569: .It ProxyUseFdpass
1.416 dtucker 570: .It PubkeyAcceptedAlgorithms
1.218 jmc 571: .It PubkeyAuthentication
1.251 dtucker 572: .It RekeyLimit
1.382 bluhm 573: .It RemoteCommand
1.218 jmc 574: .It RemoteForward
1.319 jmc 575: .It RequestTTY
1.432 djm 576: .It RequiredRSASize
1.218 jmc 577: .It SendEnv
578: .It ServerAliveInterval
579: .It ServerAliveCountMax
1.422 djm 580: .It SessionType
1.395 jmc 581: .It SetEnv
1.423 djm 582: .It StdinNull
1.347 jmc 583: .It StreamLocalBindMask
584: .It StreamLocalBindUnlink
1.218 jmc 585: .It StrictHostKeyChecking
586: .It TCPKeepAlive
587: .It Tunnel
588: .It TunnelDevice
1.354 djm 589: .It UpdateHostKeys
1.218 jmc 590: .It User
591: .It UserKnownHostsFile
592: .It VerifyHostKeyDNS
1.276 jmc 593: .It VisualHostKey
1.218 jmc 594: .It XAuthLocation
595: .El
1.360 millert 596: .Pp
1.435 djm 597: .It Fl P Ar tag
598: Specify a tag name that may be used to select configuration in
599: .Xr ssh_config 5 .
600: Refer to the
601: .Cm Tag
602: and
603: .Cm Match
604: keywords in
605: .Xr ssh_config 5
606: for more information.
1.218 jmc 607: .It Fl p Ar port
608: Port to connect to on the remote host.
609: This can be specified on a
610: per-host basis in the configuration file.
1.360 millert 611: .Pp
1.362 djm 612: .It Fl Q Ar query_option
1.425 jmc 613: Queries for the algorithms supported by one of the following features:
1.341 deraadt 614: .Ar cipher
1.332 djm 615: (supported symmetric ciphers),
1.341 deraadt 616: .Ar cipher-auth
1.340 djm 617: (supported symmetric ciphers that support authenticated encryption),
1.398 djm 618: .Ar help
619: (supported query terms for use with the
620: .Fl Q
621: flag),
1.341 deraadt 622: .Ar mac
1.332 djm 623: (supported message integrity codes),
1.341 deraadt 624: .Ar kex
1.332 djm 625: (key exchange algorithms),
1.341 deraadt 626: .Ar key
1.362 djm 627: (key types),
1.434 djm 628: .Ar key-ca-sign
629: (valid CA signature algorithms for certificates),
1.362 djm 630: .Ar key-cert
631: (certificate key types),
632: .Ar key-plain
1.398 djm 633: (non-certificate key types),
1.410 dtucker 634: .Ar key-sig
635: (all key types and signature algorithms),
1.356 djm 636: .Ar protocol-version
1.398 djm 637: (supported SSH protocol versions), and
638: .Ar sig
639: (supported signature algorithms).
1.410 dtucker 640: Alternatively, any keyword from
641: .Xr ssh_config 5
642: or
643: .Xr sshd_config 5
644: that takes an algorithm list may be used as an alias for the corresponding
645: query_option.
1.360 millert 646: .Pp
1.218 jmc 647: .It Fl q
648: Quiet mode.
1.271 djm 649: Causes most warning and diagnostic messages to be suppressed.
1.360 millert 650: .Pp
1.218 jmc 651: .It Fl R Xo
652: .Sm off
653: .Oo Ar bind_address : Oc
654: .Ar port : host : hostport
655: .Sm on
656: .Xc
1.360 millert 657: .It Fl R Xo
658: .Sm off
659: .Oo Ar bind_address : Oc
660: .Ar port : local_socket
661: .Sm on
662: .Xc
663: .It Fl R Xo
664: .Sm off
665: .Ar remote_socket : host : hostport
666: .Sm on
667: .Xc
668: .It Fl R Xo
669: .Sm off
670: .Ar remote_socket : local_socket
671: .Sm on
672: .Xc
1.384 markus 673: .It Fl R Xo
674: .Sm off
675: .Oo Ar bind_address : Oc
676: .Ar port
677: .Sm on
678: .Xc
1.360 millert 679: Specifies that connections to the given TCP port or Unix socket on the remote
1.384 markus 680: (server) host are to be forwarded to the local side.
681: .Pp
1.360 millert 682: This works by allocating a socket to listen to either a TCP
1.218 jmc 683: .Ar port
1.360 millert 684: or to a Unix socket on the remote side.
685: Whenever a connection is made to this port or Unix socket, the
686: connection is forwarded over the secure channel, and a connection
1.384 markus 687: is made from the local machine to either an explicit destination specified by
1.218 jmc 688: .Ar host
689: port
1.360 millert 690: .Ar hostport ,
691: or
692: .Ar local_socket ,
1.384 markus 693: or, if no explicit destination was specified,
694: .Nm
695: will act as a SOCKS 4/5 proxy and forward connections to the destinations
696: requested by the remote SOCKS client.
1.2 deraadt 697: .Pp
1.218 jmc 698: Port forwardings can also be specified in the configuration file.
699: Privileged ports can be forwarded only when
700: logging in as root on the remote machine.
1.324 jmc 701: IPv6 addresses can be specified by enclosing the address in square brackets.
1.194 jakob 702: .Pp
1.360 millert 703: By default, TCP listening sockets on the server will be bound to the loopback
1.218 jmc 704: interface only.
1.280 tobias 705: This may be overridden by specifying a
1.218 jmc 706: .Ar bind_address .
707: An empty
708: .Ar bind_address ,
709: or the address
710: .Ql * ,
711: indicates that the remote socket should listen on all interfaces.
712: Specifying a remote
713: .Ar bind_address
714: will only succeed if the server's
715: .Cm GatewayPorts
716: option is enabled (see
717: .Xr sshd_config 5 ) .
1.281 djm 718: .Pp
719: If the
720: .Ar port
721: argument is
1.282 djm 722: .Ql 0 ,
1.281 djm 723: the listen port will be dynamically allocated on the server and reported
724: to the client at run time.
1.305 markus 725: When used together with
1.430 naddy 726: .Ic -O forward ,
1.305 markus 727: the allocated port will be printed to the standard output.
1.360 millert 728: .Pp
1.218 jmc 729: .It Fl S Ar ctl_path
1.304 jmc 730: Specifies the location of a control socket for connection sharing,
1.303 djm 731: or the string
732: .Dq none
733: to disable connection sharing.
1.218 jmc 734: Refer to the description of
735: .Cm ControlPath
736: and
737: .Cm ControlMaster
738: in
739: .Xr ssh_config 5
740: for details.
1.360 millert 741: .Pp
1.218 jmc 742: .It Fl s
743: May be used to request invocation of a subsystem on the remote system.
1.369 jmc 744: Subsystems facilitate the use of SSH
745: as a secure transport for other applications (e.g.\&
1.218 jmc 746: .Xr sftp 1 ) .
747: The subsystem is specified as the remote command.
1.422 djm 748: Refer to the description of
749: .Cm SessionType
750: in
751: .Xr ssh_config 5
752: for details.
1.360 millert 753: .Pp
1.218 jmc 754: .It Fl T
1.357 dtucker 755: Disable pseudo-terminal allocation.
1.360 millert 756: .Pp
1.218 jmc 757: .It Fl t
1.357 dtucker 758: Force pseudo-terminal allocation.
1.218 jmc 759: This can be used to execute arbitrary
760: screen-based programs on a remote machine, which can be very useful,
1.257 jmc 761: e.g. when implementing menu services.
1.218 jmc 762: Multiple
763: .Fl t
764: options force tty allocation, even if
1.194 jakob 765: .Nm
1.218 jmc 766: has no local tty.
1.360 millert 767: .Pp
1.218 jmc 768: .It Fl V
769: Display the version number and exit.
1.360 millert 770: .Pp
1.218 jmc 771: .It Fl v
772: Verbose mode.
773: Causes
1.176 jmc 774: .Nm
1.218 jmc 775: to print debugging messages about its progress.
776: This is helpful in
777: debugging connection, authentication, and configuration problems.
778: Multiple
779: .Fl v
780: options increase the verbosity.
781: The maximum is 3.
1.360 millert 782: .Pp
1.290 dtucker 783: .It Fl W Ar host : Ns Ar port
784: Requests that standard input and output on the client be forwarded to
785: .Ar host
786: on
787: .Ar port
788: over the secure channel.
789: Implies
790: .Fl N ,
791: .Fl T ,
792: .Cm ExitOnForwardFailure
793: and
1.373 jmc 794: .Cm ClearAllForwardings ,
795: though these can be overridden in the configuration file or using
1.372 dtucker 796: .Fl o
797: command line options.
1.360 millert 798: .Pp
1.261 stevesk 799: .It Fl w Xo
800: .Ar local_tun Ns Op : Ns Ar remote_tun
801: .Xc
802: Requests
803: tunnel
804: device forwarding with the specified
1.218 jmc 805: .Xr tun 4
1.261 stevesk 806: devices between the client
807: .Pq Ar local_tun
808: and the server
809: .Pq Ar remote_tun .
810: .Pp
1.228 jmc 811: The devices may be specified by numerical ID or the keyword
812: .Dq any ,
813: which uses the next available tunnel device.
1.261 stevesk 814: If
815: .Ar remote_tun
816: is not specified, it defaults to
817: .Dq any .
1.228 jmc 818: See also the
1.218 jmc 819: .Cm Tunnel
1.261 stevesk 820: and
821: .Cm TunnelDevice
822: directives in
1.218 jmc 823: .Xr ssh_config 5 .
1.393 djm 824: .Pp
1.261 stevesk 825: If the
826: .Cm Tunnel
1.393 djm 827: directive is unset, it will be set to the default tunnel mode, which is
1.261 stevesk 828: .Dq point-to-point .
1.393 djm 829: If a different
830: .Cm Tunnel
831: forwarding mode it desired, then it should be specified before
832: .Fl w .
1.360 millert 833: .Pp
1.218 jmc 834: .It Fl X
835: Enables X11 forwarding.
1.54 markus 836: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 837: .Pp
1.218 jmc 838: X11 forwarding should be enabled with caution.
1.168 jmc 839: Users with the ability to bypass file permissions on the remote host
1.218 jmc 840: (for the user's X authorization database)
841: can access the local X11 display through the forwarded connection.
842: An attacker may then be able to perform activities such as keystroke monitoring.
843: .Pp
844: For this reason, X11 forwarding is subjected to X11 SECURITY extension
845: restrictions by default.
1.429 jsg 846: Refer to the
1.218 jmc 847: .Nm
848: .Fl Y
849: option and the
850: .Cm ForwardX11Trusted
851: directive in
852: .Xr ssh_config 5
853: for more information.
1.360 millert 854: .Pp
1.218 jmc 855: .It Fl x
856: Disables X11 forwarding.
1.360 millert 857: .Pp
1.218 jmc 858: .It Fl Y
859: Enables trusted X11 forwarding.
860: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
861: controls.
1.360 millert 862: .Pp
1.278 djm 863: .It Fl y
864: Send log information using the
865: .Xr syslog 3
866: system module.
867: By default this information is sent to stderr.
1.218 jmc 868: .El
1.224 jmc 869: .Pp
870: .Nm
871: may additionally obtain configuration data from
872: a per-user configuration file and a system-wide configuration file.
873: The file format and configuration options are described in
874: .Xr ssh_config 5 .
1.222 jmc 875: .Sh AUTHENTICATION
1.377 djm 876: The OpenSSH SSH client supports SSH protocol 2.
1.222 jmc 877: .Pp
878: The methods available for authentication are:
1.260 jmc 879: GSSAPI-based authentication,
1.222 jmc 880: host-based authentication,
881: public key authentication,
1.421 dtucker 882: keyboard-interactive authentication,
1.222 jmc 883: and password authentication.
884: Authentication methods are tried in the order specified above,
1.369 jmc 885: though
886: .Cm PreferredAuthentications
887: can be used to change the default order.
1.222 jmc 888: .Pp
889: Host-based authentication works as follows:
1.218 jmc 890: If the machine the user logs in from is listed in
891: .Pa /etc/hosts.equiv
892: or
893: .Pa /etc/shosts.equiv
1.412 djm 894: on the remote machine, the user is non-root and the user names are
1.218 jmc 895: the same on both sides, or if the files
896: .Pa ~/.rhosts
897: or
898: .Pa ~/.shosts
899: exist in the user's home directory on the
900: remote machine and contain a line containing the name of the client
901: machine and the name of the user on that machine, the user is
1.222 jmc 902: considered for login.
903: Additionally, the server
904: .Em must
905: be able to verify the client's
906: host key (see the description of
1.218 jmc 907: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 908: and
1.222 jmc 909: .Pa ~/.ssh/known_hosts ,
910: below)
911: for login to be permitted.
1.218 jmc 912: This authentication method closes security holes due to IP
1.222 jmc 913: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 914: [Note to the administrator:
915: .Pa /etc/hosts.equiv ,
916: .Pa ~/.rhosts ,
917: and the rlogin/rsh protocol in general, are inherently insecure and should be
918: disabled if security is desired.]
1.189 dtucker 919: .Pp
1.222 jmc 920: Public key authentication works as follows:
921: The scheme is based on public-key cryptography,
922: using cryptosystems
923: where encryption and decryption are done using separate keys,
924: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 925: The idea is that each user creates a public/private
926: key pair for authentication purposes.
927: The server knows the public key, and only the user knows the private key.
1.222 jmc 928: .Nm
929: implements public key authentication protocol automatically,
1.349 sobrado 930: using one of the DSA, ECDSA, Ed25519 or RSA algorithms.
1.333 jmc 931: The HISTORY section of
1.222 jmc 932: .Xr ssl 8
1.311 jmc 933: contains a brief discussion of the DSA and RSA algorithms.
1.210 djm 934: .Pp
1.218 jmc 935: The file
936: .Pa ~/.ssh/authorized_keys
937: lists the public keys that are permitted for logging in.
938: When the user logs in, the
1.2 deraadt 939: .Nm
1.218 jmc 940: program tells the server which key pair it would like to use for
941: authentication.
1.222 jmc 942: The client proves that it has access to the private key
943: and the server checks that the corresponding public key
944: is authorized to accept the account.
1.383 djm 945: .Pp
946: The server may inform the client of errors that prevented public key
947: authentication from succeeding after authentication completes using a
948: different method.
949: These may be viewed by increasing the
950: .Cm LogLevel
951: to
952: .Cm DEBUG
953: or higher (e.g. by using the
954: .Fl v
955: flag).
1.218 jmc 956: .Pp
1.420 dtucker 957: The user creates their key pair by running
1.218 jmc 958: .Xr ssh-keygen 1 .
959: This stores the private key in
1.222 jmc 960: .Pa ~/.ssh/id_dsa
1.369 jmc 961: (DSA),
1.310 djm 962: .Pa ~/.ssh/id_ecdsa
1.369 jmc 963: (ECDSA),
1.404 naddy 964: .Pa ~/.ssh/id_ecdsa_sk
1.409 naddy 965: (authenticator-hosted ECDSA),
1.343 naddy 966: .Pa ~/.ssh/id_ed25519
1.369 jmc 967: (Ed25519),
1.406 naddy 968: .Pa ~/.ssh/id_ed25519_sk
1.409 naddy 969: (authenticator-hosted Ed25519),
1.222 jmc 970: or
971: .Pa ~/.ssh/id_rsa
1.369 jmc 972: (RSA)
1.218 jmc 973: and stores the public key in
1.222 jmc 974: .Pa ~/.ssh/id_dsa.pub
1.369 jmc 975: (DSA),
1.310 djm 976: .Pa ~/.ssh/id_ecdsa.pub
1.369 jmc 977: (ECDSA),
1.404 naddy 978: .Pa ~/.ssh/id_ecdsa_sk.pub
1.409 naddy 979: (authenticator-hosted ECDSA),
1.343 naddy 980: .Pa ~/.ssh/id_ed25519.pub
1.369 jmc 981: (Ed25519),
1.406 naddy 982: .Pa ~/.ssh/id_ed25519_sk.pub
1.409 naddy 983: (authenticator-hosted Ed25519),
1.222 jmc 984: or
985: .Pa ~/.ssh/id_rsa.pub
1.369 jmc 986: (RSA)
1.218 jmc 987: in the user's home directory.
1.222 jmc 988: The user should then copy the public key
1.218 jmc 989: to
990: .Pa ~/.ssh/authorized_keys
1.420 dtucker 991: in their home directory on the remote machine.
1.222 jmc 992: The
1.218 jmc 993: .Pa authorized_keys
994: file corresponds to the conventional
995: .Pa ~/.rhosts
996: file, and has one key
1.222 jmc 997: per line, though the lines can be very long.
1.218 jmc 998: After this, the user can log in without giving the password.
999: .Pp
1.301 jmc 1000: A variation on public key authentication
1001: is available in the form of certificate authentication:
1002: instead of a set of public/private keys,
1003: signed certificates are used.
1004: This has the advantage that a single trusted certification authority
1005: can be used in place of many public/private keys.
1.333 jmc 1006: See the CERTIFICATES section of
1.301 jmc 1007: .Xr ssh-keygen 1
1008: for more information.
1009: .Pp
1010: The most convenient way to use public key or certificate authentication
1011: may be with an authentication agent.
1.218 jmc 1012: See
1013: .Xr ssh-agent 1
1.366 jcs 1014: and (optionally) the
1015: .Cm AddKeysToAgent
1016: directive in
1017: .Xr ssh_config 5
1.218 jmc 1018: for more information.
1019: .Pp
1.421 dtucker 1020: Keyboard-interactive authentication works as follows:
1.222 jmc 1021: The server sends an arbitrary
1022: .Qq challenge
1.421 dtucker 1023: text and prompts for a response, possibly multiple times.
1024: Examples of keyboard-interactive authentication include
1.335 jmc 1025: .Bx
1026: Authentication (see
1.222 jmc 1027: .Xr login.conf 5 )
1.335 jmc 1028: and PAM (some
1029: .Pf non- Ox
1030: systems).
1.222 jmc 1031: .Pp
1032: Finally, if other authentication methods fail,
1.218 jmc 1033: .Nm
1034: prompts the user for a password.
1035: The password is sent to the remote
1036: host for checking; however, since all communications are encrypted,
1037: the password cannot be seen by someone listening on the network.
1.232 jmc 1038: .Pp
1039: .Nm
1040: automatically maintains and checks a database containing
1041: identification for all hosts it has ever been used with.
1042: Host keys are stored in
1043: .Pa ~/.ssh/known_hosts
1044: in the user's home directory.
1045: Additionally, the file
1046: .Pa /etc/ssh/ssh_known_hosts
1047: is automatically checked for known hosts.
1048: Any new hosts are automatically added to the user's file.
1049: If a host's identification ever changes,
1050: .Nm
1051: warns about this and disables password authentication to prevent
1052: server spoofing or man-in-the-middle attacks,
1053: which could otherwise be used to circumvent the encryption.
1054: The
1055: .Cm StrictHostKeyChecking
1056: option can be used to control logins to machines whose
1057: host key is not known or has changed.
1058: .Pp
1.218 jmc 1059: When the user's identity has been accepted by the server, the server
1.357 dtucker 1060: either executes the given command in a non-interactive session or,
1061: if no command has been specified, logs into the machine and gives
1062: the user a normal shell as an interactive session.
1.218 jmc 1063: All communication with
1064: the remote command or shell will be automatically encrypted.
1065: .Pp
1.430 naddy 1066: If an interactive session is requested,
1.357 dtucker 1067: .Nm
1068: by default will only request a pseudo-terminal (pty) for interactive
1069: sessions when the client has one.
1070: The flags
1071: .Fl T
1072: and
1073: .Fl t
1074: can be used to override this behaviour.
1075: .Pp
1.430 naddy 1076: If a pseudo-terminal has been allocated, the
1.218 jmc 1077: user may use the escape characters noted below.
1078: .Pp
1.357 dtucker 1079: If no pseudo-terminal has been allocated,
1.218 jmc 1080: the session is transparent and can be used to reliably transfer binary data.
1081: On most systems, setting the escape character to
1082: .Dq none
1083: will also make the session transparent even if a tty is used.
1084: .Pp
1085: The session terminates when the command or shell on the remote
1.247 jmc 1086: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 1087: .Sh ESCAPE CHARACTERS
1.218 jmc 1088: When a pseudo-terminal has been requested,
1.2 deraadt 1089: .Nm
1.218 jmc 1090: supports a number of functions through the use of an escape character.
1091: .Pp
1092: A single tilde character can be sent as
1093: .Ic ~~
1094: or by following the tilde by a character other than those described below.
1095: The escape character must always follow a newline to be interpreted as
1096: special.
1097: The escape character can be changed in configuration files using the
1098: .Cm EscapeChar
1099: configuration directive or on the command line by the
1100: .Fl e
1101: option.
1102: .Pp
1103: The supported escapes (assuming the default
1104: .Ql ~ )
1105: are:
1106: .Bl -tag -width Ds
1107: .It Cm ~.
1108: Disconnect.
1109: .It Cm ~^Z
1110: Background
1.234 jmc 1111: .Nm .
1.218 jmc 1112: .It Cm ~#
1113: List forwarded connections.
1114: .It Cm ~&
1115: Background
1.2 deraadt 1116: .Nm
1.218 jmc 1117: at logout when waiting for forwarded connection / X11 sessions to terminate.
1118: .It Cm ~?
1119: Display a list of escape characters.
1120: .It Cm ~B
1121: Send a BREAK to the remote system
1.369 jmc 1122: (only useful if the peer supports it).
1.218 jmc 1123: .It Cm ~C
1124: Open command line.
1125: Currently this allows the addition of port forwardings using the
1.279 stevesk 1126: .Fl L ,
1127: .Fl R
1.218 jmc 1128: and
1.279 stevesk 1129: .Fl D
1.225 jmc 1130: options (see above).
1.322 markus 1131: It also allows the cancellation of existing port-forwardings
1132: with
1.262 stevesk 1133: .Sm off
1.322 markus 1134: .Fl KL Oo Ar bind_address : Oc Ar port
1.262 stevesk 1135: .Sm on
1.322 markus 1136: for local,
1137: .Sm off
1138: .Fl KR Oo Ar bind_address : Oc Ar port
1139: .Sm on
1140: for remote and
1141: .Sm off
1142: .Fl KD Oo Ar bind_address : Oc Ar port
1143: .Sm on
1144: for dynamic port-forwardings.
1.218 jmc 1145: .Ic !\& Ns Ar command
1146: allows the user to execute a local command if the
1147: .Ic PermitLocalCommand
1148: option is enabled in
1.176 jmc 1149: .Xr ssh_config 5 .
1.218 jmc 1150: Basic help is available, using the
1151: .Fl h
1152: option.
1153: .It Cm ~R
1154: Request rekeying of the connection
1.369 jmc 1155: (only useful if the peer supports it).
1.327 dtucker 1156: .It Cm ~V
1157: Decrease the verbosity
1158: .Pq Ic LogLevel
1159: when errors are being written to stderr.
1160: .It Cm ~v
1.328 jmc 1161: Increase the verbosity
1.327 dtucker 1162: .Pq Ic LogLevel
1163: when errors are being written to stderr.
1.176 jmc 1164: .El
1.246 jmc 1165: .Sh TCP FORWARDING
1.402 jmc 1166: Forwarding of arbitrary TCP connections over a secure channel
1167: can be specified either on the command line or in a configuration file.
1.246 jmc 1168: One possible application of TCP forwarding is a secure connection to a
1169: mail server; another is going through firewalls.
1170: .Pp
1.402 jmc 1171: In the example below, we look at encrypting communication for an IRC client,
1172: even though the IRC server it connects to does not directly
1173: support encrypted communication.
1.246 jmc 1174: This works as follows:
1175: the user connects to the remote host using
1176: .Nm ,
1.402 jmc 1177: specifying the ports to be used to forward the connection.
1178: After that it is possible to start the program locally,
1.246 jmc 1179: and
1180: .Nm
1.402 jmc 1181: will encrypt and forward the connection to the remote server.
1.246 jmc 1182: .Pp
1.402 jmc 1183: The following example tunnels an IRC session from the client
1184: to an IRC server at
1.246 jmc 1185: .Dq server.example.com ,
1186: joining channel
1187: .Dq #users ,
1188: nickname
1189: .Dq pinky ,
1.402 jmc 1190: using the standard IRC port, 6667:
1191: .Bd -literal -offset 4n
1192: $ ssh -f -L 6667:localhost:6667 server.example.com sleep 10
1193: $ irc -c '#users' pinky IRC/127.0.0.1
1194: .Ed
1.246 jmc 1195: .Pp
1196: The
1197: .Fl f
1198: option backgrounds
1199: .Nm
1200: and the remote command
1201: .Dq sleep 10
1202: is specified to allow an amount of time
1203: (10 seconds, in the example)
1.402 jmc 1204: to start the program which is going to use the tunnel.
1.246 jmc 1205: If no connections are made within the time specified,
1206: .Nm
1207: will exit.
1208: .Sh X11 FORWARDING
1.218 jmc 1209: If the
1210: .Cm ForwardX11
1211: variable is set to
1212: .Dq yes
1213: (or see the description of the
1.227 jmc 1214: .Fl X ,
1215: .Fl x ,
1.218 jmc 1216: and
1.227 jmc 1217: .Fl Y
1.226 jmc 1218: options above)
1.218 jmc 1219: and the user is using X11 (the
1220: .Ev DISPLAY
1221: environment variable is set), the connection to the X11 display is
1222: automatically forwarded to the remote side in such a way that any X11
1223: programs started from the shell (or command) will go through the
1224: encrypted channel, and the connection to the real X server will be made
1.176 jmc 1225: from the local machine.
1.218 jmc 1226: The user should not manually set
1227: .Ev DISPLAY .
1228: Forwarding of X11 connections can be
1229: configured on the command line or in configuration files.
1230: .Pp
1231: The
1232: .Ev DISPLAY
1233: value set by
1234: .Nm
1235: will point to the server machine, but with a display number greater than zero.
1236: This is normal, and happens because
1237: .Nm
1238: creates a
1239: .Dq proxy
1240: X server on the server machine for forwarding the
1241: connections over the encrypted channel.
1.200 djm 1242: .Pp
1.218 jmc 1243: .Nm
1244: will also automatically set up Xauthority data on the server machine.
1245: For this purpose, it will generate a random authorization cookie,
1246: store it in Xauthority on the server, and verify that any forwarded
1247: connections carry this cookie and replace it by the real cookie when
1248: the connection is opened.
1249: The real authentication cookie is never
1250: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1251: .Pp
1.218 jmc 1252: If the
1253: .Cm ForwardAgent
1254: variable is set to
1255: .Dq yes
1256: (or see the description of the
1257: .Fl A
1.191 djm 1258: and
1.218 jmc 1259: .Fl a
1.226 jmc 1260: options above) and
1.218 jmc 1261: the user is using an authentication agent, the connection to the agent
1262: is automatically forwarded to the remote side.
1.252 jmc 1263: .Sh VERIFYING HOST KEYS
1264: When connecting to a server for the first time,
1265: a fingerprint of the server's public key is presented to the user
1266: (unless the option
1267: .Cm StrictHostKeyChecking
1268: has been disabled).
1269: Fingerprints can be determined using
1270: .Xr ssh-keygen 1 :
1271: .Pp
1272: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1273: .Pp
1.274 grunk 1274: If the fingerprint is already known, it can be matched
1275: and the key can be accepted or rejected.
1.358 djm 1276: If only legacy (MD5) fingerprints for the server are available, the
1277: .Xr ssh-keygen 1
1278: .Fl E
1279: option may be used to downgrade the fingerprint algorithm to match.
1280: .Pp
1.274 grunk 1281: Because of the difficulty of comparing host keys
1.352 djm 1282: just by looking at fingerprint strings,
1.274 grunk 1283: there is also support to compare host keys visually,
1284: using
1285: .Em random art .
1286: By setting the
1.275 grunk 1287: .Cm VisualHostKey
1.274 grunk 1288: option to
1.275 grunk 1289: .Dq yes ,
1.274 grunk 1290: a small ASCII graphic gets displayed on every login to a server, no matter
1291: if the session itself is interactive or not.
1292: By learning the pattern a known server produces, a user can easily
1293: find out that the host key has changed when a completely different pattern
1294: is displayed.
1295: Because these patterns are not unambiguous however, a pattern that looks
1296: similar to the pattern remembered only gives a good probability that the
1297: host key is the same, not guaranteed proof.
1298: .Pp
1299: To get a listing of the fingerprints along with their random art for
1300: all known hosts, the following command line can be used:
1301: .Pp
1302: .Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1303: .Pp
1.252 jmc 1304: If the fingerprint is unknown,
1305: an alternative method of verification is available:
1306: SSH fingerprints verified by DNS.
1307: An additional resource record (RR),
1308: SSHFP,
1309: is added to a zonefile
1310: and the connecting client is able to match the fingerprint
1311: with that of the key presented.
1312: .Pp
1313: In this example, we are connecting a client to a server,
1314: .Dq host.example.com .
1315: The SSHFP resource records should first be added to the zonefile for
1316: host.example.com:
1317: .Bd -literal -offset indent
1.259 jakob 1318: $ ssh-keygen -r host.example.com.
1.252 jmc 1319: .Ed
1320: .Pp
1321: The output lines will have to be added to the zonefile.
1322: To check that the zone is answering fingerprint queries:
1323: .Pp
1324: .Dl $ dig -t SSHFP host.example.com
1325: .Pp
1326: Finally the client connects:
1327: .Bd -literal -offset indent
1328: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1329: [...]
1330: Matching host key fingerprint found in DNS.
1331: Are you sure you want to continue connecting (yes/no)?
1332: .Ed
1333: .Pp
1334: See the
1335: .Cm VerifyHostKeyDNS
1336: option in
1337: .Xr ssh_config 5
1338: for more information.
1.250 jmc 1339: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1340: .Nm
1341: contains support for Virtual Private Network (VPN) tunnelling
1342: using the
1343: .Xr tun 4
1344: network pseudo-device,
1345: allowing two networks to be joined securely.
1346: The
1347: .Xr sshd_config 5
1348: configuration option
1349: .Cm PermitTunnel
1350: controls whether the server supports this,
1351: and at what level (layer 2 or 3 traffic).
1352: .Pp
1353: The following example would connect client network 10.0.50.0/24
1.265 otto 1354: with remote network 10.0.99.0/24 using a point-to-point connection
1355: from 10.1.1.1 to 10.1.1.2,
1356: provided that the SSH server running on the gateway to the remote network,
1357: at 192.168.1.15, allows it.
1358: .Pp
1359: On the client:
1.250 jmc 1360: .Bd -literal -offset indent
1361: # ssh -f -w 0:1 192.168.1.15 true
1.265 otto 1362: # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1363: # route add 10.0.99.0/24 10.1.1.2
1364: .Ed
1365: .Pp
1366: On the server:
1367: .Bd -literal -offset indent
1368: # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1369: # route add 10.0.50.0/24 10.1.1.1
1.250 jmc 1370: .Ed
1371: .Pp
1372: Client access may be more finely tuned via the
1373: .Pa /root/.ssh/authorized_keys
1374: file (see below) and the
1375: .Cm PermitRootLogin
1376: server option.
1.255 jmc 1377: The following entry would permit connections on
1.250 jmc 1378: .Xr tun 4
1.255 jmc 1379: device 1 from user
1.250 jmc 1380: .Dq jane
1.255 jmc 1381: and on tun device 2 from user
1.250 jmc 1382: .Dq john ,
1383: if
1384: .Cm PermitRootLogin
1385: is set to
1386: .Dq forced-commands-only :
1387: .Bd -literal -offset 2n
1388: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1389: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1390: .Ed
1391: .Pp
1.264 ray 1392: Since an SSH-based setup entails a fair amount of overhead,
1.250 jmc 1393: it may be more suited to temporary setups,
1394: such as for wireless VPNs.
1395: More permanent VPNs are better provided by tools such as
1396: .Xr ipsecctl 8
1397: and
1398: .Xr isakmpd 8 .
1.2 deraadt 1399: .Sh ENVIRONMENT
1400: .Nm
1.1 deraadt 1401: will normally set the following environment variables:
1.237 jmc 1402: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1403: .It Ev DISPLAY
1404: The
1405: .Ev DISPLAY
1.40 aaron 1406: variable indicates the location of the X11 server.
1.44 aaron 1407: It is automatically set by
1.2 deraadt 1408: .Nm
1409: to point to a value of the form
1.233 jmc 1410: .Dq hostname:n ,
1411: where
1412: .Dq hostname
1413: indicates the host where the shell runs, and
1414: .Sq n
1415: is an integer \*(Ge 1.
1.40 aaron 1416: .Nm
1417: uses this special value to forward X11 connections over the secure
1418: channel.
1.107 markus 1419: The user should normally not set
1420: .Ev DISPLAY
1421: explicitly, as that
1.1 deraadt 1422: will render the X11 connection insecure (and will require the user to
1423: manually copy any required authorization cookies).
1.2 deraadt 1424: .It Ev HOME
1.1 deraadt 1425: Set to the path of the user's home directory.
1.2 deraadt 1426: .It Ev LOGNAME
1427: Synonym for
1.12 aaron 1428: .Ev USER ;
1429: set for compatibility with systems that use this variable.
1.2 deraadt 1430: .It Ev MAIL
1.129 stevesk 1431: Set to the path of the user's mailbox.
1.40 aaron 1432: .It Ev PATH
1.2 deraadt 1433: Set to the default
1434: .Ev PATH ,
1435: as specified when compiling
1.234 jmc 1436: .Nm .
1.118 markus 1437: .It Ev SSH_ASKPASS
1438: If
1439: .Nm
1440: needs a passphrase, it will read the passphrase from the current
1441: terminal if it was run from a terminal.
1442: If
1443: .Nm
1444: does not have a terminal associated with it but
1445: .Ev DISPLAY
1446: and
1447: .Ev SSH_ASKPASS
1448: are set, it will execute the program specified by
1449: .Ev SSH_ASKPASS
1450: and open an X11 window to read the passphrase.
1451: This is particularly useful when calling
1452: .Nm
1453: from a
1.196 jmc 1454: .Pa .xsession
1.118 markus 1455: or related script.
1456: (Note that on some machines it
1457: may be necessary to redirect the input from
1458: .Pa /dev/null
1459: to make this work.)
1.413 djm 1460: .It Ev SSH_ASKPASS_REQUIRE
1.414 jmc 1461: Allows further control over the use of an askpass program.
1.413 djm 1462: If this variable is set to
1463: .Dq never
1464: then
1465: .Nm
1466: will never attempt to use one.
1467: If it is set to
1468: .Dq prefer ,
1469: then
1470: .Nm
1471: will prefer to use the askpass program instead of the TTY when requesting
1472: passwords.
1473: Finally, if the variable is set to
1474: .Dq force ,
1475: then the askpass program will be used for all passphrase input regardless
1476: of whether
1477: .Ev DISPLAY
1478: is set.
1.18 markus 1479: .It Ev SSH_AUTH_SOCK
1.233 jmc 1480: Identifies the path of a
1481: .Ux Ns -domain
1482: socket used to communicate with the agent.
1.166 stevesk 1483: .It Ev SSH_CONNECTION
1484: Identifies the client and server ends of the connection.
1.40 aaron 1485: The variable contains
1.233 jmc 1486: four space-separated values: client IP address, client port number,
1487: server IP address, and server port number.
1.73 markus 1488: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1489: This variable contains the original command line if a forced command
1.73 markus 1490: is executed.
1491: It can be used to extract the original arguments.
1.2 deraadt 1492: .It Ev SSH_TTY
1.1 deraadt 1493: This is set to the name of the tty (path to the device) associated
1.40 aaron 1494: with the current shell or command.
1495: If the current session has no tty,
1.1 deraadt 1496: this variable is not set.
1.387 djm 1497: .It Ev SSH_TUNNEL
1498: Optionally set by
1499: .Xr sshd 8
1500: to contain the interface names assigned if tunnel forwarding was
1501: requested by the client.
1.385 djm 1502: .It Ev SSH_USER_AUTH
1503: Optionally set by
1504: .Xr sshd 8 ,
1505: this variable may contain a pathname to a file that lists the authentication
1506: methods successfully used when the session was established, including any
1507: public keys that were used.
1.2 deraadt 1508: .It Ev TZ
1.214 jmc 1509: This variable is set to indicate the present time zone if it
1.257 jmc 1510: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1511: on to new connections).
1.2 deraadt 1512: .It Ev USER
1.1 deraadt 1513: Set to the name of the user logging in.
1.2 deraadt 1514: .El
1515: .Pp
1.44 aaron 1516: Additionally,
1.2 deraadt 1517: .Nm
1.44 aaron 1518: reads
1.207 djm 1519: .Pa ~/.ssh/environment ,
1.2 deraadt 1520: and adds lines of the format
1521: .Dq VARNAME=value
1.233 jmc 1522: to the environment if the file exists and users are allowed to
1.161 marc 1523: change their environment.
1.176 jmc 1524: For more information, see the
1.161 marc 1525: .Cm PermitUserEnvironment
1.162 stevesk 1526: option in
1.161 marc 1527: .Xr sshd_config 5 .
1.2 deraadt 1528: .Sh FILES
1.236 jmc 1529: .Bl -tag -width Ds -compact
1.309 jmc 1530: .It Pa ~/.rhosts
1.240 jmc 1531: This file is used for host-based authentication (see above).
1.92 markus 1532: On some machines this file may need to be
1.240 jmc 1533: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1534: because
1.2 deraadt 1535: .Xr sshd 8
1.40 aaron 1536: reads it as root.
1537: Additionally, this file must be owned by the user,
1538: and must not have write permissions for anyone else.
1539: The recommended
1.1 deraadt 1540: permission for most machines is read/write for the user, and not
1541: accessible by others.
1.2 deraadt 1542: .Pp
1.309 jmc 1543: .It Pa ~/.shosts
1.240 jmc 1544: This file is used in exactly the same way as
1545: .Pa .rhosts ,
1546: but allows host-based authentication without permitting login with
1547: rlogin/rsh.
1.272 mcbride 1548: .Pp
1.309 jmc 1549: .It Pa ~/.ssh/
1.272 mcbride 1550: This directory is the default location for all user-specific configuration
1551: and authentication information.
1552: There is no general requirement to keep the entire contents of this directory
1553: secret, but the recommended permissions are read/write/execute for the user,
1554: and not accessible by others.
1.236 jmc 1555: .Pp
1.309 jmc 1556: .It Pa ~/.ssh/authorized_keys
1.349 sobrado 1557: Lists the public keys (DSA, ECDSA, Ed25519, RSA)
1.343 naddy 1558: that can be used for logging in as this user.
1.238 jmc 1559: The format of this file is described in the
1560: .Xr sshd 8
1561: manual page.
1562: This file is not highly sensitive, but the recommended
1563: permissions are read/write for the user, and not accessible by others.
1564: .Pp
1.309 jmc 1565: .It Pa ~/.ssh/config
1.238 jmc 1566: This is the per-user configuration file.
1567: The file format and configuration options are described in
1568: .Xr ssh_config 5 .
1569: Because of the potential for abuse, this file must have strict permissions:
1.334 djm 1570: read/write for the user, and not writable by others.
1.238 jmc 1571: .Pp
1.309 jmc 1572: .It Pa ~/.ssh/environment
1.239 jmc 1573: Contains additional definitions for environment variables; see
1574: .Sx ENVIRONMENT ,
1.238 jmc 1575: above.
1576: .Pp
1.309 jmc 1577: .It Pa ~/.ssh/id_dsa
1.310 djm 1578: .It Pa ~/.ssh/id_ecdsa
1.404 naddy 1579: .It Pa ~/.ssh/id_ecdsa_sk
1.343 naddy 1580: .It Pa ~/.ssh/id_ed25519
1.406 naddy 1581: .It Pa ~/.ssh/id_ed25519_sk
1.309 jmc 1582: .It Pa ~/.ssh/id_rsa
1.238 jmc 1583: Contains the private key for authentication.
1584: These files
1585: contain sensitive data and should be readable by the user but not
1586: accessible by others (read/write/execute).
1587: .Nm
1588: will simply ignore a private key file if it is accessible by others.
1589: It is possible to specify a passphrase when
1590: generating the key which will be used to encrypt the
1.389 djm 1591: sensitive part of this file using AES-128.
1.238 jmc 1592: .Pp
1.309 jmc 1593: .It Pa ~/.ssh/id_dsa.pub
1.310 djm 1594: .It Pa ~/.ssh/id_ecdsa.pub
1.404 naddy 1595: .It Pa ~/.ssh/id_ecdsa_sk.pub
1.343 naddy 1596: .It Pa ~/.ssh/id_ed25519.pub
1.406 naddy 1597: .It Pa ~/.ssh/id_ed25519_sk.pub
1.309 jmc 1598: .It Pa ~/.ssh/id_rsa.pub
1.238 jmc 1599: Contains the public key for authentication.
1600: These files are not
1601: sensitive and can (but need not) be readable by anyone.
1602: .Pp
1.309 jmc 1603: .It Pa ~/.ssh/known_hosts
1.244 jmc 1604: Contains a list of host keys for all hosts the user has logged into
1605: that are not already in the systemwide list of known host keys.
1.238 jmc 1606: See
1.244 jmc 1607: .Xr sshd 8
1608: for further details of the format of this file.
1.238 jmc 1609: .Pp
1.309 jmc 1610: .It Pa ~/.ssh/rc
1.238 jmc 1611: Commands in this file are executed by
1612: .Nm
1.245 jmc 1613: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1614: started.
1615: See the
1616: .Xr sshd 8
1617: manual page for more information.
1618: .Pp
1.309 jmc 1619: .It Pa /etc/hosts.equiv
1.240 jmc 1620: This file is for host-based authentication (see above).
1621: It should only be writable by root.
1.236 jmc 1622: .Pp
1.309 jmc 1623: .It Pa /etc/shosts.equiv
1.240 jmc 1624: This file is used in exactly the same way as
1625: .Pa hosts.equiv ,
1626: but allows host-based authentication without permitting login with
1627: rlogin/rsh.
1.236 jmc 1628: .Pp
1.238 jmc 1629: .It Pa /etc/ssh/ssh_config
1630: Systemwide configuration file.
1631: The file format and configuration options are described in
1632: .Xr ssh_config 5 .
1633: .Pp
1.309 jmc 1634: .It Pa /etc/ssh/ssh_host_key
1635: .It Pa /etc/ssh/ssh_host_dsa_key
1.310 djm 1636: .It Pa /etc/ssh/ssh_host_ecdsa_key
1.343 naddy 1637: .It Pa /etc/ssh/ssh_host_ed25519_key
1.309 jmc 1638: .It Pa /etc/ssh/ssh_host_rsa_key
1.325 dtucker 1639: These files contain the private parts of the host keys
1.245 jmc 1640: and are used for host-based authentication.
1.238 jmc 1641: .Pp
1.309 jmc 1642: .It Pa /etc/ssh/ssh_known_hosts
1.238 jmc 1643: Systemwide list of known host keys.
1644: This file should be prepared by the
1645: system administrator to contain the public host keys of all machines in the
1646: organization.
1.244 jmc 1647: It should be world-readable.
1648: See
1.238 jmc 1649: .Xr sshd 8
1.244 jmc 1650: for further details of the format of this file.
1.236 jmc 1651: .Pp
1.309 jmc 1652: .It Pa /etc/ssh/sshrc
1.1 deraadt 1653: Commands in this file are executed by
1.2 deraadt 1654: .Nm
1.245 jmc 1655: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1656: See the
1.2 deraadt 1657: .Xr sshd 8
1.1 deraadt 1658: manual page for more information.
1.58 itojun 1659: .El
1.312 jmc 1660: .Sh EXIT STATUS
1661: .Nm
1662: exits with the exit status of the remote command or with 255
1663: if an error occurred.
1.2 deraadt 1664: .Sh SEE ALSO
1665: .Xr scp 1 ,
1.83 djm 1666: .Xr sftp 1 ,
1.2 deraadt 1667: .Xr ssh-add 1 ,
1668: .Xr ssh-agent 1 ,
1669: .Xr ssh-keygen 1 ,
1.242 jmc 1670: .Xr ssh-keyscan 1 ,
1.250 jmc 1671: .Xr tun 4 ,
1.159 stevesk 1672: .Xr ssh_config 5 ,
1.160 naddy 1673: .Xr ssh-keysign 8 ,
1.87 itojun 1674: .Xr sshd 8
1.329 jmc 1675: .Sh STANDARDS
1.106 markus 1676: .Rs
1.329 jmc 1677: .%A S. Lehtinen
1678: .%A C. Lonvick
1679: .%D January 2006
1.256 jmc 1680: .%R RFC 4250
1.329 jmc 1681: .%T The Secure Shell (SSH) Protocol Assigned Numbers
1.256 jmc 1682: .Re
1.329 jmc 1683: .Pp
1.256 jmc 1684: .Rs
1.329 jmc 1685: .%A T. Ylonen
1686: .%A C. Lonvick
1687: .%D January 2006
1.256 jmc 1688: .%R RFC 4251
1.329 jmc 1689: .%T The Secure Shell (SSH) Protocol Architecture
1.256 jmc 1690: .Re
1.329 jmc 1691: .Pp
1.256 jmc 1692: .Rs
1.329 jmc 1693: .%A T. Ylonen
1694: .%A C. Lonvick
1695: .%D January 2006
1.256 jmc 1696: .%R RFC 4252
1.329 jmc 1697: .%T The Secure Shell (SSH) Authentication Protocol
1.256 jmc 1698: .Re
1.329 jmc 1699: .Pp
1.256 jmc 1700: .Rs
1.329 jmc 1701: .%A T. Ylonen
1702: .%A C. Lonvick
1703: .%D January 2006
1.256 jmc 1704: .%R RFC 4253
1.329 jmc 1705: .%T The Secure Shell (SSH) Transport Layer Protocol
1.256 jmc 1706: .Re
1.329 jmc 1707: .Pp
1.256 jmc 1708: .Rs
1.329 jmc 1709: .%A T. Ylonen
1710: .%A C. Lonvick
1711: .%D January 2006
1.256 jmc 1712: .%R RFC 4254
1.329 jmc 1713: .%T The Secure Shell (SSH) Connection Protocol
1.256 jmc 1714: .Re
1.329 jmc 1715: .Pp
1.256 jmc 1716: .Rs
1.329 jmc 1717: .%A J. Schlyter
1718: .%A W. Griffin
1719: .%D January 2006
1.256 jmc 1720: .%R RFC 4255
1.329 jmc 1721: .%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
1.256 jmc 1722: .Re
1.329 jmc 1723: .Pp
1.256 jmc 1724: .Rs
1.329 jmc 1725: .%A F. Cusack
1726: .%A M. Forssen
1727: .%D January 2006
1.256 jmc 1728: .%R RFC 4256
1.329 jmc 1729: .%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)
1.256 jmc 1730: .Re
1.329 jmc 1731: .Pp
1.256 jmc 1732: .Rs
1.329 jmc 1733: .%A J. Galbraith
1734: .%A P. Remaker
1735: .%D January 2006
1.256 jmc 1736: .%R RFC 4335
1.329 jmc 1737: .%T The Secure Shell (SSH) Session Channel Break Extension
1.256 jmc 1738: .Re
1.329 jmc 1739: .Pp
1.256 jmc 1740: .Rs
1.329 jmc 1741: .%A M. Bellare
1742: .%A T. Kohno
1743: .%A C. Namprempre
1744: .%D January 2006
1.256 jmc 1745: .%R RFC 4344
1.329 jmc 1746: .%T The Secure Shell (SSH) Transport Layer Encryption Modes
1.256 jmc 1747: .Re
1.329 jmc 1748: .Pp
1.256 jmc 1749: .Rs
1.329 jmc 1750: .%A B. Harris
1751: .%D January 2006
1.256 jmc 1752: .%R RFC 4345
1.329 jmc 1753: .%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol
1.258 djm 1754: .Re
1.329 jmc 1755: .Pp
1.258 djm 1756: .Rs
1.329 jmc 1757: .%A M. Friedl
1758: .%A N. Provos
1759: .%A W. Simpson
1760: .%D March 2006
1.258 djm 1761: .%R RFC 4419
1.329 jmc 1762: .%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
1.266 markus 1763: .Re
1.329 jmc 1764: .Pp
1.266 markus 1765: .Rs
1.329 jmc 1766: .%A J. Galbraith
1767: .%A R. Thayer
1768: .%D November 2006
1.266 markus 1769: .%R RFC 4716
1.329 jmc 1770: .%T The Secure Shell (SSH) Public Key File Format
1.313 djm 1771: .Re
1.329 jmc 1772: .Pp
1.313 djm 1773: .Rs
1.329 jmc 1774: .%A D. Stebila
1775: .%A J. Green
1776: .%D December 2009
1.313 djm 1777: .%R RFC 5656
1.329 jmc 1778: .%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
1.274 grunk 1779: .Re
1.329 jmc 1780: .Pp
1.274 grunk 1781: .Rs
1782: .%A A. Perrig
1783: .%A D. Song
1784: .%D 1999
1.329 jmc 1785: .%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
1786: .%T Hash Visualization: a New Technique to improve Real-World Security
1.106 markus 1787: .Re
1.173 jmc 1788: .Sh AUTHORS
1789: OpenSSH is a derivative of the original and free
1790: ssh 1.2.12 release by Tatu Ylonen.
1791: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1792: Theo de Raadt and Dug Song
1793: removed many bugs, re-added newer features and
1794: created OpenSSH.
1795: Markus Friedl contributed the support for SSH
1796: protocol versions 1.5 and 2.0.
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