Annotation of src/usr.bin/ssh/ssh.1, Revision 1.438
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: .\"
1.438 ! djm 36: .\" $OpenBSD: ssh.1,v 1.437 2023/07/23 20:04:45 naddy Exp $
! 37: .Dd $Mdocdate: July 23 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
1.360 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 ...
1.438 ! djm 69: .Nm
! 70: .Op Fl Q Ar query_option
1.44 aaron 71: .Sh DESCRIPTION
1.2 deraadt 72: .Nm
1.96 deraadt 73: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 74: executing commands on a remote machine.
1.365 mmcc 75: It is intended to provide secure encrypted communications between
1.40 aaron 76: two untrusted hosts over an insecure network.
1.348 millert 77: X11 connections, arbitrary TCP ports and
78: .Ux Ns -domain
79: sockets can also be forwarded over the secure channel.
1.2 deraadt 80: .Pp
81: .Nm
1.44 aaron 82: connects and logs into the specified
1.388 jmc 83: .Ar destination ,
1.386 millert 84: which may be specified as either
1.388 jmc 85: .Sm off
86: .Oo user @ Oc hostname
87: .Sm on
88: or a URI of the form
89: .Sm off
90: .No ssh:// Oo user @ Oc hostname Op : port .
91: .Sm on
1.1 deraadt 92: The user must prove
1.420 dtucker 93: their identity to the remote machine using one of several methods
1.365 mmcc 94: (see below).
1.49 markus 95: .Pp
1.386 millert 96: If a
1.176 jmc 97: .Ar command
98: is specified,
1.427 dtucker 99: it will be executed on the remote host instead of a login shell.
100: A complete command line may be specified as
101: .Ar command ,
102: or it may have additional arguments.
103: If supplied, the arguments will be appended to the command, separated by
104: spaces, before it is sent to the server to be executed.
1.2 deraadt 105: .Pp
1.218 jmc 106: The options are as follows:
1.361 millert 107: .Pp
1.360 millert 108: .Bl -tag -width Ds -compact
1.218 jmc 109: .It Fl 4
110: Forces
1.2 deraadt 111: .Nm
1.218 jmc 112: to use IPv4 addresses only.
1.360 millert 113: .Pp
1.218 jmc 114: .It Fl 6
115: Forces
1.2 deraadt 116: .Nm
1.218 jmc 117: to use IPv6 addresses only.
1.360 millert 118: .Pp
1.218 jmc 119: .It Fl A
1.407 jmc 120: Enables forwarding of connections from an authentication agent such as
121: .Xr ssh-agent 1 .
1.218 jmc 122: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 123: .Pp
1.218 jmc 124: Agent forwarding should be enabled with caution.
125: Users with the ability to bypass file permissions on the remote host
1.285 sobrado 126: (for the agent's
1.286 sobrado 127: .Ux Ns -domain
128: socket) can access the local agent through the forwarded connection.
1.218 jmc 129: An attacker cannot obtain key material from the agent,
130: however they can perform operations on the keys that enable them to
131: authenticate using the identities loaded into the agent.
1.407 jmc 132: A safer alternative may be to use a jump host
133: (see
134: .Fl J ) .
1.360 millert 135: .Pp
1.218 jmc 136: .It Fl a
137: Disables forwarding of the authentication agent connection.
1.390 djm 138: .Pp
1.391 jmc 139: .It Fl B Ar bind_interface
1.390 djm 140: Bind to the address of
1.391 jmc 141: .Ar bind_interface
1.390 djm 142: before attempting to connect to the destination host.
143: This is only useful on systems with more than one address.
1.360 millert 144: .Pp
1.218 jmc 145: .It Fl b Ar bind_address
146: Use
147: .Ar bind_address
148: on the local machine as the source address
149: of the connection.
150: Only useful on systems with more than one address.
1.360 millert 151: .Pp
1.218 jmc 152: .It Fl C
153: Requests compression of all data (including stdin, stdout, stderr, and
1.348 millert 154: data for forwarded X11, TCP and
155: .Ux Ns -domain
156: connections).
1.218 jmc 157: The compression algorithm is the same used by
1.377 djm 158: .Xr gzip 1 .
1.218 jmc 159: Compression is desirable on modem lines and other
160: slow connections, but will only slow down things on fast networks.
161: The default value can be set on a host-by-host basis in the
162: configuration files; see the
163: .Cm Compression
1.431 jmc 164: option in
165: .Xr ssh_config 5 .
1.360 millert 166: .Pp
1.218 jmc 167: .It Fl c Ar cipher_spec
168: Selects the cipher specification for encrypting the session.
169: .Ar cipher_spec
170: is a comma-separated list of ciphers
171: listed in order of preference.
1.283 jmc 172: See the
173: .Cm Ciphers
1.307 dtucker 174: keyword in
175: .Xr ssh_config 5
176: for more information.
1.360 millert 177: .Pp
1.218 jmc 178: .It Fl D Xo
179: .Sm off
180: .Oo Ar bind_address : Oc
181: .Ar port
182: .Sm on
183: .Xc
184: Specifies a local
185: .Dq dynamic
186: application-level port forwarding.
187: This works by allocating a socket to listen to
188: .Ar port
189: on the local side, optionally bound to the specified
190: .Ar bind_address .
191: Whenever a connection is made to this port, the
192: connection is forwarded over the secure channel, and the application
193: protocol is then used to determine where to connect to from the
194: remote machine.
195: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.107 markus 196: .Nm
1.218 jmc 197: will act as a SOCKS server.
198: Only root can forward privileged ports.
199: Dynamic port forwardings can also be specified in the configuration file.
1.49 markus 200: .Pp
1.308 djm 201: IPv6 addresses can be specified by enclosing the address in square brackets.
1.218 jmc 202: Only the superuser can forward privileged ports.
203: By default, the local port is bound in accordance with the
204: .Cm GatewayPorts
205: setting.
206: However, an explicit
207: .Ar bind_address
208: may be used to bind the connection to a specific address.
209: The
210: .Ar bind_address
211: of
212: .Dq localhost
213: indicates that the listening port be bound for local use only, while an
214: empty address or
215: .Sq *
216: indicates that the port should be available from all interfaces.
1.360 millert 217: .Pp
1.331 dtucker 218: .It Fl E Ar log_file
219: Append debug logs to
220: .Ar log_file
221: instead of standard error.
1.360 millert 222: .Pp
1.229 jmc 223: .It Fl e Ar escape_char
1.218 jmc 224: Sets the escape character for sessions with a pty (default:
225: .Ql ~ ) .
226: The escape character is only recognized at the beginning of a line.
227: The escape character followed by a dot
228: .Pq Ql \&.
229: closes the connection;
230: followed by control-Z suspends the connection;
231: and followed by itself sends the escape character once.
232: Setting the character to
1.2 deraadt 233: .Dq none
1.218 jmc 234: disables any escapes and makes the session fully transparent.
1.360 millert 235: .Pp
1.218 jmc 236: .It Fl F Ar configfile
237: Specifies an alternative per-user configuration file.
238: If a configuration file is given on the command line,
239: the system-wide configuration file
240: .Pq Pa /etc/ssh/ssh_config
241: will be ignored.
242: The default for the per-user configuration file is
243: .Pa ~/.ssh/config .
1.411 naddy 244: If set to
245: .Dq none ,
246: no configuration files will be read.
1.360 millert 247: .Pp
1.218 jmc 248: .It Fl f
249: Requests
250: .Nm
251: to go to background just before command execution.
252: This is useful if
1.176 jmc 253: .Nm
1.218 jmc 254: is going to ask for passwords or passphrases, but the user
255: wants it in the background.
256: This implies
257: .Fl n .
258: The recommended way to start X11 programs at a remote site is with
259: something like
260: .Ic ssh -f host xterm .
1.277 djm 261: .Pp
262: If the
263: .Cm ExitOnForwardFailure
264: configuration option is set to
265: .Dq yes ,
266: then a client started with
267: .Fl f
268: will wait for all remote port forwards to be successfully established
269: before placing itself in the background.
1.424 djm 270: Refer to the description of
271: .Cm ForkAfterAuthentication
272: in
273: .Xr ssh_config 5
274: for details.
1.360 millert 275: .Pp
1.350 djm 276: .It Fl G
277: Causes
278: .Nm
279: to print its configuration after evaluating
280: .Cm Host
281: and
282: .Cm Match
283: blocks and exit.
1.360 millert 284: .Pp
1.218 jmc 285: .It Fl g
286: Allows remote hosts to connect to local forwarded ports.
1.346 djm 287: If used on a multiplexed connection, then this option must be specified
288: on the master process.
1.360 millert 289: .Pp
1.291 markus 290: .It Fl I Ar pkcs11
1.294 jmc 291: Specify the PKCS#11 shared library
1.176 jmc 292: .Nm
1.401 naddy 293: should use to communicate with a PKCS#11 token providing keys for user
294: authentication.
1.360 millert 295: .Pp
1.218 jmc 296: .It Fl i Ar identity_file
297: Selects a file from which the identity (private key) for
1.310 djm 298: public key authentication is read.
1.426 dtucker 299: You can also specify a public key file to use the corresponding
300: private key that is loaded in
301: .Xr ssh-agent 1
302: when the private key file is not present locally.
1.218 jmc 303: The default is
1.428 dtucker 304: .Pa ~/.ssh/id_rsa ,
1.343 naddy 305: .Pa ~/.ssh/id_ecdsa ,
1.404 naddy 306: .Pa ~/.ssh/id_ecdsa_sk ,
1.406 naddy 307: .Pa ~/.ssh/id_ed25519 ,
308: .Pa ~/.ssh/id_ed25519_sk
1.310 djm 309: and
1.428 dtucker 310: .Pa ~/.ssh/id_dsa .
1.218 jmc 311: Identity files may also be specified on
312: a per-host basis in the configuration file.
313: It is possible to have multiple
314: .Fl i
315: options (and multiple identities specified in
316: configuration files).
1.364 jmc 317: If no certificates have been explicitly specified by the
1.363 djm 318: .Cm CertificateFile
319: directive,
1.302 djm 320: .Nm
321: will also try to load certificate information from the filename obtained
322: by appending
323: .Pa -cert.pub
324: to identity filenames.
1.360 millert 325: .Pp
1.386 millert 326: .It Fl J Ar destination
1.437 naddy 327: Connect to the target host by first making an
1.375 djm 328: .Nm
1.386 millert 329: connection to the jump host described by
330: .Ar destination
1.376 jmc 331: and then establishing a TCP forwarding to the ultimate destination from
1.375 djm 332: there.
333: Multiple jump hops may be specified separated by comma characters.
334: This is a shortcut to specify a
335: .Cm ProxyJump
336: configuration directive.
1.400 djm 337: Note that configuration directives supplied on the command-line generally
338: apply to the destination host and not any specified jump hosts.
339: Use
340: .Pa ~/.ssh/config
341: to specify configuration for jump hosts.
1.375 djm 342: .Pp
1.269 djm 343: .It Fl K
344: Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
345: credentials to the server.
1.360 millert 346: .Pp
1.218 jmc 347: .It Fl k
348: Disables forwarding (delegation) of GSSAPI credentials to the server.
1.360 millert 349: .Pp
1.218 jmc 350: .It Fl L Xo
351: .Sm off
352: .Oo Ar bind_address : Oc
353: .Ar port : host : hostport
354: .Sm on
355: .Xc
1.360 millert 356: .It Fl L Xo
357: .Sm off
358: .Oo Ar bind_address : Oc
359: .Ar port : remote_socket
360: .Sm on
361: .Xc
362: .It Fl L Xo
363: .Sm off
364: .Ar local_socket : host : hostport
365: .Sm on
366: .Xc
367: .It Fl L Xo
368: .Sm off
369: .Ar local_socket : remote_socket
370: .Sm on
371: .Xc
372: Specifies that connections to the given TCP port or Unix socket on the local
373: (client) host are to be forwarded to the given host and port, or Unix socket,
374: on the remote side.
375: This works by allocating a socket to listen to either a TCP
1.218 jmc 376: .Ar port
377: on the local side, optionally bound to the specified
1.360 millert 378: .Ar bind_address ,
379: or to a Unix socket.
380: Whenever a connection is made to the local port or socket, the
1.218 jmc 381: connection is forwarded over the secure channel, and a connection is
1.360 millert 382: made to either
1.218 jmc 383: .Ar host
384: port
1.360 millert 385: .Ar hostport ,
386: or the Unix socket
387: .Ar remote_socket ,
1.218 jmc 388: from the remote machine.
1.360 millert 389: .Pp
1.218 jmc 390: Port forwardings can also be specified in the configuration file.
1.360 millert 391: Only the superuser can forward privileged ports.
1.308 djm 392: IPv6 addresses can be specified by enclosing the address in square brackets.
1.360 millert 393: .Pp
1.218 jmc 394: By default, the local port is bound in accordance with the
395: .Cm GatewayPorts
396: setting.
397: However, an explicit
398: .Ar bind_address
399: may be used to bind the connection to a specific address.
1.2 deraadt 400: The
1.218 jmc 401: .Ar bind_address
402: of
403: .Dq localhost
404: indicates that the listening port be bound for local use only, while an
405: empty address or
406: .Sq *
407: indicates that the port should be available from all interfaces.
1.360 millert 408: .Pp
1.218 jmc 409: .It Fl l Ar login_name
410: Specifies the user to log in as on the remote machine.
411: This also may be specified on a per-host basis in the configuration file.
1.360 millert 412: .Pp
1.218 jmc 413: .It Fl M
414: Places the
415: .Nm
416: client into
417: .Dq master
418: mode for connection sharing.
1.231 stevesk 419: Multiple
420: .Fl M
421: options places
422: .Nm
423: into
424: .Dq master
1.397 djm 425: mode but with confirmation required using
426: .Xr ssh-askpass 1
427: before each operation that changes the multiplexing state
428: (e.g. opening a new session).
1.218 jmc 429: Refer to the description of
430: .Cm ControlMaster
431: in
432: .Xr ssh_config 5
433: for details.
1.360 millert 434: .Pp
1.218 jmc 435: .It Fl m Ar mac_spec
1.369 jmc 436: A comma-separated list of MAC (message authentication code) algorithms,
437: specified in order of preference.
1.218 jmc 438: See the
439: .Cm MACs
1.431 jmc 440: keyword in
441: .Xr ssh_config 5
442: for more information.
1.360 millert 443: .Pp
1.218 jmc 444: .It Fl N
445: Do not execute a remote command.
1.369 jmc 446: This is useful for just forwarding ports.
1.422 djm 447: Refer to the description of
448: .Cm SessionType
449: in
450: .Xr ssh_config 5
451: for details.
1.360 millert 452: .Pp
1.218 jmc 453: .It Fl n
454: Redirects stdin from
455: .Pa /dev/null
456: (actually, prevents reading from stdin).
457: This must be used when
1.2 deraadt 458: .Nm
1.218 jmc 459: is run in the background.
460: A common trick is to use this to run X11 programs on a remote machine.
461: For example,
462: .Ic ssh -n shadows.cs.hut.fi emacs &
463: will start an emacs on shadows.cs.hut.fi, and the X11
464: connection will be automatically forwarded over an encrypted channel.
465: The
1.2 deraadt 466: .Nm
1.218 jmc 467: program will be put in the background.
468: (This does not work if
1.2 deraadt 469: .Nm
1.218 jmc 470: needs to ask for a password or passphrase; see also the
471: .Fl f
472: option.)
1.423 djm 473: Refer to the description of
474: .Cm StdinNull
475: in
476: .Xr ssh_config 5
477: for details.
1.360 millert 478: .Pp
1.218 jmc 479: .It Fl O Ar ctl_cmd
480: Control an active connection multiplexing master process.
481: When the
482: .Fl O
483: option is specified, the
484: .Ar ctl_cmd
485: argument is interpreted and passed to the master process.
486: Valid commands are:
487: .Dq check
1.305 markus 488: (check that the master process is running),
489: .Dq forward
1.318 jmc 490: (request forwardings without command execution),
1.323 okan 491: .Dq cancel
492: (cancel forwardings),
1.218 jmc 493: .Dq exit
1.318 jmc 494: (request the master to exit), and
1.317 djm 495: .Dq stop
496: (request the master to stop accepting further multiplexing requests).
1.360 millert 497: .Pp
1.218 jmc 498: .It Fl o Ar option
499: Can be used to give options in the format used in the configuration file.
500: This is useful for specifying options for which there is no separate
501: command-line flag.
502: For full details of the options listed below, and their possible values, see
503: .Xr ssh_config 5 .
1.2 deraadt 504: .Pp
1.218 jmc 505: .Bl -tag -width Ds -offset indent -compact
1.366 jcs 506: .It AddKeysToAgent
1.218 jmc 507: .It AddressFamily
508: .It BatchMode
509: .It BindAddress
1.338 djm 510: .It CanonicalDomains
1.339 djm 511: .It CanonicalizeFallbackLocal
512: .It CanonicalizeHostname
513: .It CanonicalizeMaxDots
514: .It CanonicalizePermittedCNAMEs
1.399 jmc 515: .It CASignatureAlgorithms
1.363 djm 516: .It CertificateFile
1.218 jmc 517: .It CheckHostIP
518: .It Ciphers
519: .It ClearAllForwardings
520: .It Compression
1.380 naddy 521: .It ConnectionAttempts
1.218 jmc 522: .It ConnectTimeout
523: .It ControlMaster
524: .It ControlPath
1.321 djm 525: .It ControlPersist
1.218 jmc 526: .It DynamicForward
1.433 djm 527: .It EnableEscapeCommandline
1.218 jmc 528: .It EscapeChar
1.263 markus 529: .It ExitOnForwardFailure
1.353 jmc 530: .It FingerprintHash
1.424 djm 531: .It ForkAfterAuthentication
1.218 jmc 532: .It ForwardAgent
533: .It ForwardX11
1.321 djm 534: .It ForwardX11Timeout
1.218 jmc 535: .It ForwardX11Trusted
536: .It GatewayPorts
537: .It GlobalKnownHostsFile
538: .It GSSAPIAuthentication
539: .It GSSAPIDelegateCredentials
540: .It HashKnownHosts
541: .It Host
1.418 naddy 542: .It HostbasedAcceptedAlgorithms
1.218 jmc 543: .It HostbasedAuthentication
544: .It HostKeyAlgorithms
545: .It HostKeyAlias
1.403 jmc 546: .It Hostname
1.374 jmc 547: .It IdentitiesOnly
1.371 markus 548: .It IdentityAgent
1.218 jmc 549: .It IdentityFile
1.316 jmc 550: .It IPQoS
1.321 djm 551: .It KbdInteractiveAuthentication
1.218 jmc 552: .It KbdInteractiveDevices
1.314 jmc 553: .It KexAlgorithms
1.415 djm 554: .It KnownHostsCommand
1.218 jmc 555: .It LocalCommand
556: .It LocalForward
557: .It LogLevel
558: .It MACs
1.337 jmc 559: .It Match
1.218 jmc 560: .It NoHostAuthenticationForLocalhost
561: .It NumberOfPasswordPrompts
562: .It PasswordAuthentication
563: .It PermitLocalCommand
1.419 markus 564: .It PermitRemoteOpen
1.291 markus 565: .It PKCS11Provider
1.218 jmc 566: .It Port
567: .It PreferredAuthentications
568: .It ProxyCommand
1.375 djm 569: .It ProxyJump
1.336 jmc 570: .It ProxyUseFdpass
1.416 dtucker 571: .It PubkeyAcceptedAlgorithms
1.218 jmc 572: .It PubkeyAuthentication
1.251 dtucker 573: .It RekeyLimit
1.382 bluhm 574: .It RemoteCommand
1.218 jmc 575: .It RemoteForward
1.319 jmc 576: .It RequestTTY
1.432 djm 577: .It RequiredRSASize
1.218 jmc 578: .It SendEnv
579: .It ServerAliveInterval
580: .It ServerAliveCountMax
1.422 djm 581: .It SessionType
1.395 jmc 582: .It SetEnv
1.423 djm 583: .It StdinNull
1.347 jmc 584: .It StreamLocalBindMask
585: .It StreamLocalBindUnlink
1.218 jmc 586: .It StrictHostKeyChecking
587: .It TCPKeepAlive
588: .It Tunnel
589: .It TunnelDevice
1.354 djm 590: .It UpdateHostKeys
1.218 jmc 591: .It User
592: .It UserKnownHostsFile
593: .It VerifyHostKeyDNS
1.276 jmc 594: .It VisualHostKey
1.218 jmc 595: .It XAuthLocation
596: .El
1.360 millert 597: .Pp
1.435 djm 598: .It Fl P Ar tag
599: Specify a tag name that may be used to select configuration in
600: .Xr ssh_config 5 .
601: Refer to the
602: .Cm Tag
603: and
604: .Cm Match
605: keywords in
606: .Xr ssh_config 5
607: for more information.
1.218 jmc 608: .It Fl p Ar port
609: Port to connect to on the remote host.
610: This can be specified on a
611: per-host basis in the configuration file.
1.360 millert 612: .Pp
1.362 djm 613: .It Fl Q Ar query_option
1.425 jmc 614: Queries for the algorithms supported by one of the following features:
1.341 deraadt 615: .Ar cipher
1.332 djm 616: (supported symmetric ciphers),
1.341 deraadt 617: .Ar cipher-auth
1.340 djm 618: (supported symmetric ciphers that support authenticated encryption),
1.398 djm 619: .Ar help
620: (supported query terms for use with the
621: .Fl Q
622: flag),
1.341 deraadt 623: .Ar mac
1.332 djm 624: (supported message integrity codes),
1.341 deraadt 625: .Ar kex
1.332 djm 626: (key exchange algorithms),
1.341 deraadt 627: .Ar key
1.362 djm 628: (key types),
1.434 djm 629: .Ar key-ca-sign
630: (valid CA signature algorithms for certificates),
1.362 djm 631: .Ar key-cert
632: (certificate key types),
633: .Ar key-plain
1.398 djm 634: (non-certificate key types),
1.410 dtucker 635: .Ar key-sig
636: (all key types and signature algorithms),
1.356 djm 637: .Ar protocol-version
1.398 djm 638: (supported SSH protocol versions), and
639: .Ar sig
640: (supported signature algorithms).
1.410 dtucker 641: Alternatively, any keyword from
642: .Xr ssh_config 5
643: or
644: .Xr sshd_config 5
645: that takes an algorithm list may be used as an alias for the corresponding
646: query_option.
1.360 millert 647: .Pp
1.218 jmc 648: .It Fl q
649: Quiet mode.
1.271 djm 650: Causes most warning and diagnostic messages to be suppressed.
1.360 millert 651: .Pp
1.218 jmc 652: .It Fl R Xo
653: .Sm off
654: .Oo Ar bind_address : Oc
655: .Ar port : host : hostport
656: .Sm on
657: .Xc
1.360 millert 658: .It Fl R Xo
659: .Sm off
660: .Oo Ar bind_address : Oc
661: .Ar port : local_socket
662: .Sm on
663: .Xc
664: .It Fl R Xo
665: .Sm off
666: .Ar remote_socket : host : hostport
667: .Sm on
668: .Xc
669: .It Fl R Xo
670: .Sm off
671: .Ar remote_socket : local_socket
672: .Sm on
673: .Xc
1.384 markus 674: .It Fl R Xo
675: .Sm off
676: .Oo Ar bind_address : Oc
677: .Ar port
678: .Sm on
679: .Xc
1.360 millert 680: Specifies that connections to the given TCP port or Unix socket on the remote
1.384 markus 681: (server) host are to be forwarded to the local side.
682: .Pp
1.360 millert 683: This works by allocating a socket to listen to either a TCP
1.218 jmc 684: .Ar port
1.360 millert 685: or to a Unix socket on the remote side.
686: Whenever a connection is made to this port or Unix socket, the
687: connection is forwarded over the secure channel, and a connection
1.384 markus 688: is made from the local machine to either an explicit destination specified by
1.218 jmc 689: .Ar host
690: port
1.360 millert 691: .Ar hostport ,
692: or
693: .Ar local_socket ,
1.384 markus 694: or, if no explicit destination was specified,
695: .Nm
696: will act as a SOCKS 4/5 proxy and forward connections to the destinations
697: requested by the remote SOCKS client.
1.2 deraadt 698: .Pp
1.218 jmc 699: Port forwardings can also be specified in the configuration file.
700: Privileged ports can be forwarded only when
701: logging in as root on the remote machine.
1.324 jmc 702: IPv6 addresses can be specified by enclosing the address in square brackets.
1.194 jakob 703: .Pp
1.360 millert 704: By default, TCP listening sockets on the server will be bound to the loopback
1.218 jmc 705: interface only.
1.280 tobias 706: This may be overridden by specifying a
1.218 jmc 707: .Ar bind_address .
708: An empty
709: .Ar bind_address ,
710: or the address
711: .Ql * ,
712: indicates that the remote socket should listen on all interfaces.
713: Specifying a remote
714: .Ar bind_address
715: will only succeed if the server's
716: .Cm GatewayPorts
717: option is enabled (see
718: .Xr sshd_config 5 ) .
1.281 djm 719: .Pp
720: If the
721: .Ar port
722: argument is
1.282 djm 723: .Ql 0 ,
1.281 djm 724: the listen port will be dynamically allocated on the server and reported
725: to the client at run time.
1.305 markus 726: When used together with
1.430 naddy 727: .Ic -O forward ,
1.305 markus 728: the allocated port will be printed to the standard output.
1.360 millert 729: .Pp
1.218 jmc 730: .It Fl S Ar ctl_path
1.304 jmc 731: Specifies the location of a control socket for connection sharing,
1.303 djm 732: or the string
733: .Dq none
734: to disable connection sharing.
1.218 jmc 735: Refer to the description of
736: .Cm ControlPath
737: and
738: .Cm ControlMaster
739: in
740: .Xr ssh_config 5
741: for details.
1.360 millert 742: .Pp
1.218 jmc 743: .It Fl s
744: May be used to request invocation of a subsystem on the remote system.
1.369 jmc 745: Subsystems facilitate the use of SSH
746: as a secure transport for other applications (e.g.\&
1.218 jmc 747: .Xr sftp 1 ) .
748: The subsystem is specified as the remote command.
1.422 djm 749: Refer to the description of
750: .Cm SessionType
751: in
752: .Xr ssh_config 5
753: for details.
1.360 millert 754: .Pp
1.218 jmc 755: .It Fl T
1.357 dtucker 756: Disable pseudo-terminal allocation.
1.360 millert 757: .Pp
1.218 jmc 758: .It Fl t
1.357 dtucker 759: Force pseudo-terminal allocation.
1.218 jmc 760: This can be used to execute arbitrary
761: screen-based programs on a remote machine, which can be very useful,
1.257 jmc 762: e.g. when implementing menu services.
1.218 jmc 763: Multiple
764: .Fl t
765: options force tty allocation, even if
1.194 jakob 766: .Nm
1.218 jmc 767: has no local tty.
1.360 millert 768: .Pp
1.218 jmc 769: .It Fl V
770: Display the version number and exit.
1.360 millert 771: .Pp
1.218 jmc 772: .It Fl v
773: Verbose mode.
774: Causes
1.176 jmc 775: .Nm
1.218 jmc 776: to print debugging messages about its progress.
777: This is helpful in
778: debugging connection, authentication, and configuration problems.
779: Multiple
780: .Fl v
781: options increase the verbosity.
782: The maximum is 3.
1.360 millert 783: .Pp
1.290 dtucker 784: .It Fl W Ar host : Ns Ar port
785: Requests that standard input and output on the client be forwarded to
786: .Ar host
787: on
788: .Ar port
789: over the secure channel.
790: Implies
791: .Fl N ,
792: .Fl T ,
793: .Cm ExitOnForwardFailure
794: and
1.373 jmc 795: .Cm ClearAllForwardings ,
796: though these can be overridden in the configuration file or using
1.372 dtucker 797: .Fl o
798: command line options.
1.360 millert 799: .Pp
1.261 stevesk 800: .It Fl w Xo
801: .Ar local_tun Ns Op : Ns Ar remote_tun
802: .Xc
803: Requests
804: tunnel
805: device forwarding with the specified
1.218 jmc 806: .Xr tun 4
1.261 stevesk 807: devices between the client
808: .Pq Ar local_tun
809: and the server
810: .Pq Ar remote_tun .
811: .Pp
1.228 jmc 812: The devices may be specified by numerical ID or the keyword
813: .Dq any ,
814: which uses the next available tunnel device.
1.261 stevesk 815: If
816: .Ar remote_tun
817: is not specified, it defaults to
818: .Dq any .
1.228 jmc 819: See also the
1.218 jmc 820: .Cm Tunnel
1.261 stevesk 821: and
822: .Cm TunnelDevice
823: directives in
1.218 jmc 824: .Xr ssh_config 5 .
1.393 djm 825: .Pp
1.261 stevesk 826: If the
827: .Cm Tunnel
1.393 djm 828: directive is unset, it will be set to the default tunnel mode, which is
1.261 stevesk 829: .Dq point-to-point .
1.393 djm 830: If a different
831: .Cm Tunnel
832: forwarding mode it desired, then it should be specified before
833: .Fl w .
1.360 millert 834: .Pp
1.218 jmc 835: .It Fl X
836: Enables X11 forwarding.
1.54 markus 837: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 838: .Pp
1.218 jmc 839: X11 forwarding should be enabled with caution.
1.168 jmc 840: Users with the ability to bypass file permissions on the remote host
1.218 jmc 841: (for the user's X authorization database)
842: can access the local X11 display through the forwarded connection.
843: An attacker may then be able to perform activities such as keystroke monitoring.
844: .Pp
845: For this reason, X11 forwarding is subjected to X11 SECURITY extension
846: restrictions by default.
1.429 jsg 847: Refer to the
1.218 jmc 848: .Nm
849: .Fl Y
850: option and the
851: .Cm ForwardX11Trusted
852: directive in
853: .Xr ssh_config 5
854: for more information.
1.360 millert 855: .Pp
1.218 jmc 856: .It Fl x
857: Disables X11 forwarding.
1.360 millert 858: .Pp
1.218 jmc 859: .It Fl Y
860: Enables trusted X11 forwarding.
861: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
862: controls.
1.360 millert 863: .Pp
1.278 djm 864: .It Fl y
865: Send log information using the
866: .Xr syslog 3
867: system module.
868: By default this information is sent to stderr.
1.218 jmc 869: .El
1.224 jmc 870: .Pp
871: .Nm
872: may additionally obtain configuration data from
873: a per-user configuration file and a system-wide configuration file.
874: The file format and configuration options are described in
875: .Xr ssh_config 5 .
1.222 jmc 876: .Sh AUTHENTICATION
1.377 djm 877: The OpenSSH SSH client supports SSH protocol 2.
1.222 jmc 878: .Pp
879: The methods available for authentication are:
1.260 jmc 880: GSSAPI-based authentication,
1.222 jmc 881: host-based authentication,
882: public key authentication,
1.421 dtucker 883: keyboard-interactive authentication,
1.222 jmc 884: and password authentication.
885: Authentication methods are tried in the order specified above,
1.369 jmc 886: though
887: .Cm PreferredAuthentications
888: can be used to change the default order.
1.222 jmc 889: .Pp
890: Host-based authentication works as follows:
1.218 jmc 891: If the machine the user logs in from is listed in
892: .Pa /etc/hosts.equiv
893: or
894: .Pa /etc/shosts.equiv
1.412 djm 895: on the remote machine, the user is non-root and the user names are
1.218 jmc 896: the same on both sides, or if the files
897: .Pa ~/.rhosts
898: or
899: .Pa ~/.shosts
900: exist in the user's home directory on the
901: remote machine and contain a line containing the name of the client
902: machine and the name of the user on that machine, the user is
1.222 jmc 903: considered for login.
904: Additionally, the server
905: .Em must
906: be able to verify the client's
907: host key (see the description of
1.218 jmc 908: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 909: and
1.222 jmc 910: .Pa ~/.ssh/known_hosts ,
911: below)
912: for login to be permitted.
1.218 jmc 913: This authentication method closes security holes due to IP
1.222 jmc 914: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 915: [Note to the administrator:
916: .Pa /etc/hosts.equiv ,
917: .Pa ~/.rhosts ,
918: and the rlogin/rsh protocol in general, are inherently insecure and should be
919: disabled if security is desired.]
1.189 dtucker 920: .Pp
1.222 jmc 921: Public key authentication works as follows:
922: The scheme is based on public-key cryptography,
923: using cryptosystems
924: where encryption and decryption are done using separate keys,
925: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 926: The idea is that each user creates a public/private
927: key pair for authentication purposes.
928: The server knows the public key, and only the user knows the private key.
1.222 jmc 929: .Nm
930: implements public key authentication protocol automatically,
1.349 sobrado 931: using one of the DSA, ECDSA, Ed25519 or RSA algorithms.
1.333 jmc 932: The HISTORY section of
1.222 jmc 933: .Xr ssl 8
1.311 jmc 934: contains a brief discussion of the DSA and RSA algorithms.
1.210 djm 935: .Pp
1.218 jmc 936: The file
937: .Pa ~/.ssh/authorized_keys
938: lists the public keys that are permitted for logging in.
939: When the user logs in, the
1.2 deraadt 940: .Nm
1.218 jmc 941: program tells the server which key pair it would like to use for
942: authentication.
1.222 jmc 943: The client proves that it has access to the private key
944: and the server checks that the corresponding public key
945: is authorized to accept the account.
1.383 djm 946: .Pp
947: The server may inform the client of errors that prevented public key
948: authentication from succeeding after authentication completes using a
949: different method.
950: These may be viewed by increasing the
951: .Cm LogLevel
952: to
953: .Cm DEBUG
954: or higher (e.g. by using the
955: .Fl v
956: flag).
1.218 jmc 957: .Pp
1.420 dtucker 958: The user creates their key pair by running
1.218 jmc 959: .Xr ssh-keygen 1 .
960: This stores the private key in
1.222 jmc 961: .Pa ~/.ssh/id_dsa
1.369 jmc 962: (DSA),
1.310 djm 963: .Pa ~/.ssh/id_ecdsa
1.369 jmc 964: (ECDSA),
1.404 naddy 965: .Pa ~/.ssh/id_ecdsa_sk
1.409 naddy 966: (authenticator-hosted ECDSA),
1.343 naddy 967: .Pa ~/.ssh/id_ed25519
1.369 jmc 968: (Ed25519),
1.406 naddy 969: .Pa ~/.ssh/id_ed25519_sk
1.409 naddy 970: (authenticator-hosted Ed25519),
1.222 jmc 971: or
972: .Pa ~/.ssh/id_rsa
1.369 jmc 973: (RSA)
1.218 jmc 974: and stores the public key in
1.222 jmc 975: .Pa ~/.ssh/id_dsa.pub
1.369 jmc 976: (DSA),
1.310 djm 977: .Pa ~/.ssh/id_ecdsa.pub
1.369 jmc 978: (ECDSA),
1.404 naddy 979: .Pa ~/.ssh/id_ecdsa_sk.pub
1.409 naddy 980: (authenticator-hosted ECDSA),
1.343 naddy 981: .Pa ~/.ssh/id_ed25519.pub
1.369 jmc 982: (Ed25519),
1.406 naddy 983: .Pa ~/.ssh/id_ed25519_sk.pub
1.409 naddy 984: (authenticator-hosted Ed25519),
1.222 jmc 985: or
986: .Pa ~/.ssh/id_rsa.pub
1.369 jmc 987: (RSA)
1.218 jmc 988: in the user's home directory.
1.222 jmc 989: The user should then copy the public key
1.218 jmc 990: to
991: .Pa ~/.ssh/authorized_keys
1.420 dtucker 992: in their home directory on the remote machine.
1.222 jmc 993: The
1.218 jmc 994: .Pa authorized_keys
995: file corresponds to the conventional
996: .Pa ~/.rhosts
997: file, and has one key
1.222 jmc 998: per line, though the lines can be very long.
1.218 jmc 999: After this, the user can log in without giving the password.
1000: .Pp
1.301 jmc 1001: A variation on public key authentication
1002: is available in the form of certificate authentication:
1003: instead of a set of public/private keys,
1004: signed certificates are used.
1005: This has the advantage that a single trusted certification authority
1006: can be used in place of many public/private keys.
1.333 jmc 1007: See the CERTIFICATES section of
1.301 jmc 1008: .Xr ssh-keygen 1
1009: for more information.
1010: .Pp
1011: The most convenient way to use public key or certificate authentication
1012: may be with an authentication agent.
1.218 jmc 1013: See
1014: .Xr ssh-agent 1
1.366 jcs 1015: and (optionally) the
1016: .Cm AddKeysToAgent
1017: directive in
1018: .Xr ssh_config 5
1.218 jmc 1019: for more information.
1020: .Pp
1.421 dtucker 1021: Keyboard-interactive authentication works as follows:
1.222 jmc 1022: The server sends an arbitrary
1023: .Qq challenge
1.421 dtucker 1024: text and prompts for a response, possibly multiple times.
1025: Examples of keyboard-interactive authentication include
1.335 jmc 1026: .Bx
1027: Authentication (see
1.222 jmc 1028: .Xr login.conf 5 )
1.335 jmc 1029: and PAM (some
1030: .Pf non- Ox
1031: systems).
1.222 jmc 1032: .Pp
1033: Finally, if other authentication methods fail,
1.218 jmc 1034: .Nm
1035: prompts the user for a password.
1036: The password is sent to the remote
1037: host for checking; however, since all communications are encrypted,
1038: the password cannot be seen by someone listening on the network.
1.232 jmc 1039: .Pp
1040: .Nm
1041: automatically maintains and checks a database containing
1042: identification for all hosts it has ever been used with.
1043: Host keys are stored in
1044: .Pa ~/.ssh/known_hosts
1045: in the user's home directory.
1046: Additionally, the file
1047: .Pa /etc/ssh/ssh_known_hosts
1048: is automatically checked for known hosts.
1049: Any new hosts are automatically added to the user's file.
1050: If a host's identification ever changes,
1051: .Nm
1052: warns about this and disables password authentication to prevent
1053: server spoofing or man-in-the-middle attacks,
1054: which could otherwise be used to circumvent the encryption.
1055: The
1056: .Cm StrictHostKeyChecking
1057: option can be used to control logins to machines whose
1058: host key is not known or has changed.
1059: .Pp
1.218 jmc 1060: When the user's identity has been accepted by the server, the server
1.357 dtucker 1061: either executes the given command in a non-interactive session or,
1062: if no command has been specified, logs into the machine and gives
1063: the user a normal shell as an interactive session.
1.218 jmc 1064: All communication with
1065: the remote command or shell will be automatically encrypted.
1066: .Pp
1.430 naddy 1067: If an interactive session is requested,
1.357 dtucker 1068: .Nm
1069: by default will only request a pseudo-terminal (pty) for interactive
1070: sessions when the client has one.
1071: The flags
1072: .Fl T
1073: and
1074: .Fl t
1075: can be used to override this behaviour.
1076: .Pp
1.430 naddy 1077: If a pseudo-terminal has been allocated, the
1.218 jmc 1078: user may use the escape characters noted below.
1079: .Pp
1.357 dtucker 1080: If no pseudo-terminal has been allocated,
1.218 jmc 1081: the session is transparent and can be used to reliably transfer binary data.
1082: On most systems, setting the escape character to
1083: .Dq none
1084: will also make the session transparent even if a tty is used.
1085: .Pp
1086: The session terminates when the command or shell on the remote
1.247 jmc 1087: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 1088: .Sh ESCAPE CHARACTERS
1.218 jmc 1089: When a pseudo-terminal has been requested,
1.2 deraadt 1090: .Nm
1.218 jmc 1091: supports a number of functions through the use of an escape character.
1092: .Pp
1093: A single tilde character can be sent as
1094: .Ic ~~
1095: or by following the tilde by a character other than those described below.
1096: The escape character must always follow a newline to be interpreted as
1097: special.
1098: The escape character can be changed in configuration files using the
1099: .Cm EscapeChar
1100: configuration directive or on the command line by the
1101: .Fl e
1102: option.
1103: .Pp
1104: The supported escapes (assuming the default
1105: .Ql ~ )
1106: are:
1107: .Bl -tag -width Ds
1108: .It Cm ~.
1109: Disconnect.
1110: .It Cm ~^Z
1111: Background
1.234 jmc 1112: .Nm .
1.218 jmc 1113: .It Cm ~#
1114: List forwarded connections.
1115: .It Cm ~&
1116: Background
1.2 deraadt 1117: .Nm
1.218 jmc 1118: at logout when waiting for forwarded connection / X11 sessions to terminate.
1119: .It Cm ~?
1120: Display a list of escape characters.
1121: .It Cm ~B
1122: Send a BREAK to the remote system
1.369 jmc 1123: (only useful if the peer supports it).
1.218 jmc 1124: .It Cm ~C
1125: Open command line.
1126: Currently this allows the addition of port forwardings using the
1.279 stevesk 1127: .Fl L ,
1128: .Fl R
1.218 jmc 1129: and
1.279 stevesk 1130: .Fl D
1.225 jmc 1131: options (see above).
1.322 markus 1132: It also allows the cancellation of existing port-forwardings
1133: with
1.262 stevesk 1134: .Sm off
1.322 markus 1135: .Fl KL Oo Ar bind_address : Oc Ar port
1.262 stevesk 1136: .Sm on
1.322 markus 1137: for local,
1138: .Sm off
1139: .Fl KR Oo Ar bind_address : Oc Ar port
1140: .Sm on
1141: for remote and
1142: .Sm off
1143: .Fl KD Oo Ar bind_address : Oc Ar port
1144: .Sm on
1145: for dynamic port-forwardings.
1.218 jmc 1146: .Ic !\& Ns Ar command
1147: allows the user to execute a local command if the
1148: .Ic PermitLocalCommand
1149: option is enabled in
1.176 jmc 1150: .Xr ssh_config 5 .
1.218 jmc 1151: Basic help is available, using the
1152: .Fl h
1153: option.
1154: .It Cm ~R
1155: Request rekeying of the connection
1.369 jmc 1156: (only useful if the peer supports it).
1.327 dtucker 1157: .It Cm ~V
1158: Decrease the verbosity
1159: .Pq Ic LogLevel
1160: when errors are being written to stderr.
1161: .It Cm ~v
1.328 jmc 1162: Increase the verbosity
1.327 dtucker 1163: .Pq Ic LogLevel
1164: when errors are being written to stderr.
1.176 jmc 1165: .El
1.246 jmc 1166: .Sh TCP FORWARDING
1.402 jmc 1167: Forwarding of arbitrary TCP connections over a secure channel
1168: can be specified either on the command line or in a configuration file.
1.246 jmc 1169: One possible application of TCP forwarding is a secure connection to a
1170: mail server; another is going through firewalls.
1171: .Pp
1.402 jmc 1172: In the example below, we look at encrypting communication for an IRC client,
1173: even though the IRC server it connects to does not directly
1174: support encrypted communication.
1.246 jmc 1175: This works as follows:
1176: the user connects to the remote host using
1177: .Nm ,
1.402 jmc 1178: specifying the ports to be used to forward the connection.
1179: After that it is possible to start the program locally,
1.246 jmc 1180: and
1181: .Nm
1.402 jmc 1182: will encrypt and forward the connection to the remote server.
1.246 jmc 1183: .Pp
1.402 jmc 1184: The following example tunnels an IRC session from the client
1185: to an IRC server at
1.246 jmc 1186: .Dq server.example.com ,
1187: joining channel
1188: .Dq #users ,
1189: nickname
1190: .Dq pinky ,
1.402 jmc 1191: using the standard IRC port, 6667:
1192: .Bd -literal -offset 4n
1193: $ ssh -f -L 6667:localhost:6667 server.example.com sleep 10
1194: $ irc -c '#users' pinky IRC/127.0.0.1
1195: .Ed
1.246 jmc 1196: .Pp
1197: The
1198: .Fl f
1199: option backgrounds
1200: .Nm
1201: and the remote command
1202: .Dq sleep 10
1203: is specified to allow an amount of time
1204: (10 seconds, in the example)
1.402 jmc 1205: to start the program which is going to use the tunnel.
1.246 jmc 1206: If no connections are made within the time specified,
1207: .Nm
1208: will exit.
1209: .Sh X11 FORWARDING
1.218 jmc 1210: If the
1211: .Cm ForwardX11
1212: variable is set to
1213: .Dq yes
1214: (or see the description of the
1.227 jmc 1215: .Fl X ,
1216: .Fl x ,
1.218 jmc 1217: and
1.227 jmc 1218: .Fl Y
1.226 jmc 1219: options above)
1.218 jmc 1220: and the user is using X11 (the
1221: .Ev DISPLAY
1222: environment variable is set), the connection to the X11 display is
1223: automatically forwarded to the remote side in such a way that any X11
1224: programs started from the shell (or command) will go through the
1225: encrypted channel, and the connection to the real X server will be made
1.176 jmc 1226: from the local machine.
1.218 jmc 1227: The user should not manually set
1228: .Ev DISPLAY .
1229: Forwarding of X11 connections can be
1230: configured on the command line or in configuration files.
1231: .Pp
1232: The
1233: .Ev DISPLAY
1234: value set by
1235: .Nm
1236: will point to the server machine, but with a display number greater than zero.
1237: This is normal, and happens because
1238: .Nm
1239: creates a
1240: .Dq proxy
1241: X server on the server machine for forwarding the
1242: connections over the encrypted channel.
1.200 djm 1243: .Pp
1.218 jmc 1244: .Nm
1245: will also automatically set up Xauthority data on the server machine.
1246: For this purpose, it will generate a random authorization cookie,
1247: store it in Xauthority on the server, and verify that any forwarded
1248: connections carry this cookie and replace it by the real cookie when
1249: the connection is opened.
1250: The real authentication cookie is never
1251: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1252: .Pp
1.218 jmc 1253: If the
1254: .Cm ForwardAgent
1255: variable is set to
1256: .Dq yes
1257: (or see the description of the
1258: .Fl A
1.191 djm 1259: and
1.218 jmc 1260: .Fl a
1.226 jmc 1261: options above) and
1.218 jmc 1262: the user is using an authentication agent, the connection to the agent
1263: is automatically forwarded to the remote side.
1.252 jmc 1264: .Sh VERIFYING HOST KEYS
1265: When connecting to a server for the first time,
1266: a fingerprint of the server's public key is presented to the user
1267: (unless the option
1268: .Cm StrictHostKeyChecking
1269: has been disabled).
1270: Fingerprints can be determined using
1271: .Xr ssh-keygen 1 :
1272: .Pp
1273: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1274: .Pp
1.274 grunk 1275: If the fingerprint is already known, it can be matched
1276: and the key can be accepted or rejected.
1.358 djm 1277: If only legacy (MD5) fingerprints for the server are available, the
1278: .Xr ssh-keygen 1
1279: .Fl E
1280: option may be used to downgrade the fingerprint algorithm to match.
1281: .Pp
1.274 grunk 1282: Because of the difficulty of comparing host keys
1.352 djm 1283: just by looking at fingerprint strings,
1.274 grunk 1284: there is also support to compare host keys visually,
1285: using
1286: .Em random art .
1287: By setting the
1.275 grunk 1288: .Cm VisualHostKey
1.274 grunk 1289: option to
1.275 grunk 1290: .Dq yes ,
1.274 grunk 1291: a small ASCII graphic gets displayed on every login to a server, no matter
1292: if the session itself is interactive or not.
1293: By learning the pattern a known server produces, a user can easily
1294: find out that the host key has changed when a completely different pattern
1295: is displayed.
1296: Because these patterns are not unambiguous however, a pattern that looks
1297: similar to the pattern remembered only gives a good probability that the
1298: host key is the same, not guaranteed proof.
1299: .Pp
1300: To get a listing of the fingerprints along with their random art for
1301: all known hosts, the following command line can be used:
1302: .Pp
1303: .Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1304: .Pp
1.252 jmc 1305: If the fingerprint is unknown,
1306: an alternative method of verification is available:
1307: SSH fingerprints verified by DNS.
1308: An additional resource record (RR),
1309: SSHFP,
1310: is added to a zonefile
1311: and the connecting client is able to match the fingerprint
1312: with that of the key presented.
1313: .Pp
1314: In this example, we are connecting a client to a server,
1315: .Dq host.example.com .
1316: The SSHFP resource records should first be added to the zonefile for
1317: host.example.com:
1318: .Bd -literal -offset indent
1.259 jakob 1319: $ ssh-keygen -r host.example.com.
1.252 jmc 1320: .Ed
1321: .Pp
1322: The output lines will have to be added to the zonefile.
1323: To check that the zone is answering fingerprint queries:
1324: .Pp
1325: .Dl $ dig -t SSHFP host.example.com
1326: .Pp
1327: Finally the client connects:
1328: .Bd -literal -offset indent
1329: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1330: [...]
1331: Matching host key fingerprint found in DNS.
1332: Are you sure you want to continue connecting (yes/no)?
1333: .Ed
1334: .Pp
1335: See the
1336: .Cm VerifyHostKeyDNS
1337: option in
1338: .Xr ssh_config 5
1339: for more information.
1.250 jmc 1340: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1341: .Nm
1342: contains support for Virtual Private Network (VPN) tunnelling
1343: using the
1344: .Xr tun 4
1345: network pseudo-device,
1346: allowing two networks to be joined securely.
1347: The
1348: .Xr sshd_config 5
1349: configuration option
1350: .Cm PermitTunnel
1351: controls whether the server supports this,
1352: and at what level (layer 2 or 3 traffic).
1353: .Pp
1354: The following example would connect client network 10.0.50.0/24
1.265 otto 1355: with remote network 10.0.99.0/24 using a point-to-point connection
1356: from 10.1.1.1 to 10.1.1.2,
1357: provided that the SSH server running on the gateway to the remote network,
1358: at 192.168.1.15, allows it.
1359: .Pp
1360: On the client:
1.250 jmc 1361: .Bd -literal -offset indent
1362: # ssh -f -w 0:1 192.168.1.15 true
1.265 otto 1363: # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1364: # route add 10.0.99.0/24 10.1.1.2
1365: .Ed
1366: .Pp
1367: On the server:
1368: .Bd -literal -offset indent
1369: # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1370: # route add 10.0.50.0/24 10.1.1.1
1.250 jmc 1371: .Ed
1372: .Pp
1373: Client access may be more finely tuned via the
1374: .Pa /root/.ssh/authorized_keys
1375: file (see below) and the
1376: .Cm PermitRootLogin
1377: server option.
1.255 jmc 1378: The following entry would permit connections on
1.250 jmc 1379: .Xr tun 4
1.255 jmc 1380: device 1 from user
1.250 jmc 1381: .Dq jane
1.255 jmc 1382: and on tun device 2 from user
1.250 jmc 1383: .Dq john ,
1384: if
1385: .Cm PermitRootLogin
1386: is set to
1387: .Dq forced-commands-only :
1388: .Bd -literal -offset 2n
1389: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1390: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1391: .Ed
1392: .Pp
1.264 ray 1393: Since an SSH-based setup entails a fair amount of overhead,
1.250 jmc 1394: it may be more suited to temporary setups,
1395: such as for wireless VPNs.
1396: More permanent VPNs are better provided by tools such as
1397: .Xr ipsecctl 8
1398: and
1399: .Xr isakmpd 8 .
1.2 deraadt 1400: .Sh ENVIRONMENT
1401: .Nm
1.1 deraadt 1402: will normally set the following environment variables:
1.237 jmc 1403: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1404: .It Ev DISPLAY
1405: The
1406: .Ev DISPLAY
1.40 aaron 1407: variable indicates the location of the X11 server.
1.44 aaron 1408: It is automatically set by
1.2 deraadt 1409: .Nm
1410: to point to a value of the form
1.233 jmc 1411: .Dq hostname:n ,
1412: where
1413: .Dq hostname
1414: indicates the host where the shell runs, and
1415: .Sq n
1416: is an integer \*(Ge 1.
1.40 aaron 1417: .Nm
1418: uses this special value to forward X11 connections over the secure
1419: channel.
1.107 markus 1420: The user should normally not set
1421: .Ev DISPLAY
1422: explicitly, as that
1.1 deraadt 1423: will render the X11 connection insecure (and will require the user to
1424: manually copy any required authorization cookies).
1.2 deraadt 1425: .It Ev HOME
1.1 deraadt 1426: Set to the path of the user's home directory.
1.2 deraadt 1427: .It Ev LOGNAME
1428: Synonym for
1.12 aaron 1429: .Ev USER ;
1430: set for compatibility with systems that use this variable.
1.2 deraadt 1431: .It Ev MAIL
1.129 stevesk 1432: Set to the path of the user's mailbox.
1.40 aaron 1433: .It Ev PATH
1.2 deraadt 1434: Set to the default
1435: .Ev PATH ,
1436: as specified when compiling
1.234 jmc 1437: .Nm .
1.118 markus 1438: .It Ev SSH_ASKPASS
1439: If
1440: .Nm
1441: needs a passphrase, it will read the passphrase from the current
1442: terminal if it was run from a terminal.
1443: If
1444: .Nm
1445: does not have a terminal associated with it but
1446: .Ev DISPLAY
1447: and
1448: .Ev SSH_ASKPASS
1449: are set, it will execute the program specified by
1450: .Ev SSH_ASKPASS
1451: and open an X11 window to read the passphrase.
1452: This is particularly useful when calling
1453: .Nm
1454: from a
1.196 jmc 1455: .Pa .xsession
1.118 markus 1456: or related script.
1457: (Note that on some machines it
1458: may be necessary to redirect the input from
1459: .Pa /dev/null
1460: to make this work.)
1.413 djm 1461: .It Ev SSH_ASKPASS_REQUIRE
1.414 jmc 1462: Allows further control over the use of an askpass program.
1.413 djm 1463: If this variable is set to
1464: .Dq never
1465: then
1466: .Nm
1467: will never attempt to use one.
1468: If it is set to
1469: .Dq prefer ,
1470: then
1471: .Nm
1472: will prefer to use the askpass program instead of the TTY when requesting
1473: passwords.
1474: Finally, if the variable is set to
1475: .Dq force ,
1476: then the askpass program will be used for all passphrase input regardless
1477: of whether
1478: .Ev DISPLAY
1479: is set.
1.18 markus 1480: .It Ev SSH_AUTH_SOCK
1.233 jmc 1481: Identifies the path of a
1482: .Ux Ns -domain
1483: socket used to communicate with the agent.
1.166 stevesk 1484: .It Ev SSH_CONNECTION
1485: Identifies the client and server ends of the connection.
1.40 aaron 1486: The variable contains
1.233 jmc 1487: four space-separated values: client IP address, client port number,
1488: server IP address, and server port number.
1.73 markus 1489: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1490: This variable contains the original command line if a forced command
1.73 markus 1491: is executed.
1492: It can be used to extract the original arguments.
1.2 deraadt 1493: .It Ev SSH_TTY
1.1 deraadt 1494: This is set to the name of the tty (path to the device) associated
1.40 aaron 1495: with the current shell or command.
1496: If the current session has no tty,
1.1 deraadt 1497: this variable is not set.
1.387 djm 1498: .It Ev SSH_TUNNEL
1499: Optionally set by
1500: .Xr sshd 8
1501: to contain the interface names assigned if tunnel forwarding was
1502: requested by the client.
1.385 djm 1503: .It Ev SSH_USER_AUTH
1504: Optionally set by
1505: .Xr sshd 8 ,
1506: this variable may contain a pathname to a file that lists the authentication
1507: methods successfully used when the session was established, including any
1508: public keys that were used.
1.2 deraadt 1509: .It Ev TZ
1.214 jmc 1510: This variable is set to indicate the present time zone if it
1.257 jmc 1511: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1512: on to new connections).
1.2 deraadt 1513: .It Ev USER
1.1 deraadt 1514: Set to the name of the user logging in.
1.2 deraadt 1515: .El
1516: .Pp
1.44 aaron 1517: Additionally,
1.2 deraadt 1518: .Nm
1.44 aaron 1519: reads
1.207 djm 1520: .Pa ~/.ssh/environment ,
1.2 deraadt 1521: and adds lines of the format
1522: .Dq VARNAME=value
1.233 jmc 1523: to the environment if the file exists and users are allowed to
1.161 marc 1524: change their environment.
1.176 jmc 1525: For more information, see the
1.161 marc 1526: .Cm PermitUserEnvironment
1.162 stevesk 1527: option in
1.161 marc 1528: .Xr sshd_config 5 .
1.2 deraadt 1529: .Sh FILES
1.236 jmc 1530: .Bl -tag -width Ds -compact
1.309 jmc 1531: .It Pa ~/.rhosts
1.240 jmc 1532: This file is used for host-based authentication (see above).
1.92 markus 1533: On some machines this file may need to be
1.240 jmc 1534: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1535: because
1.2 deraadt 1536: .Xr sshd 8
1.40 aaron 1537: reads it as root.
1538: Additionally, this file must be owned by the user,
1539: and must not have write permissions for anyone else.
1540: The recommended
1.1 deraadt 1541: permission for most machines is read/write for the user, and not
1542: accessible by others.
1.2 deraadt 1543: .Pp
1.309 jmc 1544: .It Pa ~/.shosts
1.240 jmc 1545: This file is used in exactly the same way as
1546: .Pa .rhosts ,
1547: but allows host-based authentication without permitting login with
1548: rlogin/rsh.
1.272 mcbride 1549: .Pp
1.309 jmc 1550: .It Pa ~/.ssh/
1.272 mcbride 1551: This directory is the default location for all user-specific configuration
1552: and authentication information.
1553: There is no general requirement to keep the entire contents of this directory
1554: secret, but the recommended permissions are read/write/execute for the user,
1555: and not accessible by others.
1.236 jmc 1556: .Pp
1.309 jmc 1557: .It Pa ~/.ssh/authorized_keys
1.349 sobrado 1558: Lists the public keys (DSA, ECDSA, Ed25519, RSA)
1.343 naddy 1559: that can be used for logging in as this user.
1.238 jmc 1560: The format of this file is described in the
1561: .Xr sshd 8
1562: manual page.
1563: This file is not highly sensitive, but the recommended
1564: permissions are read/write for the user, and not accessible by others.
1565: .Pp
1.309 jmc 1566: .It Pa ~/.ssh/config
1.238 jmc 1567: This is the per-user configuration file.
1568: The file format and configuration options are described in
1569: .Xr ssh_config 5 .
1570: Because of the potential for abuse, this file must have strict permissions:
1.334 djm 1571: read/write for the user, and not writable by others.
1.238 jmc 1572: .Pp
1.309 jmc 1573: .It Pa ~/.ssh/environment
1.239 jmc 1574: Contains additional definitions for environment variables; see
1575: .Sx ENVIRONMENT ,
1.238 jmc 1576: above.
1577: .Pp
1.309 jmc 1578: .It Pa ~/.ssh/id_dsa
1.310 djm 1579: .It Pa ~/.ssh/id_ecdsa
1.404 naddy 1580: .It Pa ~/.ssh/id_ecdsa_sk
1.343 naddy 1581: .It Pa ~/.ssh/id_ed25519
1.406 naddy 1582: .It Pa ~/.ssh/id_ed25519_sk
1.309 jmc 1583: .It Pa ~/.ssh/id_rsa
1.238 jmc 1584: Contains the private key for authentication.
1585: These files
1586: contain sensitive data and should be readable by the user but not
1587: accessible by others (read/write/execute).
1588: .Nm
1589: will simply ignore a private key file if it is accessible by others.
1590: It is possible to specify a passphrase when
1591: generating the key which will be used to encrypt the
1.389 djm 1592: sensitive part of this file using AES-128.
1.238 jmc 1593: .Pp
1.309 jmc 1594: .It Pa ~/.ssh/id_dsa.pub
1.310 djm 1595: .It Pa ~/.ssh/id_ecdsa.pub
1.404 naddy 1596: .It Pa ~/.ssh/id_ecdsa_sk.pub
1.343 naddy 1597: .It Pa ~/.ssh/id_ed25519.pub
1.406 naddy 1598: .It Pa ~/.ssh/id_ed25519_sk.pub
1.309 jmc 1599: .It Pa ~/.ssh/id_rsa.pub
1.238 jmc 1600: Contains the public key for authentication.
1601: These files are not
1602: sensitive and can (but need not) be readable by anyone.
1603: .Pp
1.309 jmc 1604: .It Pa ~/.ssh/known_hosts
1.244 jmc 1605: Contains a list of host keys for all hosts the user has logged into
1606: that are not already in the systemwide list of known host keys.
1.238 jmc 1607: See
1.244 jmc 1608: .Xr sshd 8
1609: for further details of the format of this file.
1.238 jmc 1610: .Pp
1.309 jmc 1611: .It Pa ~/.ssh/rc
1.238 jmc 1612: Commands in this file are executed by
1613: .Nm
1.245 jmc 1614: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1615: started.
1616: See the
1617: .Xr sshd 8
1618: manual page for more information.
1619: .Pp
1.309 jmc 1620: .It Pa /etc/hosts.equiv
1.240 jmc 1621: This file is for host-based authentication (see above).
1622: It should only be writable by root.
1.236 jmc 1623: .Pp
1.309 jmc 1624: .It Pa /etc/shosts.equiv
1.240 jmc 1625: This file is used in exactly the same way as
1626: .Pa hosts.equiv ,
1627: but allows host-based authentication without permitting login with
1628: rlogin/rsh.
1.236 jmc 1629: .Pp
1.238 jmc 1630: .It Pa /etc/ssh/ssh_config
1631: Systemwide configuration file.
1632: The file format and configuration options are described in
1633: .Xr ssh_config 5 .
1634: .Pp
1.309 jmc 1635: .It Pa /etc/ssh/ssh_host_key
1636: .It Pa /etc/ssh/ssh_host_dsa_key
1.310 djm 1637: .It Pa /etc/ssh/ssh_host_ecdsa_key
1.343 naddy 1638: .It Pa /etc/ssh/ssh_host_ed25519_key
1.309 jmc 1639: .It Pa /etc/ssh/ssh_host_rsa_key
1.325 dtucker 1640: These files contain the private parts of the host keys
1.245 jmc 1641: and are used for host-based authentication.
1.238 jmc 1642: .Pp
1.309 jmc 1643: .It Pa /etc/ssh/ssh_known_hosts
1.238 jmc 1644: Systemwide list of known host keys.
1645: This file should be prepared by the
1646: system administrator to contain the public host keys of all machines in the
1647: organization.
1.244 jmc 1648: It should be world-readable.
1649: See
1.238 jmc 1650: .Xr sshd 8
1.244 jmc 1651: for further details of the format of this file.
1.236 jmc 1652: .Pp
1.309 jmc 1653: .It Pa /etc/ssh/sshrc
1.1 deraadt 1654: Commands in this file are executed by
1.2 deraadt 1655: .Nm
1.245 jmc 1656: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1657: See the
1.2 deraadt 1658: .Xr sshd 8
1.1 deraadt 1659: manual page for more information.
1.58 itojun 1660: .El
1.312 jmc 1661: .Sh EXIT STATUS
1662: .Nm
1663: exits with the exit status of the remote command or with 255
1664: if an error occurred.
1.2 deraadt 1665: .Sh SEE ALSO
1666: .Xr scp 1 ,
1.83 djm 1667: .Xr sftp 1 ,
1.2 deraadt 1668: .Xr ssh-add 1 ,
1669: .Xr ssh-agent 1 ,
1670: .Xr ssh-keygen 1 ,
1.242 jmc 1671: .Xr ssh-keyscan 1 ,
1.250 jmc 1672: .Xr tun 4 ,
1.159 stevesk 1673: .Xr ssh_config 5 ,
1.160 naddy 1674: .Xr ssh-keysign 8 ,
1.87 itojun 1675: .Xr sshd 8
1.329 jmc 1676: .Sh STANDARDS
1.106 markus 1677: .Rs
1.329 jmc 1678: .%A S. Lehtinen
1679: .%A C. Lonvick
1680: .%D January 2006
1.256 jmc 1681: .%R RFC 4250
1.329 jmc 1682: .%T The Secure Shell (SSH) Protocol Assigned Numbers
1.256 jmc 1683: .Re
1.329 jmc 1684: .Pp
1.256 jmc 1685: .Rs
1.329 jmc 1686: .%A T. Ylonen
1687: .%A C. Lonvick
1688: .%D January 2006
1.256 jmc 1689: .%R RFC 4251
1.329 jmc 1690: .%T The Secure Shell (SSH) Protocol Architecture
1.256 jmc 1691: .Re
1.329 jmc 1692: .Pp
1.256 jmc 1693: .Rs
1.329 jmc 1694: .%A T. Ylonen
1695: .%A C. Lonvick
1696: .%D January 2006
1.256 jmc 1697: .%R RFC 4252
1.329 jmc 1698: .%T The Secure Shell (SSH) Authentication Protocol
1.256 jmc 1699: .Re
1.329 jmc 1700: .Pp
1.256 jmc 1701: .Rs
1.329 jmc 1702: .%A T. Ylonen
1703: .%A C. Lonvick
1704: .%D January 2006
1.256 jmc 1705: .%R RFC 4253
1.329 jmc 1706: .%T The Secure Shell (SSH) Transport Layer Protocol
1.256 jmc 1707: .Re
1.329 jmc 1708: .Pp
1.256 jmc 1709: .Rs
1.329 jmc 1710: .%A T. Ylonen
1711: .%A C. Lonvick
1712: .%D January 2006
1.256 jmc 1713: .%R RFC 4254
1.329 jmc 1714: .%T The Secure Shell (SSH) Connection Protocol
1.256 jmc 1715: .Re
1.329 jmc 1716: .Pp
1.256 jmc 1717: .Rs
1.329 jmc 1718: .%A J. Schlyter
1719: .%A W. Griffin
1720: .%D January 2006
1.256 jmc 1721: .%R RFC 4255
1.329 jmc 1722: .%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
1.256 jmc 1723: .Re
1.329 jmc 1724: .Pp
1.256 jmc 1725: .Rs
1.329 jmc 1726: .%A F. Cusack
1727: .%A M. Forssen
1728: .%D January 2006
1.256 jmc 1729: .%R RFC 4256
1.329 jmc 1730: .%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)
1.256 jmc 1731: .Re
1.329 jmc 1732: .Pp
1.256 jmc 1733: .Rs
1.329 jmc 1734: .%A J. Galbraith
1735: .%A P. Remaker
1736: .%D January 2006
1.256 jmc 1737: .%R RFC 4335
1.329 jmc 1738: .%T The Secure Shell (SSH) Session Channel Break Extension
1.256 jmc 1739: .Re
1.329 jmc 1740: .Pp
1.256 jmc 1741: .Rs
1.329 jmc 1742: .%A M. Bellare
1743: .%A T. Kohno
1744: .%A C. Namprempre
1745: .%D January 2006
1.256 jmc 1746: .%R RFC 4344
1.329 jmc 1747: .%T The Secure Shell (SSH) Transport Layer Encryption Modes
1.256 jmc 1748: .Re
1.329 jmc 1749: .Pp
1.256 jmc 1750: .Rs
1.329 jmc 1751: .%A B. Harris
1752: .%D January 2006
1.256 jmc 1753: .%R RFC 4345
1.329 jmc 1754: .%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol
1.258 djm 1755: .Re
1.329 jmc 1756: .Pp
1.258 djm 1757: .Rs
1.329 jmc 1758: .%A M. Friedl
1759: .%A N. Provos
1760: .%A W. Simpson
1761: .%D March 2006
1.258 djm 1762: .%R RFC 4419
1.329 jmc 1763: .%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
1.266 markus 1764: .Re
1.329 jmc 1765: .Pp
1.266 markus 1766: .Rs
1.329 jmc 1767: .%A J. Galbraith
1768: .%A R. Thayer
1769: .%D November 2006
1.266 markus 1770: .%R RFC 4716
1.329 jmc 1771: .%T The Secure Shell (SSH) Public Key File Format
1.313 djm 1772: .Re
1.329 jmc 1773: .Pp
1.313 djm 1774: .Rs
1.329 jmc 1775: .%A D. Stebila
1776: .%A J. Green
1777: .%D December 2009
1.313 djm 1778: .%R RFC 5656
1.329 jmc 1779: .%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
1.274 grunk 1780: .Re
1.329 jmc 1781: .Pp
1.274 grunk 1782: .Rs
1783: .%A A. Perrig
1784: .%A D. Song
1785: .%D 1999
1.329 jmc 1786: .%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
1787: .%T Hash Visualization: a New Technique to improve Real-World Security
1.106 markus 1788: .Re
1.173 jmc 1789: .Sh AUTHORS
1790: OpenSSH is a derivative of the original and free
1791: ssh 1.2.12 release by Tatu Ylonen.
1792: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1793: Theo de Raadt and Dug Song
1794: removed many bugs, re-added newer features and
1795: created OpenSSH.
1796: Markus Friedl contributed the support for SSH
1797: protocol versions 1.5 and 2.0.
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