Annotation of src/usr.bin/ssh/ssh.1, Revision 1.434
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: .\"
1.434 ! djm 36: .\" $OpenBSD: ssh.1,v 1.433 2022/11/28 01:37:36 djm Exp $
! 37: .Dd $Mdocdate: November 28 2022 $
1.2 deraadt 38: .Dt SSH 1
39: .Os
40: .Sh NAME
41: .Nm ssh
1.408 jmc 42: .Nd OpenSSH remote login client
1.2 deraadt 43: .Sh SYNOPSIS
44: .Nm ssh
1.377 djm 45: .Op Fl 46AaCfGgKkMNnqsTtVvXxYy
1.390 djm 46: .Op Fl B Ar bind_interface
1.108 markus 47: .Op Fl b Ar bind_address
1.51 markus 48: .Op Fl c Ar cipher_spec
1.306 jmc 49: .Op Fl D Oo Ar bind_address : Oc Ns Ar port
1.331 dtucker 50: .Op Fl E Ar log_file
1.2 deraadt 51: .Op Fl e Ar escape_char
1.176 jmc 52: .Op Fl F Ar configfile
1.292 jmc 53: .Op Fl I Ar pkcs11
1.2 deraadt 54: .Op Fl i Ar identity_file
1.386 millert 55: .Op Fl J Ar destination
1.360 millert 56: .Op Fl L Ar address
1.176 jmc 57: .Op Fl l Ar login_name
58: .Op Fl m Ar mac_spec
1.198 djm 59: .Op Fl O Ar ctl_cmd
1.176 jmc 60: .Op Fl o Ar option
61: .Op Fl p Ar port
1.362 djm 62: .Op Fl Q Ar query_option
1.360 millert 63: .Op Fl R Ar address
1.198 djm 64: .Op Fl S Ar ctl_path
1.290 dtucker 65: .Op Fl W Ar host : Ns Ar port
1.306 jmc 66: .Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun
1.386 millert 67: .Ar destination
1.427 dtucker 68: .Op Ar command Op Ar argument ...
1.44 aaron 69: .Sh DESCRIPTION
1.2 deraadt 70: .Nm
1.96 deraadt 71: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 72: executing commands on a remote machine.
1.365 mmcc 73: It is intended to provide secure encrypted communications between
1.40 aaron 74: two untrusted hosts over an insecure network.
1.348 millert 75: X11 connections, arbitrary TCP ports and
76: .Ux Ns -domain
77: sockets can also be forwarded over the secure channel.
1.2 deraadt 78: .Pp
79: .Nm
1.44 aaron 80: connects and logs into the specified
1.388 jmc 81: .Ar destination ,
1.386 millert 82: which may be specified as either
1.388 jmc 83: .Sm off
84: .Oo user @ Oc hostname
85: .Sm on
86: or a URI of the form
87: .Sm off
88: .No ssh:// Oo user @ Oc hostname Op : port .
89: .Sm on
1.1 deraadt 90: The user must prove
1.420 dtucker 91: their identity to the remote machine using one of several methods
1.365 mmcc 92: (see below).
1.49 markus 93: .Pp
1.386 millert 94: If a
1.176 jmc 95: .Ar command
96: is specified,
1.427 dtucker 97: it will be executed on the remote host instead of a login shell.
98: A complete command line may be specified as
99: .Ar command ,
100: or it may have additional arguments.
101: If supplied, the arguments will be appended to the command, separated by
102: spaces, before it is sent to the server to be executed.
1.2 deraadt 103: .Pp
1.218 jmc 104: The options are as follows:
1.361 millert 105: .Pp
1.360 millert 106: .Bl -tag -width Ds -compact
1.218 jmc 107: .It Fl 4
108: Forces
1.2 deraadt 109: .Nm
1.218 jmc 110: to use IPv4 addresses only.
1.360 millert 111: .Pp
1.218 jmc 112: .It Fl 6
113: Forces
1.2 deraadt 114: .Nm
1.218 jmc 115: to use IPv6 addresses only.
1.360 millert 116: .Pp
1.218 jmc 117: .It Fl A
1.407 jmc 118: Enables forwarding of connections from an authentication agent such as
119: .Xr ssh-agent 1 .
1.218 jmc 120: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 121: .Pp
1.218 jmc 122: Agent forwarding should be enabled with caution.
123: Users with the ability to bypass file permissions on the remote host
1.285 sobrado 124: (for the agent's
1.286 sobrado 125: .Ux Ns -domain
126: socket) can access the local agent through the forwarded connection.
1.218 jmc 127: An attacker cannot obtain key material from the agent,
128: however they can perform operations on the keys that enable them to
129: authenticate using the identities loaded into the agent.
1.407 jmc 130: A safer alternative may be to use a jump host
131: (see
132: .Fl J ) .
1.360 millert 133: .Pp
1.218 jmc 134: .It Fl a
135: Disables forwarding of the authentication agent connection.
1.390 djm 136: .Pp
1.391 jmc 137: .It Fl B Ar bind_interface
1.390 djm 138: Bind to the address of
1.391 jmc 139: .Ar bind_interface
1.390 djm 140: before attempting to connect to the destination host.
141: This is only useful on systems with more than one address.
1.360 millert 142: .Pp
1.218 jmc 143: .It Fl b Ar bind_address
144: Use
145: .Ar bind_address
146: on the local machine as the source address
147: of the connection.
148: Only useful on systems with more than one address.
1.360 millert 149: .Pp
1.218 jmc 150: .It Fl C
151: Requests compression of all data (including stdin, stdout, stderr, and
1.348 millert 152: data for forwarded X11, TCP and
153: .Ux Ns -domain
154: connections).
1.218 jmc 155: The compression algorithm is the same used by
1.377 djm 156: .Xr gzip 1 .
1.218 jmc 157: Compression is desirable on modem lines and other
158: slow connections, but will only slow down things on fast networks.
159: The default value can be set on a host-by-host basis in the
160: configuration files; see the
161: .Cm Compression
1.431 jmc 162: option in
163: .Xr ssh_config 5 .
1.360 millert 164: .Pp
1.218 jmc 165: .It Fl c Ar cipher_spec
166: Selects the cipher specification for encrypting the session.
167: .Ar cipher_spec
168: is a comma-separated list of ciphers
169: listed in order of preference.
1.283 jmc 170: See the
171: .Cm Ciphers
1.307 dtucker 172: keyword in
173: .Xr ssh_config 5
174: for more information.
1.360 millert 175: .Pp
1.218 jmc 176: .It Fl D Xo
177: .Sm off
178: .Oo Ar bind_address : Oc
179: .Ar port
180: .Sm on
181: .Xc
182: Specifies a local
183: .Dq dynamic
184: application-level port forwarding.
185: This works by allocating a socket to listen to
186: .Ar port
187: on the local side, optionally bound to the specified
188: .Ar bind_address .
189: Whenever a connection is made to this port, the
190: connection is forwarded over the secure channel, and the application
191: protocol is then used to determine where to connect to from the
192: remote machine.
193: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.107 markus 194: .Nm
1.218 jmc 195: will act as a SOCKS server.
196: Only root can forward privileged ports.
197: Dynamic port forwardings can also be specified in the configuration file.
1.49 markus 198: .Pp
1.308 djm 199: IPv6 addresses can be specified by enclosing the address in square brackets.
1.218 jmc 200: Only the superuser can forward privileged ports.
201: By default, the local port is bound in accordance with the
202: .Cm GatewayPorts
203: setting.
204: However, an explicit
205: .Ar bind_address
206: may be used to bind the connection to a specific address.
207: The
208: .Ar bind_address
209: of
210: .Dq localhost
211: indicates that the listening port be bound for local use only, while an
212: empty address or
213: .Sq *
214: indicates that the port should be available from all interfaces.
1.360 millert 215: .Pp
1.331 dtucker 216: .It Fl E Ar log_file
217: Append debug logs to
218: .Ar log_file
219: instead of standard error.
1.360 millert 220: .Pp
1.229 jmc 221: .It Fl e Ar escape_char
1.218 jmc 222: Sets the escape character for sessions with a pty (default:
223: .Ql ~ ) .
224: The escape character is only recognized at the beginning of a line.
225: The escape character followed by a dot
226: .Pq Ql \&.
227: closes the connection;
228: followed by control-Z suspends the connection;
229: and followed by itself sends the escape character once.
230: Setting the character to
1.2 deraadt 231: .Dq none
1.218 jmc 232: disables any escapes and makes the session fully transparent.
1.360 millert 233: .Pp
1.218 jmc 234: .It Fl F Ar configfile
235: Specifies an alternative per-user configuration file.
236: If a configuration file is given on the command line,
237: the system-wide configuration file
238: .Pq Pa /etc/ssh/ssh_config
239: will be ignored.
240: The default for the per-user configuration file is
241: .Pa ~/.ssh/config .
1.411 naddy 242: If set to
243: .Dq none ,
244: no configuration files will be read.
1.360 millert 245: .Pp
1.218 jmc 246: .It Fl f
247: Requests
248: .Nm
249: to go to background just before command execution.
250: This is useful if
1.176 jmc 251: .Nm
1.218 jmc 252: is going to ask for passwords or passphrases, but the user
253: wants it in the background.
254: This implies
255: .Fl n .
256: The recommended way to start X11 programs at a remote site is with
257: something like
258: .Ic ssh -f host xterm .
1.277 djm 259: .Pp
260: If the
261: .Cm ExitOnForwardFailure
262: configuration option is set to
263: .Dq yes ,
264: then a client started with
265: .Fl f
266: will wait for all remote port forwards to be successfully established
267: before placing itself in the background.
1.424 djm 268: Refer to the description of
269: .Cm ForkAfterAuthentication
270: in
271: .Xr ssh_config 5
272: for details.
1.360 millert 273: .Pp
1.350 djm 274: .It Fl G
275: Causes
276: .Nm
277: to print its configuration after evaluating
278: .Cm Host
279: and
280: .Cm Match
281: blocks and exit.
1.360 millert 282: .Pp
1.218 jmc 283: .It Fl g
284: Allows remote hosts to connect to local forwarded ports.
1.346 djm 285: If used on a multiplexed connection, then this option must be specified
286: on the master process.
1.360 millert 287: .Pp
1.291 markus 288: .It Fl I Ar pkcs11
1.294 jmc 289: Specify the PKCS#11 shared library
1.176 jmc 290: .Nm
1.401 naddy 291: should use to communicate with a PKCS#11 token providing keys for user
292: authentication.
1.360 millert 293: .Pp
1.218 jmc 294: .It Fl i Ar identity_file
295: Selects a file from which the identity (private key) for
1.310 djm 296: public key authentication is read.
1.426 dtucker 297: You can also specify a public key file to use the corresponding
298: private key that is loaded in
299: .Xr ssh-agent 1
300: when the private key file is not present locally.
1.218 jmc 301: The default is
1.428 dtucker 302: .Pa ~/.ssh/id_rsa ,
1.343 naddy 303: .Pa ~/.ssh/id_ecdsa ,
1.404 naddy 304: .Pa ~/.ssh/id_ecdsa_sk ,
1.406 naddy 305: .Pa ~/.ssh/id_ed25519 ,
306: .Pa ~/.ssh/id_ed25519_sk
1.310 djm 307: and
1.428 dtucker 308: .Pa ~/.ssh/id_dsa .
1.218 jmc 309: Identity files may also be specified on
310: a per-host basis in the configuration file.
311: It is possible to have multiple
312: .Fl i
313: options (and multiple identities specified in
314: configuration files).
1.364 jmc 315: If no certificates have been explicitly specified by the
1.363 djm 316: .Cm CertificateFile
317: directive,
1.302 djm 318: .Nm
319: will also try to load certificate information from the filename obtained
320: by appending
321: .Pa -cert.pub
322: to identity filenames.
1.360 millert 323: .Pp
1.386 millert 324: .It Fl J Ar destination
1.375 djm 325: Connect to the target host by first making a
326: .Nm
1.386 millert 327: connection to the jump host described by
328: .Ar destination
1.376 jmc 329: and then establishing a TCP forwarding to the ultimate destination from
1.375 djm 330: there.
331: Multiple jump hops may be specified separated by comma characters.
332: This is a shortcut to specify a
333: .Cm ProxyJump
334: configuration directive.
1.400 djm 335: Note that configuration directives supplied on the command-line generally
336: apply to the destination host and not any specified jump hosts.
337: Use
338: .Pa ~/.ssh/config
339: to specify configuration for jump hosts.
1.375 djm 340: .Pp
1.269 djm 341: .It Fl K
342: Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
343: credentials to the server.
1.360 millert 344: .Pp
1.218 jmc 345: .It Fl k
346: Disables forwarding (delegation) of GSSAPI credentials to the server.
1.360 millert 347: .Pp
1.218 jmc 348: .It Fl L Xo
349: .Sm off
350: .Oo Ar bind_address : Oc
351: .Ar port : host : hostport
352: .Sm on
353: .Xc
1.360 millert 354: .It Fl L Xo
355: .Sm off
356: .Oo Ar bind_address : Oc
357: .Ar port : remote_socket
358: .Sm on
359: .Xc
360: .It Fl L Xo
361: .Sm off
362: .Ar local_socket : host : hostport
363: .Sm on
364: .Xc
365: .It Fl L Xo
366: .Sm off
367: .Ar local_socket : remote_socket
368: .Sm on
369: .Xc
370: Specifies that connections to the given TCP port or Unix socket on the local
371: (client) host are to be forwarded to the given host and port, or Unix socket,
372: on the remote side.
373: This works by allocating a socket to listen to either a TCP
1.218 jmc 374: .Ar port
375: on the local side, optionally bound to the specified
1.360 millert 376: .Ar bind_address ,
377: or to a Unix socket.
378: Whenever a connection is made to the local port or socket, the
1.218 jmc 379: connection is forwarded over the secure channel, and a connection is
1.360 millert 380: made to either
1.218 jmc 381: .Ar host
382: port
1.360 millert 383: .Ar hostport ,
384: or the Unix socket
385: .Ar remote_socket ,
1.218 jmc 386: from the remote machine.
1.360 millert 387: .Pp
1.218 jmc 388: Port forwardings can also be specified in the configuration file.
1.360 millert 389: Only the superuser can forward privileged ports.
1.308 djm 390: IPv6 addresses can be specified by enclosing the address in square brackets.
1.360 millert 391: .Pp
1.218 jmc 392: By default, the local port is bound in accordance with the
393: .Cm GatewayPorts
394: setting.
395: However, an explicit
396: .Ar bind_address
397: may be used to bind the connection to a specific address.
1.2 deraadt 398: The
1.218 jmc 399: .Ar bind_address
400: of
401: .Dq localhost
402: indicates that the listening port be bound for local use only, while an
403: empty address or
404: .Sq *
405: indicates that the port should be available from all interfaces.
1.360 millert 406: .Pp
1.218 jmc 407: .It Fl l Ar login_name
408: Specifies the user to log in as on the remote machine.
409: This also may be specified on a per-host basis in the configuration file.
1.360 millert 410: .Pp
1.218 jmc 411: .It Fl M
412: Places the
413: .Nm
414: client into
415: .Dq master
416: mode for connection sharing.
1.231 stevesk 417: Multiple
418: .Fl M
419: options places
420: .Nm
421: into
422: .Dq master
1.397 djm 423: mode but with confirmation required using
424: .Xr ssh-askpass 1
425: before each operation that changes the multiplexing state
426: (e.g. opening a new session).
1.218 jmc 427: Refer to the description of
428: .Cm ControlMaster
429: in
430: .Xr ssh_config 5
431: for details.
1.360 millert 432: .Pp
1.218 jmc 433: .It Fl m Ar mac_spec
1.369 jmc 434: A comma-separated list of MAC (message authentication code) algorithms,
435: specified in order of preference.
1.218 jmc 436: See the
437: .Cm MACs
1.431 jmc 438: keyword in
439: .Xr ssh_config 5
440: for more information.
1.360 millert 441: .Pp
1.218 jmc 442: .It Fl N
443: Do not execute a remote command.
1.369 jmc 444: This is useful for just forwarding ports.
1.422 djm 445: Refer to the description of
446: .Cm SessionType
447: in
448: .Xr ssh_config 5
449: for details.
1.360 millert 450: .Pp
1.218 jmc 451: .It Fl n
452: Redirects stdin from
453: .Pa /dev/null
454: (actually, prevents reading from stdin).
455: This must be used when
1.2 deraadt 456: .Nm
1.218 jmc 457: is run in the background.
458: A common trick is to use this to run X11 programs on a remote machine.
459: For example,
460: .Ic ssh -n shadows.cs.hut.fi emacs &
461: will start an emacs on shadows.cs.hut.fi, and the X11
462: connection will be automatically forwarded over an encrypted channel.
463: The
1.2 deraadt 464: .Nm
1.218 jmc 465: program will be put in the background.
466: (This does not work if
1.2 deraadt 467: .Nm
1.218 jmc 468: needs to ask for a password or passphrase; see also the
469: .Fl f
470: option.)
1.423 djm 471: Refer to the description of
472: .Cm StdinNull
473: in
474: .Xr ssh_config 5
475: for details.
1.360 millert 476: .Pp
1.218 jmc 477: .It Fl O Ar ctl_cmd
478: Control an active connection multiplexing master process.
479: When the
480: .Fl O
481: option is specified, the
482: .Ar ctl_cmd
483: argument is interpreted and passed to the master process.
484: Valid commands are:
485: .Dq check
1.305 markus 486: (check that the master process is running),
487: .Dq forward
1.318 jmc 488: (request forwardings without command execution),
1.323 okan 489: .Dq cancel
490: (cancel forwardings),
1.218 jmc 491: .Dq exit
1.318 jmc 492: (request the master to exit), and
1.317 djm 493: .Dq stop
494: (request the master to stop accepting further multiplexing requests).
1.360 millert 495: .Pp
1.218 jmc 496: .It Fl o Ar option
497: Can be used to give options in the format used in the configuration file.
498: This is useful for specifying options for which there is no separate
499: command-line flag.
500: For full details of the options listed below, and their possible values, see
501: .Xr ssh_config 5 .
1.2 deraadt 502: .Pp
1.218 jmc 503: .Bl -tag -width Ds -offset indent -compact
1.366 jcs 504: .It AddKeysToAgent
1.218 jmc 505: .It AddressFamily
506: .It BatchMode
507: .It BindAddress
1.338 djm 508: .It CanonicalDomains
1.339 djm 509: .It CanonicalizeFallbackLocal
510: .It CanonicalizeHostname
511: .It CanonicalizeMaxDots
512: .It CanonicalizePermittedCNAMEs
1.399 jmc 513: .It CASignatureAlgorithms
1.363 djm 514: .It CertificateFile
1.218 jmc 515: .It CheckHostIP
516: .It Ciphers
517: .It ClearAllForwardings
518: .It Compression
1.380 naddy 519: .It ConnectionAttempts
1.218 jmc 520: .It ConnectTimeout
521: .It ControlMaster
522: .It ControlPath
1.321 djm 523: .It ControlPersist
1.218 jmc 524: .It DynamicForward
1.433 djm 525: .It EnableEscapeCommandline
1.218 jmc 526: .It EscapeChar
1.263 markus 527: .It ExitOnForwardFailure
1.353 jmc 528: .It FingerprintHash
1.424 djm 529: .It ForkAfterAuthentication
1.218 jmc 530: .It ForwardAgent
531: .It ForwardX11
1.321 djm 532: .It ForwardX11Timeout
1.218 jmc 533: .It ForwardX11Trusted
534: .It GatewayPorts
535: .It GlobalKnownHostsFile
536: .It GSSAPIAuthentication
537: .It GSSAPIDelegateCredentials
538: .It HashKnownHosts
539: .It Host
1.418 naddy 540: .It HostbasedAcceptedAlgorithms
1.218 jmc 541: .It HostbasedAuthentication
542: .It HostKeyAlgorithms
543: .It HostKeyAlias
1.403 jmc 544: .It Hostname
1.374 jmc 545: .It IdentitiesOnly
1.371 markus 546: .It IdentityAgent
1.218 jmc 547: .It IdentityFile
1.316 jmc 548: .It IPQoS
1.321 djm 549: .It KbdInteractiveAuthentication
1.218 jmc 550: .It KbdInteractiveDevices
1.314 jmc 551: .It KexAlgorithms
1.415 djm 552: .It KnownHostsCommand
1.218 jmc 553: .It LocalCommand
554: .It LocalForward
555: .It LogLevel
556: .It MACs
1.337 jmc 557: .It Match
1.218 jmc 558: .It NoHostAuthenticationForLocalhost
559: .It NumberOfPasswordPrompts
560: .It PasswordAuthentication
561: .It PermitLocalCommand
1.419 markus 562: .It PermitRemoteOpen
1.291 markus 563: .It PKCS11Provider
1.218 jmc 564: .It Port
565: .It PreferredAuthentications
566: .It ProxyCommand
1.375 djm 567: .It ProxyJump
1.336 jmc 568: .It ProxyUseFdpass
1.416 dtucker 569: .It PubkeyAcceptedAlgorithms
1.218 jmc 570: .It PubkeyAuthentication
1.251 dtucker 571: .It RekeyLimit
1.382 bluhm 572: .It RemoteCommand
1.218 jmc 573: .It RemoteForward
1.319 jmc 574: .It RequestTTY
1.432 djm 575: .It RequiredRSASize
1.218 jmc 576: .It SendEnv
577: .It ServerAliveInterval
578: .It ServerAliveCountMax
1.422 djm 579: .It SessionType
1.395 jmc 580: .It SetEnv
1.423 djm 581: .It StdinNull
1.347 jmc 582: .It StreamLocalBindMask
583: .It StreamLocalBindUnlink
1.218 jmc 584: .It StrictHostKeyChecking
585: .It TCPKeepAlive
586: .It Tunnel
587: .It TunnelDevice
1.354 djm 588: .It UpdateHostKeys
1.218 jmc 589: .It User
590: .It UserKnownHostsFile
591: .It VerifyHostKeyDNS
1.276 jmc 592: .It VisualHostKey
1.218 jmc 593: .It XAuthLocation
594: .El
1.360 millert 595: .Pp
1.218 jmc 596: .It Fl p Ar port
597: Port to connect to on the remote host.
598: This can be specified on a
599: per-host basis in the configuration file.
1.360 millert 600: .Pp
1.362 djm 601: .It Fl Q Ar query_option
1.425 jmc 602: Queries for the algorithms supported by one of the following features:
1.341 deraadt 603: .Ar cipher
1.332 djm 604: (supported symmetric ciphers),
1.341 deraadt 605: .Ar cipher-auth
1.340 djm 606: (supported symmetric ciphers that support authenticated encryption),
1.398 djm 607: .Ar help
608: (supported query terms for use with the
609: .Fl Q
610: flag),
1.341 deraadt 611: .Ar mac
1.332 djm 612: (supported message integrity codes),
1.341 deraadt 613: .Ar kex
1.332 djm 614: (key exchange algorithms),
1.341 deraadt 615: .Ar key
1.362 djm 616: (key types),
1.434 ! djm 617: .Ar key-ca-sign
! 618: (valid CA signature algorithms for certificates),
1.362 djm 619: .Ar key-cert
620: (certificate key types),
621: .Ar key-plain
1.398 djm 622: (non-certificate key types),
1.410 dtucker 623: .Ar key-sig
624: (all key types and signature algorithms),
1.356 djm 625: .Ar protocol-version
1.398 djm 626: (supported SSH protocol versions), and
627: .Ar sig
628: (supported signature algorithms).
1.410 dtucker 629: Alternatively, any keyword from
630: .Xr ssh_config 5
631: or
632: .Xr sshd_config 5
633: that takes an algorithm list may be used as an alias for the corresponding
634: query_option.
1.360 millert 635: .Pp
1.218 jmc 636: .It Fl q
637: Quiet mode.
1.271 djm 638: Causes most warning and diagnostic messages to be suppressed.
1.360 millert 639: .Pp
1.218 jmc 640: .It Fl R Xo
641: .Sm off
642: .Oo Ar bind_address : Oc
643: .Ar port : host : hostport
644: .Sm on
645: .Xc
1.360 millert 646: .It Fl R Xo
647: .Sm off
648: .Oo Ar bind_address : Oc
649: .Ar port : local_socket
650: .Sm on
651: .Xc
652: .It Fl R Xo
653: .Sm off
654: .Ar remote_socket : host : hostport
655: .Sm on
656: .Xc
657: .It Fl R Xo
658: .Sm off
659: .Ar remote_socket : local_socket
660: .Sm on
661: .Xc
1.384 markus 662: .It Fl R Xo
663: .Sm off
664: .Oo Ar bind_address : Oc
665: .Ar port
666: .Sm on
667: .Xc
1.360 millert 668: Specifies that connections to the given TCP port or Unix socket on the remote
1.384 markus 669: (server) host are to be forwarded to the local side.
670: .Pp
1.360 millert 671: This works by allocating a socket to listen to either a TCP
1.218 jmc 672: .Ar port
1.360 millert 673: or to a Unix socket on the remote side.
674: Whenever a connection is made to this port or Unix socket, the
675: connection is forwarded over the secure channel, and a connection
1.384 markus 676: is made from the local machine to either an explicit destination specified by
1.218 jmc 677: .Ar host
678: port
1.360 millert 679: .Ar hostport ,
680: or
681: .Ar local_socket ,
1.384 markus 682: or, if no explicit destination was specified,
683: .Nm
684: will act as a SOCKS 4/5 proxy and forward connections to the destinations
685: requested by the remote SOCKS client.
1.2 deraadt 686: .Pp
1.218 jmc 687: Port forwardings can also be specified in the configuration file.
688: Privileged ports can be forwarded only when
689: logging in as root on the remote machine.
1.324 jmc 690: IPv6 addresses can be specified by enclosing the address in square brackets.
1.194 jakob 691: .Pp
1.360 millert 692: By default, TCP listening sockets on the server will be bound to the loopback
1.218 jmc 693: interface only.
1.280 tobias 694: This may be overridden by specifying a
1.218 jmc 695: .Ar bind_address .
696: An empty
697: .Ar bind_address ,
698: or the address
699: .Ql * ,
700: indicates that the remote socket should listen on all interfaces.
701: Specifying a remote
702: .Ar bind_address
703: will only succeed if the server's
704: .Cm GatewayPorts
705: option is enabled (see
706: .Xr sshd_config 5 ) .
1.281 djm 707: .Pp
708: If the
709: .Ar port
710: argument is
1.282 djm 711: .Ql 0 ,
1.281 djm 712: the listen port will be dynamically allocated on the server and reported
713: to the client at run time.
1.305 markus 714: When used together with
1.430 naddy 715: .Ic -O forward ,
1.305 markus 716: the allocated port will be printed to the standard output.
1.360 millert 717: .Pp
1.218 jmc 718: .It Fl S Ar ctl_path
1.304 jmc 719: Specifies the location of a control socket for connection sharing,
1.303 djm 720: or the string
721: .Dq none
722: to disable connection sharing.
1.218 jmc 723: Refer to the description of
724: .Cm ControlPath
725: and
726: .Cm ControlMaster
727: in
728: .Xr ssh_config 5
729: for details.
1.360 millert 730: .Pp
1.218 jmc 731: .It Fl s
732: May be used to request invocation of a subsystem on the remote system.
1.369 jmc 733: Subsystems facilitate the use of SSH
734: as a secure transport for other applications (e.g.\&
1.218 jmc 735: .Xr sftp 1 ) .
736: The subsystem is specified as the remote command.
1.422 djm 737: Refer to the description of
738: .Cm SessionType
739: in
740: .Xr ssh_config 5
741: for details.
1.360 millert 742: .Pp
1.218 jmc 743: .It Fl T
1.357 dtucker 744: Disable pseudo-terminal allocation.
1.360 millert 745: .Pp
1.218 jmc 746: .It Fl t
1.357 dtucker 747: Force pseudo-terminal allocation.
1.218 jmc 748: This can be used to execute arbitrary
749: screen-based programs on a remote machine, which can be very useful,
1.257 jmc 750: e.g. when implementing menu services.
1.218 jmc 751: Multiple
752: .Fl t
753: options force tty allocation, even if
1.194 jakob 754: .Nm
1.218 jmc 755: has no local tty.
1.360 millert 756: .Pp
1.218 jmc 757: .It Fl V
758: Display the version number and exit.
1.360 millert 759: .Pp
1.218 jmc 760: .It Fl v
761: Verbose mode.
762: Causes
1.176 jmc 763: .Nm
1.218 jmc 764: to print debugging messages about its progress.
765: This is helpful in
766: debugging connection, authentication, and configuration problems.
767: Multiple
768: .Fl v
769: options increase the verbosity.
770: The maximum is 3.
1.360 millert 771: .Pp
1.290 dtucker 772: .It Fl W Ar host : Ns Ar port
773: Requests that standard input and output on the client be forwarded to
774: .Ar host
775: on
776: .Ar port
777: over the secure channel.
778: Implies
779: .Fl N ,
780: .Fl T ,
781: .Cm ExitOnForwardFailure
782: and
1.373 jmc 783: .Cm ClearAllForwardings ,
784: though these can be overridden in the configuration file or using
1.372 dtucker 785: .Fl o
786: command line options.
1.360 millert 787: .Pp
1.261 stevesk 788: .It Fl w Xo
789: .Ar local_tun Ns Op : Ns Ar remote_tun
790: .Xc
791: Requests
792: tunnel
793: device forwarding with the specified
1.218 jmc 794: .Xr tun 4
1.261 stevesk 795: devices between the client
796: .Pq Ar local_tun
797: and the server
798: .Pq Ar remote_tun .
799: .Pp
1.228 jmc 800: The devices may be specified by numerical ID or the keyword
801: .Dq any ,
802: which uses the next available tunnel device.
1.261 stevesk 803: If
804: .Ar remote_tun
805: is not specified, it defaults to
806: .Dq any .
1.228 jmc 807: See also the
1.218 jmc 808: .Cm Tunnel
1.261 stevesk 809: and
810: .Cm TunnelDevice
811: directives in
1.218 jmc 812: .Xr ssh_config 5 .
1.393 djm 813: .Pp
1.261 stevesk 814: If the
815: .Cm Tunnel
1.393 djm 816: directive is unset, it will be set to the default tunnel mode, which is
1.261 stevesk 817: .Dq point-to-point .
1.393 djm 818: If a different
819: .Cm Tunnel
820: forwarding mode it desired, then it should be specified before
821: .Fl w .
1.360 millert 822: .Pp
1.218 jmc 823: .It Fl X
824: Enables X11 forwarding.
1.54 markus 825: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 826: .Pp
1.218 jmc 827: X11 forwarding should be enabled with caution.
1.168 jmc 828: Users with the ability to bypass file permissions on the remote host
1.218 jmc 829: (for the user's X authorization database)
830: can access the local X11 display through the forwarded connection.
831: An attacker may then be able to perform activities such as keystroke monitoring.
832: .Pp
833: For this reason, X11 forwarding is subjected to X11 SECURITY extension
834: restrictions by default.
1.429 jsg 835: Refer to the
1.218 jmc 836: .Nm
837: .Fl Y
838: option and the
839: .Cm ForwardX11Trusted
840: directive in
841: .Xr ssh_config 5
842: for more information.
1.360 millert 843: .Pp
1.218 jmc 844: .It Fl x
845: Disables X11 forwarding.
1.360 millert 846: .Pp
1.218 jmc 847: .It Fl Y
848: Enables trusted X11 forwarding.
849: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
850: controls.
1.360 millert 851: .Pp
1.278 djm 852: .It Fl y
853: Send log information using the
854: .Xr syslog 3
855: system module.
856: By default this information is sent to stderr.
1.218 jmc 857: .El
1.224 jmc 858: .Pp
859: .Nm
860: may additionally obtain configuration data from
861: a per-user configuration file and a system-wide configuration file.
862: The file format and configuration options are described in
863: .Xr ssh_config 5 .
1.222 jmc 864: .Sh AUTHENTICATION
1.377 djm 865: The OpenSSH SSH client supports SSH protocol 2.
1.222 jmc 866: .Pp
867: The methods available for authentication are:
1.260 jmc 868: GSSAPI-based authentication,
1.222 jmc 869: host-based authentication,
870: public key authentication,
1.421 dtucker 871: keyboard-interactive authentication,
1.222 jmc 872: and password authentication.
873: Authentication methods are tried in the order specified above,
1.369 jmc 874: though
875: .Cm PreferredAuthentications
876: can be used to change the default order.
1.222 jmc 877: .Pp
878: Host-based authentication works as follows:
1.218 jmc 879: If the machine the user logs in from is listed in
880: .Pa /etc/hosts.equiv
881: or
882: .Pa /etc/shosts.equiv
1.412 djm 883: on the remote machine, the user is non-root and the user names are
1.218 jmc 884: the same on both sides, or if the files
885: .Pa ~/.rhosts
886: or
887: .Pa ~/.shosts
888: exist in the user's home directory on the
889: remote machine and contain a line containing the name of the client
890: machine and the name of the user on that machine, the user is
1.222 jmc 891: considered for login.
892: Additionally, the server
893: .Em must
894: be able to verify the client's
895: host key (see the description of
1.218 jmc 896: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 897: and
1.222 jmc 898: .Pa ~/.ssh/known_hosts ,
899: below)
900: for login to be permitted.
1.218 jmc 901: This authentication method closes security holes due to IP
1.222 jmc 902: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 903: [Note to the administrator:
904: .Pa /etc/hosts.equiv ,
905: .Pa ~/.rhosts ,
906: and the rlogin/rsh protocol in general, are inherently insecure and should be
907: disabled if security is desired.]
1.189 dtucker 908: .Pp
1.222 jmc 909: Public key authentication works as follows:
910: The scheme is based on public-key cryptography,
911: using cryptosystems
912: where encryption and decryption are done using separate keys,
913: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 914: The idea is that each user creates a public/private
915: key pair for authentication purposes.
916: The server knows the public key, and only the user knows the private key.
1.222 jmc 917: .Nm
918: implements public key authentication protocol automatically,
1.349 sobrado 919: using one of the DSA, ECDSA, Ed25519 or RSA algorithms.
1.333 jmc 920: The HISTORY section of
1.222 jmc 921: .Xr ssl 8
1.311 jmc 922: contains a brief discussion of the DSA and RSA algorithms.
1.210 djm 923: .Pp
1.218 jmc 924: The file
925: .Pa ~/.ssh/authorized_keys
926: lists the public keys that are permitted for logging in.
927: When the user logs in, the
1.2 deraadt 928: .Nm
1.218 jmc 929: program tells the server which key pair it would like to use for
930: authentication.
1.222 jmc 931: The client proves that it has access to the private key
932: and the server checks that the corresponding public key
933: is authorized to accept the account.
1.383 djm 934: .Pp
935: The server may inform the client of errors that prevented public key
936: authentication from succeeding after authentication completes using a
937: different method.
938: These may be viewed by increasing the
939: .Cm LogLevel
940: to
941: .Cm DEBUG
942: or higher (e.g. by using the
943: .Fl v
944: flag).
1.218 jmc 945: .Pp
1.420 dtucker 946: The user creates their key pair by running
1.218 jmc 947: .Xr ssh-keygen 1 .
948: This stores the private key in
1.222 jmc 949: .Pa ~/.ssh/id_dsa
1.369 jmc 950: (DSA),
1.310 djm 951: .Pa ~/.ssh/id_ecdsa
1.369 jmc 952: (ECDSA),
1.404 naddy 953: .Pa ~/.ssh/id_ecdsa_sk
1.409 naddy 954: (authenticator-hosted ECDSA),
1.343 naddy 955: .Pa ~/.ssh/id_ed25519
1.369 jmc 956: (Ed25519),
1.406 naddy 957: .Pa ~/.ssh/id_ed25519_sk
1.409 naddy 958: (authenticator-hosted Ed25519),
1.222 jmc 959: or
960: .Pa ~/.ssh/id_rsa
1.369 jmc 961: (RSA)
1.218 jmc 962: and stores the public key in
1.222 jmc 963: .Pa ~/.ssh/id_dsa.pub
1.369 jmc 964: (DSA),
1.310 djm 965: .Pa ~/.ssh/id_ecdsa.pub
1.369 jmc 966: (ECDSA),
1.404 naddy 967: .Pa ~/.ssh/id_ecdsa_sk.pub
1.409 naddy 968: (authenticator-hosted ECDSA),
1.343 naddy 969: .Pa ~/.ssh/id_ed25519.pub
1.369 jmc 970: (Ed25519),
1.406 naddy 971: .Pa ~/.ssh/id_ed25519_sk.pub
1.409 naddy 972: (authenticator-hosted Ed25519),
1.222 jmc 973: or
974: .Pa ~/.ssh/id_rsa.pub
1.369 jmc 975: (RSA)
1.218 jmc 976: in the user's home directory.
1.222 jmc 977: The user should then copy the public key
1.218 jmc 978: to
979: .Pa ~/.ssh/authorized_keys
1.420 dtucker 980: in their home directory on the remote machine.
1.222 jmc 981: The
1.218 jmc 982: .Pa authorized_keys
983: file corresponds to the conventional
984: .Pa ~/.rhosts
985: file, and has one key
1.222 jmc 986: per line, though the lines can be very long.
1.218 jmc 987: After this, the user can log in without giving the password.
988: .Pp
1.301 jmc 989: A variation on public key authentication
990: is available in the form of certificate authentication:
991: instead of a set of public/private keys,
992: signed certificates are used.
993: This has the advantage that a single trusted certification authority
994: can be used in place of many public/private keys.
1.333 jmc 995: See the CERTIFICATES section of
1.301 jmc 996: .Xr ssh-keygen 1
997: for more information.
998: .Pp
999: The most convenient way to use public key or certificate authentication
1000: may be with an authentication agent.
1.218 jmc 1001: See
1002: .Xr ssh-agent 1
1.366 jcs 1003: and (optionally) the
1004: .Cm AddKeysToAgent
1005: directive in
1006: .Xr ssh_config 5
1.218 jmc 1007: for more information.
1008: .Pp
1.421 dtucker 1009: Keyboard-interactive authentication works as follows:
1.222 jmc 1010: The server sends an arbitrary
1011: .Qq challenge
1.421 dtucker 1012: text and prompts for a response, possibly multiple times.
1013: Examples of keyboard-interactive authentication include
1.335 jmc 1014: .Bx
1015: Authentication (see
1.222 jmc 1016: .Xr login.conf 5 )
1.335 jmc 1017: and PAM (some
1018: .Pf non- Ox
1019: systems).
1.222 jmc 1020: .Pp
1021: Finally, if other authentication methods fail,
1.218 jmc 1022: .Nm
1023: prompts the user for a password.
1024: The password is sent to the remote
1025: host for checking; however, since all communications are encrypted,
1026: the password cannot be seen by someone listening on the network.
1.232 jmc 1027: .Pp
1028: .Nm
1029: automatically maintains and checks a database containing
1030: identification for all hosts it has ever been used with.
1031: Host keys are stored in
1032: .Pa ~/.ssh/known_hosts
1033: in the user's home directory.
1034: Additionally, the file
1035: .Pa /etc/ssh/ssh_known_hosts
1036: is automatically checked for known hosts.
1037: Any new hosts are automatically added to the user's file.
1038: If a host's identification ever changes,
1039: .Nm
1040: warns about this and disables password authentication to prevent
1041: server spoofing or man-in-the-middle attacks,
1042: which could otherwise be used to circumvent the encryption.
1043: The
1044: .Cm StrictHostKeyChecking
1045: option can be used to control logins to machines whose
1046: host key is not known or has changed.
1047: .Pp
1.218 jmc 1048: When the user's identity has been accepted by the server, the server
1.357 dtucker 1049: either executes the given command in a non-interactive session or,
1050: if no command has been specified, logs into the machine and gives
1051: the user a normal shell as an interactive session.
1.218 jmc 1052: All communication with
1053: the remote command or shell will be automatically encrypted.
1054: .Pp
1.430 naddy 1055: If an interactive session is requested,
1.357 dtucker 1056: .Nm
1057: by default will only request a pseudo-terminal (pty) for interactive
1058: sessions when the client has one.
1059: The flags
1060: .Fl T
1061: and
1062: .Fl t
1063: can be used to override this behaviour.
1064: .Pp
1.430 naddy 1065: If a pseudo-terminal has been allocated, the
1.218 jmc 1066: user may use the escape characters noted below.
1067: .Pp
1.357 dtucker 1068: If no pseudo-terminal has been allocated,
1.218 jmc 1069: the session is transparent and can be used to reliably transfer binary data.
1070: On most systems, setting the escape character to
1071: .Dq none
1072: will also make the session transparent even if a tty is used.
1073: .Pp
1074: The session terminates when the command or shell on the remote
1.247 jmc 1075: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 1076: .Sh ESCAPE CHARACTERS
1.218 jmc 1077: When a pseudo-terminal has been requested,
1.2 deraadt 1078: .Nm
1.218 jmc 1079: supports a number of functions through the use of an escape character.
1080: .Pp
1081: A single tilde character can be sent as
1082: .Ic ~~
1083: or by following the tilde by a character other than those described below.
1084: The escape character must always follow a newline to be interpreted as
1085: special.
1086: The escape character can be changed in configuration files using the
1087: .Cm EscapeChar
1088: configuration directive or on the command line by the
1089: .Fl e
1090: option.
1091: .Pp
1092: The supported escapes (assuming the default
1093: .Ql ~ )
1094: are:
1095: .Bl -tag -width Ds
1096: .It Cm ~.
1097: Disconnect.
1098: .It Cm ~^Z
1099: Background
1.234 jmc 1100: .Nm .
1.218 jmc 1101: .It Cm ~#
1102: List forwarded connections.
1103: .It Cm ~&
1104: Background
1.2 deraadt 1105: .Nm
1.218 jmc 1106: at logout when waiting for forwarded connection / X11 sessions to terminate.
1107: .It Cm ~?
1108: Display a list of escape characters.
1109: .It Cm ~B
1110: Send a BREAK to the remote system
1.369 jmc 1111: (only useful if the peer supports it).
1.218 jmc 1112: .It Cm ~C
1113: Open command line.
1114: Currently this allows the addition of port forwardings using the
1.279 stevesk 1115: .Fl L ,
1116: .Fl R
1.218 jmc 1117: and
1.279 stevesk 1118: .Fl D
1.225 jmc 1119: options (see above).
1.322 markus 1120: It also allows the cancellation of existing port-forwardings
1121: with
1.262 stevesk 1122: .Sm off
1.322 markus 1123: .Fl KL Oo Ar bind_address : Oc Ar port
1.262 stevesk 1124: .Sm on
1.322 markus 1125: for local,
1126: .Sm off
1127: .Fl KR Oo Ar bind_address : Oc Ar port
1128: .Sm on
1129: for remote and
1130: .Sm off
1131: .Fl KD Oo Ar bind_address : Oc Ar port
1132: .Sm on
1133: for dynamic port-forwardings.
1.218 jmc 1134: .Ic !\& Ns Ar command
1135: allows the user to execute a local command if the
1136: .Ic PermitLocalCommand
1137: option is enabled in
1.176 jmc 1138: .Xr ssh_config 5 .
1.218 jmc 1139: Basic help is available, using the
1140: .Fl h
1141: option.
1142: .It Cm ~R
1143: Request rekeying of the connection
1.369 jmc 1144: (only useful if the peer supports it).
1.327 dtucker 1145: .It Cm ~V
1146: Decrease the verbosity
1147: .Pq Ic LogLevel
1148: when errors are being written to stderr.
1149: .It Cm ~v
1.328 jmc 1150: Increase the verbosity
1.327 dtucker 1151: .Pq Ic LogLevel
1152: when errors are being written to stderr.
1.176 jmc 1153: .El
1.246 jmc 1154: .Sh TCP FORWARDING
1.402 jmc 1155: Forwarding of arbitrary TCP connections over a secure channel
1156: can be specified either on the command line or in a configuration file.
1.246 jmc 1157: One possible application of TCP forwarding is a secure connection to a
1158: mail server; another is going through firewalls.
1159: .Pp
1.402 jmc 1160: In the example below, we look at encrypting communication for an IRC client,
1161: even though the IRC server it connects to does not directly
1162: support encrypted communication.
1.246 jmc 1163: This works as follows:
1164: the user connects to the remote host using
1165: .Nm ,
1.402 jmc 1166: specifying the ports to be used to forward the connection.
1167: After that it is possible to start the program locally,
1.246 jmc 1168: and
1169: .Nm
1.402 jmc 1170: will encrypt and forward the connection to the remote server.
1.246 jmc 1171: .Pp
1.402 jmc 1172: The following example tunnels an IRC session from the client
1173: to an IRC server at
1.246 jmc 1174: .Dq server.example.com ,
1175: joining channel
1176: .Dq #users ,
1177: nickname
1178: .Dq pinky ,
1.402 jmc 1179: using the standard IRC port, 6667:
1180: .Bd -literal -offset 4n
1181: $ ssh -f -L 6667:localhost:6667 server.example.com sleep 10
1182: $ irc -c '#users' pinky IRC/127.0.0.1
1183: .Ed
1.246 jmc 1184: .Pp
1185: The
1186: .Fl f
1187: option backgrounds
1188: .Nm
1189: and the remote command
1190: .Dq sleep 10
1191: is specified to allow an amount of time
1192: (10 seconds, in the example)
1.402 jmc 1193: to start the program which is going to use the tunnel.
1.246 jmc 1194: If no connections are made within the time specified,
1195: .Nm
1196: will exit.
1197: .Sh X11 FORWARDING
1.218 jmc 1198: If the
1199: .Cm ForwardX11
1200: variable is set to
1201: .Dq yes
1202: (or see the description of the
1.227 jmc 1203: .Fl X ,
1204: .Fl x ,
1.218 jmc 1205: and
1.227 jmc 1206: .Fl Y
1.226 jmc 1207: options above)
1.218 jmc 1208: and the user is using X11 (the
1209: .Ev DISPLAY
1210: environment variable is set), the connection to the X11 display is
1211: automatically forwarded to the remote side in such a way that any X11
1212: programs started from the shell (or command) will go through the
1213: encrypted channel, and the connection to the real X server will be made
1.176 jmc 1214: from the local machine.
1.218 jmc 1215: The user should not manually set
1216: .Ev DISPLAY .
1217: Forwarding of X11 connections can be
1218: configured on the command line or in configuration files.
1219: .Pp
1220: The
1221: .Ev DISPLAY
1222: value set by
1223: .Nm
1224: will point to the server machine, but with a display number greater than zero.
1225: This is normal, and happens because
1226: .Nm
1227: creates a
1228: .Dq proxy
1229: X server on the server machine for forwarding the
1230: connections over the encrypted channel.
1.200 djm 1231: .Pp
1.218 jmc 1232: .Nm
1233: will also automatically set up Xauthority data on the server machine.
1234: For this purpose, it will generate a random authorization cookie,
1235: store it in Xauthority on the server, and verify that any forwarded
1236: connections carry this cookie and replace it by the real cookie when
1237: the connection is opened.
1238: The real authentication cookie is never
1239: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1240: .Pp
1.218 jmc 1241: If the
1242: .Cm ForwardAgent
1243: variable is set to
1244: .Dq yes
1245: (or see the description of the
1246: .Fl A
1.191 djm 1247: and
1.218 jmc 1248: .Fl a
1.226 jmc 1249: options above) and
1.218 jmc 1250: the user is using an authentication agent, the connection to the agent
1251: is automatically forwarded to the remote side.
1.252 jmc 1252: .Sh VERIFYING HOST KEYS
1253: When connecting to a server for the first time,
1254: a fingerprint of the server's public key is presented to the user
1255: (unless the option
1256: .Cm StrictHostKeyChecking
1257: has been disabled).
1258: Fingerprints can be determined using
1259: .Xr ssh-keygen 1 :
1260: .Pp
1261: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1262: .Pp
1.274 grunk 1263: If the fingerprint is already known, it can be matched
1264: and the key can be accepted or rejected.
1.358 djm 1265: If only legacy (MD5) fingerprints for the server are available, the
1266: .Xr ssh-keygen 1
1267: .Fl E
1268: option may be used to downgrade the fingerprint algorithm to match.
1269: .Pp
1.274 grunk 1270: Because of the difficulty of comparing host keys
1.352 djm 1271: just by looking at fingerprint strings,
1.274 grunk 1272: there is also support to compare host keys visually,
1273: using
1274: .Em random art .
1275: By setting the
1.275 grunk 1276: .Cm VisualHostKey
1.274 grunk 1277: option to
1.275 grunk 1278: .Dq yes ,
1.274 grunk 1279: a small ASCII graphic gets displayed on every login to a server, no matter
1280: if the session itself is interactive or not.
1281: By learning the pattern a known server produces, a user can easily
1282: find out that the host key has changed when a completely different pattern
1283: is displayed.
1284: Because these patterns are not unambiguous however, a pattern that looks
1285: similar to the pattern remembered only gives a good probability that the
1286: host key is the same, not guaranteed proof.
1287: .Pp
1288: To get a listing of the fingerprints along with their random art for
1289: all known hosts, the following command line can be used:
1290: .Pp
1291: .Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1292: .Pp
1.252 jmc 1293: If the fingerprint is unknown,
1294: an alternative method of verification is available:
1295: SSH fingerprints verified by DNS.
1296: An additional resource record (RR),
1297: SSHFP,
1298: is added to a zonefile
1299: and the connecting client is able to match the fingerprint
1300: with that of the key presented.
1301: .Pp
1302: In this example, we are connecting a client to a server,
1303: .Dq host.example.com .
1304: The SSHFP resource records should first be added to the zonefile for
1305: host.example.com:
1306: .Bd -literal -offset indent
1.259 jakob 1307: $ ssh-keygen -r host.example.com.
1.252 jmc 1308: .Ed
1309: .Pp
1310: The output lines will have to be added to the zonefile.
1311: To check that the zone is answering fingerprint queries:
1312: .Pp
1313: .Dl $ dig -t SSHFP host.example.com
1314: .Pp
1315: Finally the client connects:
1316: .Bd -literal -offset indent
1317: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1318: [...]
1319: Matching host key fingerprint found in DNS.
1320: Are you sure you want to continue connecting (yes/no)?
1321: .Ed
1322: .Pp
1323: See the
1324: .Cm VerifyHostKeyDNS
1325: option in
1326: .Xr ssh_config 5
1327: for more information.
1.250 jmc 1328: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1329: .Nm
1330: contains support for Virtual Private Network (VPN) tunnelling
1331: using the
1332: .Xr tun 4
1333: network pseudo-device,
1334: allowing two networks to be joined securely.
1335: The
1336: .Xr sshd_config 5
1337: configuration option
1338: .Cm PermitTunnel
1339: controls whether the server supports this,
1340: and at what level (layer 2 or 3 traffic).
1341: .Pp
1342: The following example would connect client network 10.0.50.0/24
1.265 otto 1343: with remote network 10.0.99.0/24 using a point-to-point connection
1344: from 10.1.1.1 to 10.1.1.2,
1345: provided that the SSH server running on the gateway to the remote network,
1346: at 192.168.1.15, allows it.
1347: .Pp
1348: On the client:
1.250 jmc 1349: .Bd -literal -offset indent
1350: # ssh -f -w 0:1 192.168.1.15 true
1.265 otto 1351: # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1352: # route add 10.0.99.0/24 10.1.1.2
1353: .Ed
1354: .Pp
1355: On the server:
1356: .Bd -literal -offset indent
1357: # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1358: # route add 10.0.50.0/24 10.1.1.1
1.250 jmc 1359: .Ed
1360: .Pp
1361: Client access may be more finely tuned via the
1362: .Pa /root/.ssh/authorized_keys
1363: file (see below) and the
1364: .Cm PermitRootLogin
1365: server option.
1.255 jmc 1366: The following entry would permit connections on
1.250 jmc 1367: .Xr tun 4
1.255 jmc 1368: device 1 from user
1.250 jmc 1369: .Dq jane
1.255 jmc 1370: and on tun device 2 from user
1.250 jmc 1371: .Dq john ,
1372: if
1373: .Cm PermitRootLogin
1374: is set to
1375: .Dq forced-commands-only :
1376: .Bd -literal -offset 2n
1377: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1378: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1379: .Ed
1380: .Pp
1.264 ray 1381: Since an SSH-based setup entails a fair amount of overhead,
1.250 jmc 1382: it may be more suited to temporary setups,
1383: such as for wireless VPNs.
1384: More permanent VPNs are better provided by tools such as
1385: .Xr ipsecctl 8
1386: and
1387: .Xr isakmpd 8 .
1.2 deraadt 1388: .Sh ENVIRONMENT
1389: .Nm
1.1 deraadt 1390: will normally set the following environment variables:
1.237 jmc 1391: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1392: .It Ev DISPLAY
1393: The
1394: .Ev DISPLAY
1.40 aaron 1395: variable indicates the location of the X11 server.
1.44 aaron 1396: It is automatically set by
1.2 deraadt 1397: .Nm
1398: to point to a value of the form
1.233 jmc 1399: .Dq hostname:n ,
1400: where
1401: .Dq hostname
1402: indicates the host where the shell runs, and
1403: .Sq n
1404: is an integer \*(Ge 1.
1.40 aaron 1405: .Nm
1406: uses this special value to forward X11 connections over the secure
1407: channel.
1.107 markus 1408: The user should normally not set
1409: .Ev DISPLAY
1410: explicitly, as that
1.1 deraadt 1411: will render the X11 connection insecure (and will require the user to
1412: manually copy any required authorization cookies).
1.2 deraadt 1413: .It Ev HOME
1.1 deraadt 1414: Set to the path of the user's home directory.
1.2 deraadt 1415: .It Ev LOGNAME
1416: Synonym for
1.12 aaron 1417: .Ev USER ;
1418: set for compatibility with systems that use this variable.
1.2 deraadt 1419: .It Ev MAIL
1.129 stevesk 1420: Set to the path of the user's mailbox.
1.40 aaron 1421: .It Ev PATH
1.2 deraadt 1422: Set to the default
1423: .Ev PATH ,
1424: as specified when compiling
1.234 jmc 1425: .Nm .
1.118 markus 1426: .It Ev SSH_ASKPASS
1427: If
1428: .Nm
1429: needs a passphrase, it will read the passphrase from the current
1430: terminal if it was run from a terminal.
1431: If
1432: .Nm
1433: does not have a terminal associated with it but
1434: .Ev DISPLAY
1435: and
1436: .Ev SSH_ASKPASS
1437: are set, it will execute the program specified by
1438: .Ev SSH_ASKPASS
1439: and open an X11 window to read the passphrase.
1440: This is particularly useful when calling
1441: .Nm
1442: from a
1.196 jmc 1443: .Pa .xsession
1.118 markus 1444: or related script.
1445: (Note that on some machines it
1446: may be necessary to redirect the input from
1447: .Pa /dev/null
1448: to make this work.)
1.413 djm 1449: .It Ev SSH_ASKPASS_REQUIRE
1.414 jmc 1450: Allows further control over the use of an askpass program.
1.413 djm 1451: If this variable is set to
1452: .Dq never
1453: then
1454: .Nm
1455: will never attempt to use one.
1456: If it is set to
1457: .Dq prefer ,
1458: then
1459: .Nm
1460: will prefer to use the askpass program instead of the TTY when requesting
1461: passwords.
1462: Finally, if the variable is set to
1463: .Dq force ,
1464: then the askpass program will be used for all passphrase input regardless
1465: of whether
1466: .Ev DISPLAY
1467: is set.
1.18 markus 1468: .It Ev SSH_AUTH_SOCK
1.233 jmc 1469: Identifies the path of a
1470: .Ux Ns -domain
1471: socket used to communicate with the agent.
1.166 stevesk 1472: .It Ev SSH_CONNECTION
1473: Identifies the client and server ends of the connection.
1.40 aaron 1474: The variable contains
1.233 jmc 1475: four space-separated values: client IP address, client port number,
1476: server IP address, and server port number.
1.73 markus 1477: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1478: This variable contains the original command line if a forced command
1.73 markus 1479: is executed.
1480: It can be used to extract the original arguments.
1.2 deraadt 1481: .It Ev SSH_TTY
1.1 deraadt 1482: This is set to the name of the tty (path to the device) associated
1.40 aaron 1483: with the current shell or command.
1484: If the current session has no tty,
1.1 deraadt 1485: this variable is not set.
1.387 djm 1486: .It Ev SSH_TUNNEL
1487: Optionally set by
1488: .Xr sshd 8
1489: to contain the interface names assigned if tunnel forwarding was
1490: requested by the client.
1.385 djm 1491: .It Ev SSH_USER_AUTH
1492: Optionally set by
1493: .Xr sshd 8 ,
1494: this variable may contain a pathname to a file that lists the authentication
1495: methods successfully used when the session was established, including any
1496: public keys that were used.
1.2 deraadt 1497: .It Ev TZ
1.214 jmc 1498: This variable is set to indicate the present time zone if it
1.257 jmc 1499: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1500: on to new connections).
1.2 deraadt 1501: .It Ev USER
1.1 deraadt 1502: Set to the name of the user logging in.
1.2 deraadt 1503: .El
1504: .Pp
1.44 aaron 1505: Additionally,
1.2 deraadt 1506: .Nm
1.44 aaron 1507: reads
1.207 djm 1508: .Pa ~/.ssh/environment ,
1.2 deraadt 1509: and adds lines of the format
1510: .Dq VARNAME=value
1.233 jmc 1511: to the environment if the file exists and users are allowed to
1.161 marc 1512: change their environment.
1.176 jmc 1513: For more information, see the
1.161 marc 1514: .Cm PermitUserEnvironment
1.162 stevesk 1515: option in
1.161 marc 1516: .Xr sshd_config 5 .
1.2 deraadt 1517: .Sh FILES
1.236 jmc 1518: .Bl -tag -width Ds -compact
1.309 jmc 1519: .It Pa ~/.rhosts
1.240 jmc 1520: This file is used for host-based authentication (see above).
1.92 markus 1521: On some machines this file may need to be
1.240 jmc 1522: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1523: because
1.2 deraadt 1524: .Xr sshd 8
1.40 aaron 1525: reads it as root.
1526: Additionally, this file must be owned by the user,
1527: and must not have write permissions for anyone else.
1528: The recommended
1.1 deraadt 1529: permission for most machines is read/write for the user, and not
1530: accessible by others.
1.2 deraadt 1531: .Pp
1.309 jmc 1532: .It Pa ~/.shosts
1.240 jmc 1533: This file is used in exactly the same way as
1534: .Pa .rhosts ,
1535: but allows host-based authentication without permitting login with
1536: rlogin/rsh.
1.272 mcbride 1537: .Pp
1.309 jmc 1538: .It Pa ~/.ssh/
1.272 mcbride 1539: This directory is the default location for all user-specific configuration
1540: and authentication information.
1541: There is no general requirement to keep the entire contents of this directory
1542: secret, but the recommended permissions are read/write/execute for the user,
1543: and not accessible by others.
1.236 jmc 1544: .Pp
1.309 jmc 1545: .It Pa ~/.ssh/authorized_keys
1.349 sobrado 1546: Lists the public keys (DSA, ECDSA, Ed25519, RSA)
1.343 naddy 1547: that can be used for logging in as this user.
1.238 jmc 1548: The format of this file is described in the
1549: .Xr sshd 8
1550: manual page.
1551: This file is not highly sensitive, but the recommended
1552: permissions are read/write for the user, and not accessible by others.
1553: .Pp
1.309 jmc 1554: .It Pa ~/.ssh/config
1.238 jmc 1555: This is the per-user configuration file.
1556: The file format and configuration options are described in
1557: .Xr ssh_config 5 .
1558: Because of the potential for abuse, this file must have strict permissions:
1.334 djm 1559: read/write for the user, and not writable by others.
1.238 jmc 1560: .Pp
1.309 jmc 1561: .It Pa ~/.ssh/environment
1.239 jmc 1562: Contains additional definitions for environment variables; see
1563: .Sx ENVIRONMENT ,
1.238 jmc 1564: above.
1565: .Pp
1.309 jmc 1566: .It Pa ~/.ssh/id_dsa
1.310 djm 1567: .It Pa ~/.ssh/id_ecdsa
1.404 naddy 1568: .It Pa ~/.ssh/id_ecdsa_sk
1.343 naddy 1569: .It Pa ~/.ssh/id_ed25519
1.406 naddy 1570: .It Pa ~/.ssh/id_ed25519_sk
1.309 jmc 1571: .It Pa ~/.ssh/id_rsa
1.238 jmc 1572: Contains the private key for authentication.
1573: These files
1574: contain sensitive data and should be readable by the user but not
1575: accessible by others (read/write/execute).
1576: .Nm
1577: will simply ignore a private key file if it is accessible by others.
1578: It is possible to specify a passphrase when
1579: generating the key which will be used to encrypt the
1.389 djm 1580: sensitive part of this file using AES-128.
1.238 jmc 1581: .Pp
1.309 jmc 1582: .It Pa ~/.ssh/id_dsa.pub
1.310 djm 1583: .It Pa ~/.ssh/id_ecdsa.pub
1.404 naddy 1584: .It Pa ~/.ssh/id_ecdsa_sk.pub
1.343 naddy 1585: .It Pa ~/.ssh/id_ed25519.pub
1.406 naddy 1586: .It Pa ~/.ssh/id_ed25519_sk.pub
1.309 jmc 1587: .It Pa ~/.ssh/id_rsa.pub
1.238 jmc 1588: Contains the public key for authentication.
1589: These files are not
1590: sensitive and can (but need not) be readable by anyone.
1591: .Pp
1.309 jmc 1592: .It Pa ~/.ssh/known_hosts
1.244 jmc 1593: Contains a list of host keys for all hosts the user has logged into
1594: that are not already in the systemwide list of known host keys.
1.238 jmc 1595: See
1.244 jmc 1596: .Xr sshd 8
1597: for further details of the format of this file.
1.238 jmc 1598: .Pp
1.309 jmc 1599: .It Pa ~/.ssh/rc
1.238 jmc 1600: Commands in this file are executed by
1601: .Nm
1.245 jmc 1602: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1603: started.
1604: See the
1605: .Xr sshd 8
1606: manual page for more information.
1607: .Pp
1.309 jmc 1608: .It Pa /etc/hosts.equiv
1.240 jmc 1609: This file is for host-based authentication (see above).
1610: It should only be writable by root.
1.236 jmc 1611: .Pp
1.309 jmc 1612: .It Pa /etc/shosts.equiv
1.240 jmc 1613: This file is used in exactly the same way as
1614: .Pa hosts.equiv ,
1615: but allows host-based authentication without permitting login with
1616: rlogin/rsh.
1.236 jmc 1617: .Pp
1.238 jmc 1618: .It Pa /etc/ssh/ssh_config
1619: Systemwide configuration file.
1620: The file format and configuration options are described in
1621: .Xr ssh_config 5 .
1622: .Pp
1.309 jmc 1623: .It Pa /etc/ssh/ssh_host_key
1624: .It Pa /etc/ssh/ssh_host_dsa_key
1.310 djm 1625: .It Pa /etc/ssh/ssh_host_ecdsa_key
1.343 naddy 1626: .It Pa /etc/ssh/ssh_host_ed25519_key
1.309 jmc 1627: .It Pa /etc/ssh/ssh_host_rsa_key
1.325 dtucker 1628: These files contain the private parts of the host keys
1.245 jmc 1629: and are used for host-based authentication.
1.238 jmc 1630: .Pp
1.309 jmc 1631: .It Pa /etc/ssh/ssh_known_hosts
1.238 jmc 1632: Systemwide list of known host keys.
1633: This file should be prepared by the
1634: system administrator to contain the public host keys of all machines in the
1635: organization.
1.244 jmc 1636: It should be world-readable.
1637: See
1.238 jmc 1638: .Xr sshd 8
1.244 jmc 1639: for further details of the format of this file.
1.236 jmc 1640: .Pp
1.309 jmc 1641: .It Pa /etc/ssh/sshrc
1.1 deraadt 1642: Commands in this file are executed by
1.2 deraadt 1643: .Nm
1.245 jmc 1644: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1645: See the
1.2 deraadt 1646: .Xr sshd 8
1.1 deraadt 1647: manual page for more information.
1.58 itojun 1648: .El
1.312 jmc 1649: .Sh EXIT STATUS
1650: .Nm
1651: exits with the exit status of the remote command or with 255
1652: if an error occurred.
1.2 deraadt 1653: .Sh SEE ALSO
1654: .Xr scp 1 ,
1.83 djm 1655: .Xr sftp 1 ,
1.2 deraadt 1656: .Xr ssh-add 1 ,
1657: .Xr ssh-agent 1 ,
1658: .Xr ssh-keygen 1 ,
1.242 jmc 1659: .Xr ssh-keyscan 1 ,
1.250 jmc 1660: .Xr tun 4 ,
1.159 stevesk 1661: .Xr ssh_config 5 ,
1.160 naddy 1662: .Xr ssh-keysign 8 ,
1.87 itojun 1663: .Xr sshd 8
1.329 jmc 1664: .Sh STANDARDS
1.106 markus 1665: .Rs
1.329 jmc 1666: .%A S. Lehtinen
1667: .%A C. Lonvick
1668: .%D January 2006
1.256 jmc 1669: .%R RFC 4250
1.329 jmc 1670: .%T The Secure Shell (SSH) Protocol Assigned Numbers
1.256 jmc 1671: .Re
1.329 jmc 1672: .Pp
1.256 jmc 1673: .Rs
1.329 jmc 1674: .%A T. Ylonen
1675: .%A C. Lonvick
1676: .%D January 2006
1.256 jmc 1677: .%R RFC 4251
1.329 jmc 1678: .%T The Secure Shell (SSH) Protocol Architecture
1.256 jmc 1679: .Re
1.329 jmc 1680: .Pp
1.256 jmc 1681: .Rs
1.329 jmc 1682: .%A T. Ylonen
1683: .%A C. Lonvick
1684: .%D January 2006
1.256 jmc 1685: .%R RFC 4252
1.329 jmc 1686: .%T The Secure Shell (SSH) Authentication Protocol
1.256 jmc 1687: .Re
1.329 jmc 1688: .Pp
1.256 jmc 1689: .Rs
1.329 jmc 1690: .%A T. Ylonen
1691: .%A C. Lonvick
1692: .%D January 2006
1.256 jmc 1693: .%R RFC 4253
1.329 jmc 1694: .%T The Secure Shell (SSH) Transport Layer Protocol
1.256 jmc 1695: .Re
1.329 jmc 1696: .Pp
1.256 jmc 1697: .Rs
1.329 jmc 1698: .%A T. Ylonen
1699: .%A C. Lonvick
1700: .%D January 2006
1.256 jmc 1701: .%R RFC 4254
1.329 jmc 1702: .%T The Secure Shell (SSH) Connection Protocol
1.256 jmc 1703: .Re
1.329 jmc 1704: .Pp
1.256 jmc 1705: .Rs
1.329 jmc 1706: .%A J. Schlyter
1707: .%A W. Griffin
1708: .%D January 2006
1.256 jmc 1709: .%R RFC 4255
1.329 jmc 1710: .%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
1.256 jmc 1711: .Re
1.329 jmc 1712: .Pp
1.256 jmc 1713: .Rs
1.329 jmc 1714: .%A F. Cusack
1715: .%A M. Forssen
1716: .%D January 2006
1.256 jmc 1717: .%R RFC 4256
1.329 jmc 1718: .%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)
1.256 jmc 1719: .Re
1.329 jmc 1720: .Pp
1.256 jmc 1721: .Rs
1.329 jmc 1722: .%A J. Galbraith
1723: .%A P. Remaker
1724: .%D January 2006
1.256 jmc 1725: .%R RFC 4335
1.329 jmc 1726: .%T The Secure Shell (SSH) Session Channel Break Extension
1.256 jmc 1727: .Re
1.329 jmc 1728: .Pp
1.256 jmc 1729: .Rs
1.329 jmc 1730: .%A M. Bellare
1731: .%A T. Kohno
1732: .%A C. Namprempre
1733: .%D January 2006
1.256 jmc 1734: .%R RFC 4344
1.329 jmc 1735: .%T The Secure Shell (SSH) Transport Layer Encryption Modes
1.256 jmc 1736: .Re
1.329 jmc 1737: .Pp
1.256 jmc 1738: .Rs
1.329 jmc 1739: .%A B. Harris
1740: .%D January 2006
1.256 jmc 1741: .%R RFC 4345
1.329 jmc 1742: .%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol
1.258 djm 1743: .Re
1.329 jmc 1744: .Pp
1.258 djm 1745: .Rs
1.329 jmc 1746: .%A M. Friedl
1747: .%A N. Provos
1748: .%A W. Simpson
1749: .%D March 2006
1.258 djm 1750: .%R RFC 4419
1.329 jmc 1751: .%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
1.266 markus 1752: .Re
1.329 jmc 1753: .Pp
1.266 markus 1754: .Rs
1.329 jmc 1755: .%A J. Galbraith
1756: .%A R. Thayer
1757: .%D November 2006
1.266 markus 1758: .%R RFC 4716
1.329 jmc 1759: .%T The Secure Shell (SSH) Public Key File Format
1.313 djm 1760: .Re
1.329 jmc 1761: .Pp
1.313 djm 1762: .Rs
1.329 jmc 1763: .%A D. Stebila
1764: .%A J. Green
1765: .%D December 2009
1.313 djm 1766: .%R RFC 5656
1.329 jmc 1767: .%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
1.274 grunk 1768: .Re
1.329 jmc 1769: .Pp
1.274 grunk 1770: .Rs
1771: .%A A. Perrig
1772: .%A D. Song
1773: .%D 1999
1.329 jmc 1774: .%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
1775: .%T Hash Visualization: a New Technique to improve Real-World Security
1.106 markus 1776: .Re
1.173 jmc 1777: .Sh AUTHORS
1778: OpenSSH is a derivative of the original and free
1779: ssh 1.2.12 release by Tatu Ylonen.
1780: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1781: Theo de Raadt and Dug Song
1782: removed many bugs, re-added newer features and
1783: created OpenSSH.
1784: Markus Friedl contributed the support for SSH
1785: protocol versions 1.5 and 2.0.
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