Annotation of src/usr.bin/ssh/ssh.1, Revision 1.252
1.1 deraadt 1: .\" -*- nroff -*-
2: .\"
3: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5: .\" All rights reserved
6: .\"
1.59 deraadt 7: .\" As far as I am concerned, the code I have written for this software
8: .\" can be used freely for any purpose. Any derived versions of this
9: .\" software must be clearly marked as such, and if the derived work is
10: .\" incompatible with the protocol description in the RFC file, it must be
11: .\" called by a name other than "ssh" or "Secure Shell".
12: .\"
1.93 deraadt 13: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
14: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
15: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
1.59 deraadt 16: .\"
17: .\" Redistribution and use in source and binary forms, with or without
18: .\" modification, are permitted provided that the following conditions
19: .\" are met:
20: .\" 1. Redistributions of source code must retain the above copyright
21: .\" notice, this list of conditions and the following disclaimer.
22: .\" 2. Redistributions in binary form must reproduce the above copyright
23: .\" notice, this list of conditions and the following disclaimer in the
24: .\" documentation and/or other materials provided with the distribution.
1.1 deraadt 25: .\"
1.59 deraadt 26: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.1 deraadt 36: .\"
1.252 ! jmc 37: .\" $OpenBSD: ssh.1,v 1.251 2006/01/20 00:14:55 dtucker Exp $
1.2 deraadt 38: .Dd September 25, 1999
39: .Dt SSH 1
40: .Os
41: .Sh NAME
42: .Nm ssh
1.96 deraadt 43: .Nd OpenSSH SSH client (remote login program)
1.2 deraadt 44: .Sh SYNOPSIS
45: .Nm ssh
1.191 djm 46: .Op Fl 1246AaCfgkMNnqsTtVvXxY
1.108 markus 47: .Op Fl b Ar bind_address
1.51 markus 48: .Op Fl c Ar cipher_spec
1.210 djm 49: .Oo Fl D\ \&
50: .Sm off
51: .Oo Ar bind_address : Oc
52: .Ar port
53: .Sm on
54: .Oc
1.2 deraadt 55: .Op Fl e Ar escape_char
1.176 jmc 56: .Op Fl F Ar configfile
1.211 jmc 57: .Bk -words
1.2 deraadt 58: .Op Fl i Ar identity_file
1.211 jmc 59: .Ek
1.202 jmc 60: .Oo Fl L\ \&
1.12 aaron 61: .Sm off
1.200 djm 62: .Oo Ar bind_address : Oc
1.202 jmc 63: .Ar port : host : hostport
1.12 aaron 64: .Sm on
65: .Oc
1.211 jmc 66: .Bk -words
1.176 jmc 67: .Op Fl l Ar login_name
1.211 jmc 68: .Ek
1.176 jmc 69: .Op Fl m Ar mac_spec
1.198 djm 70: .Op Fl O Ar ctl_cmd
1.176 jmc 71: .Op Fl o Ar option
72: .Op Fl p Ar port
1.202 jmc 73: .Oo Fl R\ \&
1.12 aaron 74: .Sm off
1.200 djm 75: .Oo Ar bind_address : Oc
1.202 jmc 76: .Ar port : host : hostport
1.12 aaron 77: .Sm on
78: .Oc
1.198 djm 79: .Op Fl S Ar ctl_path
1.216 jmc 80: .Bk -words
81: .Op Fl w Ar tunnel : Ns Ar tunnel
1.176 jmc 82: .Oo Ar user Ns @ Oc Ns Ar hostname
1.2 deraadt 83: .Op Ar command
1.216 jmc 84: .Ek
1.44 aaron 85: .Sh DESCRIPTION
1.2 deraadt 86: .Nm
1.96 deraadt 87: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 88: executing commands on a remote machine.
1.176 jmc 89: It is intended to replace rlogin and rsh,
90: and provide secure encrypted communications between
1.40 aaron 91: two untrusted hosts over an insecure network.
1.247 jmc 92: X11 connections and arbitrary TCP ports
1.176 jmc 93: can also be forwarded over the secure channel.
1.2 deraadt 94: .Pp
95: .Nm
1.44 aaron 96: connects and logs into the specified
1.176 jmc 97: .Ar hostname
98: (with optional
99: .Ar user
100: name).
1.1 deraadt 101: The user must prove
1.49 markus 102: his/her identity to the remote machine using one of several methods
1.221 jmc 103: depending on the protocol version used (see below).
1.49 markus 104: .Pp
1.176 jmc 105: If
106: .Ar command
107: is specified,
1.219 jmc 108: it is executed on the remote host instead of a login shell.
1.2 deraadt 109: .Pp
1.218 jmc 110: The options are as follows:
111: .Bl -tag -width Ds
112: .It Fl 1
113: Forces
1.2 deraadt 114: .Nm
1.218 jmc 115: to try protocol version 1 only.
116: .It Fl 2
117: Forces
1.2 deraadt 118: .Nm
1.218 jmc 119: to try protocol version 2 only.
120: .It Fl 4
121: Forces
1.2 deraadt 122: .Nm
1.218 jmc 123: to use IPv4 addresses only.
124: .It Fl 6
125: Forces
1.2 deraadt 126: .Nm
1.218 jmc 127: to use IPv6 addresses only.
128: .It Fl A
129: Enables forwarding of the authentication agent connection.
130: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 131: .Pp
1.218 jmc 132: Agent forwarding should be enabled with caution.
133: Users with the ability to bypass file permissions on the remote host
134: (for the agent's Unix-domain socket)
135: can access the local agent through the forwarded connection.
136: An attacker cannot obtain key material from the agent,
137: however they can perform operations on the keys that enable them to
138: authenticate using the identities loaded into the agent.
139: .It Fl a
140: Disables forwarding of the authentication agent connection.
141: .It Fl b Ar bind_address
142: Use
143: .Ar bind_address
144: on the local machine as the source address
145: of the connection.
146: Only useful on systems with more than one address.
147: .It Fl C
148: Requests compression of all data (including stdin, stdout, stderr, and
1.247 jmc 149: data for forwarded X11 and TCP connections).
1.218 jmc 150: The compression algorithm is the same used by
151: .Xr gzip 1 ,
152: and the
153: .Dq level
154: can be controlled by the
155: .Cm CompressionLevel
156: option for protocol version 1.
157: Compression is desirable on modem lines and other
158: slow connections, but will only slow down things on fast networks.
159: The default value can be set on a host-by-host basis in the
160: configuration files; see the
161: .Cm Compression
162: option.
163: .It Fl c Ar cipher_spec
164: Selects the cipher specification for encrypting the session.
1.2 deraadt 165: .Pp
1.218 jmc 166: Protocol version 1 allows specification of a single cipher.
167: The supported values are
168: .Dq 3des ,
1.220 jmc 169: .Dq blowfish ,
1.218 jmc 170: and
171: .Dq des .
172: .Ar 3des
173: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
174: It is believed to be secure.
175: .Ar blowfish
176: is a fast block cipher; it appears very secure and is much faster than
177: .Ar 3des .
178: .Ar des
179: is only supported in the
1.2 deraadt 180: .Nm
1.218 jmc 181: client for interoperability with legacy protocol 1 implementations
182: that do not support the
183: .Ar 3des
184: cipher.
185: Its use is strongly discouraged due to cryptographic weaknesses.
186: The default is
187: .Dq 3des .
1.49 markus 188: .Pp
1.230 jmc 189: For protocol version 2,
1.218 jmc 190: .Ar cipher_spec
191: is a comma-separated list of ciphers
192: listed in order of preference.
1.230 jmc 193: The supported ciphers are:
194: 3des-cbc,
195: aes128-cbc,
196: aes192-cbc,
197: aes256-cbc,
198: aes128-ctr,
199: aes192-ctr,
200: aes256-ctr,
201: arcfour128,
202: arcfour256,
203: arcfour,
204: blowfish-cbc,
1.218 jmc 205: and
1.230 jmc 206: cast128-cbc.
1.220 jmc 207: The default is:
208: .Bd -literal -offset indent
209: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
210: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
211: aes192-ctr,aes256-ctr
1.218 jmc 212: .Ed
213: .It Fl D Xo
214: .Sm off
215: .Oo Ar bind_address : Oc
216: .Ar port
217: .Sm on
218: .Xc
219: Specifies a local
220: .Dq dynamic
221: application-level port forwarding.
222: This works by allocating a socket to listen to
223: .Ar port
224: on the local side, optionally bound to the specified
225: .Ar bind_address .
226: Whenever a connection is made to this port, the
227: connection is forwarded over the secure channel, and the application
228: protocol is then used to determine where to connect to from the
229: remote machine.
230: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.107 markus 231: .Nm
1.218 jmc 232: will act as a SOCKS server.
233: Only root can forward privileged ports.
234: Dynamic port forwardings can also be specified in the configuration file.
1.49 markus 235: .Pp
1.218 jmc 236: IPv6 addresses can be specified with an alternative syntax:
237: .Sm off
238: .Xo
239: .Op Ar bind_address No /
240: .Ar port
241: .Xc
242: .Sm on
243: or by enclosing the address in square brackets.
244: Only the superuser can forward privileged ports.
245: By default, the local port is bound in accordance with the
246: .Cm GatewayPorts
247: setting.
248: However, an explicit
249: .Ar bind_address
250: may be used to bind the connection to a specific address.
251: The
252: .Ar bind_address
253: of
254: .Dq localhost
255: indicates that the listening port be bound for local use only, while an
256: empty address or
257: .Sq *
258: indicates that the port should be available from all interfaces.
1.229 jmc 259: .It Fl e Ar escape_char
1.218 jmc 260: Sets the escape character for sessions with a pty (default:
261: .Ql ~ ) .
262: The escape character is only recognized at the beginning of a line.
263: The escape character followed by a dot
264: .Pq Ql \&.
265: closes the connection;
266: followed by control-Z suspends the connection;
267: and followed by itself sends the escape character once.
268: Setting the character to
1.2 deraadt 269: .Dq none
1.218 jmc 270: disables any escapes and makes the session fully transparent.
271: .It Fl F Ar configfile
272: Specifies an alternative per-user configuration file.
273: If a configuration file is given on the command line,
274: the system-wide configuration file
275: .Pq Pa /etc/ssh/ssh_config
276: will be ignored.
277: The default for the per-user configuration file is
278: .Pa ~/.ssh/config .
279: .It Fl f
280: Requests
281: .Nm
282: to go to background just before command execution.
283: This is useful if
1.176 jmc 284: .Nm
1.218 jmc 285: is going to ask for passwords or passphrases, but the user
286: wants it in the background.
287: This implies
288: .Fl n .
289: The recommended way to start X11 programs at a remote site is with
290: something like
291: .Ic ssh -f host xterm .
292: .It Fl g
293: Allows remote hosts to connect to local forwarded ports.
294: .It Fl I Ar smartcard_device
1.229 jmc 295: Specify the device
1.176 jmc 296: .Nm
1.218 jmc 297: should use to communicate with a smartcard used for storing the user's
298: private RSA key.
1.229 jmc 299: This option is only available if support for smartcard devices
300: is compiled in (default is no support).
1.218 jmc 301: .It Fl i Ar identity_file
302: Selects a file from which the identity (private key) for
303: RSA or DSA authentication is read.
304: The default is
305: .Pa ~/.ssh/identity
306: for protocol version 1, and
307: .Pa ~/.ssh/id_rsa
1.149 jakob 308: and
1.218 jmc 309: .Pa ~/.ssh/id_dsa
310: for protocol version 2.
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).
317: .It Fl k
318: Disables forwarding (delegation) of GSSAPI credentials to the server.
319: .It Fl L Xo
320: .Sm off
321: .Oo Ar bind_address : Oc
322: .Ar port : host : hostport
323: .Sm on
324: .Xc
325: Specifies that the given port on the local (client) host is to be
326: forwarded to the given host and port on the remote side.
327: This works by allocating a socket to listen to
328: .Ar port
329: on the local side, optionally bound to the specified
330: .Ar bind_address .
331: Whenever a connection is made to this port, the
332: connection is forwarded over the secure channel, and a connection is
333: made to
334: .Ar host
335: port
336: .Ar hostport
337: from the remote machine.
338: Port forwardings can also be specified in the configuration file.
339: IPv6 addresses can be specified with an alternative syntax:
340: .Sm off
341: .Xo
342: .Op Ar bind_address No /
343: .Ar port No / Ar host No /
344: .Ar hostport
345: .Xc
346: .Sm on
347: or by enclosing the address in square brackets.
348: Only the superuser can forward privileged ports.
349: By default, the local port is bound in accordance with the
350: .Cm GatewayPorts
351: setting.
352: However, an explicit
353: .Ar bind_address
354: may be used to bind the connection to a specific address.
1.2 deraadt 355: The
1.218 jmc 356: .Ar bind_address
357: of
358: .Dq localhost
359: indicates that the listening port be bound for local use only, while an
360: empty address or
361: .Sq *
362: indicates that the port should be available from all interfaces.
363: .It Fl l Ar login_name
364: Specifies the user to log in as on the remote machine.
365: This also may be specified on a per-host basis in the configuration file.
366: .It Fl M
367: Places the
368: .Nm
369: client into
370: .Dq master
371: mode for connection sharing.
1.231 stevesk 372: Multiple
373: .Fl M
374: options places
375: .Nm
376: into
377: .Dq master
378: mode with confirmation required before slave connections are accepted.
1.218 jmc 379: Refer to the description of
380: .Cm ControlMaster
381: in
382: .Xr ssh_config 5
383: for details.
384: .It Fl m Ar mac_spec
385: Additionally, for protocol version 2 a comma-separated list of MAC
386: (message authentication code) algorithms can
387: be specified in order of preference.
388: See the
389: .Cm MACs
390: keyword for more information.
391: .It Fl N
392: Do not execute a remote command.
393: This is useful for just forwarding ports
394: (protocol version 2 only).
395: .It Fl n
396: Redirects stdin from
397: .Pa /dev/null
398: (actually, prevents reading from stdin).
399: This must be used when
1.2 deraadt 400: .Nm
1.218 jmc 401: is run in the background.
402: A common trick is to use this to run X11 programs on a remote machine.
403: For example,
404: .Ic ssh -n shadows.cs.hut.fi emacs &
405: will start an emacs on shadows.cs.hut.fi, and the X11
406: connection will be automatically forwarded over an encrypted channel.
407: The
1.2 deraadt 408: .Nm
1.218 jmc 409: program will be put in the background.
410: (This does not work if
1.2 deraadt 411: .Nm
1.218 jmc 412: needs to ask for a password or passphrase; see also the
413: .Fl f
414: option.)
415: .It Fl O Ar ctl_cmd
416: Control an active connection multiplexing master process.
417: When the
418: .Fl O
419: option is specified, the
420: .Ar ctl_cmd
421: argument is interpreted and passed to the master process.
422: Valid commands are:
423: .Dq check
424: (check that the master process is running) and
425: .Dq exit
426: (request the master to exit).
427: .It Fl o Ar option
428: Can be used to give options in the format used in the configuration file.
429: This is useful for specifying options for which there is no separate
430: command-line flag.
431: For full details of the options listed below, and their possible values, see
432: .Xr ssh_config 5 .
1.2 deraadt 433: .Pp
1.218 jmc 434: .Bl -tag -width Ds -offset indent -compact
435: .It AddressFamily
436: .It BatchMode
437: .It BindAddress
438: .It ChallengeResponseAuthentication
439: .It CheckHostIP
440: .It Cipher
441: .It Ciphers
442: .It ClearAllForwardings
443: .It Compression
444: .It CompressionLevel
445: .It ConnectionAttempts
446: .It ConnectTimeout
447: .It ControlMaster
448: .It ControlPath
449: .It DynamicForward
450: .It EscapeChar
451: .It ForwardAgent
452: .It ForwardX11
453: .It ForwardX11Trusted
454: .It GatewayPorts
455: .It GlobalKnownHostsFile
456: .It GSSAPIAuthentication
457: .It GSSAPIDelegateCredentials
458: .It HashKnownHosts
459: .It Host
460: .It HostbasedAuthentication
461: .It HostKeyAlgorithms
462: .It HostKeyAlias
463: .It HostName
464: .It IdentityFile
465: .It IdentitiesOnly
466: .It KbdInteractiveDevices
467: .It LocalCommand
468: .It LocalForward
469: .It LogLevel
470: .It MACs
471: .It NoHostAuthenticationForLocalhost
472: .It NumberOfPasswordPrompts
473: .It PasswordAuthentication
474: .It PermitLocalCommand
475: .It Port
476: .It PreferredAuthentications
477: .It Protocol
478: .It ProxyCommand
479: .It PubkeyAuthentication
1.251 dtucker 480: .It RekeyLimit
1.218 jmc 481: .It RemoteForward
482: .It RhostsRSAAuthentication
483: .It RSAAuthentication
484: .It SendEnv
485: .It ServerAliveInterval
486: .It ServerAliveCountMax
487: .It SmartcardDevice
488: .It StrictHostKeyChecking
489: .It TCPKeepAlive
490: .It Tunnel
491: .It TunnelDevice
492: .It UsePrivilegedPort
493: .It User
494: .It UserKnownHostsFile
495: .It VerifyHostKeyDNS
496: .It XAuthLocation
497: .El
498: .It Fl p Ar port
499: Port to connect to on the remote host.
500: This can be specified on a
501: per-host basis in the configuration file.
502: .It Fl q
503: Quiet mode.
504: Causes all warning and diagnostic messages to be suppressed.
505: .It Fl R Xo
506: .Sm off
507: .Oo Ar bind_address : Oc
508: .Ar port : host : hostport
509: .Sm on
510: .Xc
511: Specifies that the given port on the remote (server) host is to be
512: forwarded to the given host and port on the local side.
513: This works by allocating a socket to listen to
514: .Ar port
515: on the remote side, and whenever a connection is made to this port, the
516: connection is forwarded over the secure channel, and a connection is
517: made to
518: .Ar host
519: port
520: .Ar hostport
521: from the local machine.
1.2 deraadt 522: .Pp
1.218 jmc 523: Port forwardings can also be specified in the configuration file.
524: Privileged ports can be forwarded only when
525: logging in as root on the remote machine.
526: IPv6 addresses can be specified by enclosing the address in square braces or
527: using an alternative syntax:
528: .Sm off
529: .Xo
530: .Op Ar bind_address No /
531: .Ar host No / Ar port No /
532: .Ar hostport
533: .Xc .
534: .Sm on
1.194 jakob 535: .Pp
1.218 jmc 536: By default, the listening socket on the server will be bound to the loopback
537: interface only.
538: This may be overriden by specifying a
539: .Ar bind_address .
540: An empty
541: .Ar bind_address ,
542: or the address
543: .Ql * ,
544: indicates that the remote socket should listen on all interfaces.
545: Specifying a remote
546: .Ar bind_address
547: will only succeed if the server's
548: .Cm GatewayPorts
549: option is enabled (see
550: .Xr sshd_config 5 ) .
551: .It Fl S Ar ctl_path
552: Specifies the location of a control socket for connection sharing.
553: Refer to the description of
554: .Cm ControlPath
555: and
556: .Cm ControlMaster
557: in
558: .Xr ssh_config 5
559: for details.
560: .It Fl s
561: May be used to request invocation of a subsystem on the remote system.
562: Subsystems are a feature of the SSH2 protocol which facilitate the use
563: of SSH as a secure transport for other applications (eg.\&
564: .Xr sftp 1 ) .
565: The subsystem is specified as the remote command.
566: .It Fl T
567: Disable pseudo-tty allocation.
568: .It Fl t
569: Force pseudo-tty allocation.
570: This can be used to execute arbitrary
571: screen-based programs on a remote machine, which can be very useful,
572: e.g., when implementing menu services.
573: Multiple
574: .Fl t
575: options force tty allocation, even if
1.194 jakob 576: .Nm
1.218 jmc 577: has no local tty.
578: .It Fl V
579: Display the version number and exit.
580: .It Fl v
581: Verbose mode.
582: Causes
1.176 jmc 583: .Nm
1.218 jmc 584: to print debugging messages about its progress.
585: This is helpful in
586: debugging connection, authentication, and configuration problems.
587: Multiple
588: .Fl v
589: options increase the verbosity.
590: The maximum is 3.
591: .It Fl w Ar tunnel : Ns Ar tunnel
592: Requests a
593: .Xr tun 4
1.228 jmc 594: device on the client
595: (first
596: .Ar tunnel
597: arg)
598: and server
599: (second
600: .Ar tunnel
601: arg).
602: The devices may be specified by numerical ID or the keyword
603: .Dq any ,
604: which uses the next available tunnel device.
605: See also the
1.218 jmc 606: .Cm Tunnel
607: directive in
608: .Xr ssh_config 5 .
609: .It Fl X
610: Enables X11 forwarding.
1.54 markus 611: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 612: .Pp
1.218 jmc 613: X11 forwarding should be enabled with caution.
1.168 jmc 614: Users with the ability to bypass file permissions on the remote host
1.218 jmc 615: (for the user's X authorization database)
616: can access the local X11 display through the forwarded connection.
617: An attacker may then be able to perform activities such as keystroke monitoring.
618: .Pp
619: For this reason, X11 forwarding is subjected to X11 SECURITY extension
620: restrictions by default.
621: Please refer to the
622: .Nm
623: .Fl Y
624: option and the
625: .Cm ForwardX11Trusted
626: directive in
627: .Xr ssh_config 5
628: for more information.
629: .It Fl x
630: Disables X11 forwarding.
631: .It Fl Y
632: Enables trusted X11 forwarding.
633: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
634: controls.
635: .El
1.224 jmc 636: .Pp
637: .Nm
638: may additionally obtain configuration data from
639: a per-user configuration file and a system-wide configuration file.
640: The file format and configuration options are described in
641: .Xr ssh_config 5 .
642: .Pp
643: .Nm
644: exits with the exit status of the remote command or with 255
645: if an error occurred.
1.222 jmc 646: .Sh AUTHENTICATION
1.249 jmc 647: The OpenSSH SSH client supports SSH protocols 1 and 2.
1.222 jmc 648: Protocol 2 is the default, with
649: .Nm
650: falling back to protocol 1 if it detects protocol 2 is unsupported.
651: These settings may be altered using the
652: .Cm Protocol
653: option in
654: .Xr ssh_config 5 ,
655: or enforced using the
656: .Fl 1
657: and
658: .Fl 2
659: options (see above).
660: Both protocols support similar authentication methods,
661: but protocol 2 is preferred since
662: it provides additional mechanisms for confidentiality
663: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
664: and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
665: Protocol 1 lacks a strong mechanism for ensuring the
666: integrity of the connection.
667: .Pp
668: The methods available for authentication are:
669: host-based authentication,
670: public key authentication,
671: challenge-response authentication,
672: and password authentication.
673: Authentication methods are tried in the order specified above,
674: though protocol 2 has a configuration option to change the default order:
675: .Cm PreferredAuthentications .
676: .Pp
677: Host-based authentication works as follows:
1.218 jmc 678: If the machine the user logs in from is listed in
679: .Pa /etc/hosts.equiv
680: or
681: .Pa /etc/shosts.equiv
682: on the remote machine, and the user names are
683: the same on both sides, or if the files
684: .Pa ~/.rhosts
685: or
686: .Pa ~/.shosts
687: exist in the user's home directory on the
688: remote machine and contain a line containing the name of the client
689: machine and the name of the user on that machine, the user is
1.222 jmc 690: considered for login.
691: Additionally, the server
692: .Em must
693: be able to verify the client's
694: host key (see the description of
1.218 jmc 695: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 696: and
1.222 jmc 697: .Pa ~/.ssh/known_hosts ,
698: below)
699: for login to be permitted.
1.218 jmc 700: This authentication method closes security holes due to IP
1.222 jmc 701: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 702: [Note to the administrator:
703: .Pa /etc/hosts.equiv ,
704: .Pa ~/.rhosts ,
705: and the rlogin/rsh protocol in general, are inherently insecure and should be
706: disabled if security is desired.]
1.189 dtucker 707: .Pp
1.222 jmc 708: Public key authentication works as follows:
709: The scheme is based on public-key cryptography,
710: using cryptosystems
711: where encryption and decryption are done using separate keys,
712: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 713: The idea is that each user creates a public/private
714: key pair for authentication purposes.
715: The server knows the public key, and only the user knows the private key.
1.222 jmc 716: .Nm
717: implements public key authentication protocol automatically,
718: using either the RSA or DSA algorithms.
719: Protocol 1 is restricted to using only RSA keys,
720: but protocol 2 may use either.
721: The
722: .Sx HISTORY
723: section of
724: .Xr ssl 8
725: contains a brief discussion of the two algorithms.
1.210 djm 726: .Pp
1.218 jmc 727: The file
728: .Pa ~/.ssh/authorized_keys
729: lists the public keys that are permitted for logging in.
730: When the user logs in, the
1.2 deraadt 731: .Nm
1.218 jmc 732: program tells the server which key pair it would like to use for
733: authentication.
1.222 jmc 734: The client proves that it has access to the private key
735: and the server checks that the corresponding public key
736: is authorized to accept the account.
1.218 jmc 737: .Pp
1.222 jmc 738: The user creates his/her key pair by running
1.218 jmc 739: .Xr ssh-keygen 1 .
740: This stores the private key in
1.207 djm 741: .Pa ~/.ssh/identity
1.222 jmc 742: (protocol 1),
743: .Pa ~/.ssh/id_dsa
744: (protocol 2 DSA),
745: or
746: .Pa ~/.ssh/id_rsa
747: (protocol 2 RSA)
1.218 jmc 748: and stores the public key in
749: .Pa ~/.ssh/identity.pub
1.222 jmc 750: (protocol 1),
751: .Pa ~/.ssh/id_dsa.pub
752: (protocol 2 DSA),
753: or
754: .Pa ~/.ssh/id_rsa.pub
755: (protocol 2 RSA)
1.218 jmc 756: in the user's home directory.
1.222 jmc 757: The user should then copy the public key
1.218 jmc 758: to
759: .Pa ~/.ssh/authorized_keys
1.222 jmc 760: in his/her home directory on the remote machine.
761: The
1.218 jmc 762: .Pa authorized_keys
763: file corresponds to the conventional
764: .Pa ~/.rhosts
765: file, and has one key
1.222 jmc 766: per line, though the lines can be very long.
1.218 jmc 767: After this, the user can log in without giving the password.
768: .Pp
1.222 jmc 769: The most convenient way to use public key authentication may be with an
1.218 jmc 770: authentication agent.
771: See
772: .Xr ssh-agent 1
773: for more information.
774: .Pp
1.222 jmc 775: Challenge-response authentication works as follows:
776: The server sends an arbitrary
777: .Qq challenge
778: text, and prompts for a response.
779: Protocol 2 allows multiple challenges and responses;
780: protocol 1 is restricted to just one challenge/response.
781: Examples of challenge-response authentication include
782: BSD Authentication (see
783: .Xr login.conf 5 )
784: and PAM (some non-OpenBSD systems).
785: .Pp
786: Finally, if other authentication methods fail,
1.218 jmc 787: .Nm
788: prompts the user for a password.
789: The password is sent to the remote
790: host for checking; however, since all communications are encrypted,
791: the password cannot be seen by someone listening on the network.
1.232 jmc 792: .Pp
793: .Nm
794: automatically maintains and checks a database containing
795: identification for all hosts it has ever been used with.
796: Host keys are stored in
797: .Pa ~/.ssh/known_hosts
798: in the user's home directory.
799: Additionally, the file
800: .Pa /etc/ssh/ssh_known_hosts
801: is automatically checked for known hosts.
802: Any new hosts are automatically added to the user's file.
803: If a host's identification ever changes,
804: .Nm
805: warns about this and disables password authentication to prevent
806: server spoofing or man-in-the-middle attacks,
807: which could otherwise be used to circumvent the encryption.
808: The
809: .Cm StrictHostKeyChecking
810: option can be used to control logins to machines whose
811: host key is not known or has changed.
812: .Pp
1.218 jmc 813: When the user's identity has been accepted by the server, the server
814: either executes the given command, or logs into the machine and gives
815: the user a normal shell on the remote machine.
816: All communication with
817: the remote command or shell will be automatically encrypted.
818: .Pp
819: If a pseudo-terminal has been allocated (normal login session), the
820: user may use the escape characters noted below.
821: .Pp
822: If no pseudo-tty has been allocated,
823: the session is transparent and can be used to reliably transfer binary data.
824: On most systems, setting the escape character to
825: .Dq none
826: will also make the session transparent even if a tty is used.
827: .Pp
828: The session terminates when the command or shell on the remote
1.247 jmc 829: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 830: .Sh ESCAPE CHARACTERS
1.218 jmc 831: When a pseudo-terminal has been requested,
1.2 deraadt 832: .Nm
1.218 jmc 833: supports a number of functions through the use of an escape character.
834: .Pp
835: A single tilde character can be sent as
836: .Ic ~~
837: or by following the tilde by a character other than those described below.
838: The escape character must always follow a newline to be interpreted as
839: special.
840: The escape character can be changed in configuration files using the
841: .Cm EscapeChar
842: configuration directive or on the command line by the
843: .Fl e
844: option.
845: .Pp
846: The supported escapes (assuming the default
847: .Ql ~ )
848: are:
849: .Bl -tag -width Ds
850: .It Cm ~.
851: Disconnect.
852: .It Cm ~^Z
853: Background
1.234 jmc 854: .Nm .
1.218 jmc 855: .It Cm ~#
856: List forwarded connections.
857: .It Cm ~&
858: Background
1.2 deraadt 859: .Nm
1.218 jmc 860: at logout when waiting for forwarded connection / X11 sessions to terminate.
861: .It Cm ~?
862: Display a list of escape characters.
863: .It Cm ~B
864: Send a BREAK to the remote system
865: (only useful for SSH protocol version 2 and if the peer supports it).
866: .It Cm ~C
867: Open command line.
868: Currently this allows the addition of port forwardings using the
869: .Fl L
870: and
871: .Fl R
1.225 jmc 872: options (see above).
1.218 jmc 873: It also allows the cancellation of existing remote port-forwardings
874: using
875: .Fl KR Ar hostport .
876: .Ic !\& Ns Ar command
877: allows the user to execute a local command if the
878: .Ic PermitLocalCommand
879: option is enabled in
1.176 jmc 880: .Xr ssh_config 5 .
1.218 jmc 881: Basic help is available, using the
882: .Fl h
883: option.
884: .It Cm ~R
885: Request rekeying of the connection
886: (only useful for SSH protocol version 2 and if the peer supports it).
1.176 jmc 887: .El
1.246 jmc 888: .Sh TCP FORWARDING
889: Forwarding of arbitrary TCP connections over the secure channel can
890: be specified either on the command line or in a configuration file.
891: One possible application of TCP forwarding is a secure connection to a
892: mail server; another is going through firewalls.
893: .Pp
894: In the example below, we look at encrypting communication between
895: an IRC client and server, even though the IRC server does not directly
896: support encrypted communications.
897: This works as follows:
898: the user connects to the remote host using
899: .Nm ,
900: specifying a port to be used to forward connections
901: to the remote server.
902: After that it is possible to start the service which is to be encrypted
903: on the client machine,
904: connecting to the same local port,
905: and
906: .Nm
907: will encrypt and forward the connection.
908: .Pp
909: The following example tunnels an IRC session from client machine
910: .Dq 127.0.0.1
911: (localhost)
912: to remote server
913: .Dq server.example.com :
914: .Bd -literal -offset 4n
915: $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
916: $ irc -c '#users' -p 1234 pinky 127.0.0.1
917: .Ed
918: .Pp
919: This tunnels a connection to IRC server
920: .Dq server.example.com ,
921: joining channel
922: .Dq #users ,
923: nickname
924: .Dq pinky ,
925: using port 1234.
926: It doesn't matter which port is used,
927: as long as it's greater than 1023
928: (remember, only root can open sockets on privileged ports)
929: and doesn't conflict with any ports already in use.
930: The connection is forwarded to port 6667 on the remote server,
931: since that's the standard port for IRC services.
932: .Pp
933: The
934: .Fl f
935: option backgrounds
936: .Nm
937: and the remote command
938: .Dq sleep 10
939: is specified to allow an amount of time
940: (10 seconds, in the example)
941: to start the service which is to be tunnelled.
942: If no connections are made within the time specified,
943: .Nm
944: will exit.
945: .Sh X11 FORWARDING
1.218 jmc 946: If the
947: .Cm ForwardX11
948: variable is set to
949: .Dq yes
950: (or see the description of the
1.227 jmc 951: .Fl X ,
952: .Fl x ,
1.218 jmc 953: and
1.227 jmc 954: .Fl Y
1.226 jmc 955: options above)
1.218 jmc 956: and the user is using X11 (the
957: .Ev DISPLAY
958: environment variable is set), the connection to the X11 display is
959: automatically forwarded to the remote side in such a way that any X11
960: programs started from the shell (or command) will go through the
961: encrypted channel, and the connection to the real X server will be made
1.176 jmc 962: from the local machine.
1.218 jmc 963: The user should not manually set
964: .Ev DISPLAY .
965: Forwarding of X11 connections can be
966: configured on the command line or in configuration files.
967: .Pp
968: The
969: .Ev DISPLAY
970: value set by
971: .Nm
972: will point to the server machine, but with a display number greater than zero.
973: This is normal, and happens because
974: .Nm
975: creates a
976: .Dq proxy
977: X server on the server machine for forwarding the
978: connections over the encrypted channel.
1.200 djm 979: .Pp
1.218 jmc 980: .Nm
981: will also automatically set up Xauthority data on the server machine.
982: For this purpose, it will generate a random authorization cookie,
983: store it in Xauthority on the server, and verify that any forwarded
984: connections carry this cookie and replace it by the real cookie when
985: the connection is opened.
986: The real authentication cookie is never
987: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 988: .Pp
1.218 jmc 989: If the
990: .Cm ForwardAgent
991: variable is set to
992: .Dq yes
993: (or see the description of the
994: .Fl A
1.191 djm 995: and
1.218 jmc 996: .Fl a
1.226 jmc 997: options above) and
1.218 jmc 998: the user is using an authentication agent, the connection to the agent
999: is automatically forwarded to the remote side.
1.252 ! jmc 1000: .Sh VERIFYING HOST KEYS
! 1001: When connecting to a server for the first time,
! 1002: a fingerprint of the server's public key is presented to the user
! 1003: (unless the option
! 1004: .Cm StrictHostKeyChecking
! 1005: has been disabled).
! 1006: Fingerprints can be determined using
! 1007: .Xr ssh-keygen 1 :
! 1008: .Pp
! 1009: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
! 1010: .Pp
! 1011: If the fingerprint is already known,
! 1012: it can be matched and verified,
! 1013: and the key can be accepted.
! 1014: If the fingerprint is unknown,
! 1015: an alternative method of verification is available:
! 1016: SSH fingerprints verified by DNS.
! 1017: An additional resource record (RR),
! 1018: SSHFP,
! 1019: is added to a zonefile
! 1020: and the connecting client is able to match the fingerprint
! 1021: with that of the key presented.
! 1022: .Pp
! 1023: In this example, we are connecting a client to a server,
! 1024: .Dq host.example.com .
! 1025: The SSHFP resource records should first be added to the zonefile for
! 1026: host.example.com:
! 1027: .Bd -literal -offset indent
! 1028: $ ssh-keygen -f /etc/ssh/ssh_host_rsa_key.pub -r host.example.com.
! 1029: $ ssh-keygen -f /etc/ssh/ssh_host_dsa_key.pub -r host.example.com.
! 1030: .Ed
! 1031: .Pp
! 1032: The output lines will have to be added to the zonefile.
! 1033: To check that the zone is answering fingerprint queries:
! 1034: .Pp
! 1035: .Dl $ dig -t SSHFP host.example.com
! 1036: .Pp
! 1037: Finally the client connects:
! 1038: .Bd -literal -offset indent
! 1039: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
! 1040: [...]
! 1041: Matching host key fingerprint found in DNS.
! 1042: Are you sure you want to continue connecting (yes/no)?
! 1043: .Ed
! 1044: .Pp
! 1045: See the
! 1046: .Cm VerifyHostKeyDNS
! 1047: option in
! 1048: .Xr ssh_config 5
! 1049: for more information.
1.250 jmc 1050: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1051: .Nm
1052: contains support for Virtual Private Network (VPN) tunnelling
1053: using the
1054: .Xr tun 4
1055: network pseudo-device,
1056: allowing two networks to be joined securely.
1057: The
1058: .Xr sshd_config 5
1059: configuration option
1060: .Cm PermitTunnel
1061: controls whether the server supports this,
1062: and at what level (layer 2 or 3 traffic).
1063: .Pp
1064: The following example would connect client network 10.0.50.0/24
1065: with remote network 10.0.99.0/24, provided that the SSH server
1066: running on the gateway to the remote network,
1067: at 192.168.1.15, allows it:
1068: .Bd -literal -offset indent
1069: # ssh -f -w 0:1 192.168.1.15 true
1070: # ifconfig tun0 10.0.50.1 10.0.99.1 netmask 255.255.255.252
1071: .Ed
1072: .Pp
1073: Client access may be more finely tuned via the
1074: .Pa /root/.ssh/authorized_keys
1075: file (see below) and the
1076: .Cm PermitRootLogin
1077: server option.
1078: The following entry would permit connections on the first
1079: .Xr tun 4
1080: device from user
1081: .Dq jane
1082: and on the second device from user
1083: .Dq john ,
1084: if
1085: .Cm PermitRootLogin
1086: is set to
1087: .Dq forced-commands-only :
1088: .Bd -literal -offset 2n
1089: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1090: tunnel="2",command="sh /etc/netstart tun1" ssh-rsa ... john
1091: .Ed
1092: .Pp
1093: Since a SSH-based setup entails a fair amount of overhead,
1094: it may be more suited to temporary setups,
1095: such as for wireless VPNs.
1096: More permanent VPNs are better provided by tools such as
1097: .Xr ipsecctl 8
1098: and
1099: .Xr isakmpd 8 .
1.2 deraadt 1100: .Sh ENVIRONMENT
1101: .Nm
1.1 deraadt 1102: will normally set the following environment variables:
1.237 jmc 1103: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1104: .It Ev DISPLAY
1105: The
1106: .Ev DISPLAY
1.40 aaron 1107: variable indicates the location of the X11 server.
1.44 aaron 1108: It is automatically set by
1.2 deraadt 1109: .Nm
1110: to point to a value of the form
1.233 jmc 1111: .Dq hostname:n ,
1112: where
1113: .Dq hostname
1114: indicates the host where the shell runs, and
1115: .Sq n
1116: is an integer \*(Ge 1.
1.40 aaron 1117: .Nm
1118: uses this special value to forward X11 connections over the secure
1119: channel.
1.107 markus 1120: The user should normally not set
1121: .Ev DISPLAY
1122: explicitly, as that
1.1 deraadt 1123: will render the X11 connection insecure (and will require the user to
1124: manually copy any required authorization cookies).
1.2 deraadt 1125: .It Ev HOME
1.1 deraadt 1126: Set to the path of the user's home directory.
1.2 deraadt 1127: .It Ev LOGNAME
1128: Synonym for
1.12 aaron 1129: .Ev USER ;
1130: set for compatibility with systems that use this variable.
1.2 deraadt 1131: .It Ev MAIL
1.129 stevesk 1132: Set to the path of the user's mailbox.
1.40 aaron 1133: .It Ev PATH
1.2 deraadt 1134: Set to the default
1135: .Ev PATH ,
1136: as specified when compiling
1.234 jmc 1137: .Nm .
1.118 markus 1138: .It Ev SSH_ASKPASS
1139: If
1140: .Nm
1141: needs a passphrase, it will read the passphrase from the current
1142: terminal if it was run from a terminal.
1143: If
1144: .Nm
1145: does not have a terminal associated with it but
1146: .Ev DISPLAY
1147: and
1148: .Ev SSH_ASKPASS
1149: are set, it will execute the program specified by
1150: .Ev SSH_ASKPASS
1151: and open an X11 window to read the passphrase.
1152: This is particularly useful when calling
1153: .Nm
1154: from a
1.196 jmc 1155: .Pa .xsession
1.118 markus 1156: or related script.
1157: (Note that on some machines it
1158: may be necessary to redirect the input from
1159: .Pa /dev/null
1160: to make this work.)
1.18 markus 1161: .It Ev SSH_AUTH_SOCK
1.233 jmc 1162: Identifies the path of a
1163: .Ux Ns -domain
1164: socket used to communicate with the agent.
1.166 stevesk 1165: .It Ev SSH_CONNECTION
1166: Identifies the client and server ends of the connection.
1.40 aaron 1167: The variable contains
1.233 jmc 1168: four space-separated values: client IP address, client port number,
1169: server IP address, and server port number.
1.73 markus 1170: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1171: This variable contains the original command line if a forced command
1.73 markus 1172: is executed.
1173: It can be used to extract the original arguments.
1.2 deraadt 1174: .It Ev SSH_TTY
1.1 deraadt 1175: This is set to the name of the tty (path to the device) associated
1.40 aaron 1176: with the current shell or command.
1177: If the current session has no tty,
1.1 deraadt 1178: this variable is not set.
1.2 deraadt 1179: .It Ev TZ
1.214 jmc 1180: This variable is set to indicate the present time zone if it
1.56 deraadt 1181: was set when the daemon was started (i.e., the daemon passes the value
1.1 deraadt 1182: on to new connections).
1.2 deraadt 1183: .It Ev USER
1.1 deraadt 1184: Set to the name of the user logging in.
1.2 deraadt 1185: .El
1186: .Pp
1.44 aaron 1187: Additionally,
1.2 deraadt 1188: .Nm
1.44 aaron 1189: reads
1.207 djm 1190: .Pa ~/.ssh/environment ,
1.2 deraadt 1191: and adds lines of the format
1192: .Dq VARNAME=value
1.233 jmc 1193: to the environment if the file exists and users are allowed to
1.161 marc 1194: change their environment.
1.176 jmc 1195: For more information, see the
1.161 marc 1196: .Cm PermitUserEnvironment
1.162 stevesk 1197: option in
1.161 marc 1198: .Xr sshd_config 5 .
1.2 deraadt 1199: .Sh FILES
1.236 jmc 1200: .Bl -tag -width Ds -compact
1201: .It ~/.rhosts
1.240 jmc 1202: This file is used for host-based authentication (see above).
1.92 markus 1203: On some machines this file may need to be
1.240 jmc 1204: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1205: because
1.2 deraadt 1206: .Xr sshd 8
1.40 aaron 1207: reads it as root.
1208: Additionally, this file must be owned by the user,
1209: and must not have write permissions for anyone else.
1210: The recommended
1.1 deraadt 1211: permission for most machines is read/write for the user, and not
1212: accessible by others.
1.2 deraadt 1213: .Pp
1.236 jmc 1214: .It ~/.shosts
1.240 jmc 1215: This file is used in exactly the same way as
1216: .Pa .rhosts ,
1217: but allows host-based authentication without permitting login with
1218: rlogin/rsh.
1.236 jmc 1219: .Pp
1.238 jmc 1220: .It ~/.ssh/authorized_keys
1221: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1222: The format of this file is described in the
1223: .Xr sshd 8
1224: manual page.
1225: This file is not highly sensitive, but the recommended
1226: permissions are read/write for the user, and not accessible by others.
1227: .Pp
1228: .It ~/.ssh/config
1229: This is the per-user configuration file.
1230: The file format and configuration options are described in
1231: .Xr ssh_config 5 .
1232: Because of the potential for abuse, this file must have strict permissions:
1233: read/write for the user, and not accessible by others.
1234: .Pp
1235: .It ~/.ssh/environment
1.239 jmc 1236: Contains additional definitions for environment variables; see
1237: .Sx ENVIRONMENT ,
1.238 jmc 1238: above.
1239: .Pp
1240: .It ~/.ssh/identity
1241: .It ~/.ssh/id_dsa
1242: .It ~/.ssh/id_rsa
1243: Contains the private key for authentication.
1244: These files
1245: contain sensitive data and should be readable by the user but not
1246: accessible by others (read/write/execute).
1247: .Nm
1248: will simply ignore a private key file if it is accessible by others.
1249: It is possible to specify a passphrase when
1250: generating the key which will be used to encrypt the
1251: sensitive part of this file using 3DES.
1252: .Pp
1253: .It ~/.ssh/identity.pub
1254: .It ~/.ssh/id_dsa.pub
1255: .It ~/.ssh/id_rsa.pub
1256: Contains the public key for authentication.
1257: These files are not
1258: sensitive and can (but need not) be readable by anyone.
1259: They are
1260: never used automatically and are not necessary: they are only provided for
1261: the convenience of the user.
1262: .Pp
1263: .It ~/.ssh/known_hosts
1.244 jmc 1264: Contains a list of host keys for all hosts the user has logged into
1265: that are not already in the systemwide list of known host keys.
1.238 jmc 1266: See
1.244 jmc 1267: .Xr sshd 8
1268: for further details of the format of this file.
1.238 jmc 1269: .Pp
1270: .It ~/.ssh/rc
1271: Commands in this file are executed by
1272: .Nm
1.245 jmc 1273: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1274: started.
1275: See the
1276: .Xr sshd 8
1277: manual page for more information.
1278: .Pp
1.236 jmc 1279: .It /etc/hosts.equiv
1.240 jmc 1280: This file is for host-based authentication (see above).
1281: It should only be writable by root.
1.236 jmc 1282: .Pp
1283: .It /etc/shosts.equiv
1.240 jmc 1284: This file is used in exactly the same way as
1285: .Pa hosts.equiv ,
1286: but allows host-based authentication without permitting login with
1287: rlogin/rsh.
1.236 jmc 1288: .Pp
1.238 jmc 1289: .It Pa /etc/ssh/ssh_config
1290: Systemwide configuration file.
1291: The file format and configuration options are described in
1292: .Xr ssh_config 5 .
1293: .Pp
1294: .It /etc/ssh/ssh_host_key
1295: .It /etc/ssh/ssh_host_dsa_key
1296: .It /etc/ssh/ssh_host_rsa_key
1297: These three files contain the private parts of the host keys
1.245 jmc 1298: and are used for host-based authentication.
1299: If protocol version 1 is used,
1.238 jmc 1300: .Nm
1301: must be setuid root, since the host key is readable only by root.
1302: For protocol version 2,
1303: .Nm
1304: uses
1305: .Xr ssh-keysign 8
1.245 jmc 1306: to access the host keys,
1307: eliminating the requirement that
1.238 jmc 1308: .Nm
1.245 jmc 1309: be setuid root when host-based authentication is used.
1.238 jmc 1310: By default
1.2 deraadt 1311: .Nm
1.238 jmc 1312: is not setuid root.
1313: .Pp
1314: .It /etc/ssh/ssh_known_hosts
1315: Systemwide list of known host keys.
1316: This file should be prepared by the
1317: system administrator to contain the public host keys of all machines in the
1318: organization.
1.244 jmc 1319: It should be world-readable.
1320: See
1.238 jmc 1321: .Xr sshd 8
1.244 jmc 1322: for further details of the format of this file.
1.236 jmc 1323: .Pp
1.238 jmc 1324: .It /etc/ssh/sshrc
1.1 deraadt 1325: Commands in this file are executed by
1.2 deraadt 1326: .Nm
1.245 jmc 1327: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1328: See the
1.2 deraadt 1329: .Xr sshd 8
1.1 deraadt 1330: manual page for more information.
1.58 itojun 1331: .El
1.2 deraadt 1332: .Sh SEE ALSO
1333: .Xr scp 1 ,
1.83 djm 1334: .Xr sftp 1 ,
1.2 deraadt 1335: .Xr ssh-add 1 ,
1336: .Xr ssh-agent 1 ,
1337: .Xr ssh-keygen 1 ,
1.242 jmc 1338: .Xr ssh-keyscan 1 ,
1.250 jmc 1339: .Xr tun 4 ,
1.176 jmc 1340: .Xr hosts.equiv 5 ,
1.159 stevesk 1341: .Xr ssh_config 5 ,
1.160 naddy 1342: .Xr ssh-keysign 8 ,
1.87 itojun 1343: .Xr sshd 8
1.106 markus 1344: .Rs
1345: .%A T. Ylonen
1346: .%A T. Kivinen
1347: .%A M. Saarinen
1348: .%A T. Rinne
1349: .%A S. Lehtinen
1350: .%T "SSH Protocol Architecture"
1.150 markus 1351: .%N draft-ietf-secsh-architecture-12.txt
1352: .%D January 2002
1.106 markus 1353: .%O work in progress material
1354: .Re
1.173 jmc 1355: .Sh AUTHORS
1356: OpenSSH is a derivative of the original and free
1357: ssh 1.2.12 release by Tatu Ylonen.
1358: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1359: Theo de Raadt and Dug Song
1360: removed many bugs, re-added newer features and
1361: created OpenSSH.
1362: Markus Friedl contributed the support for SSH
1363: protocol versions 1.5 and 2.0.
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