Annotation of src/usr.bin/ssh/ssh.1, Revision 1.221
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: .\"
1.221 ! jmc 37: .\" $OpenBSD: ssh.1,v 1.220 2005/12/16 18:12:22 jmc 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.
1.176 jmc 92: X11 connections and arbitrary TCP/IP ports
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
149: data for forwarded X11 and TCP/IP connections).
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
1.218 jmc 189: For protocol version 2
190: .Ar cipher_spec
191: is a comma-separated list of ciphers
192: listed in order of preference.
193: The supported ciphers are
194: .Dq 3des-cbc ,
195: .Dq aes128-cbc ,
196: .Dq aes192-cbc ,
197: .Dq aes256-cbc ,
198: .Dq aes128-ctr ,
199: .Dq aes192-ctr ,
200: .Dq aes256-ctr ,
201: .Dq arcfour128 ,
202: .Dq arcfour256 ,
203: .Dq arcfour ,
204: .Dq blowfish-cbc ,
205: and
206: .Dq 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.
259: .It Fl e Ar ch | ^ch | none
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
295: Specifies which smartcard device to use.
296: The argument is the device
1.176 jmc 297: .Nm
1.218 jmc 298: should use to communicate with a smartcard used for storing the user's
299: private RSA key.
300: .It Fl i Ar identity_file
301: Selects a file from which the identity (private key) for
302: RSA or DSA authentication is read.
303: The default is
304: .Pa ~/.ssh/identity
305: for protocol version 1, and
306: .Pa ~/.ssh/id_rsa
1.149 jakob 307: and
1.218 jmc 308: .Pa ~/.ssh/id_dsa
309: for protocol version 2.
310: Identity files may also be specified on
311: a per-host basis in the configuration file.
312: It is possible to have multiple
313: .Fl i
314: options (and multiple identities specified in
315: configuration files).
316: .It Fl k
317: Disables forwarding (delegation) of GSSAPI credentials to the server.
318: .It Fl L Xo
319: .Sm off
320: .Oo Ar bind_address : Oc
321: .Ar port : host : hostport
322: .Sm on
323: .Xc
324: Specifies that the given port on the local (client) host is to be
325: forwarded to the given host and port on the remote side.
326: This works by allocating a socket to listen to
327: .Ar port
328: on the local side, optionally bound to the specified
329: .Ar bind_address .
330: Whenever a connection is made to this port, the
331: connection is forwarded over the secure channel, and a connection is
332: made to
333: .Ar host
334: port
335: .Ar hostport
336: from the remote machine.
337: Port forwardings can also be specified in the configuration file.
338: IPv6 addresses can be specified with an alternative syntax:
339: .Sm off
340: .Xo
341: .Op Ar bind_address No /
342: .Ar port No / Ar host No /
343: .Ar hostport
344: .Xc
345: .Sm on
346: or by enclosing the address in square brackets.
347: Only the superuser can forward privileged ports.
348: By default, the local port is bound in accordance with the
349: .Cm GatewayPorts
350: setting.
351: However, an explicit
352: .Ar bind_address
353: may be used to bind the connection to a specific address.
1.2 deraadt 354: The
1.218 jmc 355: .Ar bind_address
356: of
357: .Dq localhost
358: indicates that the listening port be bound for local use only, while an
359: empty address or
360: .Sq *
361: indicates that the port should be available from all interfaces.
362: .It Fl l Ar login_name
363: Specifies the user to log in as on the remote machine.
364: This also may be specified on a per-host basis in the configuration file.
365: .It Fl M
366: Places the
367: .Nm
368: client into
369: .Dq master
370: mode for connection sharing.
371: Refer to the description of
372: .Cm ControlMaster
373: in
374: .Xr ssh_config 5
375: for details.
376: .It Fl m Ar mac_spec
377: Additionally, for protocol version 2 a comma-separated list of MAC
378: (message authentication code) algorithms can
379: be specified in order of preference.
380: See the
381: .Cm MACs
382: keyword for more information.
383: .It Fl N
384: Do not execute a remote command.
385: This is useful for just forwarding ports
386: (protocol version 2 only).
387: .It Fl n
388: Redirects stdin from
389: .Pa /dev/null
390: (actually, prevents reading from stdin).
391: This must be used when
1.2 deraadt 392: .Nm
1.218 jmc 393: is run in the background.
394: A common trick is to use this to run X11 programs on a remote machine.
395: For example,
396: .Ic ssh -n shadows.cs.hut.fi emacs &
397: will start an emacs on shadows.cs.hut.fi, and the X11
398: connection will be automatically forwarded over an encrypted channel.
399: The
1.2 deraadt 400: .Nm
1.218 jmc 401: program will be put in the background.
402: (This does not work if
1.2 deraadt 403: .Nm
1.218 jmc 404: needs to ask for a password or passphrase; see also the
405: .Fl f
406: option.)
407: .It Fl O Ar ctl_cmd
408: Control an active connection multiplexing master process.
409: When the
410: .Fl O
411: option is specified, the
412: .Ar ctl_cmd
413: argument is interpreted and passed to the master process.
414: Valid commands are:
415: .Dq check
416: (check that the master process is running) and
417: .Dq exit
418: (request the master to exit).
419: .It Fl o Ar option
420: Can be used to give options in the format used in the configuration file.
421: This is useful for specifying options for which there is no separate
422: command-line flag.
423: For full details of the options listed below, and their possible values, see
424: .Xr ssh_config 5 .
1.2 deraadt 425: .Pp
1.218 jmc 426: .Bl -tag -width Ds -offset indent -compact
427: .It AddressFamily
428: .It BatchMode
429: .It BindAddress
430: .It ChallengeResponseAuthentication
431: .It CheckHostIP
432: .It Cipher
433: .It Ciphers
434: .It ClearAllForwardings
435: .It Compression
436: .It CompressionLevel
437: .It ConnectionAttempts
438: .It ConnectTimeout
439: .It ControlMaster
440: .It ControlPath
441: .It DynamicForward
442: .It EscapeChar
443: .It ForwardAgent
444: .It ForwardX11
445: .It ForwardX11Trusted
446: .It GatewayPorts
447: .It GlobalKnownHostsFile
448: .It GSSAPIAuthentication
449: .It GSSAPIDelegateCredentials
450: .It HashKnownHosts
451: .It Host
452: .It HostbasedAuthentication
453: .It HostKeyAlgorithms
454: .It HostKeyAlias
455: .It HostName
456: .It IdentityFile
457: .It IdentitiesOnly
458: .It KbdInteractiveDevices
459: .It LocalCommand
460: .It LocalForward
461: .It LogLevel
462: .It MACs
463: .It NoHostAuthenticationForLocalhost
464: .It NumberOfPasswordPrompts
465: .It PasswordAuthentication
466: .It PermitLocalCommand
467: .It Port
468: .It PreferredAuthentications
469: .It Protocol
470: .It ProxyCommand
471: .It PubkeyAuthentication
472: .It RemoteForward
473: .It RhostsRSAAuthentication
474: .It RSAAuthentication
475: .It SendEnv
476: .It ServerAliveInterval
477: .It ServerAliveCountMax
478: .It SmartcardDevice
479: .It StrictHostKeyChecking
480: .It TCPKeepAlive
481: .It Tunnel
482: .It TunnelDevice
483: .It UsePrivilegedPort
484: .It User
485: .It UserKnownHostsFile
486: .It VerifyHostKeyDNS
487: .It XAuthLocation
488: .El
489: .It Fl p Ar port
490: Port to connect to on the remote host.
491: This can be specified on a
492: per-host basis in the configuration file.
493: .It Fl q
494: Quiet mode.
495: Causes all warning and diagnostic messages to be suppressed.
496: .It Fl R Xo
497: .Sm off
498: .Oo Ar bind_address : Oc
499: .Ar port : host : hostport
500: .Sm on
501: .Xc
502: Specifies that the given port on the remote (server) host is to be
503: forwarded to the given host and port on the local side.
504: This works by allocating a socket to listen to
505: .Ar port
506: on the remote side, and whenever a connection is made to this port, the
507: connection is forwarded over the secure channel, and a connection is
508: made to
509: .Ar host
510: port
511: .Ar hostport
512: from the local machine.
1.2 deraadt 513: .Pp
1.218 jmc 514: Port forwardings can also be specified in the configuration file.
515: Privileged ports can be forwarded only when
516: logging in as root on the remote machine.
517: IPv6 addresses can be specified by enclosing the address in square braces or
518: using an alternative syntax:
519: .Sm off
520: .Xo
521: .Op Ar bind_address No /
522: .Ar host No / Ar port No /
523: .Ar hostport
524: .Xc .
525: .Sm on
1.194 jakob 526: .Pp
1.218 jmc 527: By default, the listening socket on the server will be bound to the loopback
528: interface only.
529: This may be overriden by specifying a
530: .Ar bind_address .
531: An empty
532: .Ar bind_address ,
533: or the address
534: .Ql * ,
535: indicates that the remote socket should listen on all interfaces.
536: Specifying a remote
537: .Ar bind_address
538: will only succeed if the server's
539: .Cm GatewayPorts
540: option is enabled (see
541: .Xr sshd_config 5 ) .
542: .It Fl S Ar ctl_path
543: Specifies the location of a control socket for connection sharing.
544: Refer to the description of
545: .Cm ControlPath
546: and
547: .Cm ControlMaster
548: in
549: .Xr ssh_config 5
550: for details.
551: .It Fl s
552: May be used to request invocation of a subsystem on the remote system.
553: Subsystems are a feature of the SSH2 protocol which facilitate the use
554: of SSH as a secure transport for other applications (eg.\&
555: .Xr sftp 1 ) .
556: The subsystem is specified as the remote command.
557: .It Fl T
558: Disable pseudo-tty allocation.
559: .It Fl t
560: Force pseudo-tty allocation.
561: This can be used to execute arbitrary
562: screen-based programs on a remote machine, which can be very useful,
563: e.g., when implementing menu services.
564: Multiple
565: .Fl t
566: options force tty allocation, even if
1.194 jakob 567: .Nm
1.218 jmc 568: has no local tty.
569: .It Fl V
570: Display the version number and exit.
571: .It Fl v
572: Verbose mode.
573: Causes
1.176 jmc 574: .Nm
1.218 jmc 575: to print debugging messages about its progress.
576: This is helpful in
577: debugging connection, authentication, and configuration problems.
578: Multiple
579: .Fl v
580: options increase the verbosity.
581: The maximum is 3.
582: .It Fl w Ar tunnel : Ns Ar tunnel
583: Requests a
584: .Xr tun 4
585: device on the client and server like the
586: .Cm Tunnel
587: directive in
588: .Xr ssh_config 5 .
589: .It Fl X
590: Enables X11 forwarding.
1.54 markus 591: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 592: .Pp
1.218 jmc 593: X11 forwarding should be enabled with caution.
1.168 jmc 594: Users with the ability to bypass file permissions on the remote host
1.218 jmc 595: (for the user's X authorization database)
596: can access the local X11 display through the forwarded connection.
597: An attacker may then be able to perform activities such as keystroke monitoring.
598: .Pp
599: For this reason, X11 forwarding is subjected to X11 SECURITY extension
600: restrictions by default.
601: Please refer to the
602: .Nm
603: .Fl Y
604: option and the
605: .Cm ForwardX11Trusted
606: directive in
607: .Xr ssh_config 5
608: for more information.
609: .It Fl x
610: Disables X11 forwarding.
611: .It Fl Y
612: Enables trusted X11 forwarding.
613: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
614: controls.
615: .El
616: .Ss SSH protocol version 1
617: The first authentication method is the
618: .Em rhosts
619: or
620: .Em hosts.equiv
621: method combined with RSA-based host authentication.
622: If the machine the user logs in from is listed in
623: .Pa /etc/hosts.equiv
624: or
625: .Pa /etc/shosts.equiv
626: on the remote machine, and the user names are
627: the same on both sides, or if the files
628: .Pa ~/.rhosts
629: or
630: .Pa ~/.shosts
631: exist in the user's home directory on the
632: remote machine and contain a line containing the name of the client
633: machine and the name of the user on that machine, the user is
634: considered for log in.
635: Additionally, if the server can verify the client's
636: host key (see
637: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 638: and
1.218 jmc 639: .Pa ~/.ssh/known_hosts
640: in the
641: .Sx FILES
642: section), only then is login permitted.
643: This authentication method closes security holes due to IP
644: spoofing, DNS spoofing and routing spoofing.
645: [Note to the administrator:
646: .Pa /etc/hosts.equiv ,
647: .Pa ~/.rhosts ,
648: and the rlogin/rsh protocol in general, are inherently insecure and should be
649: disabled if security is desired.]
1.189 dtucker 650: .Pp
1.218 jmc 651: As a second authentication method,
1.176 jmc 652: .Nm
1.218 jmc 653: supports RSA based authentication.
654: The scheme is based on public-key cryptography: there are cryptosystems
655: where encryption and decryption are done using separate keys, and it
656: is not possible to derive the decryption key from the encryption key.
657: RSA is one such system.
658: The idea is that each user creates a public/private
659: key pair for authentication purposes.
660: The server knows the public key, and only the user knows the private key.
1.210 djm 661: .Pp
1.218 jmc 662: The file
663: .Pa ~/.ssh/authorized_keys
664: lists the public keys that are permitted for logging in.
665: When the user logs in, the
1.2 deraadt 666: .Nm
1.218 jmc 667: program tells the server which key pair it would like to use for
668: authentication.
669: The server checks if this key is permitted, and if so,
670: sends the user (actually the
1.2 deraadt 671: .Nm
1.218 jmc 672: program running on behalf of the user) a challenge, a random number,
673: encrypted by the user's public key.
674: The challenge can only be decrypted using the proper private key.
675: The user's client then decrypts the challenge using the private key,
676: proving that he/she knows the private key
677: but without disclosing it to the server.
678: .Pp
1.176 jmc 679: .Nm
1.218 jmc 680: implements the RSA authentication protocol automatically.
681: The user creates his/her RSA key pair by running
682: .Xr ssh-keygen 1 .
683: This stores the private key in
1.207 djm 684: .Pa ~/.ssh/identity
1.218 jmc 685: and stores the public key in
686: .Pa ~/.ssh/identity.pub
687: in the user's home directory.
688: The user should then copy the
689: .Pa identity.pub
690: to
691: .Pa ~/.ssh/authorized_keys
692: in his/her home directory on the remote machine (the
693: .Pa authorized_keys
694: file corresponds to the conventional
695: .Pa ~/.rhosts
696: file, and has one key
697: per line, though the lines can be very long).
698: After this, the user can log in without giving the password.
699: .Pp
700: The most convenient way to use RSA authentication may be with an
701: authentication agent.
702: See
703: .Xr ssh-agent 1
704: for more information.
705: .Pp
706: If other authentication methods fail,
707: .Nm
708: prompts the user for a password.
709: The password is sent to the remote
710: host for checking; however, since all communications are encrypted,
711: the password cannot be seen by someone listening on the network.
712: .Ss SSH protocol version 2
713: When a user connects using protocol version 2,
714: similar authentication methods are available.
715: Using the default values for
716: .Cm PreferredAuthentications ,
717: the client will try to authenticate first using the hostbased method;
718: if this method fails, public key authentication is attempted,
719: and finally if this method fails, keyboard-interactive and
720: password authentication are tried.
721: .Pp
722: The public key method is similar to RSA authentication described
723: in the previous section and allows the RSA or DSA algorithm to be used:
724: The client uses his private key,
1.207 djm 725: .Pa ~/.ssh/id_dsa
1.218 jmc 726: or
727: .Pa ~/.ssh/id_rsa ,
728: to sign the session identifier and sends the result to the server.
729: The server checks whether the matching public key is listed in
730: .Pa ~/.ssh/authorized_keys
731: and grants access if both the key is found and the signature is correct.
732: The session identifier is derived from a shared Diffie-Hellman value
733: and is only known to the client and the server.
734: .Pp
735: If public key authentication fails or is not available, a password
736: can be sent encrypted to the remote host to prove the user's identity.
737: .Pp
738: Additionally,
1.190 djm 739: .Nm
1.218 jmc 740: supports hostbased or challenge response authentication.
741: .Pp
742: Protocol 2 provides additional mechanisms for confidentiality
743: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
744: and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
745: Note that protocol 1 lacks a strong mechanism for ensuring the
746: integrity of the connection.
747: .Ss Login session and remote execution
748: When the user's identity has been accepted by the server, the server
749: either executes the given command, or logs into the machine and gives
750: the user a normal shell on the remote machine.
751: All communication with
752: the remote command or shell will be automatically encrypted.
753: .Pp
754: If a pseudo-terminal has been allocated (normal login session), the
755: user may use the escape characters noted below.
756: .Pp
757: If no pseudo-tty has been allocated,
758: the session is transparent and can be used to reliably transfer binary data.
759: On most systems, setting the escape character to
760: .Dq none
761: will also make the session transparent even if a tty is used.
762: .Pp
763: The session terminates when the command or shell on the remote
764: machine exits and all X11 and TCP/IP connections have been closed.
765: The exit status of the remote program is returned as the exit status of
766: .Nm ssh .
767: .Pp
1.2 deraadt 768: .Nm
1.218 jmc 769: may additionally obtain configuration data from
770: a per-user configuration file and a system-wide configuration file.
771: The file format and configuration options are described in
772: .Xr ssh_config 5 .
773: .Ss Escape Characters
774: When a pseudo-terminal has been requested,
1.2 deraadt 775: .Nm
1.218 jmc 776: supports a number of functions through the use of an escape character.
777: .Pp
778: A single tilde character can be sent as
779: .Ic ~~
780: or by following the tilde by a character other than those described below.
781: The escape character must always follow a newline to be interpreted as
782: special.
783: The escape character can be changed in configuration files using the
784: .Cm EscapeChar
785: configuration directive or on the command line by the
786: .Fl e
787: option.
788: .Pp
789: The supported escapes (assuming the default
790: .Ql ~ )
791: are:
792: .Bl -tag -width Ds
793: .It Cm ~.
794: Disconnect.
795: .It Cm ~^Z
796: Background
797: .Nm ssh .
798: .It Cm ~#
799: List forwarded connections.
800: .It Cm ~&
801: Background
1.2 deraadt 802: .Nm
1.218 jmc 803: at logout when waiting for forwarded connection / X11 sessions to terminate.
804: .It Cm ~?
805: Display a list of escape characters.
806: .It Cm ~B
807: Send a BREAK to the remote system
808: (only useful for SSH protocol version 2 and if the peer supports it).
809: .It Cm ~C
810: Open command line.
811: Currently this allows the addition of port forwardings using the
812: .Fl L
813: and
814: .Fl R
815: options (see below).
816: It also allows the cancellation of existing remote port-forwardings
817: using
818: .Fl KR Ar hostport .
819: .Ic !\& Ns Ar command
820: allows the user to execute a local command if the
821: .Ic PermitLocalCommand
822: option is enabled in
1.176 jmc 823: .Xr ssh_config 5 .
1.218 jmc 824: Basic help is available, using the
825: .Fl h
826: option.
827: .It Cm ~R
828: Request rekeying of the connection
829: (only useful for SSH protocol version 2 and if the peer supports it).
1.176 jmc 830: .El
1.218 jmc 831: .Ss X11 and TCP forwarding
832: If the
833: .Cm ForwardX11
834: variable is set to
835: .Dq yes
836: (or see the description of the
837: .Fl X
838: and
839: .Fl x
840: options described later)
841: and the user is using X11 (the
842: .Ev DISPLAY
843: environment variable is set), the connection to the X11 display is
844: automatically forwarded to the remote side in such a way that any X11
845: programs started from the shell (or command) will go through the
846: encrypted channel, and the connection to the real X server will be made
1.176 jmc 847: from the local machine.
1.218 jmc 848: The user should not manually set
849: .Ev DISPLAY .
850: Forwarding of X11 connections can be
851: configured on the command line or in configuration files.
852: .Pp
853: The
854: .Ev DISPLAY
855: value set by
856: .Nm
857: will point to the server machine, but with a display number greater than zero.
858: This is normal, and happens because
859: .Nm
860: creates a
861: .Dq proxy
862: X server on the server machine for forwarding the
863: connections over the encrypted channel.
1.200 djm 864: .Pp
1.218 jmc 865: .Nm
866: will also automatically set up Xauthority data on the server machine.
867: For this purpose, it will generate a random authorization cookie,
868: store it in Xauthority on the server, and verify that any forwarded
869: connections carry this cookie and replace it by the real cookie when
870: the connection is opened.
871: The real authentication cookie is never
872: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 873: .Pp
1.218 jmc 874: If the
875: .Cm ForwardAgent
876: variable is set to
877: .Dq yes
878: (or see the description of the
879: .Fl A
1.191 djm 880: and
1.218 jmc 881: .Fl a
882: options described later) and
883: the user is using an authentication agent, the connection to the agent
884: is automatically forwarded to the remote side.
885: .Pp
886: Forwarding of arbitrary TCP/IP connections over the secure channel can
887: be specified either on the command line or in a configuration file.
888: One possible application of TCP/IP forwarding is a secure connection to an
889: electronic purse; another is going through firewalls.
890: .Ss Server authentication
1.73 markus 891: .Nm
1.218 jmc 892: automatically maintains and checks a database containing
893: identifications for all hosts it has ever been used with.
894: Host keys are stored in
895: .Pa ~/.ssh/known_hosts
896: in the user's home directory.
897: Additionally, the file
898: .Pa /etc/ssh/ssh_known_hosts
899: is automatically checked for known hosts.
900: Any new hosts are automatically added to the user's file.
901: If a host's identification ever changes,
1.2 deraadt 902: .Nm
1.218 jmc 903: warns about this and disables password authentication to prevent a
904: trojan horse from getting the user's password.
905: Another purpose of this mechanism is to prevent man-in-the-middle attacks
906: which could otherwise be used to circumvent the encryption.
907: The
908: .Cm StrictHostKeyChecking
909: option can be used to prevent logins to machines whose
910: host key is not known or has changed.
1.203 djm 911: .Pp
912: .Nm
1.218 jmc 913: can be configured to verify host identification using fingerprint resource
914: records (SSHFP) published in DNS.
915: The
916: .Cm VerifyHostKeyDNS
917: option can be used to control how DNS lookups are performed.
918: SSHFP resource records can be generated using
919: .Xr ssh-keygen 1 .
1.2 deraadt 920: .Sh ENVIRONMENT
921: .Nm
1.1 deraadt 922: will normally set the following environment variables:
1.176 jmc 923: .Bl -tag -width LOGNAME
1.2 deraadt 924: .It Ev DISPLAY
925: The
926: .Ev DISPLAY
1.40 aaron 927: variable indicates the location of the X11 server.
1.44 aaron 928: It is automatically set by
1.2 deraadt 929: .Nm
930: to point to a value of the form
931: .Dq hostname:n
932: where hostname indicates
1.176 jmc 933: the host where the shell runs, and n is an integer \*(Ge 1.
1.40 aaron 934: .Nm
935: uses this special value to forward X11 connections over the secure
936: channel.
1.107 markus 937: The user should normally not set
938: .Ev DISPLAY
939: explicitly, as that
1.1 deraadt 940: will render the X11 connection insecure (and will require the user to
941: manually copy any required authorization cookies).
1.2 deraadt 942: .It Ev HOME
1.1 deraadt 943: Set to the path of the user's home directory.
1.2 deraadt 944: .It Ev LOGNAME
945: Synonym for
1.12 aaron 946: .Ev USER ;
947: set for compatibility with systems that use this variable.
1.2 deraadt 948: .It Ev MAIL
1.129 stevesk 949: Set to the path of the user's mailbox.
1.40 aaron 950: .It Ev PATH
1.2 deraadt 951: Set to the default
952: .Ev PATH ,
953: as specified when compiling
1.12 aaron 954: .Nm ssh .
1.118 markus 955: .It Ev SSH_ASKPASS
956: If
957: .Nm
958: needs a passphrase, it will read the passphrase from the current
959: terminal if it was run from a terminal.
960: If
961: .Nm
962: does not have a terminal associated with it but
963: .Ev DISPLAY
964: and
965: .Ev SSH_ASKPASS
966: are set, it will execute the program specified by
967: .Ev SSH_ASKPASS
968: and open an X11 window to read the passphrase.
969: This is particularly useful when calling
970: .Nm
971: from a
1.196 jmc 972: .Pa .xsession
1.118 markus 973: or related script.
974: (Note that on some machines it
975: may be necessary to redirect the input from
976: .Pa /dev/null
977: to make this work.)
1.18 markus 978: .It Ev SSH_AUTH_SOCK
1.129 stevesk 979: Identifies the path of a unix-domain socket used to communicate with the
1.17 markus 980: agent.
1.166 stevesk 981: .It Ev SSH_CONNECTION
982: Identifies the client and server ends of the connection.
1.40 aaron 983: The variable contains
1.166 stevesk 984: four space-separated values: client ip-address, client port number,
985: server ip-address and server port number.
1.73 markus 986: .It Ev SSH_ORIGINAL_COMMAND
987: The variable contains the original command line if a forced command
988: is executed.
989: It can be used to extract the original arguments.
1.2 deraadt 990: .It Ev SSH_TTY
1.1 deraadt 991: This is set to the name of the tty (path to the device) associated
1.40 aaron 992: with the current shell or command.
993: If the current session has no tty,
1.1 deraadt 994: this variable is not set.
1.2 deraadt 995: .It Ev TZ
1.214 jmc 996: This variable is set to indicate the present time zone if it
1.56 deraadt 997: was set when the daemon was started (i.e., the daemon passes the value
1.1 deraadt 998: on to new connections).
1.2 deraadt 999: .It Ev USER
1.1 deraadt 1000: Set to the name of the user logging in.
1.2 deraadt 1001: .El
1002: .Pp
1.44 aaron 1003: Additionally,
1.2 deraadt 1004: .Nm
1.44 aaron 1005: reads
1.207 djm 1006: .Pa ~/.ssh/environment ,
1.2 deraadt 1007: and adds lines of the format
1008: .Dq VARNAME=value
1.161 marc 1009: to the environment if the file exists and if users are allowed to
1010: change their environment.
1.176 jmc 1011: For more information, see the
1.161 marc 1012: .Cm PermitUserEnvironment
1.162 stevesk 1013: option in
1.161 marc 1014: .Xr sshd_config 5 .
1.2 deraadt 1015: .Sh FILES
1.36 markus 1016: .Bl -tag -width Ds
1.207 djm 1017: .It Pa ~/.ssh/known_hosts
1.129 stevesk 1018: Records host keys for all hosts the user has logged into that are not
1.2 deraadt 1019: in
1.147 deraadt 1020: .Pa /etc/ssh/ssh_known_hosts .
1.2 deraadt 1021: See
1022: .Xr sshd 8 .
1.207 djm 1023: .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1.102 itojun 1024: Contains the authentication identity of the user.
1025: They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1.48 markus 1026: These files
1027: contain sensitive data and should be readable by the user but not
1.15 markus 1028: accessible by others (read/write/execute).
1029: Note that
1030: .Nm
1.48 markus 1031: ignores a private key file if it is accessible by others.
1.15 markus 1032: It is possible to specify a passphrase when
1.1 deraadt 1033: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 1034: sensitive part of this file using 3DES.
1.207 djm 1035: .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1.1 deraadt 1036: Contains the public key for authentication (public part of the
1.40 aaron 1037: identity file in human-readable form).
1.48 markus 1038: The contents of the
1.207 djm 1039: .Pa ~/.ssh/identity.pub
1.176 jmc 1040: file should be added to the file
1.207 djm 1041: .Pa ~/.ssh/authorized_keys
1.2 deraadt 1042: on all machines
1.137 deraadt 1043: where the user wishes to log in using protocol version 1 RSA authentication.
1.48 markus 1044: The contents of the
1.207 djm 1045: .Pa ~/.ssh/id_dsa.pub
1.102 itojun 1046: and
1.207 djm 1047: .Pa ~/.ssh/id_rsa.pub
1.48 markus 1048: file should be added to
1.207 djm 1049: .Pa ~/.ssh/authorized_keys
1.48 markus 1050: on all machines
1.137 deraadt 1051: where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1.48 markus 1052: These files are not
1.40 aaron 1053: sensitive and can (but need not) be readable by anyone.
1.48 markus 1054: These files are
1.84 markus 1055: never used automatically and are not necessary; they are only provided for
1.1 deraadt 1056: the convenience of the user.
1.207 djm 1057: .It Pa ~/.ssh/config
1.40 aaron 1058: This is the per-user configuration file.
1.158 stevesk 1059: The file format and configuration options are described in
1060: .Xr ssh_config 5 .
1.183 djm 1061: Because of the potential for abuse, this file must have strict permissions:
1062: read/write for the user, and not accessible by others.
1.207 djm 1063: .It Pa ~/.ssh/authorized_keys
1.115 markus 1064: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1.40 aaron 1065: The format of this file is described in the
1.2 deraadt 1066: .Xr sshd 8
1.40 aaron 1067: manual page.
1.176 jmc 1068: In the simplest form the format is the same as the
1069: .Pa .pub
1.116 markus 1070: identity files.
1.48 markus 1071: This file is not highly sensitive, but the recommended
1072: permissions are read/write for the user, and not accessible by others.
1.147 deraadt 1073: .It Pa /etc/ssh/ssh_known_hosts
1.40 aaron 1074: Systemwide list of known host keys.
1.116 markus 1075: This file should be prepared by the
1.1 deraadt 1076: system administrator to contain the public host keys of all machines in the
1.40 aaron 1077: organization.
1078: This file should be world-readable.
1079: This file contains
1.1 deraadt 1080: public keys, one per line, in the following format (fields separated
1.116 markus 1081: by spaces): system name, public key and optional comment field.
1.40 aaron 1082: When different names are used
1.1 deraadt 1083: for the same machine, all such names should be listed, separated by
1.40 aaron 1084: commas.
1.176 jmc 1085: The format is described in the
1.2 deraadt 1086: .Xr sshd 8
1.1 deraadt 1087: manual page.
1.2 deraadt 1088: .Pp
1.1 deraadt 1089: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1090: .Xr sshd 8
1.1 deraadt 1091: to verify the client host when logging in; other names are needed because
1.2 deraadt 1092: .Nm
1.1 deraadt 1093: does not convert the user-supplied name to a canonical name before
1094: checking the key, because someone with access to the name servers
1095: would then be able to fool host authentication.
1.147 deraadt 1096: .It Pa /etc/ssh/ssh_config
1.40 aaron 1097: Systemwide configuration file.
1.158 stevesk 1098: The file format and configuration options are described in
1099: .Xr ssh_config 5 .
1.147 deraadt 1100: .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1.141 markus 1101: These three files contain the private parts of the host keys
1102: and are used for
1103: .Cm RhostsRSAAuthentication
1104: and
1105: .Cm HostbasedAuthentication .
1.155 stevesk 1106: If the protocol version 1
1107: .Cm RhostsRSAAuthentication
1.157 deraadt 1108: method is used,
1.155 stevesk 1109: .Nm
1110: must be setuid root, since the host key is readable only by root.
1111: For protocol version 2,
1112: .Nm
1113: uses
1114: .Xr ssh-keysign 8
1115: to access the host keys for
1116: .Cm HostbasedAuthentication .
1117: This eliminates the requirement that
1118: .Nm
1119: be setuid root when that authentication method is used.
1120: By default
1.141 markus 1121: .Nm
1.155 stevesk 1122: is not setuid root.
1.207 djm 1123: .It Pa ~/.rhosts
1.2 deraadt 1124: This file is used in
1.195 markus 1125: .Cm RhostsRSAAuthentication
1126: and
1127: .Cm HostbasedAuthentication
1.2 deraadt 1128: authentication to list the
1.40 aaron 1129: host/user pairs that are permitted to log in.
1130: (Note that this file is
1.1 deraadt 1131: also used by rlogin and rsh, which makes using this file insecure.)
1132: Each line of the file contains a host name (in the canonical form
1133: returned by name servers), and then a user name on that host,
1.40 aaron 1134: separated by a space.
1.92 markus 1135: On some machines this file may need to be
1.1 deraadt 1136: world-readable if the user's home directory is on a NFS partition,
1137: because
1.2 deraadt 1138: .Xr sshd 8
1.40 aaron 1139: reads it as root.
1140: Additionally, this file must be owned by the user,
1141: and must not have write permissions for anyone else.
1142: The recommended
1.1 deraadt 1143: permission for most machines is read/write for the user, and not
1144: accessible by others.
1.2 deraadt 1145: .Pp
1.195 markus 1146: Note that
1.2 deraadt 1147: .Xr sshd 8
1.195 markus 1148: allows authentication only in combination with client host key
1149: authentication before permitting log in.
1.137 deraadt 1150: If the server machine does not have the client's host key in
1.147 deraadt 1151: .Pa /etc/ssh/ssh_known_hosts ,
1.137 deraadt 1152: it can be stored in
1.207 djm 1153: .Pa ~/.ssh/known_hosts .
1.2 deraadt 1154: The easiest way to do this is to
1.1 deraadt 1155: connect back to the client from the server machine using ssh; this
1.48 markus 1156: will automatically add the host key to
1.207 djm 1157: .Pa ~/.ssh/known_hosts .
1158: .It Pa ~/.shosts
1.2 deraadt 1159: This file is used exactly the same way as
1.176 jmc 1160: .Pa .rhosts .
1.2 deraadt 1161: The purpose for
1.195 markus 1162: having this file is to be able to use
1163: .Cm RhostsRSAAuthentication
1164: and
1165: .Cm HostbasedAuthentication
1166: authentication without permitting login with
1.176 jmc 1167: .Xr rlogin
1.2 deraadt 1168: or
1169: .Xr rsh 1 .
1170: .It Pa /etc/hosts.equiv
1171: This file is used during
1.195 markus 1172: .Cm RhostsRSAAuthentication
1173: and
1174: .Cm HostbasedAuthentication
1.173 jmc 1175: authentication.
1.40 aaron 1176: It contains
1.176 jmc 1177: canonical hosts names, one per line (the full format is described in the
1.2 deraadt 1178: .Xr sshd 8
1.40 aaron 1179: manual page).
1180: If the client host is found in this file, login is
1.1 deraadt 1181: automatically permitted provided client and server user names are the
1.40 aaron 1182: same.
1.195 markus 1183: Additionally, successful client host key authentication is required.
1.40 aaron 1184: This file should only be writable by root.
1.2 deraadt 1185: .It Pa /etc/shosts.equiv
1.44 aaron 1186: This file is processed exactly as
1.2 deraadt 1187: .Pa /etc/hosts.equiv .
1.1 deraadt 1188: This file may be useful to permit logins using
1.2 deraadt 1189: .Nm
1.1 deraadt 1190: but not using rsh/rlogin.
1.147 deraadt 1191: .It Pa /etc/ssh/sshrc
1.1 deraadt 1192: Commands in this file are executed by
1.2 deraadt 1193: .Nm
1.1 deraadt 1194: when the user logs in just before the user's shell (or command) is started.
1195: See the
1.2 deraadt 1196: .Xr sshd 8
1.1 deraadt 1197: manual page for more information.
1.207 djm 1198: .It Pa ~/.ssh/rc
1.1 deraadt 1199: Commands in this file are executed by
1.2 deraadt 1200: .Nm
1.1 deraadt 1201: when the user logs in just before the user's shell (or command) is
1202: started.
1.44 aaron 1203: See the
1.2 deraadt 1204: .Xr sshd 8
1.1 deraadt 1205: manual page for more information.
1.207 djm 1206: .It Pa ~/.ssh/environment
1.31 markus 1207: Contains additional definitions for environment variables, see section
1208: .Sx ENVIRONMENT
1209: above.
1.58 itojun 1210: .El
1.145 markus 1211: .Sh DIAGNOSTICS
1212: .Nm
1213: exits with the exit status of the remote command or with 255
1214: if an error occurred.
1.2 deraadt 1215: .Sh SEE ALSO
1.176 jmc 1216: .Xr gzip 1 ,
1.2 deraadt 1217: .Xr rsh 1 ,
1218: .Xr scp 1 ,
1.83 djm 1219: .Xr sftp 1 ,
1.2 deraadt 1220: .Xr ssh-add 1 ,
1221: .Xr ssh-agent 1 ,
1222: .Xr ssh-keygen 1 ,
1223: .Xr telnet 1 ,
1.176 jmc 1224: .Xr hosts.equiv 5 ,
1.159 stevesk 1225: .Xr ssh_config 5 ,
1.160 naddy 1226: .Xr ssh-keysign 8 ,
1.87 itojun 1227: .Xr sshd 8
1.106 markus 1228: .Rs
1229: .%A T. Ylonen
1230: .%A T. Kivinen
1231: .%A M. Saarinen
1232: .%A T. Rinne
1233: .%A S. Lehtinen
1234: .%T "SSH Protocol Architecture"
1.150 markus 1235: .%N draft-ietf-secsh-architecture-12.txt
1236: .%D January 2002
1.106 markus 1237: .%O work in progress material
1238: .Re
1.173 jmc 1239: .Sh AUTHORS
1240: OpenSSH is a derivative of the original and free
1241: ssh 1.2.12 release by Tatu Ylonen.
1242: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1243: Theo de Raadt and Dug Song
1244: removed many bugs, re-added newer features and
1245: created OpenSSH.
1246: Markus Friedl contributed the support for SSH
1247: protocol versions 1.5 and 2.0.
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