1.\" $NetBSD: ssh.1,v 1.16 2015/08/13 10:33:21 christos Exp $ 2.\" -*- nroff -*- 3.\" 4.\" Author: Tatu Ylonen <ylo@cs.hut.fi> 5.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 6.\" All rights reserved 7.\" 8.\" As far as I am concerned, the code I have written for this software 9.\" can be used freely for any purpose. Any derived versions of this 10.\" software must be clearly marked as such, and if the derived work is 11.\" incompatible with the protocol description in the RFC file, it must be 12.\" called by a name other than "ssh" or "Secure Shell". 13.\" 14.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. 15.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. 16.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. 17.\" 18.\" Redistribution and use in source and binary forms, with or without 19.\" modification, are permitted provided that the following conditions 20.\" are met: 21.\" 1. Redistributions of source code must retain the above copyright 22.\" notice, this list of conditions and the following disclaimer. 23.\" 2. Redistributions in binary form must reproduce the above copyright 24.\" notice, this list of conditions and the following disclaimer in the 25.\" documentation and/or other materials provided with the distribution. 26.\" 27.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 28.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 29.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 30.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 31.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 32.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 33.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 34.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 35.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 36.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 37.\" 38.\" $OpenBSD: ssh.1,v 1.361 2015/07/20 18:44:12 millert Exp $ 39.Dd July 20 2015 40.Dt SSH 1 41.Os 42.Sh NAME 43.Nm ssh 44.Nd OpenSSH SSH client (remote login program) 45.Sh SYNOPSIS 46.Nm ssh 47.Bk -words 48.Op Fl 1246AaCfGgKkMNnqsTtVvXxYy 49.Op Fl b Ar bind_address 50.Op Fl c Ar cipher_spec 51.Op Fl D Oo Ar bind_address : Oc Ns Ar port 52.Op Fl E Ar log_file 53.Op Fl e Ar escape_char 54.Op Fl F Ar configfile 55.Op Fl I Ar pkcs11 56.Op Fl i Ar identity_file 57.Op Fl L Ar address 58.Op Fl l Ar login_name 59.Op Fl m Ar mac_spec 60.Op Fl O Ar ctl_cmd 61.Op Fl o Ar option 62.Op Fl p Ar port 63.Op Fl Q Cm cipher | cipher-auth | mac | kex | key | protocol-version 64.Op Fl R Ar address 65.Op Fl S Ar ctl_path 66.Op Fl W Ar host : Ns Ar port 67.Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun 68.Oo Ar user Ns @ Oc Ns Ar hostname 69.Op Ar command 70.Ek 71.Sh DESCRIPTION 72.Nm 73(SSH client) is a program for logging into a remote machine and for 74executing commands on a remote machine. 75It is intended to replace rlogin and rsh, 76and provide secure encrypted communications between 77two untrusted hosts over an insecure network. 78X11 connections, arbitrary TCP ports and 79.Ux Ns -domain 80sockets can also be forwarded over the secure channel. 81.Pp 82.Nm 83connects and logs into the specified 84.Ar hostname 85(with optional 86.Ar user 87name). 88The user must prove 89his/her identity to the remote machine using one of several methods 90depending on the protocol version used (see below). 91.Pp 92If 93.Ar command 94is specified, 95it is executed on the remote host instead of a login shell. 96.Pp 97The options are as follows: 98.Pp 99.Bl -tag -width Ds -compact 100.It Fl 1 101Forces 102.Nm 103to try protocol version 1 only. 104.Pp 105.It Fl 2 106Forces 107.Nm 108to try protocol version 2 only. 109.Pp 110.It Fl 4 111Forces 112.Nm 113to use IPv4 addresses only. 114.Pp 115.It Fl 6 116Forces 117.Nm 118to use IPv6 addresses only. 119.Pp 120.It Fl A 121Enables forwarding of the authentication agent connection. 122This can also be specified on a per-host basis in a configuration file. 123.Pp 124Agent forwarding should be enabled with caution. 125Users with the ability to bypass file permissions on the remote host 126(for the agent's 127.Ux Ns -domain 128socket) can access the local agent through the forwarded connection. 129An attacker cannot obtain key material from the agent, 130however they can perform operations on the keys that enable them to 131authenticate using the identities loaded into the agent. 132.Pp 133.It Fl a 134Disables forwarding of the authentication agent connection. 135.Pp 136.It Fl b Ar bind_address 137Use 138.Ar bind_address 139on the local machine as the source address 140of the connection. 141Only useful on systems with more than one address. 142.Pp 143.It Fl C 144Requests compression of all data (including stdin, stdout, stderr, and 145data for forwarded X11, TCP and 146.Ux Ns -domain 147connections). 148The compression algorithm is the same used by 149.Xr gzip 1 , 150and the 151.Dq level 152can be controlled by the 153.Cm CompressionLevel 154option for protocol version 1. 155Compression is desirable on modem lines and other 156slow connections, but will only slow down things on fast networks. 157The default value can be set on a host-by-host basis in the 158configuration files; see the 159.Cm Compression 160option. 161.Pp 162.It Fl c Ar cipher_spec 163Selects the cipher specification for encrypting the session. 164.Pp 165Protocol version 1 allows specification of a single cipher. 166The supported values are 167.Dq 3des , 168.Dq blowfish , 169and 170.Dq des . 171For protocol version 2, 172.Ar cipher_spec 173is a comma-separated list of ciphers 174listed in order of preference. 175See the 176.Cm Ciphers 177keyword in 178.Xr ssh_config 5 179for more information. 180.Pp 181.It Fl D Xo 182.Sm off 183.Oo Ar bind_address : Oc 184.Ar port 185.Sm on 186.Xc 187Specifies a local 188.Dq dynamic 189application-level port forwarding. 190This works by allocating a socket to listen to 191.Ar port 192on the local side, optionally bound to the specified 193.Ar bind_address . 194Whenever a connection is made to this port, the 195connection is forwarded over the secure channel, and the application 196protocol is then used to determine where to connect to from the 197remote machine. 198Currently the SOCKS4 and SOCKS5 protocols are supported, and 199.Nm 200will act as a SOCKS server. 201Only root can forward privileged ports. 202Dynamic port forwardings can also be specified in the configuration file. 203.Pp 204IPv6 addresses can be specified by enclosing the address in square brackets. 205Only the superuser can forward privileged ports. 206By default, the local port is bound in accordance with the 207.Cm GatewayPorts 208setting. 209However, an explicit 210.Ar bind_address 211may be used to bind the connection to a specific address. 212The 213.Ar bind_address 214of 215.Dq localhost 216indicates that the listening port be bound for local use only, while an 217empty address or 218.Sq * 219indicates that the port should be available from all interfaces. 220.Pp 221.It Fl E Ar log_file 222Append debug logs to 223.Ar log_file 224instead of standard error. 225.Pp 226.It Fl e Ar escape_char 227Sets the escape character for sessions with a pty (default: 228.Ql ~ ) . 229The escape character is only recognized at the beginning of a line. 230The escape character followed by a dot 231.Pq Ql \&. 232closes the connection; 233followed by control-Z suspends the connection; 234and followed by itself sends the escape character once. 235Setting the character to 236.Dq none 237disables any escapes and makes the session fully transparent. 238.Pp 239.It Fl F Ar configfile 240Specifies an alternative per-user configuration file. 241If a configuration file is given on the command line, 242the system-wide configuration file 243.Pq Pa /etc/ssh/ssh_config 244will be ignored. 245The default for the per-user configuration file is 246.Pa ~/.ssh/config . 247.Pp 248.It Fl f 249Requests 250.Nm 251to go to background just before command execution. 252This is useful if 253.Nm 254is going to ask for passwords or passphrases, but the user 255wants it in the background. 256This implies 257.Fl n . 258The recommended way to start X11 programs at a remote site is with 259something like 260.Ic ssh -f host xterm . 261.Pp 262If the 263.Cm ExitOnForwardFailure 264configuration option is set to 265.Dq yes , 266then a client started with 267.Fl f 268will wait for all remote port forwards to be successfully established 269before placing itself in the background. 270.Pp 271.It Fl G 272Causes 273.Nm 274to print its configuration after evaluating 275.Cm Host 276and 277.Cm Match 278blocks and exit. 279.Pp 280.It Fl g 281Allows remote hosts to connect to local forwarded ports. 282If used on a multiplexed connection, then this option must be specified 283on the master process. 284.Pp 285.It Fl I Ar pkcs11 286Specify the PKCS#11 shared library 287.Nm 288should use to communicate with a PKCS#11 token providing the user's 289private RSA key. 290.Pp 291.It Fl i Ar identity_file 292Selects a file from which the identity (private key) for 293public key authentication is read. 294The default is 295.Pa ~/.ssh/identity 296for protocol version 1, and 297.Pa ~/.ssh/id_dsa , 298.Pa ~/.ssh/id_ecdsa , 299.Pa ~/.ssh/id_ed25519 300and 301.Pa ~/.ssh/id_rsa 302for protocol version 2. 303Identity files may also be specified on 304a per-host basis in the configuration file. 305It is possible to have multiple 306.Fl i 307options (and multiple identities specified in 308configuration files). 309.Nm 310will also try to load certificate information from the filename obtained 311by appending 312.Pa -cert.pub 313to identity filenames. 314.Pp 315.It Fl K 316Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI 317credentials to the server. 318.Pp 319.It Fl k 320Disables forwarding (delegation) of GSSAPI credentials to the server. 321.Pp 322.It Fl L Xo 323.Sm off 324.Oo Ar bind_address : Oc 325.Ar port : host : hostport 326.Sm on 327.Xc 328.It Fl L Xo 329.Sm off 330.Oo Ar bind_address : Oc 331.Ar port : remote_socket 332.Sm on 333.Xc 334.It Fl L Xo 335.Sm off 336.Ar local_socket : host : hostport 337.Sm on 338.Xc 339.It Fl L Xo 340.Sm off 341.Ar local_socket : remote_socket 342.Sm on 343.Xc 344Specifies that connections to the given TCP port or Unix socket on the local 345(client) host are to be forwarded to the given host and port, or Unix socket, 346on the remote side. 347This works by allocating a socket to listen to either a TCP 348.Ar port 349on the local side, optionally bound to the specified 350.Ar bind_address , 351or to a Unix socket. 352Whenever a connection is made to the local port or socket, the 353connection is forwarded over the secure channel, and a connection is 354made to either 355.Ar host 356port 357.Ar hostport , 358or the Unix socket 359.Ar remote_socket , 360from the remote machine. 361.Pp 362Port forwardings can also be specified in the configuration file. 363Only the superuser can forward privileged ports. 364IPv6 addresses can be specified by enclosing the address in square brackets. 365.Pp 366By default, the local port is bound in accordance with the 367.Cm GatewayPorts 368setting. 369However, an explicit 370.Ar bind_address 371may be used to bind the connection to a specific address. 372The 373.Ar bind_address 374of 375.Dq localhost 376indicates that the listening port be bound for local use only, while an 377empty address or 378.Sq * 379indicates that the port should be available from all interfaces. 380.Pp 381.It Fl l Ar login_name 382Specifies the user to log in as on the remote machine. 383This also may be specified on a per-host basis in the configuration file. 384.Pp 385.It Fl M 386Places the 387.Nm 388client into 389.Dq master 390mode for connection sharing. 391Multiple 392.Fl M 393options places 394.Nm 395into 396.Dq master 397mode with confirmation required before slave connections are accepted. 398Refer to the description of 399.Cm ControlMaster 400in 401.Xr ssh_config 5 402for details. 403.Pp 404.It Fl m Ar mac_spec 405Additionally, for protocol version 2 a comma-separated list of MAC 406(message authentication code) algorithms can 407be specified in order of preference. 408See the 409.Cm MACs 410keyword for more information. 411.Pp 412.It Fl N 413Do not execute a remote command. 414This is useful for just forwarding ports 415(protocol version 2 only). 416.Pp 417.It Fl n 418Redirects stdin from 419.Pa /dev/null 420(actually, prevents reading from stdin). 421This must be used when 422.Nm 423is run in the background. 424A common trick is to use this to run X11 programs on a remote machine. 425For example, 426.Ic ssh -n shadows.cs.hut.fi emacs & 427will start an emacs on shadows.cs.hut.fi, and the X11 428connection will be automatically forwarded over an encrypted channel. 429The 430.Nm 431program will be put in the background. 432(This does not work if 433.Nm 434needs to ask for a password or passphrase; see also the 435.Fl f 436option.) 437.Pp 438.It Fl O Ar ctl_cmd 439Control an active connection multiplexing master process. 440When the 441.Fl O 442option is specified, the 443.Ar ctl_cmd 444argument is interpreted and passed to the master process. 445Valid commands are: 446.Dq check 447(check that the master process is running), 448.Dq forward 449(request forwardings without command execution), 450.Dq cancel 451(cancel forwardings), 452.Dq exit 453(request the master to exit), and 454.Dq stop 455(request the master to stop accepting further multiplexing requests). 456.Pp 457.It Fl o Ar option 458Can be used to give options in the format used in the configuration file. 459This is useful for specifying options for which there is no separate 460command-line flag. 461For full details of the options listed below, and their possible values, see 462.Xr ssh_config 5 . 463.Pp 464.Bl -tag -width Ds -offset indent -compact 465.It AddressFamily 466.It BatchMode 467.It BindAddress 468.It CanonicalDomains 469.It CanonicalizeFallbackLocal 470.It CanonicalizeHostname 471.It CanonicalizeMaxDots 472.It CanonicalizePermittedCNAMEs 473.It ChallengeResponseAuthentication 474.It CheckHostIP 475.It Cipher 476.It Ciphers 477.It ClearAllForwardings 478.It Compression 479.It CompressionLevel 480.It ConnectionAttempts 481.It ConnectTimeout 482.It ControlMaster 483.It ControlPath 484.It ControlPersist 485.It DynamicForward 486.It EscapeChar 487.It ExitOnForwardFailure 488.It FingerprintHash 489.It ForwardAgent 490.It ForwardX11 491.It ForwardX11Timeout 492.It ForwardX11Trusted 493.It GatewayPorts 494.It GlobalKnownHostsFile 495.It GSSAPIAuthentication 496.It GSSAPIDelegateCredentials 497.It HashKnownHosts 498.It Host 499.It HostbasedAuthentication 500.It HostbasedKeyTypes 501.It HostKeyAlgorithms 502.It HostKeyAlias 503.It HostName 504.It IdentityFile 505.It IdentitiesOnly 506.It IPQoS 507.It KbdInteractiveAuthentication 508.It KbdInteractiveDevices 509.It KexAlgorithms 510.It LocalCommand 511.It LocalForward 512.It LogLevel 513.It MACs 514.It Match 515.It NoHostAuthenticationForLocalhost 516.It NumberOfPasswordPrompts 517.It PasswordAuthentication 518.It PermitLocalCommand 519.It PKCS11Provider 520.It Port 521.It PreferredAuthentications 522.It Protocol 523.It ProxyCommand 524.It ProxyUseFdpass 525.It PubkeyAcceptedKeyTypes 526.It PubkeyAuthentication 527.It RekeyLimit 528.It RemoteForward 529.It RequestTTY 530.It RhostsRSAAuthentication 531.It RSAAuthentication 532.It SendEnv 533.It ServerAliveInterval 534.It ServerAliveCountMax 535.It StreamLocalBindMask 536.It StreamLocalBindUnlink 537.It StrictHostKeyChecking 538.It TCPKeepAlive 539.It Tunnel 540.It TunnelDevice 541.It UpdateHostKeys 542.It UsePrivilegedPort 543.It User 544.It UserKnownHostsFile 545.It VerifyHostKeyDNS 546.It VisualHostKey 547.It XAuthLocation 548.El 549.Pp 550.It Fl p Ar port 551Port to connect to on the remote host. 552This can be specified on a 553per-host basis in the configuration file. 554.Pp 555.It Fl Q Cm cipher | cipher-auth | mac | kex | key | protocol-version 556Queries 557.Nm 558for the algorithms supported for the specified version 2. 559The available features are: 560.Ar cipher 561(supported symmetric ciphers), 562.Ar cipher-auth 563(supported symmetric ciphers that support authenticated encryption), 564.Ar mac 565(supported message integrity codes), 566.Ar kex 567(key exchange algorithms), 568.Ar key 569(key types) and 570.Ar protocol-version 571(supported SSH protocol versions). 572.Pp 573.It Fl q 574Quiet mode. 575Causes most warning and diagnostic messages to be suppressed. 576.Pp 577.It Fl R Xo 578.Sm off 579.Oo Ar bind_address : Oc 580.Ar port : host : hostport 581.Sm on 582.Xc 583.It Fl R Xo 584.Sm off 585.Oo Ar bind_address : Oc 586.Ar port : local_socket 587.Sm on 588.Xc 589.It Fl R Xo 590.Sm off 591.Ar remote_socket : host : hostport 592.Sm on 593.Xc 594.It Fl R Xo 595.Sm off 596.Ar remote_socket : local_socket 597.Sm on 598.Xc 599Specifies that connections to the given TCP port or Unix socket on the remote 600(server) host are to be forwarded to the given host and port, or Unix socket, 601on the local side. 602This works by allocating a socket to listen to either a TCP 603.Ar port 604or to a Unix socket on the remote side. 605Whenever a connection is made to this port or Unix socket, the 606connection is forwarded over the secure channel, and a connection 607is made to either 608.Ar host 609port 610.Ar hostport , 611or 612.Ar local_socket , 613from the local machine. 614.Pp 615Port forwardings can also be specified in the configuration file. 616Privileged ports can be forwarded only when 617logging in as root on the remote machine. 618IPv6 addresses can be specified by enclosing the address in square brackets. 619.Pp 620By default, TCP listening sockets on the server will be bound to the loopback 621interface only. 622This may be overridden by specifying a 623.Ar bind_address . 624An empty 625.Ar bind_address , 626or the address 627.Ql * , 628indicates that the remote socket should listen on all interfaces. 629Specifying a remote 630.Ar bind_address 631will only succeed if the server's 632.Cm GatewayPorts 633option is enabled (see 634.Xr sshd_config 5 ) . 635.Pp 636If the 637.Ar port 638argument is 639.Ql 0 , 640the listen port will be dynamically allocated on the server and reported 641to the client at run time. 642When used together with 643.Ic -O forward 644the allocated port will be printed to the standard output. 645.Pp 646.It Fl S Ar ctl_path 647Specifies the location of a control socket for connection sharing, 648or the string 649.Dq none 650to disable connection sharing. 651Refer to the description of 652.Cm ControlPath 653and 654.Cm ControlMaster 655in 656.Xr ssh_config 5 657for details. 658.Pp 659.It Fl s 660May be used to request invocation of a subsystem on the remote system. 661Subsystems are a feature of the SSH2 protocol which facilitate the use 662of SSH as a secure transport for other applications (eg.\& 663.Xr sftp 1 ) . 664The subsystem is specified as the remote command. 665.Pp 666.It Fl T 667Disable pseudo-terminal allocation. 668.Pp 669.It Fl t 670Force pseudo-terminal allocation. 671This can be used to execute arbitrary 672screen-based programs on a remote machine, which can be very useful, 673e.g. when implementing menu services. 674Multiple 675.Fl t 676options force tty allocation, even if 677.Nm 678has no local tty. 679.Pp 680.It Fl V 681Display the version number and exit. 682.Pp 683.It Fl v 684Verbose mode. 685Causes 686.Nm 687to print debugging messages about its progress. 688This is helpful in 689debugging connection, authentication, and configuration problems. 690Multiple 691.Fl v 692options increase the verbosity. 693The maximum is 3. 694.Pp 695.It Fl W Ar host : Ns Ar port 696Requests that standard input and output on the client be forwarded to 697.Ar host 698on 699.Ar port 700over the secure channel. 701Implies 702.Fl N , 703.Fl T , 704.Cm ExitOnForwardFailure 705and 706.Cm ClearAllForwardings . 707Works with Protocol version 2 only. 708.Pp 709.It Fl w Xo 710.Ar local_tun Ns Op : Ns Ar remote_tun 711.Xc 712Requests 713tunnel 714device forwarding with the specified 715.Xr tun 4 716devices between the client 717.Pq Ar local_tun 718and the server 719.Pq Ar remote_tun . 720.Pp 721The devices may be specified by numerical ID or the keyword 722.Dq any , 723which uses the next available tunnel device. 724If 725.Ar remote_tun 726is not specified, it defaults to 727.Dq any . 728See also the 729.Cm Tunnel 730and 731.Cm TunnelDevice 732directives in 733.Xr ssh_config 5 . 734If the 735.Cm Tunnel 736directive is unset, it is set to the default tunnel mode, which is 737.Dq point-to-point . 738.Pp 739.It Fl X 740Enables X11 forwarding. 741This can also be specified on a per-host basis in a configuration file. 742.Pp 743X11 forwarding should be enabled with caution. 744Users with the ability to bypass file permissions on the remote host 745(for the user's X authorization database) 746can access the local X11 display through the forwarded connection. 747An attacker may then be able to perform activities such as keystroke monitoring. 748.Pp 749For this reason, X11 forwarding is subjected to X11 SECURITY extension 750restrictions by default. 751Please refer to the 752.Nm 753.Fl Y 754option and the 755.Cm ForwardX11Trusted 756directive in 757.Xr ssh_config 5 758for more information. 759.Pp 760.It Fl x 761Disables X11 forwarding. 762.Pp 763.It Fl Y 764Enables trusted X11 forwarding. 765Trusted X11 forwardings are not subjected to the X11 SECURITY extension 766controls. 767.Pp 768.It Fl y 769Send log information using the 770.Xr syslog 3 771system module. 772By default this information is sent to stderr. 773.El 774.Pp 775.Nm 776may additionally obtain configuration data from 777a per-user configuration file and a system-wide configuration file. 778The file format and configuration options are described in 779.Xr ssh_config 5 . 780.Sh AUTHENTICATION 781The OpenSSH SSH client supports SSH protocols 1 and 2. 782The default is to use protocol 2 only, 783though this can be changed via the 784.Cm Protocol 785option in 786.Xr ssh_config 5 787or the 788.Fl 1 789and 790.Fl 2 791options (see above). 792Both protocols support similar authentication methods, 793but protocol 2 is the default since 794it provides additional mechanisms for confidentiality 795(the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) 796and integrity (hmac-md5, hmac-sha1, 797hmac-sha2-256, hmac-sha2-512, 798umac-64, umac-128, hmac-ripemd160). 799Protocol 1 lacks a strong mechanism for ensuring the 800integrity of the connection. 801.Pp 802The methods available for authentication are: 803GSSAPI-based authentication, 804host-based authentication, 805public key authentication, 806challenge-response authentication, 807and password authentication. 808Authentication methods are tried in the order specified above, 809though protocol 2 has a configuration option to change the default order: 810.Cm PreferredAuthentications . 811.Pp 812Host-based authentication works as follows: 813If the machine the user logs in from is listed in 814.Pa /etc/hosts.equiv 815or 816.Pa /etc/shosts.equiv 817on the remote machine, and the user names are 818the same on both sides, or if the files 819.Pa ~/.rhosts 820or 821.Pa ~/.shosts 822exist in the user's home directory on the 823remote machine and contain a line containing the name of the client 824machine and the name of the user on that machine, the user is 825considered for login. 826Additionally, the server 827.Em must 828be able to verify the client's 829host key (see the description of 830.Pa /etc/ssh/ssh_known_hosts 831and 832.Pa ~/.ssh/known_hosts , 833below) 834for login to be permitted. 835This authentication method closes security holes due to IP 836spoofing, DNS spoofing, and routing spoofing. 837[Note to the administrator: 838.Pa /etc/hosts.equiv , 839.Pa ~/.rhosts , 840and the rlogin/rsh protocol in general, are inherently insecure and should be 841disabled if security is desired.] 842.Pp 843Public key authentication works as follows: 844The scheme is based on public-key cryptography, 845using cryptosystems 846where encryption and decryption are done using separate keys, 847and it is unfeasible to derive the decryption key from the encryption key. 848The idea is that each user creates a public/private 849key pair for authentication purposes. 850The server knows the public key, and only the user knows the private key. 851.Nm 852implements public key authentication protocol automatically, 853using one of the DSA, ECDSA, Ed25519 or RSA algorithms. 854Protocol 1 is restricted to using only RSA keys, 855but protocol 2 may use any. 856The HISTORY section of 857.Xr ssl 8 858contains a brief discussion of the DSA and RSA algorithms. 859.Pp 860The file 861.Pa ~/.ssh/authorized_keys 862lists the public keys that are permitted for logging in. 863When the user logs in, the 864.Nm 865program tells the server which key pair it would like to use for 866authentication. 867The client proves that it has access to the private key 868and the server checks that the corresponding public key 869is authorized to accept the account. 870.Pp 871The user creates his/her key pair by running 872.Xr ssh-keygen 1 . 873This stores the private key in 874.Pa ~/.ssh/identity 875(protocol 1), 876.Pa ~/.ssh/id_dsa 877(protocol 2 DSA), 878.Pa ~/.ssh/id_ecdsa 879(protocol 2 ECDSA), 880.Pa ~/.ssh/id_ed25519 881(protocol 2 Ed25519), 882or 883.Pa ~/.ssh/id_rsa 884(protocol 2 RSA) 885and stores the public key in 886.Pa ~/.ssh/identity.pub 887(protocol 1), 888.Pa ~/.ssh/id_dsa.pub 889(protocol 2 DSA), 890.Pa ~/.ssh/id_ecdsa.pub 891(protocol 2 ECDSA), 892.Pa ~/.ssh/id_ed25519.pub 893(protocol 2 Ed25519), 894or 895.Pa ~/.ssh/id_rsa.pub 896(protocol 2 RSA) 897in the user's home directory. 898The user should then copy the public key 899to 900.Pa ~/.ssh/authorized_keys 901in his/her home directory on the remote machine. 902The 903.Pa authorized_keys 904file corresponds to the conventional 905.Pa ~/.rhosts 906file, and has one key 907per line, though the lines can be very long. 908After this, the user can log in without giving the password. 909.Pp 910A variation on public key authentication 911is available in the form of certificate authentication: 912instead of a set of public/private keys, 913signed certificates are used. 914This has the advantage that a single trusted certification authority 915can be used in place of many public/private keys. 916See the CERTIFICATES section of 917.Xr ssh-keygen 1 918for more information. 919.Pp 920The most convenient way to use public key or certificate authentication 921may be with an authentication agent. 922See 923.Xr ssh-agent 1 924for more information. 925.Pp 926Challenge-response authentication works as follows: 927The server sends an arbitrary 928.Qq challenge 929text, and prompts for a response. 930Protocol 2 allows multiple challenges and responses; 931protocol 1 is restricted to just one challenge/response. 932Examples of challenge-response authentication include 933.Bx 934Authentication (see 935.Xr login.conf 5 ) 936and PAM (some 937.Pf non- Ox 938systems). 939.Pp 940Finally, if other authentication methods fail, 941.Nm 942prompts the user for a password. 943The password is sent to the remote 944host for checking; however, since all communications are encrypted, 945the password cannot be seen by someone listening on the network. 946.Pp 947.Nm 948automatically maintains and checks a database containing 949identification for all hosts it has ever been used with. 950Host keys are stored in 951.Pa ~/.ssh/known_hosts 952in the user's home directory. 953Additionally, the file 954.Pa /etc/ssh/ssh_known_hosts 955is automatically checked for known hosts. 956Any new hosts are automatically added to the user's file. 957If a host's identification ever changes, 958.Nm 959warns about this and disables password authentication to prevent 960server spoofing or man-in-the-middle attacks, 961which could otherwise be used to circumvent the encryption. 962The 963.Cm StrictHostKeyChecking 964option can be used to control logins to machines whose 965host key is not known or has changed. 966.Pp 967When the user's identity has been accepted by the server, the server 968either executes the given command in a non-interactive session or, 969if no command has been specified, logs into the machine and gives 970the user a normal shell as an interactive session. 971All communication with 972the remote command or shell will be automatically encrypted. 973.Pp 974If an interactive session is requested 975.Nm 976by default will only request a pseudo-terminal (pty) for interactive 977sessions when the client has one. 978The flags 979.Fl T 980and 981.Fl t 982can be used to override this behaviour. 983.Pp 984If a pseudo-terminal has been allocated the 985user may use the escape characters noted below. 986.Pp 987If no pseudo-terminal has been allocated, 988the session is transparent and can be used to reliably transfer binary data. 989On most systems, setting the escape character to 990.Dq none 991will also make the session transparent even if a tty is used. 992.Pp 993The session terminates when the command or shell on the remote 994machine exits and all X11 and TCP connections have been closed. 995.Sh ESCAPE CHARACTERS 996When a pseudo-terminal has been requested, 997.Nm 998supports a number of functions through the use of an escape character. 999.Pp 1000A single tilde character can be sent as 1001.Ic ~~ 1002or by following the tilde by a character other than those described below. 1003The escape character must always follow a newline to be interpreted as 1004special. 1005The escape character can be changed in configuration files using the 1006.Cm EscapeChar 1007configuration directive or on the command line by the 1008.Fl e 1009option. 1010.Pp 1011The supported escapes (assuming the default 1012.Ql ~ ) 1013are: 1014.Bl -tag -width Ds 1015.It Cm ~. 1016Disconnect. 1017.It Cm ~^Z 1018Background 1019.Nm . 1020.It Cm ~# 1021List forwarded connections. 1022.It Cm ~& 1023Background 1024.Nm 1025at logout when waiting for forwarded connection / X11 sessions to terminate. 1026.It Cm ~? 1027Display a list of escape characters. 1028.It Cm ~B 1029Send a BREAK to the remote system 1030(only useful for SSH protocol version 2 and if the peer supports it). 1031.It Cm ~C 1032Open command line. 1033Currently this allows the addition of port forwardings using the 1034.Fl L , 1035.Fl R 1036and 1037.Fl D 1038options (see above). 1039It also allows the cancellation of existing port-forwardings 1040with 1041.Sm off 1042.Fl KL Oo Ar bind_address : Oc Ar port 1043.Sm on 1044for local, 1045.Sm off 1046.Fl KR Oo Ar bind_address : Oc Ar port 1047.Sm on 1048for remote and 1049.Sm off 1050.Fl KD Oo Ar bind_address : Oc Ar port 1051.Sm on 1052for dynamic port-forwardings. 1053.Ic !\& Ns Ar command 1054allows the user to execute a local command if the 1055.Ic PermitLocalCommand 1056option is enabled in 1057.Xr ssh_config 5 . 1058Basic help is available, using the 1059.Fl h 1060option. 1061.It Cm ~R 1062Request rekeying of the connection 1063(only useful for SSH protocol version 2 and if the peer supports it). 1064.It Cm ~V 1065Decrease the verbosity 1066.Pq Ic LogLevel 1067when errors are being written to stderr. 1068.It Cm ~v 1069Increase the verbosity 1070.Pq Ic LogLevel 1071when errors are being written to stderr. 1072.El 1073.Sh TCP FORWARDING 1074Forwarding of arbitrary TCP connections over the secure channel can 1075be specified either on the command line or in a configuration file. 1076One possible application of TCP forwarding is a secure connection to a 1077mail server; another is going through firewalls. 1078.Pp 1079In the example below, we look at encrypting communication between 1080an IRC client and server, even though the IRC server does not directly 1081support encrypted communications. 1082This works as follows: 1083the user connects to the remote host using 1084.Nm , 1085specifying a port to be used to forward connections 1086to the remote server. 1087After that it is possible to start the service which is to be encrypted 1088on the client machine, 1089connecting to the same local port, 1090and 1091.Nm 1092will encrypt and forward the connection. 1093.Pp 1094The following example tunnels an IRC session from client machine 1095.Dq 127.0.0.1 1096(localhost) 1097to remote server 1098.Dq server.example.com : 1099.Bd -literal -offset 4n 1100$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 1101$ irc -c '#users' -p 1234 pinky 127.0.0.1 1102.Ed 1103.Pp 1104This tunnels a connection to IRC server 1105.Dq server.example.com , 1106joining channel 1107.Dq #users , 1108nickname 1109.Dq pinky , 1110using port 1234. 1111It doesn't matter which port is used, 1112as long as it's greater than 1023 1113(remember, only root can open sockets on privileged ports) 1114and doesn't conflict with any ports already in use. 1115The connection is forwarded to port 6667 on the remote server, 1116since that's the standard port for IRC services. 1117.Pp 1118The 1119.Fl f 1120option backgrounds 1121.Nm 1122and the remote command 1123.Dq sleep 10 1124is specified to allow an amount of time 1125(10 seconds, in the example) 1126to start the service which is to be tunnelled. 1127If no connections are made within the time specified, 1128.Nm 1129will exit. 1130.Sh X11 FORWARDING 1131If the 1132.Cm ForwardX11 1133variable is set to 1134.Dq yes 1135(or see the description of the 1136.Fl X , 1137.Fl x , 1138and 1139.Fl Y 1140options above) 1141and the user is using X11 (the 1142.Ev DISPLAY 1143environment variable is set), the connection to the X11 display is 1144automatically forwarded to the remote side in such a way that any X11 1145programs started from the shell (or command) will go through the 1146encrypted channel, and the connection to the real X server will be made 1147from the local machine. 1148The user should not manually set 1149.Ev DISPLAY . 1150Forwarding of X11 connections can be 1151configured on the command line or in configuration files. 1152.Pp 1153The 1154.Ev DISPLAY 1155value set by 1156.Nm 1157will point to the server machine, but with a display number greater than zero. 1158This is normal, and happens because 1159.Nm 1160creates a 1161.Dq proxy 1162X server on the server machine for forwarding the 1163connections over the encrypted channel. 1164.Pp 1165.Nm 1166will also automatically set up Xauthority data on the server machine. 1167For this purpose, it will generate a random authorization cookie, 1168store it in Xauthority on the server, and verify that any forwarded 1169connections carry this cookie and replace it by the real cookie when 1170the connection is opened. 1171The real authentication cookie is never 1172sent to the server machine (and no cookies are sent in the plain). 1173.Pp 1174If the 1175.Cm ForwardAgent 1176variable is set to 1177.Dq yes 1178(or see the description of the 1179.Fl A 1180and 1181.Fl a 1182options above) and 1183the user is using an authentication agent, the connection to the agent 1184is automatically forwarded to the remote side. 1185.Sh VERIFYING HOST KEYS 1186When connecting to a server for the first time, 1187a fingerprint of the server's public key is presented to the user 1188(unless the option 1189.Cm StrictHostKeyChecking 1190has been disabled). 1191Fingerprints can be determined using 1192.Xr ssh-keygen 1 : 1193.Pp 1194.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key 1195.Pp 1196If the fingerprint is already known, it can be matched 1197and the key can be accepted or rejected. 1198If only legacy (MD5) fingerprints for the server are available, the 1199.Xr ssh-keygen 1 1200.Fl E 1201option may be used to downgrade the fingerprint algorithm to match. 1202.Pp 1203Because of the difficulty of comparing host keys 1204just by looking at fingerprint strings, 1205there is also support to compare host keys visually, 1206using 1207.Em random art . 1208By setting the 1209.Cm VisualHostKey 1210option to 1211.Dq yes , 1212a small ASCII graphic gets displayed on every login to a server, no matter 1213if the session itself is interactive or not. 1214By learning the pattern a known server produces, a user can easily 1215find out that the host key has changed when a completely different pattern 1216is displayed. 1217Because these patterns are not unambiguous however, a pattern that looks 1218similar to the pattern remembered only gives a good probability that the 1219host key is the same, not guaranteed proof. 1220.Pp 1221To get a listing of the fingerprints along with their random art for 1222all known hosts, the following command line can be used: 1223.Pp 1224.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts 1225.Pp 1226If the fingerprint is unknown, 1227an alternative method of verification is available: 1228SSH fingerprints verified by DNS. 1229An additional resource record (RR), 1230SSHFP, 1231is added to a zonefile 1232and the connecting client is able to match the fingerprint 1233with that of the key presented. 1234.Pp 1235In this example, we are connecting a client to a server, 1236.Dq host.example.com . 1237The SSHFP resource records should first be added to the zonefile for 1238host.example.com: 1239.Bd -literal -offset indent 1240$ ssh-keygen -r host.example.com. 1241.Ed 1242.Pp 1243The output lines will have to be added to the zonefile. 1244To check that the zone is answering fingerprint queries: 1245.Pp 1246.Dl $ dig -t SSHFP host.example.com 1247.Pp 1248Finally the client connects: 1249.Bd -literal -offset indent 1250$ ssh -o "VerifyHostKeyDNS ask" host.example.com 1251[...] 1252Matching host key fingerprint found in DNS. 1253Are you sure you want to continue connecting (yes/no)? 1254.Ed 1255.Pp 1256See the 1257.Cm VerifyHostKeyDNS 1258option in 1259.Xr ssh_config 5 1260for more information. 1261.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS 1262.Nm 1263contains support for Virtual Private Network (VPN) tunnelling 1264using the 1265.Xr tun 4 1266network pseudo-device, 1267allowing two networks to be joined securely. 1268The 1269.Xr sshd_config 5 1270configuration option 1271.Cm PermitTunnel 1272controls whether the server supports this, 1273and at what level (layer 2 or 3 traffic). 1274.Pp 1275The following example would connect client network 10.0.50.0/24 1276with remote network 10.0.99.0/24 using a point-to-point connection 1277from 10.1.1.1 to 10.1.1.2, 1278provided that the SSH server running on the gateway to the remote network, 1279at 192.168.1.15, allows it. 1280.Pp 1281On the client: 1282.Bd -literal -offset indent 1283# ssh -f -w 0:1 192.168.1.15 true 1284# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252 1285# route add 10.0.99.0/24 10.1.1.2 1286.Ed 1287.Pp 1288On the server: 1289.Bd -literal -offset indent 1290# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252 1291# route add 10.0.50.0/24 10.1.1.1 1292.Ed 1293.Pp 1294Client access may be more finely tuned via the 1295.Pa /root/.ssh/authorized_keys 1296file (see below) and the 1297.Cm PermitRootLogin 1298server option. 1299The following entry would permit connections on 1300.Xr tun 4 1301device 1 from user 1302.Dq jane 1303and on tun device 2 from user 1304.Dq john , 1305if 1306.Cm PermitRootLogin 1307is set to 1308.Dq forced-commands-only : 1309.Bd -literal -offset 2n 1310tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane 1311tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john 1312.Ed 1313.Pp 1314Since an SSH-based setup entails a fair amount of overhead, 1315it may be more suited to temporary setups, 1316such as for wireless VPNs. 1317More permanent VPNs are better provided by tools such as 1318.Xr ipsecctl 8 1319and 1320.Xr isakmpd 8 . 1321.Sh ENVIRONMENT 1322.Nm 1323will normally set the following environment variables: 1324.Bl -tag -width "SSH_ORIGINAL_COMMAND" 1325.It Ev DISPLAY 1326The 1327.Ev DISPLAY 1328variable indicates the location of the X11 server. 1329It is automatically set by 1330.Nm 1331to point to a value of the form 1332.Dq hostname:n , 1333where 1334.Dq hostname 1335indicates the host where the shell runs, and 1336.Sq n 1337is an integer \*(Ge 1. 1338.Nm 1339uses this special value to forward X11 connections over the secure 1340channel. 1341The user should normally not set 1342.Ev DISPLAY 1343explicitly, as that 1344will render the X11 connection insecure (and will require the user to 1345manually copy any required authorization cookies). 1346.It Ev HOME 1347Set to the path of the user's home directory. 1348.It Ev LOGNAME 1349Synonym for 1350.Ev USER ; 1351set for compatibility with systems that use this variable. 1352.It Ev MAIL 1353Set to the path of the user's mailbox. 1354.It Ev PATH 1355Set to the default 1356.Ev PATH , 1357as specified when compiling 1358.Nm . 1359.It Ev SSH_ASKPASS 1360If 1361.Nm 1362needs a passphrase, it will read the passphrase from the current 1363terminal if it was run from a terminal. 1364If 1365.Nm 1366does not have a terminal associated with it but 1367.Ev DISPLAY 1368and 1369.Ev SSH_ASKPASS 1370are set, it will execute the program specified by 1371.Ev SSH_ASKPASS 1372and open an X11 window to read the passphrase. 1373This is particularly useful when calling 1374.Nm 1375from a 1376.Pa .xsession 1377or related script. 1378(Note that on some machines it 1379may be necessary to redirect the input from 1380.Pa /dev/null 1381to make this work.) 1382.It Ev SSH_AUTH_SOCK 1383Identifies the path of a 1384.Ux Ns -domain 1385socket used to communicate with the agent. 1386.It Ev SSH_CONNECTION 1387Identifies the client and server ends of the connection. 1388The variable contains 1389four space-separated values: client IP address, client port number, 1390server IP address, and server port number. 1391.It Ev SSH_ORIGINAL_COMMAND 1392This variable contains the original command line if a forced command 1393is executed. 1394It can be used to extract the original arguments. 1395.It Ev SSH_TTY 1396This is set to the name of the tty (path to the device) associated 1397with the current shell or command. 1398If the current session has no tty, 1399this variable is not set. 1400.It Ev TZ 1401This variable is set to indicate the present time zone if it 1402was set when the daemon was started (i.e. the daemon passes the value 1403on to new connections). 1404.It Ev USER 1405Set to the name of the user logging in. 1406.El 1407.Pp 1408Additionally, 1409.Nm 1410reads 1411.Pa ~/.ssh/environment , 1412and adds lines of the format 1413.Dq VARNAME=value 1414to the environment if the file exists and users are allowed to 1415change their environment. 1416For more information, see the 1417.Cm PermitUserEnvironment 1418option in 1419.Xr sshd_config 5 . 1420.Sh FILES 1421.Bl -tag -width Ds -compact 1422.It Pa ~/.rhosts 1423This file is used for host-based authentication (see above). 1424On some machines this file may need to be 1425world-readable if the user's home directory is on an NFS partition, 1426because 1427.Xr sshd 8 1428reads it as root. 1429Additionally, this file must be owned by the user, 1430and must not have write permissions for anyone else. 1431The recommended 1432permission for most machines is read/write for the user, and not 1433accessible by others. 1434.Pp 1435.It Pa ~/.shosts 1436This file is used in exactly the same way as 1437.Pa .rhosts , 1438but allows host-based authentication without permitting login with 1439rlogin/rsh. 1440.Pp 1441.It Pa ~/.ssh/ 1442This directory is the default location for all user-specific configuration 1443and authentication information. 1444There is no general requirement to keep the entire contents of this directory 1445secret, but the recommended permissions are read/write/execute for the user, 1446and not accessible by others. 1447.Pp 1448.It Pa ~/.ssh/authorized_keys 1449Lists the public keys (DSA, ECDSA, Ed25519, RSA) 1450that can be used for logging in as this user. 1451The format of this file is described in the 1452.Xr sshd 8 1453manual page. 1454This file is not highly sensitive, but the recommended 1455permissions are read/write for the user, and not accessible by others. 1456.Pp 1457.It Pa ~/.ssh/config 1458This is the per-user configuration file. 1459The file format and configuration options are described in 1460.Xr ssh_config 5 . 1461Because of the potential for abuse, this file must have strict permissions: 1462read/write for the user, and not writable by others. 1463.Pp 1464.It Pa ~/.ssh/environment 1465Contains additional definitions for environment variables; see 1466.Sx ENVIRONMENT , 1467above. 1468.Pp 1469.It Pa ~/.ssh/identity 1470.It Pa ~/.ssh/id_dsa 1471.It Pa ~/.ssh/id_ecdsa 1472.It Pa ~/.ssh/id_ed25519 1473.It Pa ~/.ssh/id_rsa 1474Contains the private key for authentication. 1475These files 1476contain sensitive data and should be readable by the user but not 1477accessible by others (read/write/execute). 1478.Nm 1479will simply ignore a private key file if it is accessible by others. 1480It is possible to specify a passphrase when 1481generating the key which will be used to encrypt the 1482sensitive part of this file using 3DES. 1483.Pp 1484.It Pa ~/.ssh/identity.pub 1485.It Pa ~/.ssh/id_dsa.pub 1486.It Pa ~/.ssh/id_ecdsa.pub 1487.It Pa ~/.ssh/id_ed25519.pub 1488.It Pa ~/.ssh/id_rsa.pub 1489Contains the public key for authentication. 1490These files are not 1491sensitive and can (but need not) be readable by anyone. 1492.Pp 1493.It Pa ~/.ssh/known_hosts 1494Contains a list of host keys for all hosts the user has logged into 1495that are not already in the systemwide list of known host keys. 1496See 1497.Xr sshd 8 1498for further details of the format of this file. 1499.Pp 1500.It Pa ~/.ssh/rc 1501Commands in this file are executed by 1502.Nm 1503when the user logs in, just before the user's shell (or command) is 1504started. 1505See the 1506.Xr sshd 8 1507manual page for more information. 1508.Pp 1509.It Pa /etc/hosts.equiv 1510This file is for host-based authentication (see above). 1511It should only be writable by root. 1512.Pp 1513.It Pa /etc/shosts.equiv 1514This file is used in exactly the same way as 1515.Pa hosts.equiv , 1516but allows host-based authentication without permitting login with 1517rlogin/rsh. 1518.Pp 1519.It Pa /etc/ssh/ssh_config 1520Systemwide configuration file. 1521The file format and configuration options are described in 1522.Xr ssh_config 5 . 1523.Pp 1524.It Pa /etc/ssh/ssh_host_key 1525.It Pa /etc/ssh/ssh_host_dsa_key 1526.It Pa /etc/ssh/ssh_host_ecdsa_key 1527.It Pa /etc/ssh/ssh_host_ed25519_key 1528.It Pa /etc/ssh/ssh_host_rsa_key 1529These files contain the private parts of the host keys 1530and are used for host-based authentication. 1531If protocol version 1 is used, 1532.Nm 1533must be setuid root, since the host key is readable only by root. 1534For protocol version 2, 1535.Nm 1536uses 1537.Xr ssh-keysign 8 1538to access the host keys, 1539eliminating the requirement that 1540.Nm 1541be setuid root when host-based authentication is used. 1542By default 1543.Nm 1544is not setuid root. 1545.Pp 1546.It Pa /etc/ssh/ssh_known_hosts 1547Systemwide list of known host keys. 1548This file should be prepared by the 1549system administrator to contain the public host keys of all machines in the 1550organization. 1551It should be world-readable. 1552See 1553.Xr sshd 8 1554for further details of the format of this file. 1555.Pp 1556.It Pa /etc/ssh/sshrc 1557Commands in this file are executed by 1558.Nm 1559when the user logs in, just before the user's shell (or command) is started. 1560See the 1561.Xr sshd 8 1562manual page for more information. 1563.El 1564.Sh EXIT STATUS 1565.Nm 1566exits with the exit status of the remote command or with 255 1567if an error occurred. 1568.Sh SEE ALSO 1569.Xr scp 1 , 1570.Xr sftp 1 , 1571.Xr ssh-add 1 , 1572.Xr ssh-agent 1 , 1573.Xr ssh-keygen 1 , 1574.Xr ssh-keyscan 1 , 1575.Xr tun 4 , 1576.Xr ssh_config 5 , 1577.Xr ssh-keysign 8 , 1578.Xr sshd 8 1579.Sh STANDARDS 1580.Rs 1581.%A S. Lehtinen 1582.%A C. Lonvick 1583.%D January 2006 1584.%R RFC 4250 1585.%T The Secure Shell (SSH) Protocol Assigned Numbers 1586.Re 1587.Pp 1588.Rs 1589.%A T. Ylonen 1590.%A C. Lonvick 1591.%D January 2006 1592.%R RFC 4251 1593.%T The Secure Shell (SSH) Protocol Architecture 1594.Re 1595.Pp 1596.Rs 1597.%A T. Ylonen 1598.%A C. Lonvick 1599.%D January 2006 1600.%R RFC 4252 1601.%T The Secure Shell (SSH) Authentication Protocol 1602.Re 1603.Pp 1604.Rs 1605.%A T. Ylonen 1606.%A C. Lonvick 1607.%D January 2006 1608.%R RFC 4253 1609.%T The Secure Shell (SSH) Transport Layer Protocol 1610.Re 1611.Pp 1612.Rs 1613.%A T. Ylonen 1614.%A C. Lonvick 1615.%D January 2006 1616.%R RFC 4254 1617.%T The Secure Shell (SSH) Connection Protocol 1618.Re 1619.Pp 1620.Rs 1621.%A J. Schlyter 1622.%A W. Griffin 1623.%D January 2006 1624.%R RFC 4255 1625.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints 1626.Re 1627.Pp 1628.Rs 1629.%A F. Cusack 1630.%A M. Forssen 1631.%D January 2006 1632.%R RFC 4256 1633.%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH) 1634.Re 1635.Pp 1636.Rs 1637.%A J. Galbraith 1638.%A P. Remaker 1639.%D January 2006 1640.%R RFC 4335 1641.%T The Secure Shell (SSH) Session Channel Break Extension 1642.Re 1643.Pp 1644.Rs 1645.%A M. Bellare 1646.%A T. Kohno 1647.%A C. Namprempre 1648.%D January 2006 1649.%R RFC 4344 1650.%T The Secure Shell (SSH) Transport Layer Encryption Modes 1651.Re 1652.Pp 1653.Rs 1654.%A B. Harris 1655.%D January 2006 1656.%R RFC 4345 1657.%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol 1658.Re 1659.Pp 1660.Rs 1661.%A M. Friedl 1662.%A N. Provos 1663.%A W. Simpson 1664.%D March 2006 1665.%R RFC 4419 1666.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol 1667.Re 1668.Pp 1669.Rs 1670.%A J. Galbraith 1671.%A R. Thayer 1672.%D November 2006 1673.%R RFC 4716 1674.%T The Secure Shell (SSH) Public Key File Format 1675.Re 1676.Pp 1677.Rs 1678.%A D. Stebila 1679.%A J. Green 1680.%D December 2009 1681.%R RFC 5656 1682.%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer 1683.Re 1684.Pp 1685.Rs 1686.%A A. Perrig 1687.%A D. Song 1688.%D 1999 1689.%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99) 1690.%T Hash Visualization: a New Technique to improve Real-World Security 1691.Re 1692.Sh AUTHORS 1693OpenSSH is a derivative of the original and free 1694ssh 1.2.12 release by Tatu Ylonen. 1695Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 1696Theo de Raadt and Dug Song 1697removed many bugs, re-added newer features and 1698created OpenSSH. 1699Markus Friedl contributed the support for SSH 1700protocol versions 1.5 and 2.0. 1701