1.\" $NetBSD: ssh.1,v 1.22 2018/04/06 18:59:00 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 1.391 2018/02/23 07:38:09 jmc Exp $ 39.Dd February 23 2018 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.Op Fl 46AaCfGgKkMNnqsTtVvXxYy 48.Op Fl B Ar bind_interface 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 J Ar destination 58.Op Fl L Ar address 59.Op Fl l Ar login_name 60.Op Fl m Ar mac_spec 61.Op Fl O Ar ctl_cmd 62.Op Fl o Ar option 63.Op Fl p Ar port 64.Op Fl Q Ar query_option 65.Op Fl R Ar address 66.Op Fl S Ar ctl_path 67.Op Fl W Ar host : Ns Ar port 68.Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun 69.Ar destination 70.Op Ar command 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 provide secure encrypted communications between 76two untrusted hosts over an insecure network. 77X11 connections, arbitrary TCP ports and 78.Ux Ns -domain 79sockets can also be forwarded over the secure channel. 80.Pp 81.Nm 82connects and logs into the specified 83.Ar destination , 84which may be specified as either 85.Sm off 86.Oo user @ Oc hostname 87.Sm on 88or a URI of the form 89.Sm off 90.No ssh:// Oo user @ Oc hostname Op : port . 91.Sm on 92The user must prove 93his/her identity to the remote machine using one of several methods 94(see below). 95.Pp 96If a 97.Ar command 98is specified, 99it is executed on the remote host instead of a login shell. 100.Pp 101The options are as follows: 102.Pp 103.Bl -tag -width Ds -compact 104.It Fl 4 105Forces 106.Nm 107to use IPv4 addresses only. 108.Pp 109.It Fl 6 110Forces 111.Nm 112to use IPv6 addresses only. 113.Pp 114.It Fl A 115Enables forwarding of the authentication agent connection. 116This can also be specified on a per-host basis in a configuration file. 117.Pp 118Agent forwarding should be enabled with caution. 119Users with the ability to bypass file permissions on the remote host 120(for the agent's 121.Ux Ns -domain 122socket) can access the local agent through the forwarded connection. 123An attacker cannot obtain key material from the agent, 124however they can perform operations on the keys that enable them to 125authenticate using the identities loaded into the agent. 126.Pp 127.It Fl a 128Disables forwarding of the authentication agent connection. 129.Pp 130.It Fl B Ar bind_interface 131Bind to the address of 132.Ar bind_interface 133before attempting to connect to the destination host. 134This is only useful on systems with more than one address. 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 . 150Compression is desirable on modem lines and other 151slow connections, but will only slow down things on fast networks. 152The default value can be set on a host-by-host basis in the 153configuration files; see the 154.Cm Compression 155option. 156.Pp 157.It Fl c Ar cipher_spec 158Selects the cipher specification for encrypting the session. 159.Ar cipher_spec 160is a comma-separated list of ciphers 161listed in order of preference. 162See the 163.Cm Ciphers 164keyword in 165.Xr ssh_config 5 166for more information. 167.Pp 168.It Fl D Xo 169.Sm off 170.Oo Ar bind_address : Oc 171.Ar port 172.Sm on 173.Xc 174Specifies a local 175.Dq dynamic 176application-level port forwarding. 177This works by allocating a socket to listen to 178.Ar port 179on the local side, optionally bound to the specified 180.Ar bind_address . 181Whenever a connection is made to this port, the 182connection is forwarded over the secure channel, and the application 183protocol is then used to determine where to connect to from the 184remote machine. 185Currently the SOCKS4 and SOCKS5 protocols are supported, and 186.Nm 187will act as a SOCKS server. 188Only root can forward privileged ports. 189Dynamic port forwardings can also be specified in the configuration file. 190.Pp 191IPv6 addresses can be specified by enclosing the address in square brackets. 192Only the superuser can forward privileged ports. 193By default, the local port is bound in accordance with the 194.Cm GatewayPorts 195setting. 196However, an explicit 197.Ar bind_address 198may be used to bind the connection to a specific address. 199The 200.Ar bind_address 201of 202.Dq localhost 203indicates that the listening port be bound for local use only, while an 204empty address or 205.Sq * 206indicates that the port should be available from all interfaces. 207.Pp 208.It Fl E Ar log_file 209Append debug logs to 210.Ar log_file 211instead of standard error. 212.Pp 213.It Fl e Ar escape_char 214Sets the escape character for sessions with a pty (default: 215.Ql ~ ) . 216The escape character is only recognized at the beginning of a line. 217The escape character followed by a dot 218.Pq Ql \&. 219closes the connection; 220followed by control-Z suspends the connection; 221and followed by itself sends the escape character once. 222Setting the character to 223.Dq none 224disables any escapes and makes the session fully transparent. 225.Pp 226.It Fl F Ar configfile 227Specifies an alternative per-user configuration file. 228If a configuration file is given on the command line, 229the system-wide configuration file 230.Pq Pa /etc/ssh/ssh_config 231will be ignored. 232The default for the per-user configuration file is 233.Pa ~/.ssh/config . 234.Pp 235.It Fl f 236Requests 237.Nm 238to go to background just before command execution. 239This is useful if 240.Nm 241is going to ask for passwords or passphrases, but the user 242wants it in the background. 243This implies 244.Fl n . 245The recommended way to start X11 programs at a remote site is with 246something like 247.Ic ssh -f host xterm . 248.Pp 249If the 250.Cm ExitOnForwardFailure 251configuration option is set to 252.Dq yes , 253then a client started with 254.Fl f 255will wait for all remote port forwards to be successfully established 256before placing itself in the background. 257.Pp 258.It Fl G 259Causes 260.Nm 261to print its configuration after evaluating 262.Cm Host 263and 264.Cm Match 265blocks and exit. 266.Pp 267.It Fl g 268Allows remote hosts to connect to local forwarded ports. 269If used on a multiplexed connection, then this option must be specified 270on the master process. 271.Pp 272.It Fl I Ar pkcs11 273Specify the PKCS#11 shared library 274.Nm 275should use to communicate with a PKCS#11 token providing the user's 276private RSA key. 277.Pp 278.It Fl i Ar identity_file 279Selects a file from which the identity (private key) for 280public key authentication is read. 281The default is 282.Pa ~/.ssh/id_dsa , 283.Pa ~/.ssh/id_ecdsa , 284.Pa ~/.ssh/id_ed25519 285and 286.Pa ~/.ssh/id_rsa . 287Identity files may also be specified on 288a per-host basis in the configuration file. 289It is possible to have multiple 290.Fl i 291options (and multiple identities specified in 292configuration files). 293If no certificates have been explicitly specified by the 294.Cm CertificateFile 295directive, 296.Nm 297will also try to load certificate information from the filename obtained 298by appending 299.Pa -cert.pub 300to identity filenames. 301.Pp 302.It Fl J Ar destination 303Connect to the target host by first making a 304.Nm 305connection to the jump host described by 306.Ar destination 307and then establishing a TCP forwarding to the ultimate destination from 308there. 309Multiple jump hops may be specified separated by comma characters. 310This is a shortcut to specify a 311.Cm ProxyJump 312configuration directive. 313.Pp 314.It Fl K 315Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI 316credentials to the server. 317.Pp 318.It Fl k 319Disables forwarding (delegation) of GSSAPI credentials to the server. 320.Pp 321.It Fl L Xo 322.Sm off 323.Oo Ar bind_address : Oc 324.Ar port : host : hostport 325.Sm on 326.Xc 327.It Fl L Xo 328.Sm off 329.Oo Ar bind_address : Oc 330.Ar port : remote_socket 331.Sm on 332.Xc 333.It Fl L Xo 334.Sm off 335.Ar local_socket : host : hostport 336.Sm on 337.Xc 338.It Fl L Xo 339.Sm off 340.Ar local_socket : remote_socket 341.Sm on 342.Xc 343Specifies that connections to the given TCP port or Unix socket on the local 344(client) host are to be forwarded to the given host and port, or Unix socket, 345on the remote side. 346This works by allocating a socket to listen to either a TCP 347.Ar port 348on the local side, optionally bound to the specified 349.Ar bind_address , 350or to a Unix socket. 351Whenever a connection is made to the local port or socket, the 352connection is forwarded over the secure channel, and a connection is 353made to either 354.Ar host 355port 356.Ar hostport , 357or the Unix socket 358.Ar remote_socket , 359from the remote machine. 360.Pp 361Port forwardings can also be specified in the configuration file. 362Only the superuser can forward privileged ports. 363IPv6 addresses can be specified by enclosing the address in square brackets. 364.Pp 365By default, the local port is bound in accordance with the 366.Cm GatewayPorts 367setting. 368However, an explicit 369.Ar bind_address 370may be used to bind the connection to a specific address. 371The 372.Ar bind_address 373of 374.Dq localhost 375indicates that the listening port be bound for local use only, while an 376empty address or 377.Sq * 378indicates that the port should be available from all interfaces. 379.Pp 380.It Fl l Ar login_name 381Specifies the user to log in as on the remote machine. 382This also may be specified on a per-host basis in the configuration file. 383.Pp 384.It Fl M 385Places the 386.Nm 387client into 388.Dq master 389mode for connection sharing. 390Multiple 391.Fl M 392options places 393.Nm 394into 395.Dq master 396mode with confirmation required before slave connections are accepted. 397Refer to the description of 398.Cm ControlMaster 399in 400.Xr ssh_config 5 401for details. 402.Pp 403.It Fl m Ar mac_spec 404A comma-separated list of MAC (message authentication code) algorithms, 405specified in order of preference. 406See the 407.Cm MACs 408keyword for more information. 409.Pp 410.It Fl N 411Do not execute a remote command. 412This is useful for just forwarding ports. 413.Pp 414.It Fl n 415Redirects stdin from 416.Pa /dev/null 417(actually, prevents reading from stdin). 418This must be used when 419.Nm 420is run in the background. 421A common trick is to use this to run X11 programs on a remote machine. 422For example, 423.Ic ssh -n shadows.cs.hut.fi emacs & 424will start an emacs on shadows.cs.hut.fi, and the X11 425connection will be automatically forwarded over an encrypted channel. 426The 427.Nm 428program will be put in the background. 429(This does not work if 430.Nm 431needs to ask for a password or passphrase; see also the 432.Fl f 433option.) 434.Pp 435.It Fl O Ar ctl_cmd 436Control an active connection multiplexing master process. 437When the 438.Fl O 439option is specified, the 440.Ar ctl_cmd 441argument is interpreted and passed to the master process. 442Valid commands are: 443.Dq check 444(check that the master process is running), 445.Dq forward 446(request forwardings without command execution), 447.Dq cancel 448(cancel forwardings), 449.Dq exit 450(request the master to exit), and 451.Dq stop 452(request the master to stop accepting further multiplexing requests). 453.Pp 454.It Fl o Ar option 455Can be used to give options in the format used in the configuration file. 456This is useful for specifying options for which there is no separate 457command-line flag. 458For full details of the options listed below, and their possible values, see 459.Xr ssh_config 5 . 460.Pp 461.Bl -tag -width Ds -offset indent -compact 462.It AddKeysToAgent 463.It AddressFamily 464.It BatchMode 465.It BindAddress 466.It CanonicalDomains 467.It CanonicalizeFallbackLocal 468.It CanonicalizeHostname 469.It CanonicalizeMaxDots 470.It CanonicalizePermittedCNAMEs 471.It CertificateFile 472.It ChallengeResponseAuthentication 473.It CheckHostIP 474.It Ciphers 475.It ClearAllForwardings 476.It Compression 477.It ConnectionAttempts 478.It ConnectTimeout 479.It ControlMaster 480.It ControlPath 481.It ControlPersist 482.It DynamicForward 483.It EscapeChar 484.It ExitOnForwardFailure 485.It FingerprintHash 486.It ForwardAgent 487.It ForwardX11 488.It ForwardX11Timeout 489.It ForwardX11Trusted 490.It GatewayPorts 491.It GlobalKnownHostsFile 492.It GSSAPIAuthentication 493.It GSSAPIDelegateCredentials 494.It HashKnownHosts 495.It Host 496.It HostbasedAuthentication 497.It HostbasedKeyTypes 498.It HostKeyAlgorithms 499.It HostKeyAlias 500.It HostName 501.It IdentitiesOnly 502.It IdentityAgent 503.It IdentityFile 504.It Include 505.It IPQoS 506.It KbdInteractiveAuthentication 507.It KbdInteractiveDevices 508.It KexAlgorithms 509.It LocalCommand 510.It LocalForward 511.It LogLevel 512.It MACs 513.It Match 514.It NoHostAuthenticationForLocalhost 515.It NumberOfPasswordPrompts 516.It PasswordAuthentication 517.It PermitLocalCommand 518.It PKCS11Provider 519.It Port 520.It PreferredAuthentications 521.It ProxyCommand 522.It ProxyJump 523.It ProxyUseFdpass 524.It PubkeyAcceptedKeyTypes 525.It PubkeyAuthentication 526.It RekeyLimit 527.It RemoteCommand 528.It RemoteForward 529.It RequestTTY 530.It SendEnv 531.It ServerAliveInterval 532.It ServerAliveCountMax 533.It StreamLocalBindMask 534.It StreamLocalBindUnlink 535.It StrictHostKeyChecking 536.It TCPKeepAlive 537.It Tunnel 538.It TunnelDevice 539.It UpdateHostKeys 540.It UsePrivilegedPort 541.It User 542.It UserKnownHostsFile 543.It VerifyHostKeyDNS 544.It VisualHostKey 545.It XAuthLocation 546.El 547.Pp 548.It Fl p Ar port 549Port to connect to on the remote host. 550This can be specified on a 551per-host basis in the configuration file. 552.Pp 553.It Fl Q Ar query_option 554Queries 555.Nm 556for the algorithms supported for the specified version 2. 557The available features are: 558.Ar cipher 559(supported symmetric ciphers), 560.Ar cipher-auth 561(supported symmetric ciphers that support authenticated encryption), 562.Ar mac 563(supported message integrity codes), 564.Ar kex 565(key exchange algorithms), 566.Ar key 567(key types), 568.Ar key-cert 569(certificate key types), 570.Ar key-plain 571(non-certificate key types), and 572.Ar protocol-version 573(supported SSH protocol versions). 574.Pp 575.It Fl q 576Quiet mode. 577Causes most warning and diagnostic messages to be suppressed. 578.Pp 579.It Fl R Xo 580.Sm off 581.Oo Ar bind_address : Oc 582.Ar port : host : hostport 583.Sm on 584.Xc 585.It Fl R Xo 586.Sm off 587.Oo Ar bind_address : Oc 588.Ar port : local_socket 589.Sm on 590.Xc 591.It Fl R Xo 592.Sm off 593.Ar remote_socket : host : hostport 594.Sm on 595.Xc 596.It Fl R Xo 597.Sm off 598.Ar remote_socket : local_socket 599.Sm on 600.Xc 601.It Fl R Xo 602.Sm off 603.Oo Ar bind_address : Oc 604.Ar port 605.Sm on 606.Xc 607Specifies that connections to the given TCP port or Unix socket on the remote 608(server) host are to be forwarded to the local side. 609.Pp 610This works by allocating a socket to listen to either a TCP 611.Ar port 612or to a Unix socket on the remote side. 613Whenever a connection is made to this port or Unix socket, the 614connection is forwarded over the secure channel, and a connection 615is made from the local machine to either an explicit destination specified by 616.Ar host 617port 618.Ar hostport , 619or 620.Ar local_socket , 621or, if no explicit destination was specified, 622.Nm 623will act as a SOCKS 4/5 proxy and forward connections to the destinations 624requested by the remote SOCKS client. 625.Pp 626Port forwardings can also be specified in the configuration file. 627Privileged ports can be forwarded only when 628logging in as root on the remote machine. 629IPv6 addresses can be specified by enclosing the address in square brackets. 630.Pp 631By default, TCP listening sockets on the server will be bound to the loopback 632interface only. 633This may be overridden by specifying a 634.Ar bind_address . 635An empty 636.Ar bind_address , 637or the address 638.Ql * , 639indicates that the remote socket should listen on all interfaces. 640Specifying a remote 641.Ar bind_address 642will only succeed if the server's 643.Cm GatewayPorts 644option is enabled (see 645.Xr sshd_config 5 ) . 646.Pp 647If the 648.Ar port 649argument is 650.Ql 0 , 651the listen port will be dynamically allocated on the server and reported 652to the client at run time. 653When used together with 654.Ic -O forward 655the allocated port will be printed to the standard output. 656.Pp 657.It Fl S Ar ctl_path 658Specifies the location of a control socket for connection sharing, 659or the string 660.Dq none 661to disable connection sharing. 662Refer to the description of 663.Cm ControlPath 664and 665.Cm ControlMaster 666in 667.Xr ssh_config 5 668for details. 669.Pp 670.It Fl s 671May be used to request invocation of a subsystem on the remote system. 672Subsystems facilitate the use of SSH 673as a secure transport for other applications (e.g.\& 674.Xr sftp 1 ) . 675The subsystem is specified as the remote command. 676.Pp 677.It Fl T 678Disable pseudo-terminal allocation. 679.Pp 680.It Fl t 681Force pseudo-terminal allocation. 682This can be used to execute arbitrary 683screen-based programs on a remote machine, which can be very useful, 684e.g. when implementing menu services. 685Multiple 686.Fl t 687options force tty allocation, even if 688.Nm 689has no local tty. 690.Pp 691.It Fl V 692Display the version number and exit. 693.Pp 694.It Fl v 695Verbose mode. 696Causes 697.Nm 698to print debugging messages about its progress. 699This is helpful in 700debugging connection, authentication, and configuration problems. 701Multiple 702.Fl v 703options increase the verbosity. 704The maximum is 3. 705.Pp 706.It Fl W Ar host : Ns Ar port 707Requests that standard input and output on the client be forwarded to 708.Ar host 709on 710.Ar port 711over the secure channel. 712Implies 713.Fl N , 714.Fl T , 715.Cm ExitOnForwardFailure 716and 717.Cm ClearAllForwardings , 718though these can be overridden in the configuration file or using 719.Fl o 720command line options. 721.Pp 722.It Fl w Xo 723.Ar local_tun Ns Op : Ns Ar remote_tun 724.Xc 725Requests 726tunnel 727device forwarding with the specified 728.Xr tun 4 729devices between the client 730.Pq Ar local_tun 731and the server 732.Pq Ar remote_tun . 733.Pp 734The devices may be specified by numerical ID or the keyword 735.Dq any , 736which uses the next available tunnel device. 737If 738.Ar remote_tun 739is not specified, it defaults to 740.Dq any . 741See also the 742.Cm Tunnel 743and 744.Cm TunnelDevice 745directives in 746.Xr ssh_config 5 . 747If the 748.Cm Tunnel 749directive is unset, it is set to the default tunnel mode, which is 750.Dq point-to-point . 751.Pp 752.It Fl X 753Enables X11 forwarding. 754This can also be specified on a per-host basis in a configuration file. 755.Pp 756X11 forwarding should be enabled with caution. 757Users with the ability to bypass file permissions on the remote host 758(for the user's X authorization database) 759can access the local X11 display through the forwarded connection. 760An attacker may then be able to perform activities such as keystroke monitoring. 761.Pp 762For this reason, X11 forwarding is subjected to X11 SECURITY extension 763restrictions by default. 764Please refer to the 765.Nm 766.Fl Y 767option and the 768.Cm ForwardX11Trusted 769directive in 770.Xr ssh_config 5 771for more information. 772.Pp 773.It Fl x 774Disables X11 forwarding. 775.Pp 776.It Fl Y 777Enables trusted X11 forwarding. 778Trusted X11 forwardings are not subjected to the X11 SECURITY extension 779controls. 780.Pp 781.It Fl y 782Send log information using the 783.Xr syslog 3 784system module. 785By default this information is sent to stderr. 786.El 787.Pp 788.Nm 789may additionally obtain configuration data from 790a per-user configuration file and a system-wide configuration file. 791The file format and configuration options are described in 792.Xr ssh_config 5 . 793.Sh AUTHENTICATION 794The OpenSSH SSH client supports SSH protocol 2. 795.Pp 796The methods available for authentication are: 797GSSAPI-based authentication, 798host-based authentication, 799public key authentication, 800challenge-response authentication, 801and password authentication. 802Authentication methods are tried in the order specified above, 803though 804.Cm PreferredAuthentications 805can be used to change the default order. 806.Pp 807Host-based authentication works as follows: 808If the machine the user logs in from is listed in 809.Pa /etc/hosts.equiv 810or 811.Pa /etc/shosts.equiv 812on the remote machine, and the user names are 813the same on both sides, or if the files 814.Pa ~/.rhosts 815or 816.Pa ~/.shosts 817exist in the user's home directory on the 818remote machine and contain a line containing the name of the client 819machine and the name of the user on that machine, the user is 820considered for login. 821Additionally, the server 822.Em must 823be able to verify the client's 824host key (see the description of 825.Pa /etc/ssh/ssh_known_hosts 826and 827.Pa ~/.ssh/known_hosts , 828below) 829for login to be permitted. 830This authentication method closes security holes due to IP 831spoofing, DNS spoofing, and routing spoofing. 832[Note to the administrator: 833.Pa /etc/hosts.equiv , 834.Pa ~/.rhosts , 835and the rlogin/rsh protocol in general, are inherently insecure and should be 836disabled if security is desired.] 837.Pp 838Public key authentication works as follows: 839The scheme is based on public-key cryptography, 840using cryptosystems 841where encryption and decryption are done using separate keys, 842and it is unfeasible to derive the decryption key from the encryption key. 843The idea is that each user creates a public/private 844key pair for authentication purposes. 845The server knows the public key, and only the user knows the private key. 846.Nm 847implements public key authentication protocol automatically, 848using one of the DSA, ECDSA, Ed25519 or RSA algorithms. 849The HISTORY section of 850.Xr ssl 8 851contains a brief discussion of the DSA and RSA algorithms. 852.Pp 853The file 854.Pa ~/.ssh/authorized_keys 855lists the public keys that are permitted for logging in. 856When the user logs in, the 857.Nm 858program tells the server which key pair it would like to use for 859authentication. 860The client proves that it has access to the private key 861and the server checks that the corresponding public key 862is authorized to accept the account. 863.Pp 864The server may inform the client of errors that prevented public key 865authentication from succeeding after authentication completes using a 866different method. 867These may be viewed by increasing the 868.Cm LogLevel 869to 870.Cm DEBUG 871or higher (e.g. by using the 872.Fl v 873flag). 874.Pp 875The user creates his/her key pair by running 876.Xr ssh-keygen 1 . 877This stores the private key in 878.Pa ~/.ssh/id_dsa 879(DSA), 880.Pa ~/.ssh/id_ecdsa 881(ECDSA), 882.Pa ~/.ssh/id_ed25519 883(Ed25519), 884or 885.Pa ~/.ssh/id_rsa 886(RSA) 887and stores the public key in 888.Pa ~/.ssh/id_dsa.pub 889(DSA), 890.Pa ~/.ssh/id_ecdsa.pub 891(ECDSA), 892.Pa ~/.ssh/id_ed25519.pub 893(Ed25519), 894or 895.Pa ~/.ssh/id_rsa.pub 896(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 924and (optionally) the 925.Cm AddKeysToAgent 926directive in 927.Xr ssh_config 5 928for more information. 929.Pp 930Challenge-response authentication works as follows: 931The server sends an arbitrary 932.Qq challenge 933text, and prompts for a response. 934Examples of challenge-response authentication include 935.Bx 936Authentication (see 937.Xr login.conf 5 ) 938and PAM (some 939.Pf non- Ox 940systems). 941.Pp 942Finally, if other authentication methods fail, 943.Nm 944prompts the user for a password. 945The password is sent to the remote 946host for checking; however, since all communications are encrypted, 947the password cannot be seen by someone listening on the network. 948.Pp 949.Nm 950automatically maintains and checks a database containing 951identification for all hosts it has ever been used with. 952Host keys are stored in 953.Pa ~/.ssh/known_hosts 954in the user's home directory. 955Additionally, the file 956.Pa /etc/ssh/ssh_known_hosts 957is automatically checked for known hosts. 958Any new hosts are automatically added to the user's file. 959If a host's identification ever changes, 960.Nm 961warns about this and disables password authentication to prevent 962server spoofing or man-in-the-middle attacks, 963which could otherwise be used to circumvent the encryption. 964The 965.Cm StrictHostKeyChecking 966option can be used to control logins to machines whose 967host key is not known or has changed. 968.Pp 969When the user's identity has been accepted by the server, the server 970either executes the given command in a non-interactive session or, 971if no command has been specified, logs into the machine and gives 972the user a normal shell as an interactive session. 973All communication with 974the remote command or shell will be automatically encrypted. 975.Pp 976If an interactive session is requested 977.Nm 978by default will only request a pseudo-terminal (pty) for interactive 979sessions when the client has one. 980The flags 981.Fl T 982and 983.Fl t 984can be used to override this behaviour. 985.Pp 986If a pseudo-terminal has been allocated the 987user may use the escape characters noted below. 988.Pp 989If no pseudo-terminal has been allocated, 990the session is transparent and can be used to reliably transfer binary data. 991On most systems, setting the escape character to 992.Dq none 993will also make the session transparent even if a tty is used. 994.Pp 995The session terminates when the command or shell on the remote 996machine exits and all X11 and TCP connections have been closed. 997.Sh ESCAPE CHARACTERS 998When a pseudo-terminal has been requested, 999.Nm 1000supports a number of functions through the use of an escape character. 1001.Pp 1002A single tilde character can be sent as 1003.Ic ~~ 1004or by following the tilde by a character other than those described below. 1005The escape character must always follow a newline to be interpreted as 1006special. 1007The escape character can be changed in configuration files using the 1008.Cm EscapeChar 1009configuration directive or on the command line by the 1010.Fl e 1011option. 1012.Pp 1013The supported escapes (assuming the default 1014.Ql ~ ) 1015are: 1016.Bl -tag -width Ds 1017.It Cm ~. 1018Disconnect. 1019.It Cm ~^Z 1020Background 1021.Nm . 1022.It Cm ~# 1023List forwarded connections. 1024.It Cm ~& 1025Background 1026.Nm 1027at logout when waiting for forwarded connection / X11 sessions to terminate. 1028.It Cm ~? 1029Display a list of escape characters. 1030.It Cm ~B 1031Send a BREAK to the remote system 1032(only useful if the peer supports it). 1033.It Cm ~C 1034Open command line. 1035Currently this allows the addition of port forwardings using the 1036.Fl L , 1037.Fl R 1038and 1039.Fl D 1040options (see above). 1041It also allows the cancellation of existing port-forwardings 1042with 1043.Sm off 1044.Fl KL Oo Ar bind_address : Oc Ar port 1045.Sm on 1046for local, 1047.Sm off 1048.Fl KR Oo Ar bind_address : Oc Ar port 1049.Sm on 1050for remote and 1051.Sm off 1052.Fl KD Oo Ar bind_address : Oc Ar port 1053.Sm on 1054for dynamic port-forwardings. 1055.Ic !\& Ns Ar command 1056allows the user to execute a local command if the 1057.Ic PermitLocalCommand 1058option is enabled in 1059.Xr ssh_config 5 . 1060Basic help is available, using the 1061.Fl h 1062option. 1063.It Cm ~R 1064Request rekeying of the connection 1065(only useful if the peer supports it). 1066.It Cm ~V 1067Decrease the verbosity 1068.Pq Ic LogLevel 1069when errors are being written to stderr. 1070.It Cm ~v 1071Increase the verbosity 1072.Pq Ic LogLevel 1073when errors are being written to stderr. 1074.El 1075.Sh TCP FORWARDING 1076Forwarding of arbitrary TCP connections over the secure channel can 1077be specified either on the command line or in a configuration file. 1078One possible application of TCP forwarding is a secure connection to a 1079mail server; another is going through firewalls. 1080.Pp 1081In the example below, we look at encrypting communication between 1082an IRC client and server, even though the IRC server does not directly 1083support encrypted communications. 1084This works as follows: 1085the user connects to the remote host using 1086.Nm , 1087specifying a port to be used to forward connections 1088to the remote server. 1089After that it is possible to start the service which is to be encrypted 1090on the client machine, 1091connecting to the same local port, 1092and 1093.Nm 1094will encrypt and forward the connection. 1095.Pp 1096The following example tunnels an IRC session from client machine 1097.Dq 127.0.0.1 1098(localhost) 1099to remote server 1100.Dq server.example.com : 1101.Bd -literal -offset 4n 1102$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 1103$ irc -c '#users' -p 1234 pinky 127.0.0.1 1104.Ed 1105.Pp 1106This tunnels a connection to IRC server 1107.Dq server.example.com , 1108joining channel 1109.Dq #users , 1110nickname 1111.Dq pinky , 1112using port 1234. 1113It doesn't matter which port is used, 1114as long as it's greater than 1023 1115(remember, only root can open sockets on privileged ports) 1116and doesn't conflict with any ports already in use. 1117The connection is forwarded to port 6667 on the remote server, 1118since that's the standard port for IRC services. 1119.Pp 1120The 1121.Fl f 1122option backgrounds 1123.Nm 1124and the remote command 1125.Dq sleep 10 1126is specified to allow an amount of time 1127(10 seconds, in the example) 1128to start the service which is to be tunnelled. 1129If no connections are made within the time specified, 1130.Nm 1131will exit. 1132.Sh X11 FORWARDING 1133If the 1134.Cm ForwardX11 1135variable is set to 1136.Dq yes 1137(or see the description of the 1138.Fl X , 1139.Fl x , 1140and 1141.Fl Y 1142options above) 1143and the user is using X11 (the 1144.Ev DISPLAY 1145environment variable is set), the connection to the X11 display is 1146automatically forwarded to the remote side in such a way that any X11 1147programs started from the shell (or command) will go through the 1148encrypted channel, and the connection to the real X server will be made 1149from the local machine. 1150The user should not manually set 1151.Ev DISPLAY . 1152Forwarding of X11 connections can be 1153configured on the command line or in configuration files. 1154.Pp 1155The 1156.Ev DISPLAY 1157value set by 1158.Nm 1159will point to the server machine, but with a display number greater than zero. 1160This is normal, and happens because 1161.Nm 1162creates a 1163.Dq proxy 1164X server on the server machine for forwarding the 1165connections over the encrypted channel. 1166.Pp 1167.Nm 1168will also automatically set up Xauthority data on the server machine. 1169For this purpose, it will generate a random authorization cookie, 1170store it in Xauthority on the server, and verify that any forwarded 1171connections carry this cookie and replace it by the real cookie when 1172the connection is opened. 1173The real authentication cookie is never 1174sent to the server machine (and no cookies are sent in the plain). 1175.Pp 1176If the 1177.Cm ForwardAgent 1178variable is set to 1179.Dq yes 1180(or see the description of the 1181.Fl A 1182and 1183.Fl a 1184options above) and 1185the user is using an authentication agent, the connection to the agent 1186is automatically forwarded to the remote side. 1187.Sh VERIFYING HOST KEYS 1188When connecting to a server for the first time, 1189a fingerprint of the server's public key is presented to the user 1190(unless the option 1191.Cm StrictHostKeyChecking 1192has been disabled). 1193Fingerprints can be determined using 1194.Xr ssh-keygen 1 : 1195.Pp 1196.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key 1197.Pp 1198If the fingerprint is already known, it can be matched 1199and the key can be accepted or rejected. 1200If only legacy (MD5) fingerprints for the server are available, the 1201.Xr ssh-keygen 1 1202.Fl E 1203option may be used to downgrade the fingerprint algorithm to match. 1204.Pp 1205Because of the difficulty of comparing host keys 1206just by looking at fingerprint strings, 1207there is also support to compare host keys visually, 1208using 1209.Em random art . 1210By setting the 1211.Cm VisualHostKey 1212option to 1213.Dq yes , 1214a small ASCII graphic gets displayed on every login to a server, no matter 1215if the session itself is interactive or not. 1216By learning the pattern a known server produces, a user can easily 1217find out that the host key has changed when a completely different pattern 1218is displayed. 1219Because these patterns are not unambiguous however, a pattern that looks 1220similar to the pattern remembered only gives a good probability that the 1221host key is the same, not guaranteed proof. 1222.Pp 1223To get a listing of the fingerprints along with their random art for 1224all known hosts, the following command line can be used: 1225.Pp 1226.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts 1227.Pp 1228If the fingerprint is unknown, 1229an alternative method of verification is available: 1230SSH fingerprints verified by DNS. 1231An additional resource record (RR), 1232SSHFP, 1233is added to a zonefile 1234and the connecting client is able to match the fingerprint 1235with that of the key presented. 1236.Pp 1237In this example, we are connecting a client to a server, 1238.Dq host.example.com . 1239The SSHFP resource records should first be added to the zonefile for 1240host.example.com: 1241.Bd -literal -offset indent 1242$ ssh-keygen -r host.example.com. 1243.Ed 1244.Pp 1245The output lines will have to be added to the zonefile. 1246To check that the zone is answering fingerprint queries: 1247.Pp 1248.Dl $ dig -t SSHFP host.example.com 1249.Pp 1250Finally the client connects: 1251.Bd -literal -offset indent 1252$ ssh -o "VerifyHostKeyDNS ask" host.example.com 1253[...] 1254Matching host key fingerprint found in DNS. 1255Are you sure you want to continue connecting (yes/no)? 1256.Ed 1257.Pp 1258See the 1259.Cm VerifyHostKeyDNS 1260option in 1261.Xr ssh_config 5 1262for more information. 1263.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS 1264.Nm 1265contains support for Virtual Private Network (VPN) tunnelling 1266using the 1267.Xr tun 4 1268network pseudo-device, 1269allowing two networks to be joined securely. 1270The 1271.Xr sshd_config 5 1272configuration option 1273.Cm PermitTunnel 1274controls whether the server supports this, 1275and at what level (layer 2 or 3 traffic). 1276.Pp 1277The following example would connect client network 10.0.50.0/24 1278with remote network 10.0.99.0/24 using a point-to-point connection 1279from 10.1.1.1 to 10.1.1.2, 1280provided that the SSH server running on the gateway to the remote network, 1281at 192.168.1.15, allows it. 1282.Pp 1283On the client: 1284.Bd -literal -offset indent 1285# ssh -f -w 0:1 192.168.1.15 true 1286# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252 1287# route add 10.0.99.0/24 10.1.1.2 1288.Ed 1289.Pp 1290On the server: 1291.Bd -literal -offset indent 1292# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252 1293# route add 10.0.50.0/24 10.1.1.1 1294.Ed 1295.Pp 1296Client access may be more finely tuned via the 1297.Pa /root/.ssh/authorized_keys 1298file (see below) and the 1299.Cm PermitRootLogin 1300server option. 1301The following entry would permit connections on 1302.Xr tun 4 1303device 1 from user 1304.Dq jane 1305and on tun device 2 from user 1306.Dq john , 1307if 1308.Cm PermitRootLogin 1309is set to 1310.Dq forced-commands-only : 1311.Bd -literal -offset 2n 1312tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane 1313tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john 1314.Ed 1315.Pp 1316Since an SSH-based setup entails a fair amount of overhead, 1317it may be more suited to temporary setups, 1318such as for wireless VPNs. 1319More permanent VPNs are better provided by tools such as 1320.Xr ipsecctl 8 1321and 1322.Xr isakmpd 8 . 1323.Sh ENVIRONMENT 1324.Nm 1325will normally set the following environment variables: 1326.Bl -tag -width "SSH_ORIGINAL_COMMAND" 1327.It Ev DISPLAY 1328The 1329.Ev DISPLAY 1330variable indicates the location of the X11 server. 1331It is automatically set by 1332.Nm 1333to point to a value of the form 1334.Dq hostname:n , 1335where 1336.Dq hostname 1337indicates the host where the shell runs, and 1338.Sq n 1339is an integer \*(Ge 1. 1340.Nm 1341uses this special value to forward X11 connections over the secure 1342channel. 1343The user should normally not set 1344.Ev DISPLAY 1345explicitly, as that 1346will render the X11 connection insecure (and will require the user to 1347manually copy any required authorization cookies). 1348.It Ev HOME 1349Set to the path of the user's home directory. 1350.It Ev LOGNAME 1351Synonym for 1352.Ev USER ; 1353set for compatibility with systems that use this variable. 1354.It Ev MAIL 1355Set to the path of the user's mailbox. 1356.It Ev PATH 1357Set to the default 1358.Ev PATH , 1359as specified when compiling 1360.Nm . 1361.It Ev SSH_ASKPASS 1362If 1363.Nm 1364needs a passphrase, it will read the passphrase from the current 1365terminal if it was run from a terminal. 1366If 1367.Nm 1368does not have a terminal associated with it but 1369.Ev DISPLAY 1370and 1371.Ev SSH_ASKPASS 1372are set, it will execute the program specified by 1373.Ev SSH_ASKPASS 1374and open an X11 window to read the passphrase. 1375This is particularly useful when calling 1376.Nm 1377from a 1378.Pa .xsession 1379or related script. 1380(Note that on some machines it 1381may be necessary to redirect the input from 1382.Pa /dev/null 1383to make this work.) 1384.It Ev SSH_AUTH_SOCK 1385Identifies the path of a 1386.Ux Ns -domain 1387socket used to communicate with the agent. 1388.It Ev SSH_CONNECTION 1389Identifies the client and server ends of the connection. 1390The variable contains 1391four space-separated values: client IP address, client port number, 1392server IP address, and server port number. 1393.It Ev SSH_ORIGINAL_COMMAND 1394This variable contains the original command line if a forced command 1395is executed. 1396It can be used to extract the original arguments. 1397.It Ev SSH_TTY 1398This is set to the name of the tty (path to the device) associated 1399with the current shell or command. 1400If the current session has no tty, 1401this variable is not set. 1402.It Ev SSH_TUNNEL 1403Optionally set by 1404.Xr sshd 8 1405to contain the interface names assigned if tunnel forwarding was 1406requested by the client. 1407.It Ev SSH_USER_AUTH 1408Optionally set by 1409.Xr sshd 8 , 1410this variable may contain a pathname to a file that lists the authentication 1411methods successfully used when the session was established, including any 1412public keys that were used. 1413.It Ev TZ 1414This variable is set to indicate the present time zone if it 1415was set when the daemon was started (i.e. the daemon passes the value 1416on to new connections). 1417.It Ev USER 1418Set to the name of the user logging in. 1419.El 1420.Pp 1421Additionally, 1422.Nm 1423reads 1424.Pa ~/.ssh/environment , 1425and adds lines of the format 1426.Dq VARNAME=value 1427to the environment if the file exists and users are allowed to 1428change their environment. 1429For more information, see the 1430.Cm PermitUserEnvironment 1431option in 1432.Xr sshd_config 5 . 1433.Sh FILES 1434.Bl -tag -width Ds -compact 1435.It Pa ~/.rhosts 1436This file is used for host-based authentication (see above). 1437On some machines this file may need to be 1438world-readable if the user's home directory is on an NFS partition, 1439because 1440.Xr sshd 8 1441reads it as root. 1442Additionally, this file must be owned by the user, 1443and must not have write permissions for anyone else. 1444The recommended 1445permission for most machines is read/write for the user, and not 1446accessible by others. 1447.Pp 1448.It Pa ~/.shosts 1449This file is used in exactly the same way as 1450.Pa .rhosts , 1451but allows host-based authentication without permitting login with 1452rlogin/rsh. 1453.Pp 1454.It Pa ~/.ssh/ 1455This directory is the default location for all user-specific configuration 1456and authentication information. 1457There is no general requirement to keep the entire contents of this directory 1458secret, but the recommended permissions are read/write/execute for the user, 1459and not accessible by others. 1460.Pp 1461.It Pa ~/.ssh/authorized_keys 1462Lists the public keys (DSA, ECDSA, Ed25519, RSA) 1463that can be used for logging in as this user. 1464The format of this file is described in the 1465.Xr sshd 8 1466manual page. 1467This file is not highly sensitive, but the recommended 1468permissions are read/write for the user, and not accessible by others. 1469.Pp 1470.It Pa ~/.ssh/config 1471This is the per-user configuration file. 1472The file format and configuration options are described in 1473.Xr ssh_config 5 . 1474Because of the potential for abuse, this file must have strict permissions: 1475read/write for the user, and not writable by others. 1476.Pp 1477.It Pa ~/.ssh/environment 1478Contains additional definitions for environment variables; see 1479.Sx ENVIRONMENT , 1480above. 1481.Pp 1482.It Pa ~/.ssh/id_dsa 1483.It Pa ~/.ssh/id_ecdsa 1484.It Pa ~/.ssh/id_ed25519 1485.It Pa ~/.ssh/id_rsa 1486Contains the private key for authentication. 1487These files 1488contain sensitive data and should be readable by the user but not 1489accessible by others (read/write/execute). 1490.Nm 1491will simply ignore a private key file if it is accessible by others. 1492It is possible to specify a passphrase when 1493generating the key which will be used to encrypt the 1494sensitive part of this file using AES-128. 1495.Pp 1496.It Pa ~/.ssh/id_dsa.pub 1497.It Pa ~/.ssh/id_ecdsa.pub 1498.It Pa ~/.ssh/id_ed25519.pub 1499.It Pa ~/.ssh/id_rsa.pub 1500Contains the public key for authentication. 1501These files are not 1502sensitive and can (but need not) be readable by anyone. 1503.Pp 1504.It Pa ~/.ssh/known_hosts 1505Contains a list of host keys for all hosts the user has logged into 1506that are not already in the systemwide list of known host keys. 1507See 1508.Xr sshd 8 1509for further details of the format of this file. 1510.Pp 1511.It Pa ~/.ssh/rc 1512Commands in this file are executed by 1513.Nm 1514when the user logs in, just before the user's shell (or command) is 1515started. 1516See the 1517.Xr sshd 8 1518manual page for more information. 1519.Pp 1520.It Pa /etc/hosts.equiv 1521This file is for host-based authentication (see above). 1522It should only be writable by root. 1523.Pp 1524.It Pa /etc/shosts.equiv 1525This file is used in exactly the same way as 1526.Pa hosts.equiv , 1527but allows host-based authentication without permitting login with 1528rlogin/rsh. 1529.Pp 1530.It Pa /etc/ssh/ssh_config 1531Systemwide configuration file. 1532The file format and configuration options are described in 1533.Xr ssh_config 5 . 1534.Pp 1535.It Pa /etc/ssh/ssh_host_key 1536.It Pa /etc/ssh/ssh_host_dsa_key 1537.It Pa /etc/ssh/ssh_host_ecdsa_key 1538.It Pa /etc/ssh/ssh_host_ed25519_key 1539.It Pa /etc/ssh/ssh_host_rsa_key 1540These files contain the private parts of the host keys 1541and are used for host-based authentication. 1542.Pp 1543.It Pa /etc/ssh/ssh_known_hosts 1544Systemwide list of known host keys. 1545This file should be prepared by the 1546system administrator to contain the public host keys of all machines in the 1547organization. 1548It should be world-readable. 1549See 1550.Xr sshd 8 1551for further details of the format of this file. 1552.Pp 1553.It Pa /etc/ssh/sshrc 1554Commands in this file are executed by 1555.Nm 1556when the user logs in, just before the user's shell (or command) is started. 1557See the 1558.Xr sshd 8 1559manual page for more information. 1560.El 1561.Sh EXIT STATUS 1562.Nm 1563exits with the exit status of the remote command or with 255 1564if an error occurred. 1565.Sh SEE ALSO 1566.Xr scp 1 , 1567.Xr sftp 1 , 1568.Xr ssh-add 1 , 1569.Xr ssh-agent 1 , 1570.Xr ssh-keygen 1 , 1571.Xr ssh-keyscan 1 , 1572.Xr tun 4 , 1573.Xr ssh_config 5 , 1574.Xr ssh-keysign 8 , 1575.Xr sshd 8 1576.Sh STANDARDS 1577.Rs 1578.%A S. Lehtinen 1579.%A C. Lonvick 1580.%D January 2006 1581.%R RFC 4250 1582.%T The Secure Shell (SSH) Protocol Assigned Numbers 1583.Re 1584.Pp 1585.Rs 1586.%A T. Ylonen 1587.%A C. Lonvick 1588.%D January 2006 1589.%R RFC 4251 1590.%T The Secure Shell (SSH) Protocol Architecture 1591.Re 1592.Pp 1593.Rs 1594.%A T. Ylonen 1595.%A C. Lonvick 1596.%D January 2006 1597.%R RFC 4252 1598.%T The Secure Shell (SSH) Authentication Protocol 1599.Re 1600.Pp 1601.Rs 1602.%A T. Ylonen 1603.%A C. Lonvick 1604.%D January 2006 1605.%R RFC 4253 1606.%T The Secure Shell (SSH) Transport Layer Protocol 1607.Re 1608.Pp 1609.Rs 1610.%A T. Ylonen 1611.%A C. Lonvick 1612.%D January 2006 1613.%R RFC 4254 1614.%T The Secure Shell (SSH) Connection Protocol 1615.Re 1616.Pp 1617.Rs 1618.%A J. Schlyter 1619.%A W. Griffin 1620.%D January 2006 1621.%R RFC 4255 1622.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints 1623.Re 1624.Pp 1625.Rs 1626.%A F. Cusack 1627.%A M. Forssen 1628.%D January 2006 1629.%R RFC 4256 1630.%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH) 1631.Re 1632.Pp 1633.Rs 1634.%A J. Galbraith 1635.%A P. Remaker 1636.%D January 2006 1637.%R RFC 4335 1638.%T The Secure Shell (SSH) Session Channel Break Extension 1639.Re 1640.Pp 1641.Rs 1642.%A M. Bellare 1643.%A T. Kohno 1644.%A C. Namprempre 1645.%D January 2006 1646.%R RFC 4344 1647.%T The Secure Shell (SSH) Transport Layer Encryption Modes 1648.Re 1649.Pp 1650.Rs 1651.%A B. Harris 1652.%D January 2006 1653.%R RFC 4345 1654.%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol 1655.Re 1656.Pp 1657.Rs 1658.%A M. Friedl 1659.%A N. Provos 1660.%A W. Simpson 1661.%D March 2006 1662.%R RFC 4419 1663.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol 1664.Re 1665.Pp 1666.Rs 1667.%A J. Galbraith 1668.%A R. Thayer 1669.%D November 2006 1670.%R RFC 4716 1671.%T The Secure Shell (SSH) Public Key File Format 1672.Re 1673.Pp 1674.Rs 1675.%A D. Stebila 1676.%A J. Green 1677.%D December 2009 1678.%R RFC 5656 1679.%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer 1680.Re 1681.Pp 1682.Rs 1683.%A A. Perrig 1684.%A D. Song 1685.%D 1999 1686.%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99) 1687.%T Hash Visualization: a New Technique to improve Real-World Security 1688.Re 1689.Sh AUTHORS 1690OpenSSH is a derivative of the original and free 1691ssh 1.2.12 release by Tatu Ylonen. 1692Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 1693Theo de Raadt and Dug Song 1694removed many bugs, re-added newer features and 1695created OpenSSH. 1696Markus Friedl contributed the support for SSH 1697protocol versions 1.5 and 2.0. 1698