1.\" 2.\" Author: Tatu Ylonen <ylo@cs.hut.fi> 3.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 4.\" All rights reserved 5.\" 6.\" As far as I am concerned, the code I have written for this software 7.\" can be used freely for any purpose. Any derived versions of this 8.\" software must be clearly marked as such, and if the derived work is 9.\" incompatible with the protocol description in the RFC file, it must be 10.\" called by a name other than "ssh" or "Secure Shell". 11.\" 12.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. 13.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. 14.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. 15.\" 16.\" Redistribution and use in source and binary forms, with or without 17.\" modification, are permitted provided that the following conditions 18.\" are met: 19.\" 1. Redistributions of source code must retain the above copyright 20.\" notice, this list of conditions and the following disclaimer. 21.\" 2. Redistributions in binary form must reproduce the above copyright 22.\" notice, this list of conditions and the following disclaimer in the 23.\" documentation and/or other materials provided with the distribution. 24.\" 25.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 26.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 27.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 28.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 29.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 30.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 31.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 32.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 33.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 34.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 35.\" 36.\" $OpenBSD: ssh.1,v 1.400 2019/01/22 11:51:25 djm Exp $ 37.Dd $Mdocdate: January 22 2019 $ 38.Dt SSH 1 39.Os 40.Sh NAME 41.Nm ssh 42.Nd OpenSSH SSH client (remote login program) 43.Sh SYNOPSIS 44.Nm ssh 45.Op Fl 46AaCfGgKkMNnqsTtVvXxYy 46.Op Fl B Ar bind_interface 47.Op Fl b Ar bind_address 48.Op Fl c Ar cipher_spec 49.Op Fl D Oo Ar bind_address : Oc Ns Ar port 50.Op Fl E Ar log_file 51.Op Fl e Ar escape_char 52.Op Fl F Ar configfile 53.Op Fl I Ar pkcs11 54.Op Fl i Ar identity_file 55.Op Fl J Ar destination 56.Op Fl L Ar address 57.Op Fl l Ar login_name 58.Op Fl m Ar mac_spec 59.Op Fl O Ar ctl_cmd 60.Op Fl o Ar option 61.Op Fl p Ar port 62.Op Fl Q Ar query_option 63.Op Fl R Ar address 64.Op Fl S Ar ctl_path 65.Op Fl W Ar host : Ns Ar port 66.Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun 67.Ar destination 68.Op Ar command 69.Sh DESCRIPTION 70.Nm 71(SSH client) is a program for logging into a remote machine and for 72executing commands on a remote machine. 73It is intended to provide secure encrypted communications between 74two untrusted hosts over an insecure network. 75X11 connections, arbitrary TCP ports and 76.Ux Ns -domain 77sockets can also be forwarded over the secure channel. 78.Pp 79.Nm 80connects and logs into the specified 81.Ar destination , 82which may be specified as either 83.Sm off 84.Oo user @ Oc hostname 85.Sm on 86or a URI of the form 87.Sm off 88.No ssh:// Oo user @ Oc hostname Op : port . 89.Sm on 90The user must prove 91his/her identity to the remote machine using one of several methods 92(see below). 93.Pp 94If a 95.Ar command 96is specified, 97it is executed on the remote host instead of a login shell. 98.Pp 99The options are as follows: 100.Pp 101.Bl -tag -width Ds -compact 102.It Fl 4 103Forces 104.Nm 105to use IPv4 addresses only. 106.Pp 107.It Fl 6 108Forces 109.Nm 110to use IPv6 addresses only. 111.Pp 112.It Fl A 113Enables forwarding of the authentication agent connection. 114This can also be specified on a per-host basis in a configuration file. 115.Pp 116Agent forwarding should be enabled with caution. 117Users with the ability to bypass file permissions on the remote host 118(for the agent's 119.Ux Ns -domain 120socket) can access the local agent through the forwarded connection. 121An attacker cannot obtain key material from the agent, 122however they can perform operations on the keys that enable them to 123authenticate using the identities loaded into the agent. 124.Pp 125.It Fl a 126Disables forwarding of the authentication agent connection. 127.Pp 128.It Fl B Ar bind_interface 129Bind to the address of 130.Ar bind_interface 131before attempting to connect to the destination host. 132This is only useful on systems with more than one address. 133.Pp 134.It Fl b Ar bind_address 135Use 136.Ar bind_address 137on the local machine as the source address 138of the connection. 139Only useful on systems with more than one address. 140.Pp 141.It Fl C 142Requests compression of all data (including stdin, stdout, stderr, and 143data for forwarded X11, TCP and 144.Ux Ns -domain 145connections). 146The compression algorithm is the same used by 147.Xr gzip 1 . 148Compression is desirable on modem lines and other 149slow connections, but will only slow down things on fast networks. 150The default value can be set on a host-by-host basis in the 151configuration files; see the 152.Cm Compression 153option. 154.Pp 155.It Fl c Ar cipher_spec 156Selects the cipher specification for encrypting the session. 157.Ar cipher_spec 158is a comma-separated list of ciphers 159listed in order of preference. 160See the 161.Cm Ciphers 162keyword in 163.Xr ssh_config 5 164for more information. 165.Pp 166.It Fl D Xo 167.Sm off 168.Oo Ar bind_address : Oc 169.Ar port 170.Sm on 171.Xc 172Specifies a local 173.Dq dynamic 174application-level port forwarding. 175This works by allocating a socket to listen to 176.Ar port 177on the local side, optionally bound to the specified 178.Ar bind_address . 179Whenever a connection is made to this port, the 180connection is forwarded over the secure channel, and the application 181protocol is then used to determine where to connect to from the 182remote machine. 183Currently the SOCKS4 and SOCKS5 protocols are supported, and 184.Nm 185will act as a SOCKS server. 186Only root can forward privileged ports. 187Dynamic port forwardings can also be specified in the configuration file. 188.Pp 189IPv6 addresses can be specified by enclosing the address in square brackets. 190Only the superuser can forward privileged ports. 191By default, the local port is bound in accordance with the 192.Cm GatewayPorts 193setting. 194However, an explicit 195.Ar bind_address 196may be used to bind the connection to a specific address. 197The 198.Ar bind_address 199of 200.Dq localhost 201indicates that the listening port be bound for local use only, while an 202empty address or 203.Sq * 204indicates that the port should be available from all interfaces. 205.Pp 206.It Fl E Ar log_file 207Append debug logs to 208.Ar log_file 209instead of standard error. 210.Pp 211.It Fl e Ar escape_char 212Sets the escape character for sessions with a pty (default: 213.Ql ~ ) . 214The escape character is only recognized at the beginning of a line. 215The escape character followed by a dot 216.Pq Ql \&. 217closes the connection; 218followed by control-Z suspends the connection; 219and followed by itself sends the escape character once. 220Setting the character to 221.Dq none 222disables any escapes and makes the session fully transparent. 223.Pp 224.It Fl F Ar configfile 225Specifies an alternative per-user configuration file. 226If a configuration file is given on the command line, 227the system-wide configuration file 228.Pq Pa /etc/ssh/ssh_config 229will be ignored. 230The default for the per-user configuration file is 231.Pa ~/.ssh/config . 232.Pp 233.It Fl f 234Requests 235.Nm 236to go to background just before command execution. 237This is useful if 238.Nm 239is going to ask for passwords or passphrases, but the user 240wants it in the background. 241This implies 242.Fl n . 243The recommended way to start X11 programs at a remote site is with 244something like 245.Ic ssh -f host xterm . 246.Pp 247If the 248.Cm ExitOnForwardFailure 249configuration option is set to 250.Dq yes , 251then a client started with 252.Fl f 253will wait for all remote port forwards to be successfully established 254before placing itself in the background. 255.Pp 256.It Fl G 257Causes 258.Nm 259to print its configuration after evaluating 260.Cm Host 261and 262.Cm Match 263blocks and exit. 264.Pp 265.It Fl g 266Allows remote hosts to connect to local forwarded ports. 267If used on a multiplexed connection, then this option must be specified 268on the master process. 269.Pp 270.It Fl I Ar pkcs11 271Specify the PKCS#11 shared library 272.Nm 273should use to communicate with a PKCS#11 token providing the user's 274private RSA key. 275.Pp 276.It Fl i Ar identity_file 277Selects a file from which the identity (private key) for 278public key authentication is read. 279The default is 280.Pa ~/.ssh/id_dsa , 281.Pa ~/.ssh/id_ecdsa , 282.Pa ~/.ssh/id_ed25519 283and 284.Pa ~/.ssh/id_rsa . 285Identity files may also be specified on 286a per-host basis in the configuration file. 287It is possible to have multiple 288.Fl i 289options (and multiple identities specified in 290configuration files). 291If no certificates have been explicitly specified by the 292.Cm CertificateFile 293directive, 294.Nm 295will also try to load certificate information from the filename obtained 296by appending 297.Pa -cert.pub 298to identity filenames. 299.Pp 300.It Fl J Ar destination 301Connect to the target host by first making a 302.Nm 303connection to the jump host described by 304.Ar destination 305and then establishing a TCP forwarding to the ultimate destination from 306there. 307Multiple jump hops may be specified separated by comma characters. 308This is a shortcut to specify a 309.Cm ProxyJump 310configuration directive. 311Note that configuration directives supplied on the command-line generally 312apply to the destination host and not any specified jump hosts. 313Use 314.Pa ~/.ssh/config 315to specify configuration for jump hosts. 316.Pp 317.It Fl K 318Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI 319credentials to the server. 320.Pp 321.It Fl k 322Disables forwarding (delegation) of GSSAPI credentials to the server. 323.Pp 324.It Fl L Xo 325.Sm off 326.Oo Ar bind_address : Oc 327.Ar port : host : hostport 328.Sm on 329.Xc 330.It Fl L Xo 331.Sm off 332.Oo Ar bind_address : Oc 333.Ar port : remote_socket 334.Sm on 335.Xc 336.It Fl L Xo 337.Sm off 338.Ar local_socket : host : hostport 339.Sm on 340.Xc 341.It Fl L Xo 342.Sm off 343.Ar local_socket : remote_socket 344.Sm on 345.Xc 346Specifies that connections to the given TCP port or Unix socket on the local 347(client) host are to be forwarded to the given host and port, or Unix socket, 348on the remote side. 349This works by allocating a socket to listen to either a TCP 350.Ar port 351on the local side, optionally bound to the specified 352.Ar bind_address , 353or to a Unix socket. 354Whenever a connection is made to the local port or socket, the 355connection is forwarded over the secure channel, and a connection is 356made to either 357.Ar host 358port 359.Ar hostport , 360or the Unix socket 361.Ar remote_socket , 362from the remote machine. 363.Pp 364Port forwardings can also be specified in the configuration file. 365Only the superuser can forward privileged ports. 366IPv6 addresses can be specified by enclosing the address in square brackets. 367.Pp 368By default, the local port is bound in accordance with the 369.Cm GatewayPorts 370setting. 371However, an explicit 372.Ar bind_address 373may be used to bind the connection to a specific address. 374The 375.Ar bind_address 376of 377.Dq localhost 378indicates that the listening port be bound for local use only, while an 379empty address or 380.Sq * 381indicates that the port should be available from all interfaces. 382.Pp 383.It Fl l Ar login_name 384Specifies the user to log in as on the remote machine. 385This also may be specified on a per-host basis in the configuration file. 386.Pp 387.It Fl M 388Places the 389.Nm 390client into 391.Dq master 392mode for connection sharing. 393Multiple 394.Fl M 395options places 396.Nm 397into 398.Dq master 399mode but with confirmation required using 400.Xr ssh-askpass 1 401before each operation that changes the multiplexing state 402(e.g. opening a new session). 403Refer to the description of 404.Cm ControlMaster 405in 406.Xr ssh_config 5 407for details. 408.Pp 409.It Fl m Ar mac_spec 410A comma-separated list of MAC (message authentication code) algorithms, 411specified in order of preference. 412See the 413.Cm MACs 414keyword for more information. 415.Pp 416.It Fl N 417Do not execute a remote command. 418This is useful for just forwarding ports. 419.Pp 420.It Fl n 421Redirects stdin from 422.Pa /dev/null 423(actually, prevents reading from stdin). 424This must be used when 425.Nm 426is run in the background. 427A common trick is to use this to run X11 programs on a remote machine. 428For example, 429.Ic ssh -n shadows.cs.hut.fi emacs & 430will start an emacs on shadows.cs.hut.fi, and the X11 431connection will be automatically forwarded over an encrypted channel. 432The 433.Nm 434program will be put in the background. 435(This does not work if 436.Nm 437needs to ask for a password or passphrase; see also the 438.Fl f 439option.) 440.Pp 441.It Fl O Ar ctl_cmd 442Control an active connection multiplexing master process. 443When the 444.Fl O 445option is specified, the 446.Ar ctl_cmd 447argument is interpreted and passed to the master process. 448Valid commands are: 449.Dq check 450(check that the master process is running), 451.Dq forward 452(request forwardings without command execution), 453.Dq cancel 454(cancel forwardings), 455.Dq exit 456(request the master to exit), and 457.Dq stop 458(request the master to stop accepting further multiplexing requests). 459.Pp 460.It Fl o Ar option 461Can be used to give options in the format used in the configuration file. 462This is useful for specifying options for which there is no separate 463command-line flag. 464For full details of the options listed below, and their possible values, see 465.Xr ssh_config 5 . 466.Pp 467.Bl -tag -width Ds -offset indent -compact 468.It AddKeysToAgent 469.It AddressFamily 470.It BatchMode 471.It BindAddress 472.It CanonicalDomains 473.It CanonicalizeFallbackLocal 474.It CanonicalizeHostname 475.It CanonicalizeMaxDots 476.It CanonicalizePermittedCNAMEs 477.It CASignatureAlgorithms 478.It CertificateFile 479.It ChallengeResponseAuthentication 480.It CheckHostIP 481.It Ciphers 482.It ClearAllForwardings 483.It Compression 484.It ConnectionAttempts 485.It ConnectTimeout 486.It ControlMaster 487.It ControlPath 488.It ControlPersist 489.It DynamicForward 490.It EscapeChar 491.It ExitOnForwardFailure 492.It FingerprintHash 493.It ForwardAgent 494.It ForwardX11 495.It ForwardX11Timeout 496.It ForwardX11Trusted 497.It GatewayPorts 498.It GlobalKnownHostsFile 499.It GSSAPIAuthentication 500.It GSSAPIDelegateCredentials 501.It HashKnownHosts 502.It Host 503.It HostbasedAuthentication 504.It HostbasedKeyTypes 505.It HostKeyAlgorithms 506.It HostKeyAlias 507.It HostName 508.It IdentitiesOnly 509.It IdentityAgent 510.It IdentityFile 511.It IPQoS 512.It KbdInteractiveAuthentication 513.It KbdInteractiveDevices 514.It KexAlgorithms 515.It LocalCommand 516.It LocalForward 517.It LogLevel 518.It MACs 519.It Match 520.It NoHostAuthenticationForLocalhost 521.It NumberOfPasswordPrompts 522.It PasswordAuthentication 523.It PermitLocalCommand 524.It PKCS11Provider 525.It Port 526.It PreferredAuthentications 527.It ProxyCommand 528.It ProxyJump 529.It ProxyUseFdpass 530.It PubkeyAcceptedKeyTypes 531.It PubkeyAuthentication 532.It RekeyLimit 533.It RemoteCommand 534.It RemoteForward 535.It RequestTTY 536.It SendEnv 537.It ServerAliveInterval 538.It ServerAliveCountMax 539.It SetEnv 540.It StreamLocalBindMask 541.It StreamLocalBindUnlink 542.It StrictHostKeyChecking 543.It TCPKeepAlive 544.It Tunnel 545.It TunnelDevice 546.It UpdateHostKeys 547.It User 548.It UserKnownHostsFile 549.It VerifyHostKeyDNS 550.It VisualHostKey 551.It XAuthLocation 552.El 553.Pp 554.It Fl p Ar port 555Port to connect to on the remote host. 556This can be specified on a 557per-host basis in the configuration file. 558.Pp 559.It Fl Q Ar query_option 560Queries 561.Nm 562for the algorithms supported for the specified version 2. 563The available features are: 564.Ar cipher 565(supported symmetric ciphers), 566.Ar cipher-auth 567(supported symmetric ciphers that support authenticated encryption), 568.Ar help 569(supported query terms for use with the 570.Fl Q 571flag), 572.Ar mac 573(supported message integrity codes), 574.Ar kex 575(key exchange algorithms), 576.Ar key 577(key types), 578.Ar key-cert 579(certificate key types), 580.Ar key-plain 581(non-certificate key types), 582.Ar protocol-version 583(supported SSH protocol versions), and 584.Ar sig 585(supported signature algorithms). 586.Pp 587.It Fl q 588Quiet mode. 589Causes most warning and diagnostic messages to be suppressed. 590.Pp 591.It Fl R Xo 592.Sm off 593.Oo Ar bind_address : Oc 594.Ar port : host : hostport 595.Sm on 596.Xc 597.It Fl R Xo 598.Sm off 599.Oo Ar bind_address : Oc 600.Ar port : local_socket 601.Sm on 602.Xc 603.It Fl R Xo 604.Sm off 605.Ar remote_socket : host : hostport 606.Sm on 607.Xc 608.It Fl R Xo 609.Sm off 610.Ar remote_socket : local_socket 611.Sm on 612.Xc 613.It Fl R Xo 614.Sm off 615.Oo Ar bind_address : Oc 616.Ar port 617.Sm on 618.Xc 619Specifies that connections to the given TCP port or Unix socket on the remote 620(server) host are to be forwarded to the local side. 621.Pp 622This works by allocating a socket to listen to either a TCP 623.Ar port 624or to a Unix socket on the remote side. 625Whenever a connection is made to this port or Unix socket, the 626connection is forwarded over the secure channel, and a connection 627is made from the local machine to either an explicit destination specified by 628.Ar host 629port 630.Ar hostport , 631or 632.Ar local_socket , 633or, if no explicit destination was specified, 634.Nm 635will act as a SOCKS 4/5 proxy and forward connections to the destinations 636requested by the remote SOCKS client. 637.Pp 638Port forwardings can also be specified in the configuration file. 639Privileged ports can be forwarded only when 640logging in as root on the remote machine. 641IPv6 addresses can be specified by enclosing the address in square brackets. 642.Pp 643By default, TCP listening sockets on the server will be bound to the loopback 644interface only. 645This may be overridden by specifying a 646.Ar bind_address . 647An empty 648.Ar bind_address , 649or the address 650.Ql * , 651indicates that the remote socket should listen on all interfaces. 652Specifying a remote 653.Ar bind_address 654will only succeed if the server's 655.Cm GatewayPorts 656option is enabled (see 657.Xr sshd_config 5 ) . 658.Pp 659If the 660.Ar port 661argument is 662.Ql 0 , 663the listen port will be dynamically allocated on the server and reported 664to the client at run time. 665When used together with 666.Ic -O forward 667the allocated port will be printed to the standard output. 668.Pp 669.It Fl S Ar ctl_path 670Specifies the location of a control socket for connection sharing, 671or the string 672.Dq none 673to disable connection sharing. 674Refer to the description of 675.Cm ControlPath 676and 677.Cm ControlMaster 678in 679.Xr ssh_config 5 680for details. 681.Pp 682.It Fl s 683May be used to request invocation of a subsystem on the remote system. 684Subsystems facilitate the use of SSH 685as a secure transport for other applications (e.g.\& 686.Xr sftp 1 ) . 687The subsystem is specified as the remote command. 688.Pp 689.It Fl T 690Disable pseudo-terminal allocation. 691.Pp 692.It Fl t 693Force pseudo-terminal allocation. 694This can be used to execute arbitrary 695screen-based programs on a remote machine, which can be very useful, 696e.g. when implementing menu services. 697Multiple 698.Fl t 699options force tty allocation, even if 700.Nm 701has no local tty. 702.Pp 703.It Fl V 704Display the version number and exit. 705.Pp 706.It Fl v 707Verbose mode. 708Causes 709.Nm 710to print debugging messages about its progress. 711This is helpful in 712debugging connection, authentication, and configuration problems. 713Multiple 714.Fl v 715options increase the verbosity. 716The maximum is 3. 717.Pp 718.It Fl W Ar host : Ns Ar port 719Requests that standard input and output on the client be forwarded to 720.Ar host 721on 722.Ar port 723over the secure channel. 724Implies 725.Fl N , 726.Fl T , 727.Cm ExitOnForwardFailure 728and 729.Cm ClearAllForwardings , 730though these can be overridden in the configuration file or using 731.Fl o 732command line options. 733.Pp 734.It Fl w Xo 735.Ar local_tun Ns Op : Ns Ar remote_tun 736.Xc 737Requests 738tunnel 739device forwarding with the specified 740.Xr tun 4 741devices between the client 742.Pq Ar local_tun 743and the server 744.Pq Ar remote_tun . 745.Pp 746The devices may be specified by numerical ID or the keyword 747.Dq any , 748which uses the next available tunnel device. 749If 750.Ar remote_tun 751is not specified, it defaults to 752.Dq any . 753See also the 754.Cm Tunnel 755and 756.Cm TunnelDevice 757directives in 758.Xr ssh_config 5 . 759.Pp 760If the 761.Cm Tunnel 762directive is unset, it will be set to the default tunnel mode, which is 763.Dq point-to-point . 764If a different 765.Cm Tunnel 766forwarding mode it desired, then it should be specified before 767.Fl w . 768.Pp 769.It Fl X 770Enables X11 forwarding. 771This can also be specified on a per-host basis in a configuration file. 772.Pp 773X11 forwarding should be enabled with caution. 774Users with the ability to bypass file permissions on the remote host 775(for the user's X authorization database) 776can access the local X11 display through the forwarded connection. 777An attacker may then be able to perform activities such as keystroke monitoring. 778.Pp 779For this reason, X11 forwarding is subjected to X11 SECURITY extension 780restrictions by default. 781Please refer to the 782.Nm 783.Fl Y 784option and the 785.Cm ForwardX11Trusted 786directive in 787.Xr ssh_config 5 788for more information. 789.Pp 790.It Fl x 791Disables X11 forwarding. 792.Pp 793.It Fl Y 794Enables trusted X11 forwarding. 795Trusted X11 forwardings are not subjected to the X11 SECURITY extension 796controls. 797.Pp 798.It Fl y 799Send log information using the 800.Xr syslog 3 801system module. 802By default this information is sent to stderr. 803.El 804.Pp 805.Nm 806may additionally obtain configuration data from 807a per-user configuration file and a system-wide configuration file. 808The file format and configuration options are described in 809.Xr ssh_config 5 . 810.Sh AUTHENTICATION 811The OpenSSH SSH client supports SSH protocol 2. 812.Pp 813The methods available for authentication are: 814GSSAPI-based authentication, 815host-based authentication, 816public key authentication, 817challenge-response authentication, 818and password authentication. 819Authentication methods are tried in the order specified above, 820though 821.Cm PreferredAuthentications 822can be used to change the default order. 823.Pp 824Host-based authentication works as follows: 825If the machine the user logs in from is listed in 826.Pa /etc/hosts.equiv 827or 828.Pa /etc/shosts.equiv 829on the remote machine, and the user names are 830the same on both sides, or if the files 831.Pa ~/.rhosts 832or 833.Pa ~/.shosts 834exist in the user's home directory on the 835remote machine and contain a line containing the name of the client 836machine and the name of the user on that machine, the user is 837considered for login. 838Additionally, the server 839.Em must 840be able to verify the client's 841host key (see the description of 842.Pa /etc/ssh/ssh_known_hosts 843and 844.Pa ~/.ssh/known_hosts , 845below) 846for login to be permitted. 847This authentication method closes security holes due to IP 848spoofing, DNS spoofing, and routing spoofing. 849[Note to the administrator: 850.Pa /etc/hosts.equiv , 851.Pa ~/.rhosts , 852and the rlogin/rsh protocol in general, are inherently insecure and should be 853disabled if security is desired.] 854.Pp 855Public key authentication works as follows: 856The scheme is based on public-key cryptography, 857using cryptosystems 858where encryption and decryption are done using separate keys, 859and it is unfeasible to derive the decryption key from the encryption key. 860The idea is that each user creates a public/private 861key pair for authentication purposes. 862The server knows the public key, and only the user knows the private key. 863.Nm 864implements public key authentication protocol automatically, 865using one of the DSA, ECDSA, Ed25519 or RSA algorithms. 866The HISTORY section of 867.Xr ssl 8 868contains a brief discussion of the DSA and RSA algorithms. 869.Pp 870The file 871.Pa ~/.ssh/authorized_keys 872lists the public keys that are permitted for logging in. 873When the user logs in, the 874.Nm 875program tells the server which key pair it would like to use for 876authentication. 877The client proves that it has access to the private key 878and the server checks that the corresponding public key 879is authorized to accept the account. 880.Pp 881The server may inform the client of errors that prevented public key 882authentication from succeeding after authentication completes using a 883different method. 884These may be viewed by increasing the 885.Cm LogLevel 886to 887.Cm DEBUG 888or higher (e.g. by using the 889.Fl v 890flag). 891.Pp 892The user creates his/her key pair by running 893.Xr ssh-keygen 1 . 894This stores the private key in 895.Pa ~/.ssh/id_dsa 896(DSA), 897.Pa ~/.ssh/id_ecdsa 898(ECDSA), 899.Pa ~/.ssh/id_ed25519 900(Ed25519), 901or 902.Pa ~/.ssh/id_rsa 903(RSA) 904and stores the public key in 905.Pa ~/.ssh/id_dsa.pub 906(DSA), 907.Pa ~/.ssh/id_ecdsa.pub 908(ECDSA), 909.Pa ~/.ssh/id_ed25519.pub 910(Ed25519), 911or 912.Pa ~/.ssh/id_rsa.pub 913(RSA) 914in the user's home directory. 915The user should then copy the public key 916to 917.Pa ~/.ssh/authorized_keys 918in his/her home directory on the remote machine. 919The 920.Pa authorized_keys 921file corresponds to the conventional 922.Pa ~/.rhosts 923file, and has one key 924per line, though the lines can be very long. 925After this, the user can log in without giving the password. 926.Pp 927A variation on public key authentication 928is available in the form of certificate authentication: 929instead of a set of public/private keys, 930signed certificates are used. 931This has the advantage that a single trusted certification authority 932can be used in place of many public/private keys. 933See the CERTIFICATES section of 934.Xr ssh-keygen 1 935for more information. 936.Pp 937The most convenient way to use public key or certificate authentication 938may be with an authentication agent. 939See 940.Xr ssh-agent 1 941and (optionally) the 942.Cm AddKeysToAgent 943directive in 944.Xr ssh_config 5 945for more information. 946.Pp 947Challenge-response authentication works as follows: 948The server sends an arbitrary 949.Qq challenge 950text, and prompts for a response. 951Examples of challenge-response authentication include 952.Bx 953Authentication (see 954.Xr login.conf 5 ) 955and PAM (some 956.Pf non- Ox 957systems). 958.Pp 959Finally, if other authentication methods fail, 960.Nm 961prompts the user for a password. 962The password is sent to the remote 963host for checking; however, since all communications are encrypted, 964the password cannot be seen by someone listening on the network. 965.Pp 966.Nm 967automatically maintains and checks a database containing 968identification for all hosts it has ever been used with. 969Host keys are stored in 970.Pa ~/.ssh/known_hosts 971in the user's home directory. 972Additionally, the file 973.Pa /etc/ssh/ssh_known_hosts 974is automatically checked for known hosts. 975Any new hosts are automatically added to the user's file. 976If a host's identification ever changes, 977.Nm 978warns about this and disables password authentication to prevent 979server spoofing or man-in-the-middle attacks, 980which could otherwise be used to circumvent the encryption. 981The 982.Cm StrictHostKeyChecking 983option can be used to control logins to machines whose 984host key is not known or has changed. 985.Pp 986When the user's identity has been accepted by the server, the server 987either executes the given command in a non-interactive session or, 988if no command has been specified, logs into the machine and gives 989the user a normal shell as an interactive session. 990All communication with 991the remote command or shell will be automatically encrypted. 992.Pp 993If an interactive session is requested 994.Nm 995by default will only request a pseudo-terminal (pty) for interactive 996sessions when the client has one. 997The flags 998.Fl T 999and 1000.Fl t 1001can be used to override this behaviour. 1002.Pp 1003If a pseudo-terminal has been allocated the 1004user may use the escape characters noted below. 1005.Pp 1006If no pseudo-terminal has been allocated, 1007the session is transparent and can be used to reliably transfer binary data. 1008On most systems, setting the escape character to 1009.Dq none 1010will also make the session transparent even if a tty is used. 1011.Pp 1012The session terminates when the command or shell on the remote 1013machine exits and all X11 and TCP connections have been closed. 1014.Sh ESCAPE CHARACTERS 1015When a pseudo-terminal has been requested, 1016.Nm 1017supports a number of functions through the use of an escape character. 1018.Pp 1019A single tilde character can be sent as 1020.Ic ~~ 1021or by following the tilde by a character other than those described below. 1022The escape character must always follow a newline to be interpreted as 1023special. 1024The escape character can be changed in configuration files using the 1025.Cm EscapeChar 1026configuration directive or on the command line by the 1027.Fl e 1028option. 1029.Pp 1030The supported escapes (assuming the default 1031.Ql ~ ) 1032are: 1033.Bl -tag -width Ds 1034.It Cm ~. 1035Disconnect. 1036.It Cm ~^Z 1037Background 1038.Nm . 1039.It Cm ~# 1040List forwarded connections. 1041.It Cm ~& 1042Background 1043.Nm 1044at logout when waiting for forwarded connection / X11 sessions to terminate. 1045.It Cm ~? 1046Display a list of escape characters. 1047.It Cm ~B 1048Send a BREAK to the remote system 1049(only useful if the peer supports it). 1050.It Cm ~C 1051Open command line. 1052Currently this allows the addition of port forwardings using the 1053.Fl L , 1054.Fl R 1055and 1056.Fl D 1057options (see above). 1058It also allows the cancellation of existing port-forwardings 1059with 1060.Sm off 1061.Fl KL Oo Ar bind_address : Oc Ar port 1062.Sm on 1063for local, 1064.Sm off 1065.Fl KR Oo Ar bind_address : Oc Ar port 1066.Sm on 1067for remote and 1068.Sm off 1069.Fl KD Oo Ar bind_address : Oc Ar port 1070.Sm on 1071for dynamic port-forwardings. 1072.Ic !\& Ns Ar command 1073allows the user to execute a local command if the 1074.Ic PermitLocalCommand 1075option is enabled in 1076.Xr ssh_config 5 . 1077Basic help is available, using the 1078.Fl h 1079option. 1080.It Cm ~R 1081Request rekeying of the connection 1082(only useful if the peer supports it). 1083.It Cm ~V 1084Decrease the verbosity 1085.Pq Ic LogLevel 1086when errors are being written to stderr. 1087.It Cm ~v 1088Increase the verbosity 1089.Pq Ic LogLevel 1090when errors are being written to stderr. 1091.El 1092.Sh TCP FORWARDING 1093Forwarding of arbitrary TCP connections over the secure channel can 1094be specified either on the command line or in a configuration file. 1095One possible application of TCP forwarding is a secure connection to a 1096mail server; another is going through firewalls. 1097.Pp 1098In the example below, we look at encrypting communication between 1099an IRC client and server, even though the IRC server does not directly 1100support encrypted communications. 1101This works as follows: 1102the user connects to the remote host using 1103.Nm , 1104specifying a port to be used to forward connections 1105to the remote server. 1106After that it is possible to start the service which is to be encrypted 1107on the client machine, 1108connecting to the same local port, 1109and 1110.Nm 1111will encrypt and forward the connection. 1112.Pp 1113The following example tunnels an IRC session from client machine 1114.Dq 127.0.0.1 1115(localhost) 1116to remote server 1117.Dq server.example.com : 1118.Bd -literal -offset 4n 1119$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 1120$ irc -c '#users' -p 1234 pinky 127.0.0.1 1121.Ed 1122.Pp 1123This tunnels a connection to IRC server 1124.Dq server.example.com , 1125joining channel 1126.Dq #users , 1127nickname 1128.Dq pinky , 1129using port 1234. 1130It doesn't matter which port is used, 1131as long as it's greater than 1023 1132(remember, only root can open sockets on privileged ports) 1133and doesn't conflict with any ports already in use. 1134The connection is forwarded to port 6667 on the remote server, 1135since that's the standard port for IRC services. 1136.Pp 1137The 1138.Fl f 1139option backgrounds 1140.Nm 1141and the remote command 1142.Dq sleep 10 1143is specified to allow an amount of time 1144(10 seconds, in the example) 1145to start the service which is to be tunnelled. 1146If no connections are made within the time specified, 1147.Nm 1148will exit. 1149.Sh X11 FORWARDING 1150If the 1151.Cm ForwardX11 1152variable is set to 1153.Dq yes 1154(or see the description of the 1155.Fl X , 1156.Fl x , 1157and 1158.Fl Y 1159options above) 1160and the user is using X11 (the 1161.Ev DISPLAY 1162environment variable is set), the connection to the X11 display is 1163automatically forwarded to the remote side in such a way that any X11 1164programs started from the shell (or command) will go through the 1165encrypted channel, and the connection to the real X server will be made 1166from the local machine. 1167The user should not manually set 1168.Ev DISPLAY . 1169Forwarding of X11 connections can be 1170configured on the command line or in configuration files. 1171.Pp 1172The 1173.Ev DISPLAY 1174value set by 1175.Nm 1176will point to the server machine, but with a display number greater than zero. 1177This is normal, and happens because 1178.Nm 1179creates a 1180.Dq proxy 1181X server on the server machine for forwarding the 1182connections over the encrypted channel. 1183.Pp 1184.Nm 1185will also automatically set up Xauthority data on the server machine. 1186For this purpose, it will generate a random authorization cookie, 1187store it in Xauthority on the server, and verify that any forwarded 1188connections carry this cookie and replace it by the real cookie when 1189the connection is opened. 1190The real authentication cookie is never 1191sent to the server machine (and no cookies are sent in the plain). 1192.Pp 1193If the 1194.Cm ForwardAgent 1195variable is set to 1196.Dq yes 1197(or see the description of the 1198.Fl A 1199and 1200.Fl a 1201options above) and 1202the user is using an authentication agent, the connection to the agent 1203is automatically forwarded to the remote side. 1204.Sh VERIFYING HOST KEYS 1205When connecting to a server for the first time, 1206a fingerprint of the server's public key is presented to the user 1207(unless the option 1208.Cm StrictHostKeyChecking 1209has been disabled). 1210Fingerprints can be determined using 1211.Xr ssh-keygen 1 : 1212.Pp 1213.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key 1214.Pp 1215If the fingerprint is already known, it can be matched 1216and the key can be accepted or rejected. 1217If only legacy (MD5) fingerprints for the server are available, the 1218.Xr ssh-keygen 1 1219.Fl E 1220option may be used to downgrade the fingerprint algorithm to match. 1221.Pp 1222Because of the difficulty of comparing host keys 1223just by looking at fingerprint strings, 1224there is also support to compare host keys visually, 1225using 1226.Em random art . 1227By setting the 1228.Cm VisualHostKey 1229option to 1230.Dq yes , 1231a small ASCII graphic gets displayed on every login to a server, no matter 1232if the session itself is interactive or not. 1233By learning the pattern a known server produces, a user can easily 1234find out that the host key has changed when a completely different pattern 1235is displayed. 1236Because these patterns are not unambiguous however, a pattern that looks 1237similar to the pattern remembered only gives a good probability that the 1238host key is the same, not guaranteed proof. 1239.Pp 1240To get a listing of the fingerprints along with their random art for 1241all known hosts, the following command line can be used: 1242.Pp 1243.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts 1244.Pp 1245If the fingerprint is unknown, 1246an alternative method of verification is available: 1247SSH fingerprints verified by DNS. 1248An additional resource record (RR), 1249SSHFP, 1250is added to a zonefile 1251and the connecting client is able to match the fingerprint 1252with that of the key presented. 1253.Pp 1254In this example, we are connecting a client to a server, 1255.Dq host.example.com . 1256The SSHFP resource records should first be added to the zonefile for 1257host.example.com: 1258.Bd -literal -offset indent 1259$ ssh-keygen -r host.example.com. 1260.Ed 1261.Pp 1262The output lines will have to be added to the zonefile. 1263To check that the zone is answering fingerprint queries: 1264.Pp 1265.Dl $ dig -t SSHFP host.example.com 1266.Pp 1267Finally the client connects: 1268.Bd -literal -offset indent 1269$ ssh -o "VerifyHostKeyDNS ask" host.example.com 1270[...] 1271Matching host key fingerprint found in DNS. 1272Are you sure you want to continue connecting (yes/no)? 1273.Ed 1274.Pp 1275See the 1276.Cm VerifyHostKeyDNS 1277option in 1278.Xr ssh_config 5 1279for more information. 1280.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS 1281.Nm 1282contains support for Virtual Private Network (VPN) tunnelling 1283using the 1284.Xr tun 4 1285network pseudo-device, 1286allowing two networks to be joined securely. 1287The 1288.Xr sshd_config 5 1289configuration option 1290.Cm PermitTunnel 1291controls whether the server supports this, 1292and at what level (layer 2 or 3 traffic). 1293.Pp 1294The following example would connect client network 10.0.50.0/24 1295with remote network 10.0.99.0/24 using a point-to-point connection 1296from 10.1.1.1 to 10.1.1.2, 1297provided that the SSH server running on the gateway to the remote network, 1298at 192.168.1.15, allows it. 1299.Pp 1300On the client: 1301.Bd -literal -offset indent 1302# ssh -f -w 0:1 192.168.1.15 true 1303# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252 1304# route add 10.0.99.0/24 10.1.1.2 1305.Ed 1306.Pp 1307On the server: 1308.Bd -literal -offset indent 1309# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252 1310# route add 10.0.50.0/24 10.1.1.1 1311.Ed 1312.Pp 1313Client access may be more finely tuned via the 1314.Pa /root/.ssh/authorized_keys 1315file (see below) and the 1316.Cm PermitRootLogin 1317server option. 1318The following entry would permit connections on 1319.Xr tun 4 1320device 1 from user 1321.Dq jane 1322and on tun device 2 from user 1323.Dq john , 1324if 1325.Cm PermitRootLogin 1326is set to 1327.Dq forced-commands-only : 1328.Bd -literal -offset 2n 1329tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane 1330tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john 1331.Ed 1332.Pp 1333Since an SSH-based setup entails a fair amount of overhead, 1334it may be more suited to temporary setups, 1335such as for wireless VPNs. 1336More permanent VPNs are better provided by tools such as 1337.Xr ipsecctl 8 1338and 1339.Xr isakmpd 8 . 1340.Sh ENVIRONMENT 1341.Nm 1342will normally set the following environment variables: 1343.Bl -tag -width "SSH_ORIGINAL_COMMAND" 1344.It Ev DISPLAY 1345The 1346.Ev DISPLAY 1347variable indicates the location of the X11 server. 1348It is automatically set by 1349.Nm 1350to point to a value of the form 1351.Dq hostname:n , 1352where 1353.Dq hostname 1354indicates the host where the shell runs, and 1355.Sq n 1356is an integer \*(Ge 1. 1357.Nm 1358uses this special value to forward X11 connections over the secure 1359channel. 1360The user should normally not set 1361.Ev DISPLAY 1362explicitly, as that 1363will render the X11 connection insecure (and will require the user to 1364manually copy any required authorization cookies). 1365.It Ev HOME 1366Set to the path of the user's home directory. 1367.It Ev LOGNAME 1368Synonym for 1369.Ev USER ; 1370set for compatibility with systems that use this variable. 1371.It Ev MAIL 1372Set to the path of the user's mailbox. 1373.It Ev PATH 1374Set to the default 1375.Ev PATH , 1376as specified when compiling 1377.Nm . 1378.It Ev SSH_ASKPASS 1379If 1380.Nm 1381needs a passphrase, it will read the passphrase from the current 1382terminal if it was run from a terminal. 1383If 1384.Nm 1385does not have a terminal associated with it but 1386.Ev DISPLAY 1387and 1388.Ev SSH_ASKPASS 1389are set, it will execute the program specified by 1390.Ev SSH_ASKPASS 1391and open an X11 window to read the passphrase. 1392This is particularly useful when calling 1393.Nm 1394from a 1395.Pa .xsession 1396or related script. 1397(Note that on some machines it 1398may be necessary to redirect the input from 1399.Pa /dev/null 1400to make this work.) 1401.It Ev SSH_AUTH_SOCK 1402Identifies the path of a 1403.Ux Ns -domain 1404socket used to communicate with the agent. 1405.It Ev SSH_CONNECTION 1406Identifies the client and server ends of the connection. 1407The variable contains 1408four space-separated values: client IP address, client port number, 1409server IP address, and server port number. 1410.It Ev SSH_ORIGINAL_COMMAND 1411This variable contains the original command line if a forced command 1412is executed. 1413It can be used to extract the original arguments. 1414.It Ev SSH_TTY 1415This is set to the name of the tty (path to the device) associated 1416with the current shell or command. 1417If the current session has no tty, 1418this variable is not set. 1419.It Ev SSH_TUNNEL 1420Optionally set by 1421.Xr sshd 8 1422to contain the interface names assigned if tunnel forwarding was 1423requested by the client. 1424.It Ev SSH_USER_AUTH 1425Optionally set by 1426.Xr sshd 8 , 1427this variable may contain a pathname to a file that lists the authentication 1428methods successfully used when the session was established, including any 1429public keys that were used. 1430.It Ev TZ 1431This variable is set to indicate the present time zone if it 1432was set when the daemon was started (i.e. the daemon passes the value 1433on to new connections). 1434.It Ev USER 1435Set to the name of the user logging in. 1436.El 1437.Pp 1438Additionally, 1439.Nm 1440reads 1441.Pa ~/.ssh/environment , 1442and adds lines of the format 1443.Dq VARNAME=value 1444to the environment if the file exists and users are allowed to 1445change their environment. 1446For more information, see the 1447.Cm PermitUserEnvironment 1448option in 1449.Xr sshd_config 5 . 1450.Sh FILES 1451.Bl -tag -width Ds -compact 1452.It Pa ~/.rhosts 1453This file is used for host-based authentication (see above). 1454On some machines this file may need to be 1455world-readable if the user's home directory is on an NFS partition, 1456because 1457.Xr sshd 8 1458reads it as root. 1459Additionally, this file must be owned by the user, 1460and must not have write permissions for anyone else. 1461The recommended 1462permission for most machines is read/write for the user, and not 1463accessible by others. 1464.Pp 1465.It Pa ~/.shosts 1466This file is used in exactly the same way as 1467.Pa .rhosts , 1468but allows host-based authentication without permitting login with 1469rlogin/rsh. 1470.Pp 1471.It Pa ~/.ssh/ 1472This directory is the default location for all user-specific configuration 1473and authentication information. 1474There is no general requirement to keep the entire contents of this directory 1475secret, but the recommended permissions are read/write/execute for the user, 1476and not accessible by others. 1477.Pp 1478.It Pa ~/.ssh/authorized_keys 1479Lists the public keys (DSA, ECDSA, Ed25519, RSA) 1480that can be used for logging in as this user. 1481The format of this file is described in the 1482.Xr sshd 8 1483manual page. 1484This file is not highly sensitive, but the recommended 1485permissions are read/write for the user, and not accessible by others. 1486.Pp 1487.It Pa ~/.ssh/config 1488This is the per-user configuration file. 1489The file format and configuration options are described in 1490.Xr ssh_config 5 . 1491Because of the potential for abuse, this file must have strict permissions: 1492read/write for the user, and not writable by others. 1493.Pp 1494.It Pa ~/.ssh/environment 1495Contains additional definitions for environment variables; see 1496.Sx ENVIRONMENT , 1497above. 1498.Pp 1499.It Pa ~/.ssh/id_dsa 1500.It Pa ~/.ssh/id_ecdsa 1501.It Pa ~/.ssh/id_ed25519 1502.It Pa ~/.ssh/id_rsa 1503Contains the private key for authentication. 1504These files 1505contain sensitive data and should be readable by the user but not 1506accessible by others (read/write/execute). 1507.Nm 1508will simply ignore a private key file if it is accessible by others. 1509It is possible to specify a passphrase when 1510generating the key which will be used to encrypt the 1511sensitive part of this file using AES-128. 1512.Pp 1513.It Pa ~/.ssh/id_dsa.pub 1514.It Pa ~/.ssh/id_ecdsa.pub 1515.It Pa ~/.ssh/id_ed25519.pub 1516.It Pa ~/.ssh/id_rsa.pub 1517Contains the public key for authentication. 1518These files are not 1519sensitive and can (but need not) be readable by anyone. 1520.Pp 1521.It Pa ~/.ssh/known_hosts 1522Contains a list of host keys for all hosts the user has logged into 1523that are not already in the systemwide list of known host keys. 1524See 1525.Xr sshd 8 1526for further details of the format of this file. 1527.Pp 1528.It Pa ~/.ssh/rc 1529Commands in this file are executed by 1530.Nm 1531when the user logs in, just before the user's shell (or command) is 1532started. 1533See the 1534.Xr sshd 8 1535manual page for more information. 1536.Pp 1537.It Pa /etc/hosts.equiv 1538This file is for host-based authentication (see above). 1539It should only be writable by root. 1540.Pp 1541.It Pa /etc/shosts.equiv 1542This file is used in exactly the same way as 1543.Pa hosts.equiv , 1544but allows host-based authentication without permitting login with 1545rlogin/rsh. 1546.Pp 1547.It Pa /etc/ssh/ssh_config 1548Systemwide configuration file. 1549The file format and configuration options are described in 1550.Xr ssh_config 5 . 1551.Pp 1552.It Pa /etc/ssh/ssh_host_key 1553.It Pa /etc/ssh/ssh_host_dsa_key 1554.It Pa /etc/ssh/ssh_host_ecdsa_key 1555.It Pa /etc/ssh/ssh_host_ed25519_key 1556.It Pa /etc/ssh/ssh_host_rsa_key 1557These files contain the private parts of the host keys 1558and are used for host-based authentication. 1559.Pp 1560.It Pa /etc/ssh/ssh_known_hosts 1561Systemwide list of known host keys. 1562This file should be prepared by the 1563system administrator to contain the public host keys of all machines in the 1564organization. 1565It should be world-readable. 1566See 1567.Xr sshd 8 1568for further details of the format of this file. 1569.Pp 1570.It Pa /etc/ssh/sshrc 1571Commands in this file are executed by 1572.Nm 1573when the user logs in, just before the user's shell (or command) is started. 1574See the 1575.Xr sshd 8 1576manual page for more information. 1577.El 1578.Sh EXIT STATUS 1579.Nm 1580exits with the exit status of the remote command or with 255 1581if an error occurred. 1582.Sh SEE ALSO 1583.Xr scp 1 , 1584.Xr sftp 1 , 1585.Xr ssh-add 1 , 1586.Xr ssh-agent 1 , 1587.Xr ssh-keygen 1 , 1588.Xr ssh-keyscan 1 , 1589.Xr tun 4 , 1590.Xr ssh_config 5 , 1591.Xr ssh-keysign 8 , 1592.Xr sshd 8 1593.Sh STANDARDS 1594.Rs 1595.%A S. Lehtinen 1596.%A C. Lonvick 1597.%D January 2006 1598.%R RFC 4250 1599.%T The Secure Shell (SSH) Protocol Assigned Numbers 1600.Re 1601.Pp 1602.Rs 1603.%A T. Ylonen 1604.%A C. Lonvick 1605.%D January 2006 1606.%R RFC 4251 1607.%T The Secure Shell (SSH) Protocol Architecture 1608.Re 1609.Pp 1610.Rs 1611.%A T. Ylonen 1612.%A C. Lonvick 1613.%D January 2006 1614.%R RFC 4252 1615.%T The Secure Shell (SSH) Authentication Protocol 1616.Re 1617.Pp 1618.Rs 1619.%A T. Ylonen 1620.%A C. Lonvick 1621.%D January 2006 1622.%R RFC 4253 1623.%T The Secure Shell (SSH) Transport Layer Protocol 1624.Re 1625.Pp 1626.Rs 1627.%A T. Ylonen 1628.%A C. Lonvick 1629.%D January 2006 1630.%R RFC 4254 1631.%T The Secure Shell (SSH) Connection Protocol 1632.Re 1633.Pp 1634.Rs 1635.%A J. Schlyter 1636.%A W. Griffin 1637.%D January 2006 1638.%R RFC 4255 1639.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints 1640.Re 1641.Pp 1642.Rs 1643.%A F. Cusack 1644.%A M. Forssen 1645.%D January 2006 1646.%R RFC 4256 1647.%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH) 1648.Re 1649.Pp 1650.Rs 1651.%A J. Galbraith 1652.%A P. Remaker 1653.%D January 2006 1654.%R RFC 4335 1655.%T The Secure Shell (SSH) Session Channel Break Extension 1656.Re 1657.Pp 1658.Rs 1659.%A M. Bellare 1660.%A T. Kohno 1661.%A C. Namprempre 1662.%D January 2006 1663.%R RFC 4344 1664.%T The Secure Shell (SSH) Transport Layer Encryption Modes 1665.Re 1666.Pp 1667.Rs 1668.%A B. Harris 1669.%D January 2006 1670.%R RFC 4345 1671.%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol 1672.Re 1673.Pp 1674.Rs 1675.%A M. Friedl 1676.%A N. Provos 1677.%A W. Simpson 1678.%D March 2006 1679.%R RFC 4419 1680.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol 1681.Re 1682.Pp 1683.Rs 1684.%A J. Galbraith 1685.%A R. Thayer 1686.%D November 2006 1687.%R RFC 4716 1688.%T The Secure Shell (SSH) Public Key File Format 1689.Re 1690.Pp 1691.Rs 1692.%A D. Stebila 1693.%A J. Green 1694.%D December 2009 1695.%R RFC 5656 1696.%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer 1697.Re 1698.Pp 1699.Rs 1700.%A A. Perrig 1701.%A D. Song 1702.%D 1999 1703.%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99) 1704.%T Hash Visualization: a New Technique to improve Real-World Security 1705.Re 1706.Sh AUTHORS 1707OpenSSH is a derivative of the original and free 1708ssh 1.2.12 release by Tatu Ylonen. 1709Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 1710Theo de Raadt and Dug Song 1711removed many bugs, re-added newer features and 1712created OpenSSH. 1713Markus Friedl contributed the support for SSH 1714protocol versions 1.5 and 2.0. 1715