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 1.376 2016/07/16 06:57:55 jmc Exp $ 37.\" $FreeBSD$ 38.Dd $Mdocdate: July 16 2016 $ 39.Dt SSH 1 40.Os 41.Sh NAME 42.Nm ssh 43.Nd OpenSSH SSH client (remote login program) 44.Sh SYNOPSIS 45.Nm ssh 46.Bk -words 47.Op Fl 1246AaCfGgKkMNnqsTtVvXxYy 48.Op Fl b Ar bind_address 49.Op Fl c Ar cipher_spec 50.Op Fl D Oo Ar bind_address : Oc Ns Ar port 51.Op Fl E Ar log_file 52.Op Fl e Ar escape_char 53.Op Fl F Ar configfile 54.Op Fl I Ar pkcs11 55.Op Fl i Ar identity_file 56.Op Fl J Oo Ar user Ns @ Oc Ns Ar host Ns Op : Ns Ar port 57.Op Fl L Ar address 58.Op Fl l Ar login_name 59.Op Fl m Ar mac_spec 60.Op Fl O Ar ctl_cmd 61.Op Fl o Ar option 62.Op Fl p Ar port 63.Op Fl Q Ar query_option 64.Op Fl R Ar address 65.Op Fl S Ar ctl_path 66.Op Fl W Ar host : Ns Ar port 67.Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun 68.Oo Ar user Ns @ Oc Ns Ar hostname 69.Op Ar command 70.Ek 71.Sh DESCRIPTION 72.Nm 73(SSH client) is a program for logging into a remote machine and for 74executing commands on a remote machine. 75It is intended to 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 hostname 84(with optional 85.Ar user 86name). 87The user must prove 88his/her identity to the remote machine using one of several methods 89(see below). 90.Pp 91If 92.Ar command 93is specified, 94it is executed on the remote host instead of a login shell. 95.Pp 96The options are as follows: 97.Pp 98.Bl -tag -width Ds -compact 99.It Fl 1 100Forces 101.Nm 102to try protocol version 1 only. 103.Pp 104.It Fl 2 105Forces 106.Nm 107to try protocol version 2 only. 108.Pp 109.It Fl 4 110Forces 111.Nm 112to use IPv4 addresses only. 113.Pp 114.It Fl 6 115Forces 116.Nm 117to use IPv6 addresses only. 118.Pp 119.It Fl A 120Enables forwarding of the authentication agent connection. 121This can also be specified on a per-host basis in a configuration file. 122.Pp 123Agent forwarding should be enabled with caution. 124Users with the ability to bypass file permissions on the remote host 125(for the agent's 126.Ux Ns -domain 127socket) can access the local agent through the forwarded connection. 128An attacker cannot obtain key material from the agent, 129however they can perform operations on the keys that enable them to 130authenticate using the identities loaded into the agent. 131.Pp 132.It Fl a 133Disables forwarding of the authentication agent connection. 134.Pp 135.It Fl b Ar bind_address 136Use 137.Ar bind_address 138on the local machine as the source address 139of the connection. 140Only useful on systems with more than one address. 141.Pp 142.It Fl C 143Requests compression of all data (including stdin, stdout, stderr, and 144data for forwarded X11, TCP and 145.Ux Ns -domain 146connections). 147The compression algorithm is the same used by 148.Xr gzip 1 , 149and the 150.Dq level 151can be controlled by the 152.Cm CompressionLevel 153option for protocol version 1. 154Compression is desirable on modem lines and other 155slow connections, but will only slow down things on fast networks. 156The default value can be set on a host-by-host basis in the 157configuration files; see the 158.Cm Compression 159option. 160.Pp 161.It Fl c Ar cipher_spec 162Selects the cipher specification for encrypting the session. 163.Pp 164Protocol version 1 allows specification of a single cipher. 165The supported values are 166.Dq 3des , 167.Dq blowfish , 168and 169.Dq des . 170For protocol version 2, 171.Ar cipher_spec 172is a comma-separated list of ciphers 173listed in order of preference. 174See the 175.Cm Ciphers 176keyword in 177.Xr ssh_config 5 178for more information. 179.Pp 180.It Fl D Xo 181.Sm off 182.Oo Ar bind_address : Oc 183.Ar port 184.Sm on 185.Xc 186Specifies a local 187.Dq dynamic 188application-level port forwarding. 189This works by allocating a socket to listen to 190.Ar port 191on the local side, optionally bound to the specified 192.Ar bind_address . 193Whenever a connection is made to this port, the 194connection is forwarded over the secure channel, and the application 195protocol is then used to determine where to connect to from the 196remote machine. 197Currently the SOCKS4 and SOCKS5 protocols are supported, and 198.Nm 199will act as a SOCKS server. 200Only root can forward privileged ports. 201Dynamic port forwardings can also be specified in the configuration file. 202.Pp 203IPv6 addresses can be specified by enclosing the address in square brackets. 204Only the superuser can forward privileged ports. 205By default, the local port is bound in accordance with the 206.Cm GatewayPorts 207setting. 208However, an explicit 209.Ar bind_address 210may be used to bind the connection to a specific address. 211The 212.Ar bind_address 213of 214.Dq localhost 215indicates that the listening port be bound for local use only, while an 216empty address or 217.Sq * 218indicates that the port should be available from all interfaces. 219.Pp 220.It Fl E Ar log_file 221Append debug logs to 222.Ar log_file 223instead of standard error. 224.Pp 225.It Fl e Ar escape_char 226Sets the escape character for sessions with a pty (default: 227.Ql ~ ) . 228The escape character is only recognized at the beginning of a line. 229The escape character followed by a dot 230.Pq Ql \&. 231closes the connection; 232followed by control-Z suspends the connection; 233and followed by itself sends the escape character once. 234Setting the character to 235.Dq none 236disables any escapes and makes the session fully transparent. 237.Pp 238.It Fl F Ar configfile 239Specifies an alternative per-user configuration file. 240If a configuration file is given on the command line, 241the system-wide configuration file 242.Pq Pa /etc/ssh/ssh_config 243will be ignored. 244The default for the per-user configuration file is 245.Pa ~/.ssh/config . 246.Pp 247.It Fl f 248Requests 249.Nm 250to go to background just before command execution. 251This is useful if 252.Nm 253is going to ask for passwords or passphrases, but the user 254wants it in the background. 255This implies 256.Fl n . 257The recommended way to start X11 programs at a remote site is with 258something like 259.Ic ssh -f host xterm . 260.Pp 261If the 262.Cm ExitOnForwardFailure 263configuration option is set to 264.Dq yes , 265then a client started with 266.Fl f 267will wait for all remote port forwards to be successfully established 268before placing itself in the background. 269.Pp 270.It Fl G 271Causes 272.Nm 273to print its configuration after evaluating 274.Cm Host 275and 276.Cm Match 277blocks and exit. 278.Pp 279.It Fl g 280Allows remote hosts to connect to local forwarded ports. 281If used on a multiplexed connection, then this option must be specified 282on the master process. 283.Pp 284.It Fl I Ar pkcs11 285Specify the PKCS#11 shared library 286.Nm 287should use to communicate with a PKCS#11 token providing the user's 288private RSA key. 289.Pp 290.It Fl i Ar identity_file 291Selects a file from which the identity (private key) for 292public key authentication is read. 293The default is 294.Pa ~/.ssh/identity 295for protocol version 1, and 296.Pa ~/.ssh/id_dsa , 297.Pa ~/.ssh/id_ecdsa , 298.Pa ~/.ssh/id_ed25519 299and 300.Pa ~/.ssh/id_rsa 301for protocol version 2. 302Identity files may also be specified on 303a per-host basis in the configuration file. 304It is possible to have multiple 305.Fl i 306options (and multiple identities specified in 307configuration files). 308If no certificates have been explicitly specified by the 309.Cm CertificateFile 310directive, 311.Nm 312will also try to load certificate information from the filename obtained 313by appending 314.Pa -cert.pub 315to identity filenames. 316.Pp 317.It Fl J Xo 318.Sm off 319.Op Ar user No @ 320.Ar host 321.Op : Ar port 322.Sm on 323.Xc 324Connect to the target host by first making a 325.Nm 326connection to the jump 327.Ar host 328and then establishing a TCP forwarding to the ultimate destination from 329there. 330Multiple jump hops may be specified separated by comma characters. 331This is a shortcut to specify a 332.Cm ProxyJump 333configuration directive. 334.Pp 335.It Fl K 336Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI 337credentials to the server. 338.Pp 339.It Fl k 340Disables forwarding (delegation) of GSSAPI credentials to the server. 341.Pp 342.It Fl L Xo 343.Sm off 344.Oo Ar bind_address : Oc 345.Ar port : host : hostport 346.Sm on 347.Xc 348.It Fl L Xo 349.Sm off 350.Oo Ar bind_address : Oc 351.Ar port : remote_socket 352.Sm on 353.Xc 354.It Fl L Xo 355.Sm off 356.Ar local_socket : host : hostport 357.Sm on 358.Xc 359.It Fl L Xo 360.Sm off 361.Ar local_socket : remote_socket 362.Sm on 363.Xc 364Specifies that connections to the given TCP port or Unix socket on the local 365(client) host are to be forwarded to the given host and port, or Unix socket, 366on the remote side. 367This works by allocating a socket to listen to either a TCP 368.Ar port 369on the local side, optionally bound to the specified 370.Ar bind_address , 371or to a Unix socket. 372Whenever a connection is made to the local port or socket, the 373connection is forwarded over the secure channel, and a connection is 374made to either 375.Ar host 376port 377.Ar hostport , 378or the Unix socket 379.Ar remote_socket , 380from the remote machine. 381.Pp 382Port forwardings can also be specified in the configuration file. 383Only the superuser can forward privileged ports. 384IPv6 addresses can be specified by enclosing the address in square brackets. 385.Pp 386By default, the local port is bound in accordance with the 387.Cm GatewayPorts 388setting. 389However, an explicit 390.Ar bind_address 391may be used to bind the connection to a specific address. 392The 393.Ar bind_address 394of 395.Dq localhost 396indicates that the listening port be bound for local use only, while an 397empty address or 398.Sq * 399indicates that the port should be available from all interfaces. 400.Pp 401.It Fl l Ar login_name 402Specifies the user to log in as on the remote machine. 403This also may be specified on a per-host basis in the configuration file. 404.Pp 405.It Fl M 406Places the 407.Nm 408client into 409.Dq master 410mode for connection sharing. 411Multiple 412.Fl M 413options places 414.Nm 415into 416.Dq master 417mode with confirmation required before slave connections are accepted. 418Refer to the description of 419.Cm ControlMaster 420in 421.Xr ssh_config 5 422for details. 423.Pp 424.It Fl m Ar mac_spec 425A comma-separated list of MAC (message authentication code) algorithms, 426specified in order of preference. 427See the 428.Cm MACs 429keyword for more information. 430.Pp 431.It Fl N 432Do not execute a remote command. 433This is useful for just forwarding ports. 434.Pp 435.It Fl n 436Redirects stdin from 437.Pa /dev/null 438(actually, prevents reading from stdin). 439This must be used when 440.Nm 441is run in the background. 442A common trick is to use this to run X11 programs on a remote machine. 443For example, 444.Ic ssh -n shadows.cs.hut.fi emacs & 445will start an emacs on shadows.cs.hut.fi, and the X11 446connection will be automatically forwarded over an encrypted channel. 447The 448.Nm 449program will be put in the background. 450(This does not work if 451.Nm 452needs to ask for a password or passphrase; see also the 453.Fl f 454option.) 455.Pp 456.It Fl O Ar ctl_cmd 457Control an active connection multiplexing master process. 458When the 459.Fl O 460option is specified, the 461.Ar ctl_cmd 462argument is interpreted and passed to the master process. 463Valid commands are: 464.Dq check 465(check that the master process is running), 466.Dq forward 467(request forwardings without command execution), 468.Dq cancel 469(cancel forwardings), 470.Dq exit 471(request the master to exit), and 472.Dq stop 473(request the master to stop accepting further multiplexing requests). 474.Pp 475.It Fl o Ar option 476Can be used to give options in the format used in the configuration file. 477This is useful for specifying options for which there is no separate 478command-line flag. 479For full details of the options listed below, and their possible values, see 480.Xr ssh_config 5 . 481.Pp 482.Bl -tag -width Ds -offset indent -compact 483.It AddKeysToAgent 484.It AddressFamily 485.It BatchMode 486.It BindAddress 487.It CanonicalDomains 488.It CanonicalizeFallbackLocal 489.It CanonicalizeHostname 490.It CanonicalizeMaxDots 491.It CanonicalizePermittedCNAMEs 492.It CertificateFile 493.It ChallengeResponseAuthentication 494.It CheckHostIP 495.It Cipher 496.It Ciphers 497.It ClearAllForwardings 498.It Compression 499.It CompressionLevel 500.It ConnectionAttempts 501.It ConnectTimeout 502.It ControlMaster 503.It ControlPath 504.It ControlPersist 505.It DynamicForward 506.It EscapeChar 507.It ExitOnForwardFailure 508.It FingerprintHash 509.It ForwardAgent 510.It ForwardX11 511.It ForwardX11Timeout 512.It ForwardX11Trusted 513.It GatewayPorts 514.It GlobalKnownHostsFile 515.It GSSAPIAuthentication 516.It GSSAPIDelegateCredentials 517.It HashKnownHosts 518.It Host 519.It HostbasedAuthentication 520.It HostbasedKeyTypes 521.It HostKeyAlgorithms 522.It HostKeyAlias 523.It HostName 524.It IdentitiesOnly 525.It IdentityAgent 526.It IdentityFile 527.It Include 528.It IPQoS 529.It KbdInteractiveAuthentication 530.It KbdInteractiveDevices 531.It KexAlgorithms 532.It LocalCommand 533.It LocalForward 534.It LogLevel 535.It MACs 536.It Match 537.It NoHostAuthenticationForLocalhost 538.It NumberOfPasswordPrompts 539.It PasswordAuthentication 540.It PermitLocalCommand 541.It PKCS11Provider 542.It Port 543.It PreferredAuthentications 544.It Protocol 545.It ProxyCommand 546.It ProxyJump 547.It ProxyUseFdpass 548.It PubkeyAcceptedKeyTypes 549.It PubkeyAuthentication 550.It RekeyLimit 551.It RemoteForward 552.It RequestTTY 553.It RhostsRSAAuthentication 554.It RSAAuthentication 555.It SendEnv 556.It ServerAliveInterval 557.It ServerAliveCountMax 558.It StreamLocalBindMask 559.It StreamLocalBindUnlink 560.It StrictHostKeyChecking 561.It TCPKeepAlive 562.It Tunnel 563.It TunnelDevice 564.It UpdateHostKeys 565.It UsePrivilegedPort 566.It User 567.It UserKnownHostsFile 568.It VerifyHostKeyDNS 569.It VersionAddendum 570.It VisualHostKey 571.It XAuthLocation 572.El 573.Pp 574.It Fl p Ar port 575Port to connect to on the remote host. 576This can be specified on a 577per-host basis in the configuration file. 578.Pp 579.It Fl Q Ar query_option 580Queries 581.Nm 582for the algorithms supported for the specified version 2. 583The available features are: 584.Ar cipher 585(supported symmetric ciphers), 586.Ar cipher-auth 587(supported symmetric ciphers that support authenticated encryption), 588.Ar mac 589(supported message integrity codes), 590.Ar kex 591(key exchange algorithms), 592.Ar key 593(key types), 594.Ar key-cert 595(certificate key types), 596.Ar key-plain 597(non-certificate key types), and 598.Ar protocol-version 599(supported SSH protocol versions). 600.Pp 601.It Fl q 602Quiet mode. 603Causes most warning and diagnostic messages to be suppressed. 604.Pp 605.It Fl R Xo 606.Sm off 607.Oo Ar bind_address : Oc 608.Ar port : host : hostport 609.Sm on 610.Xc 611.It Fl R Xo 612.Sm off 613.Oo Ar bind_address : Oc 614.Ar port : local_socket 615.Sm on 616.Xc 617.It Fl R Xo 618.Sm off 619.Ar remote_socket : host : hostport 620.Sm on 621.Xc 622.It Fl R Xo 623.Sm off 624.Ar remote_socket : local_socket 625.Sm on 626.Xc 627Specifies that connections to the given TCP port or Unix socket on the remote 628(server) host are to be forwarded to the given host and port, or Unix socket, 629on the local side. 630This works by allocating a socket to listen to either a TCP 631.Ar port 632or to a Unix socket on the remote side. 633Whenever a connection is made to this port or Unix socket, the 634connection is forwarded over the secure channel, and a connection 635is made to either 636.Ar host 637port 638.Ar hostport , 639or 640.Ar local_socket , 641from the local machine. 642.Pp 643Port forwardings can also be specified in the configuration file. 644Privileged ports can be forwarded only when 645logging in as root on the remote machine. 646IPv6 addresses can be specified by enclosing the address in square brackets. 647.Pp 648By default, TCP listening sockets on the server will be bound to the loopback 649interface only. 650This may be overridden by specifying a 651.Ar bind_address . 652An empty 653.Ar bind_address , 654or the address 655.Ql * , 656indicates that the remote socket should listen on all interfaces. 657Specifying a remote 658.Ar bind_address 659will only succeed if the server's 660.Cm GatewayPorts 661option is enabled (see 662.Xr sshd_config 5 ) . 663.Pp 664If the 665.Ar port 666argument is 667.Ql 0 , 668the listen port will be dynamically allocated on the server and reported 669to the client at run time. 670When used together with 671.Ic -O forward 672the allocated port will be printed to the standard output. 673.Pp 674.It Fl S Ar ctl_path 675Specifies the location of a control socket for connection sharing, 676or the string 677.Dq none 678to disable connection sharing. 679Refer to the description of 680.Cm ControlPath 681and 682.Cm ControlMaster 683in 684.Xr ssh_config 5 685for details. 686.Pp 687.It Fl s 688May be used to request invocation of a subsystem on the remote system. 689Subsystems facilitate the use of SSH 690as a secure transport for other applications (e.g.\& 691.Xr sftp 1 ) . 692The subsystem is specified as the remote command. 693.Pp 694.It Fl T 695Disable pseudo-terminal allocation. 696.Pp 697.It Fl t 698Force pseudo-terminal allocation. 699This can be used to execute arbitrary 700screen-based programs on a remote machine, which can be very useful, 701e.g. when implementing menu services. 702Multiple 703.Fl t 704options force tty allocation, even if 705.Nm 706has no local tty. 707.Pp 708.It Fl V 709Display the version number and exit. 710.Pp 711.It Fl v 712Verbose mode. 713Causes 714.Nm 715to print debugging messages about its progress. 716This is helpful in 717debugging connection, authentication, and configuration problems. 718Multiple 719.Fl v 720options increase the verbosity. 721The maximum is 3. 722.Pp 723.It Fl W Ar host : Ns Ar port 724Requests that standard input and output on the client be forwarded to 725.Ar host 726on 727.Ar port 728over the secure channel. 729Implies 730.Fl N , 731.Fl T , 732.Cm ExitOnForwardFailure 733and 734.Cm ClearAllForwardings , 735though these can be overridden in the configuration file or using 736.Fl o 737command line options. 738.Pp 739.It Fl w Xo 740.Ar local_tun Ns Op : Ns Ar remote_tun 741.Xc 742Requests 743tunnel 744device forwarding with the specified 745.Xr tun 4 746devices between the client 747.Pq Ar local_tun 748and the server 749.Pq Ar remote_tun . 750.Pp 751The devices may be specified by numerical ID or the keyword 752.Dq any , 753which uses the next available tunnel device. 754If 755.Ar remote_tun 756is not specified, it defaults to 757.Dq any . 758See also the 759.Cm Tunnel 760and 761.Cm TunnelDevice 762directives in 763.Xr ssh_config 5 . 764If the 765.Cm Tunnel 766directive is unset, it is set to the default tunnel mode, which is 767.Dq point-to-point . 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 protocols 1 and 2. 812The default is to use protocol 2 only, 813though this can be changed via the 814.Cm Protocol 815option in 816.Xr ssh_config 5 817or the 818.Fl 1 819and 820.Fl 2 821options (see above). 822Protocol 1 should not be used 823and is only offered to support legacy devices. 824It suffers from a number of cryptographic weaknesses 825and doesn't support many of the advanced features available for protocol 2. 826.Pp 827The methods available for authentication are: 828GSSAPI-based authentication, 829host-based authentication, 830public key authentication, 831challenge-response authentication, 832and password authentication. 833Authentication methods are tried in the order specified above, 834though 835.Cm PreferredAuthentications 836can be used to change the default order. 837.Pp 838Host-based authentication works as follows: 839If the machine the user logs in from is listed in 840.Pa /etc/hosts.equiv 841or 842.Pa /etc/shosts.equiv 843on the remote machine, and the user names are 844the same on both sides, or if the files 845.Pa ~/.rhosts 846or 847.Pa ~/.shosts 848exist in the user's home directory on the 849remote machine and contain a line containing the name of the client 850machine and the name of the user on that machine, the user is 851considered for login. 852Additionally, the server 853.Em must 854be able to verify the client's 855host key (see the description of 856.Pa /etc/ssh/ssh_known_hosts 857and 858.Pa ~/.ssh/known_hosts , 859below) 860for login to be permitted. 861This authentication method closes security holes due to IP 862spoofing, DNS spoofing, and routing spoofing. 863[Note to the administrator: 864.Pa /etc/hosts.equiv , 865.Pa ~/.rhosts , 866and the rlogin/rsh protocol in general, are inherently insecure and should be 867disabled if security is desired.] 868.Pp 869Public key authentication works as follows: 870The scheme is based on public-key cryptography, 871using cryptosystems 872where encryption and decryption are done using separate keys, 873and it is unfeasible to derive the decryption key from the encryption key. 874The idea is that each user creates a public/private 875key pair for authentication purposes. 876The server knows the public key, and only the user knows the private key. 877.Nm 878implements public key authentication protocol automatically, 879using one of the DSA, ECDSA, Ed25519 or RSA algorithms. 880The HISTORY section of 881.Xr ssl 8 882contains a brief discussion of the DSA and RSA algorithms. 883.Pp 884The file 885.Pa ~/.ssh/authorized_keys 886lists the public keys that are permitted for logging in. 887When the user logs in, the 888.Nm 889program tells the server which key pair it would like to use for 890authentication. 891The client proves that it has access to the private key 892and the server checks that the corresponding public key 893is authorized to accept the account. 894.Pp 895The user creates his/her key pair by running 896.Xr ssh-keygen 1 . 897This stores the private key in 898.Pa ~/.ssh/identity 899(protocol 1), 900.Pa ~/.ssh/id_dsa 901(DSA), 902.Pa ~/.ssh/id_ecdsa 903(ECDSA), 904.Pa ~/.ssh/id_ed25519 905(Ed25519), 906or 907.Pa ~/.ssh/id_rsa 908(RSA) 909and stores the public key in 910.Pa ~/.ssh/identity.pub 911(protocol 1), 912.Pa ~/.ssh/id_dsa.pub 913(DSA), 914.Pa ~/.ssh/id_ecdsa.pub 915(ECDSA), 916.Pa ~/.ssh/id_ed25519.pub 917(Ed25519), 918or 919.Pa ~/.ssh/id_rsa.pub 920(RSA) 921in the user's home directory. 922The user should then copy the public key 923to 924.Pa ~/.ssh/authorized_keys 925in his/her home directory on the remote machine. 926The 927.Pa authorized_keys 928file corresponds to the conventional 929.Pa ~/.rhosts 930file, and has one key 931per line, though the lines can be very long. 932After this, the user can log in without giving the password. 933.Pp 934A variation on public key authentication 935is available in the form of certificate authentication: 936instead of a set of public/private keys, 937signed certificates are used. 938This has the advantage that a single trusted certification authority 939can be used in place of many public/private keys. 940See the CERTIFICATES section of 941.Xr ssh-keygen 1 942for more information. 943.Pp 944The most convenient way to use public key or certificate authentication 945may be with an authentication agent. 946See 947.Xr ssh-agent 1 948and (optionally) the 949.Cm AddKeysToAgent 950directive in 951.Xr ssh_config 5 952for more information. 953.Pp 954Challenge-response authentication works as follows: 955The server sends an arbitrary 956.Qq challenge 957text, and prompts for a response. 958Examples of challenge-response authentication include 959.Bx 960Authentication (see 961.Xr login.conf 5 ) 962and PAM (some 963.Pf non- Ox 964systems). 965.Pp 966Finally, if other authentication methods fail, 967.Nm 968prompts the user for a password. 969The password is sent to the remote 970host for checking; however, since all communications are encrypted, 971the password cannot be seen by someone listening on the network. 972.Pp 973.Nm 974automatically maintains and checks a database containing 975identification for all hosts it has ever been used with. 976Host keys are stored in 977.Pa ~/.ssh/known_hosts 978in the user's home directory. 979Additionally, the file 980.Pa /etc/ssh/ssh_known_hosts 981is automatically checked for known hosts. 982Any new hosts are automatically added to the user's file. 983If a host's identification ever changes, 984.Nm 985warns about this and disables password authentication to prevent 986server spoofing or man-in-the-middle attacks, 987which could otherwise be used to circumvent the encryption. 988The 989.Cm StrictHostKeyChecking 990option can be used to control logins to machines whose 991host key is not known or has changed. 992.Pp 993When the user's identity has been accepted by the server, the server 994either executes the given command in a non-interactive session or, 995if no command has been specified, logs into the machine and gives 996the user a normal shell as an interactive session. 997All communication with 998the remote command or shell will be automatically encrypted. 999.Pp 1000If an interactive session is requested 1001.Nm 1002by default will only request a pseudo-terminal (pty) for interactive 1003sessions when the client has one. 1004The flags 1005.Fl T 1006and 1007.Fl t 1008can be used to override this behaviour. 1009.Pp 1010If a pseudo-terminal has been allocated the 1011user may use the escape characters noted below. 1012.Pp 1013If no pseudo-terminal has been allocated, 1014the session is transparent and can be used to reliably transfer binary data. 1015On most systems, setting the escape character to 1016.Dq none 1017will also make the session transparent even if a tty is used. 1018.Pp 1019The session terminates when the command or shell on the remote 1020machine exits and all X11 and TCP connections have been closed. 1021.Sh ESCAPE CHARACTERS 1022When a pseudo-terminal has been requested, 1023.Nm 1024supports a number of functions through the use of an escape character. 1025.Pp 1026A single tilde character can be sent as 1027.Ic ~~ 1028or by following the tilde by a character other than those described below. 1029The escape character must always follow a newline to be interpreted as 1030special. 1031The escape character can be changed in configuration files using the 1032.Cm EscapeChar 1033configuration directive or on the command line by the 1034.Fl e 1035option. 1036.Pp 1037The supported escapes (assuming the default 1038.Ql ~ ) 1039are: 1040.Bl -tag -width Ds 1041.It Cm ~. 1042Disconnect. 1043.It Cm ~^Z 1044Background 1045.Nm . 1046.It Cm ~# 1047List forwarded connections. 1048.It Cm ~& 1049Background 1050.Nm 1051at logout when waiting for forwarded connection / X11 sessions to terminate. 1052.It Cm ~? 1053Display a list of escape characters. 1054.It Cm ~B 1055Send a BREAK to the remote system 1056(only useful if the peer supports it). 1057.It Cm ~C 1058Open command line. 1059Currently this allows the addition of port forwardings using the 1060.Fl L , 1061.Fl R 1062and 1063.Fl D 1064options (see above). 1065It also allows the cancellation of existing port-forwardings 1066with 1067.Sm off 1068.Fl KL Oo Ar bind_address : Oc Ar port 1069.Sm on 1070for local, 1071.Sm off 1072.Fl KR Oo Ar bind_address : Oc Ar port 1073.Sm on 1074for remote and 1075.Sm off 1076.Fl KD Oo Ar bind_address : Oc Ar port 1077.Sm on 1078for dynamic port-forwardings. 1079.Ic !\& Ns Ar command 1080allows the user to execute a local command if the 1081.Ic PermitLocalCommand 1082option is enabled in 1083.Xr ssh_config 5 . 1084Basic help is available, using the 1085.Fl h 1086option. 1087.It Cm ~R 1088Request rekeying of the connection 1089(only useful if the peer supports it). 1090.It Cm ~V 1091Decrease the verbosity 1092.Pq Ic LogLevel 1093when errors are being written to stderr. 1094.It Cm ~v 1095Increase the verbosity 1096.Pq Ic LogLevel 1097when errors are being written to stderr. 1098.El 1099.Sh TCP FORWARDING 1100Forwarding of arbitrary TCP connections over the secure channel can 1101be specified either on the command line or in a configuration file. 1102One possible application of TCP forwarding is a secure connection to a 1103mail server; another is going through firewalls. 1104.Pp 1105In the example below, we look at encrypting communication between 1106an IRC client and server, even though the IRC server does not directly 1107support encrypted communications. 1108This works as follows: 1109the user connects to the remote host using 1110.Nm , 1111specifying a port to be used to forward connections 1112to the remote server. 1113After that it is possible to start the service which is to be encrypted 1114on the client machine, 1115connecting to the same local port, 1116and 1117.Nm 1118will encrypt and forward the connection. 1119.Pp 1120The following example tunnels an IRC session from client machine 1121.Dq 127.0.0.1 1122(localhost) 1123to remote server 1124.Dq server.example.com : 1125.Bd -literal -offset 4n 1126$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 1127$ irc -c '#users' -p 1234 pinky 127.0.0.1 1128.Ed 1129.Pp 1130This tunnels a connection to IRC server 1131.Dq server.example.com , 1132joining channel 1133.Dq #users , 1134nickname 1135.Dq pinky , 1136using port 1234. 1137It doesn't matter which port is used, 1138as long as it's greater than 1023 1139(remember, only root can open sockets on privileged ports) 1140and doesn't conflict with any ports already in use. 1141The connection is forwarded to port 6667 on the remote server, 1142since that's the standard port for IRC services. 1143.Pp 1144The 1145.Fl f 1146option backgrounds 1147.Nm 1148and the remote command 1149.Dq sleep 10 1150is specified to allow an amount of time 1151(10 seconds, in the example) 1152to start the service which is to be tunnelled. 1153If no connections are made within the time specified, 1154.Nm 1155will exit. 1156.Sh X11 FORWARDING 1157If the 1158.Cm ForwardX11 1159variable is set to 1160.Dq yes 1161(or see the description of the 1162.Fl X , 1163.Fl x , 1164and 1165.Fl Y 1166options above) 1167and the user is using X11 (the 1168.Ev DISPLAY 1169environment variable is set), the connection to the X11 display is 1170automatically forwarded to the remote side in such a way that any X11 1171programs started from the shell (or command) will go through the 1172encrypted channel, and the connection to the real X server will be made 1173from the local machine. 1174The user should not manually set 1175.Ev DISPLAY . 1176Forwarding of X11 connections can be 1177configured on the command line or in configuration files. 1178.Pp 1179The 1180.Ev DISPLAY 1181value set by 1182.Nm 1183will point to the server machine, but with a display number greater than zero. 1184This is normal, and happens because 1185.Nm 1186creates a 1187.Dq proxy 1188X server on the server machine for forwarding the 1189connections over the encrypted channel. 1190.Pp 1191.Nm 1192will also automatically set up Xauthority data on the server machine. 1193For this purpose, it will generate a random authorization cookie, 1194store it in Xauthority on the server, and verify that any forwarded 1195connections carry this cookie and replace it by the real cookie when 1196the connection is opened. 1197The real authentication cookie is never 1198sent to the server machine (and no cookies are sent in the plain). 1199.Pp 1200If the 1201.Cm ForwardAgent 1202variable is set to 1203.Dq yes 1204(or see the description of the 1205.Fl A 1206and 1207.Fl a 1208options above) and 1209the user is using an authentication agent, the connection to the agent 1210is automatically forwarded to the remote side. 1211.Sh VERIFYING HOST KEYS 1212When connecting to a server for the first time, 1213a fingerprint of the server's public key is presented to the user 1214(unless the option 1215.Cm StrictHostKeyChecking 1216has been disabled). 1217Fingerprints can be determined using 1218.Xr ssh-keygen 1 : 1219.Pp 1220.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key 1221.Pp 1222If the fingerprint is already known, it can be matched 1223and the key can be accepted or rejected. 1224If only legacy (MD5) fingerprints for the server are available, the 1225.Xr ssh-keygen 1 1226.Fl E 1227option may be used to downgrade the fingerprint algorithm to match. 1228.Pp 1229Because of the difficulty of comparing host keys 1230just by looking at fingerprint strings, 1231there is also support to compare host keys visually, 1232using 1233.Em random art . 1234By setting the 1235.Cm VisualHostKey 1236option to 1237.Dq yes , 1238a small ASCII graphic gets displayed on every login to a server, no matter 1239if the session itself is interactive or not. 1240By learning the pattern a known server produces, a user can easily 1241find out that the host key has changed when a completely different pattern 1242is displayed. 1243Because these patterns are not unambiguous however, a pattern that looks 1244similar to the pattern remembered only gives a good probability that the 1245host key is the same, not guaranteed proof. 1246.Pp 1247To get a listing of the fingerprints along with their random art for 1248all known hosts, the following command line can be used: 1249.Pp 1250.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts 1251.Pp 1252If the fingerprint is unknown, 1253an alternative method of verification is available: 1254SSH fingerprints verified by DNS. 1255An additional resource record (RR), 1256SSHFP, 1257is added to a zonefile 1258and the connecting client is able to match the fingerprint 1259with that of the key presented. 1260.Pp 1261In this example, we are connecting a client to a server, 1262.Dq host.example.com . 1263The SSHFP resource records should first be added to the zonefile for 1264host.example.com: 1265.Bd -literal -offset indent 1266$ ssh-keygen -r host.example.com. 1267.Ed 1268.Pp 1269The output lines will have to be added to the zonefile. 1270To check that the zone is answering fingerprint queries: 1271.Pp 1272.Dl $ dig -t SSHFP host.example.com 1273.Pp 1274Finally the client connects: 1275.Bd -literal -offset indent 1276$ ssh -o "VerifyHostKeyDNS ask" host.example.com 1277[...] 1278Matching host key fingerprint found in DNS. 1279Are you sure you want to continue connecting (yes/no)? 1280.Ed 1281.Pp 1282See the 1283.Cm VerifyHostKeyDNS 1284option in 1285.Xr ssh_config 5 1286for more information. 1287.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS 1288.Nm 1289contains support for Virtual Private Network (VPN) tunnelling 1290using the 1291.Xr tun 4 1292network pseudo-device, 1293allowing two networks to be joined securely. 1294The 1295.Xr sshd_config 5 1296configuration option 1297.Cm PermitTunnel 1298controls whether the server supports this, 1299and at what level (layer 2 or 3 traffic). 1300.Pp 1301The following example would connect client network 10.0.50.0/24 1302with remote network 10.0.99.0/24 using a point-to-point connection 1303from 10.1.1.1 to 10.1.1.2, 1304provided that the SSH server running on the gateway to the remote network, 1305at 192.168.1.15, allows it. 1306.Pp 1307On the client: 1308.Bd -literal -offset indent 1309# ssh -f -w 0:1 192.168.1.15 true 1310# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252 1311# route add 10.0.99.0/24 10.1.1.2 1312.Ed 1313.Pp 1314On the server: 1315.Bd -literal -offset indent 1316# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252 1317# route add 10.0.50.0/24 10.1.1.1 1318.Ed 1319.Pp 1320Client access may be more finely tuned via the 1321.Pa /root/.ssh/authorized_keys 1322file (see below) and the 1323.Cm PermitRootLogin 1324server option. 1325The following entry would permit connections on 1326.Xr tun 4 1327device 1 from user 1328.Dq jane 1329and on tun device 2 from user 1330.Dq john , 1331if 1332.Cm PermitRootLogin 1333is set to 1334.Dq forced-commands-only : 1335.Bd -literal -offset 2n 1336tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane 1337tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john 1338.Ed 1339.Pp 1340Since an SSH-based setup entails a fair amount of overhead, 1341it may be more suited to temporary setups, 1342such as for wireless VPNs. 1343More permanent VPNs are better provided by tools such as 1344.Xr ipsecctl 8 1345and 1346.Xr isakmpd 8 . 1347.Sh ENVIRONMENT 1348.Nm 1349will normally set the following environment variables: 1350.Bl -tag -width "SSH_ORIGINAL_COMMAND" 1351.It Ev DISPLAY 1352The 1353.Ev DISPLAY 1354variable indicates the location of the X11 server. 1355It is automatically set by 1356.Nm 1357to point to a value of the form 1358.Dq hostname:n , 1359where 1360.Dq hostname 1361indicates the host where the shell runs, and 1362.Sq n 1363is an integer \*(Ge 1. 1364.Nm 1365uses this special value to forward X11 connections over the secure 1366channel. 1367The user should normally not set 1368.Ev DISPLAY 1369explicitly, as that 1370will render the X11 connection insecure (and will require the user to 1371manually copy any required authorization cookies). 1372.It Ev HOME 1373Set to the path of the user's home directory. 1374.It Ev LOGNAME 1375Synonym for 1376.Ev USER ; 1377set for compatibility with systems that use this variable. 1378.It Ev MAIL 1379Set to the path of the user's mailbox. 1380.It Ev PATH 1381Set to the default 1382.Ev PATH , 1383as specified when compiling 1384.Nm . 1385.It Ev SSH_ASKPASS 1386If 1387.Nm 1388needs a passphrase, it will read the passphrase from the current 1389terminal if it was run from a terminal. 1390If 1391.Nm 1392does not have a terminal associated with it but 1393.Ev DISPLAY 1394and 1395.Ev SSH_ASKPASS 1396are set, it will execute the program specified by 1397.Ev SSH_ASKPASS 1398and open an X11 window to read the passphrase. 1399This is particularly useful when calling 1400.Nm 1401from a 1402.Pa .xsession 1403or related script. 1404(Note that on some machines it 1405may be necessary to redirect the input from 1406.Pa /dev/null 1407to make this work.) 1408.It Ev SSH_AUTH_SOCK 1409Identifies the path of a 1410.Ux Ns -domain 1411socket used to communicate with the agent. 1412.It Ev SSH_CONNECTION 1413Identifies the client and server ends of the connection. 1414The variable contains 1415four space-separated values: client IP address, client port number, 1416server IP address, and server port number. 1417.It Ev SSH_ORIGINAL_COMMAND 1418This variable contains the original command line if a forced command 1419is executed. 1420It can be used to extract the original arguments. 1421.It Ev SSH_TTY 1422This is set to the name of the tty (path to the device) associated 1423with the current shell or command. 1424If the current session has no tty, 1425this variable is not set. 1426.It Ev TZ 1427This variable is set to indicate the present time zone if it 1428was set when the daemon was started (i.e. the daemon passes the value 1429on to new connections). 1430.It Ev USER 1431Set to the name of the user logging in. 1432.El 1433.Pp 1434Additionally, 1435.Nm 1436reads 1437.Pa ~/.ssh/environment , 1438and adds lines of the format 1439.Dq VARNAME=value 1440to the environment if the file exists and users are allowed to 1441change their environment. 1442For more information, see the 1443.Cm PermitUserEnvironment 1444option in 1445.Xr sshd_config 5 . 1446.Sh FILES 1447.Bl -tag -width Ds -compact 1448.It Pa ~/.rhosts 1449This file is used for host-based authentication (see above). 1450On some machines this file may need to be 1451world-readable if the user's home directory is on an NFS partition, 1452because 1453.Xr sshd 8 1454reads it as root. 1455Additionally, this file must be owned by the user, 1456and must not have write permissions for anyone else. 1457The recommended 1458permission for most machines is read/write for the user, and not 1459accessible by others. 1460.Pp 1461.It Pa ~/.shosts 1462This file is used in exactly the same way as 1463.Pa .rhosts , 1464but allows host-based authentication without permitting login with 1465rlogin/rsh. 1466.Pp 1467.It Pa ~/.ssh/ 1468This directory is the default location for all user-specific configuration 1469and authentication information. 1470There is no general requirement to keep the entire contents of this directory 1471secret, but the recommended permissions are read/write/execute for the user, 1472and not accessible by others. 1473.Pp 1474.It Pa ~/.ssh/authorized_keys 1475Lists the public keys (DSA, ECDSA, Ed25519, RSA) 1476that can be used for logging in as this user. 1477The format of this file is described in the 1478.Xr sshd 8 1479manual page. 1480This file is not highly sensitive, but the recommended 1481permissions are read/write for the user, and not accessible by others. 1482.Pp 1483.It Pa ~/.ssh/config 1484This is the per-user configuration file. 1485The file format and configuration options are described in 1486.Xr ssh_config 5 . 1487Because of the potential for abuse, this file must have strict permissions: 1488read/write for the user, and not writable by others. 1489.Pp 1490.It Pa ~/.ssh/environment 1491Contains additional definitions for environment variables; see 1492.Sx ENVIRONMENT , 1493above. 1494.Pp 1495.It Pa ~/.ssh/identity 1496.It Pa ~/.ssh/id_dsa 1497.It Pa ~/.ssh/id_ecdsa 1498.It Pa ~/.ssh/id_ed25519 1499.It Pa ~/.ssh/id_rsa 1500Contains the private key for authentication. 1501These files 1502contain sensitive data and should be readable by the user but not 1503accessible by others (read/write/execute). 1504.Nm 1505will simply ignore a private key file if it is accessible by others. 1506It is possible to specify a passphrase when 1507generating the key which will be used to encrypt the 1508sensitive part of this file using 3DES. 1509.Pp 1510.It Pa ~/.ssh/identity.pub 1511.It Pa ~/.ssh/id_dsa.pub 1512.It Pa ~/.ssh/id_ecdsa.pub 1513.It Pa ~/.ssh/id_ed25519.pub 1514.It Pa ~/.ssh/id_rsa.pub 1515Contains the public key for authentication. 1516These files are not 1517sensitive and can (but need not) be readable by anyone. 1518.Pp 1519.It Pa ~/.ssh/known_hosts 1520Contains a list of host keys for all hosts the user has logged into 1521that are not already in the systemwide list of known host keys. 1522See 1523.Xr sshd 8 1524for further details of the format of this file. 1525.Pp 1526.It Pa ~/.ssh/rc 1527Commands in this file are executed by 1528.Nm 1529when the user logs in, just before the user's shell (or command) is 1530started. 1531See the 1532.Xr sshd 8 1533manual page for more information. 1534.Pp 1535.It Pa /etc/hosts.equiv 1536This file is for host-based authentication (see above). 1537It should only be writable by root. 1538.Pp 1539.It Pa /etc/shosts.equiv 1540This file is used in exactly the same way as 1541.Pa hosts.equiv , 1542but allows host-based authentication without permitting login with 1543rlogin/rsh. 1544.Pp 1545.It Pa /etc/ssh/ssh_config 1546Systemwide configuration file. 1547The file format and configuration options are described in 1548.Xr ssh_config 5 . 1549.Pp 1550.It Pa /etc/ssh/ssh_host_key 1551.It Pa /etc/ssh/ssh_host_dsa_key 1552.It Pa /etc/ssh/ssh_host_ecdsa_key 1553.It Pa /etc/ssh/ssh_host_ed25519_key 1554.It Pa /etc/ssh/ssh_host_rsa_key 1555These files contain the private parts of the host keys 1556and are used for host-based authentication. 1557.Pp 1558.It Pa /etc/ssh/ssh_known_hosts 1559Systemwide list of known host keys. 1560This file should be prepared by the 1561system administrator to contain the public host keys of all machines in the 1562organization. 1563It should be world-readable. 1564See 1565.Xr sshd 8 1566for further details of the format of this file. 1567.Pp 1568.It Pa /etc/ssh/sshrc 1569Commands in this file are executed by 1570.Nm 1571when the user logs in, just before the user's shell (or command) is started. 1572See the 1573.Xr sshd 8 1574manual page for more information. 1575.El 1576.Sh EXIT STATUS 1577.Nm 1578exits with the exit status of the remote command or with 255 1579if an error occurred. 1580.Sh SEE ALSO 1581.Xr scp 1 , 1582.Xr sftp 1 , 1583.Xr ssh-add 1 , 1584.Xr ssh-agent 1 , 1585.Xr ssh-keygen 1 , 1586.Xr ssh-keyscan 1 , 1587.Xr tun 4 , 1588.Xr ssh_config 5 , 1589.Xr ssh-keysign 8 , 1590.Xr sshd 8 1591.Sh STANDARDS 1592.Rs 1593.%A S. Lehtinen 1594.%A C. Lonvick 1595.%D January 2006 1596.%R RFC 4250 1597.%T The Secure Shell (SSH) Protocol Assigned Numbers 1598.Re 1599.Pp 1600.Rs 1601.%A T. Ylonen 1602.%A C. Lonvick 1603.%D January 2006 1604.%R RFC 4251 1605.%T The Secure Shell (SSH) Protocol Architecture 1606.Re 1607.Pp 1608.Rs 1609.%A T. Ylonen 1610.%A C. Lonvick 1611.%D January 2006 1612.%R RFC 4252 1613.%T The Secure Shell (SSH) Authentication Protocol 1614.Re 1615.Pp 1616.Rs 1617.%A T. Ylonen 1618.%A C. Lonvick 1619.%D January 2006 1620.%R RFC 4253 1621.%T The Secure Shell (SSH) Transport Layer Protocol 1622.Re 1623.Pp 1624.Rs 1625.%A T. Ylonen 1626.%A C. Lonvick 1627.%D January 2006 1628.%R RFC 4254 1629.%T The Secure Shell (SSH) Connection Protocol 1630.Re 1631.Pp 1632.Rs 1633.%A J. Schlyter 1634.%A W. Griffin 1635.%D January 2006 1636.%R RFC 4255 1637.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints 1638.Re 1639.Pp 1640.Rs 1641.%A F. Cusack 1642.%A M. Forssen 1643.%D January 2006 1644.%R RFC 4256 1645.%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH) 1646.Re 1647.Pp 1648.Rs 1649.%A J. Galbraith 1650.%A P. Remaker 1651.%D January 2006 1652.%R RFC 4335 1653.%T The Secure Shell (SSH) Session Channel Break Extension 1654.Re 1655.Pp 1656.Rs 1657.%A M. Bellare 1658.%A T. Kohno 1659.%A C. Namprempre 1660.%D January 2006 1661.%R RFC 4344 1662.%T The Secure Shell (SSH) Transport Layer Encryption Modes 1663.Re 1664.Pp 1665.Rs 1666.%A B. Harris 1667.%D January 2006 1668.%R RFC 4345 1669.%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol 1670.Re 1671.Pp 1672.Rs 1673.%A M. Friedl 1674.%A N. Provos 1675.%A W. Simpson 1676.%D March 2006 1677.%R RFC 4419 1678.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol 1679.Re 1680.Pp 1681.Rs 1682.%A J. Galbraith 1683.%A R. Thayer 1684.%D November 2006 1685.%R RFC 4716 1686.%T The Secure Shell (SSH) Public Key File Format 1687.Re 1688.Pp 1689.Rs 1690.%A D. Stebila 1691.%A J. Green 1692.%D December 2009 1693.%R RFC 5656 1694.%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer 1695.Re 1696.Pp 1697.Rs 1698.%A A. Perrig 1699.%A D. Song 1700.%D 1999 1701.%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99) 1702.%T Hash Visualization: a New Technique to improve Real-World Security 1703.Re 1704.Sh AUTHORS 1705OpenSSH is a derivative of the original and free 1706ssh 1.2.12 release by Tatu Ylonen. 1707Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 1708Theo de Raadt and Dug Song 1709removed many bugs, re-added newer features and 1710created OpenSSH. 1711Markus Friedl contributed the support for SSH 1712protocol versions 1.5 and 2.0. 1713