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 1.348 2014/07/24 22:57:10 millert Exp $ 37.Dd $Mdocdate: July 24 2014 $ 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.Bk -words 46.Op Fl 1246AaCfgKkMNnqsTtVvXxYy 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 L Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport 56.Op Fl l Ar login_name 57.Op Fl m Ar mac_spec 58.Op Fl O Ar ctl_cmd 59.Op Fl o Ar option 60.Op Fl p Ar port 61.Op Fl Q Cm cipher | cipher-auth | mac | kex | key 62.Op Fl R Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport 63.Op Fl S Ar ctl_path 64.Op Fl W Ar host : Ns Ar port 65.Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun 66.Oo Ar user Ns @ Oc Ns Ar hostname 67.Op Ar command 68.Ek 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 replace rlogin and rsh, 74and provide secure encrypted communications between 75two untrusted hosts over an insecure network. 76X11 connections, arbitrary TCP ports and 77.Ux Ns -domain 78sockets can also be forwarded over the secure channel. 79.Pp 80.Nm 81connects and logs into the specified 82.Ar hostname 83(with optional 84.Ar user 85name). 86The user must prove 87his/her identity to the remote machine using one of several methods 88depending on the protocol version used (see below). 89.Pp 90If 91.Ar command 92is specified, 93it is executed on the remote host instead of a login shell. 94.Pp 95The options are as follows: 96.Bl -tag -width Ds 97.It Fl 1 98Forces 99.Nm 100to try protocol version 1 only. 101.It Fl 2 102Forces 103.Nm 104to try protocol version 2 only. 105.It Fl 4 106Forces 107.Nm 108to use IPv4 addresses only. 109.It Fl 6 110Forces 111.Nm 112to use IPv6 addresses only. 113.It Fl A 114Enables forwarding of the authentication agent connection. 115This can also be specified on a per-host basis in a configuration file. 116.Pp 117Agent forwarding should be enabled with caution. 118Users with the ability to bypass file permissions on the remote host 119(for the agent's 120.Ux Ns -domain 121socket) can access the local agent through the forwarded connection. 122An attacker cannot obtain key material from the agent, 123however they can perform operations on the keys that enable them to 124authenticate using the identities loaded into the agent. 125.It Fl a 126Disables forwarding of the authentication agent connection. 127.It Fl b Ar bind_address 128Use 129.Ar bind_address 130on the local machine as the source address 131of the connection. 132Only useful on systems with more than one address. 133.It Fl C 134Requests compression of all data (including stdin, stdout, stderr, and 135data for forwarded X11, TCP and 136.Ux Ns -domain 137connections). 138The compression algorithm is the same used by 139.Xr gzip 1 , 140and the 141.Dq level 142can be controlled by the 143.Cm CompressionLevel 144option for protocol version 1. 145Compression is desirable on modem lines and other 146slow connections, but will only slow down things on fast networks. 147The default value can be set on a host-by-host basis in the 148configuration files; see the 149.Cm Compression 150option. 151.It Fl c Ar cipher_spec 152Selects the cipher specification for encrypting the session. 153.Pp 154Protocol version 1 allows specification of a single cipher. 155The supported values are 156.Dq 3des , 157.Dq blowfish , 158and 159.Dq des . 160For protocol version 2, 161.Ar cipher_spec 162is a comma-separated list of ciphers 163listed in order of preference. 164See the 165.Cm Ciphers 166keyword in 167.Xr ssh_config 5 168for more information. 169.It Fl D Xo 170.Sm off 171.Oo Ar bind_address : Oc 172.Ar port 173.Sm on 174.Xc 175Specifies a local 176.Dq dynamic 177application-level port forwarding. 178This works by allocating a socket to listen to 179.Ar port 180on the local side, optionally bound to the specified 181.Ar bind_address . 182Whenever a connection is made to this port, the 183connection is forwarded over the secure channel, and the application 184protocol is then used to determine where to connect to from the 185remote machine. 186Currently the SOCKS4 and SOCKS5 protocols are supported, and 187.Nm 188will act as a SOCKS server. 189Only root can forward privileged ports. 190Dynamic port forwardings can also be specified in the configuration file. 191.Pp 192IPv6 addresses can be specified by enclosing the address in square brackets. 193Only the superuser can forward privileged ports. 194By default, the local port is bound in accordance with the 195.Cm GatewayPorts 196setting. 197However, an explicit 198.Ar bind_address 199may be used to bind the connection to a specific address. 200The 201.Ar bind_address 202of 203.Dq localhost 204indicates that the listening port be bound for local use only, while an 205empty address or 206.Sq * 207indicates that the port should be available from all interfaces. 208.It Fl E Ar log_file 209Append debug logs to 210.Ar log_file 211instead of standard error. 212.It Fl e Ar escape_char 213Sets the escape character for sessions with a pty (default: 214.Ql ~ ) . 215The escape character is only recognized at the beginning of a line. 216The escape character followed by a dot 217.Pq Ql \&. 218closes the connection; 219followed by control-Z suspends the connection; 220and followed by itself sends the escape character once. 221Setting the character to 222.Dq none 223disables any escapes and makes the session fully transparent. 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.It Fl f 233Requests 234.Nm 235to go to background just before command execution. 236This is useful if 237.Nm 238is going to ask for passwords or passphrases, but the user 239wants it in the background. 240This implies 241.Fl n . 242The recommended way to start X11 programs at a remote site is with 243something like 244.Ic ssh -f host xterm . 245.Pp 246If the 247.Cm ExitOnForwardFailure 248configuration option is set to 249.Dq yes , 250then a client started with 251.Fl f 252will wait for all remote port forwards to be successfully established 253before placing itself in the background. 254.It Fl g 255Allows remote hosts to connect to local forwarded ports. 256If used on a multiplexed connection, then this option must be specified 257on the master process. 258.It Fl I Ar pkcs11 259Specify the PKCS#11 shared library 260.Nm 261should use to communicate with a PKCS#11 token providing the user's 262private RSA key. 263.It Fl i Ar identity_file 264Selects a file from which the identity (private key) for 265public key authentication is read. 266The default is 267.Pa ~/.ssh/identity 268for protocol version 1, and 269.Pa ~/.ssh/id_dsa , 270.Pa ~/.ssh/id_ecdsa , 271.Pa ~/.ssh/id_ed25519 272and 273.Pa ~/.ssh/id_rsa 274for protocol version 2. 275Identity files may also be specified on 276a per-host basis in the configuration file. 277It is possible to have multiple 278.Fl i 279options (and multiple identities specified in 280configuration files). 281.Nm 282will also try to load certificate information from the filename obtained 283by appending 284.Pa -cert.pub 285to identity filenames. 286.It Fl K 287Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI 288credentials to the server. 289.It Fl k 290Disables forwarding (delegation) of GSSAPI credentials to the server. 291.It Fl L Xo 292.Sm off 293.Oo Ar bind_address : Oc 294.Ar port : host : hostport 295.Sm on 296.Xc 297Specifies that the given port on the local (client) host is to be 298forwarded to the given host and port on the remote side. 299This works by allocating a socket to listen to 300.Ar port 301on the local side, optionally bound to the specified 302.Ar bind_address . 303Whenever a connection is made to this port, the 304connection is forwarded over the secure channel, and a connection is 305made to 306.Ar host 307port 308.Ar hostport 309from the remote machine. 310Port forwardings can also be specified in the configuration file. 311IPv6 addresses can be specified by enclosing the address in square brackets. 312Only the superuser can forward privileged ports. 313By default, the local port is bound in accordance with the 314.Cm GatewayPorts 315setting. 316However, an explicit 317.Ar bind_address 318may be used to bind the connection to a specific address. 319The 320.Ar bind_address 321of 322.Dq localhost 323indicates that the listening port be bound for local use only, while an 324empty address or 325.Sq * 326indicates that the port should be available from all interfaces. 327.It Fl l Ar login_name 328Specifies the user to log in as on the remote machine. 329This also may be specified on a per-host basis in the configuration file. 330.It Fl M 331Places the 332.Nm 333client into 334.Dq master 335mode for connection sharing. 336Multiple 337.Fl M 338options places 339.Nm 340into 341.Dq master 342mode with confirmation required before slave connections are accepted. 343Refer to the description of 344.Cm ControlMaster 345in 346.Xr ssh_config 5 347for details. 348.It Fl m Ar mac_spec 349Additionally, for protocol version 2 a comma-separated list of MAC 350(message authentication code) algorithms can 351be specified in order of preference. 352See the 353.Cm MACs 354keyword for more information. 355.It Fl N 356Do not execute a remote command. 357This is useful for just forwarding ports 358(protocol version 2 only). 359.It Fl n 360Redirects stdin from 361.Pa /dev/null 362(actually, prevents reading from stdin). 363This must be used when 364.Nm 365is run in the background. 366A common trick is to use this to run X11 programs on a remote machine. 367For example, 368.Ic ssh -n shadows.cs.hut.fi emacs & 369will start an emacs on shadows.cs.hut.fi, and the X11 370connection will be automatically forwarded over an encrypted channel. 371The 372.Nm 373program will be put in the background. 374(This does not work if 375.Nm 376needs to ask for a password or passphrase; see also the 377.Fl f 378option.) 379.It Fl O Ar ctl_cmd 380Control an active connection multiplexing master process. 381When the 382.Fl O 383option is specified, the 384.Ar ctl_cmd 385argument is interpreted and passed to the master process. 386Valid commands are: 387.Dq check 388(check that the master process is running), 389.Dq forward 390(request forwardings without command execution), 391.Dq cancel 392(cancel forwardings), 393.Dq exit 394(request the master to exit), and 395.Dq stop 396(request the master to stop accepting further multiplexing requests). 397.It Fl o Ar option 398Can be used to give options in the format used in the configuration file. 399This is useful for specifying options for which there is no separate 400command-line flag. 401For full details of the options listed below, and their possible values, see 402.Xr ssh_config 5 . 403.Pp 404.Bl -tag -width Ds -offset indent -compact 405.It AddressFamily 406.It BatchMode 407.It BindAddress 408.It CanonicalDomains 409.It CanonicalizeFallbackLocal 410.It CanonicalizeHostname 411.It CanonicalizeMaxDots 412.It CanonicalizePermittedCNAMEs 413.It ChallengeResponseAuthentication 414.It CheckHostIP 415.It Cipher 416.It Ciphers 417.It ClearAllForwardings 418.It Compression 419.It CompressionLevel 420.It ConnectionAttempts 421.It ConnectTimeout 422.It ControlMaster 423.It ControlPath 424.It ControlPersist 425.It DynamicForward 426.It EscapeChar 427.It ExitOnForwardFailure 428.It ForwardAgent 429.It ForwardX11 430.It ForwardX11Timeout 431.It ForwardX11Trusted 432.It GatewayPorts 433.It GlobalKnownHostsFile 434.It GSSAPIAuthentication 435.It GSSAPIDelegateCredentials 436.It HashKnownHosts 437.It Host 438.It HostbasedAuthentication 439.It HostKeyAlgorithms 440.It HostKeyAlias 441.It HostName 442.It IdentityFile 443.It IdentitiesOnly 444.It IPQoS 445.It KbdInteractiveAuthentication 446.It KbdInteractiveDevices 447.It KexAlgorithms 448.It LocalCommand 449.It LocalForward 450.It LogLevel 451.It MACs 452.It Match 453.It NoHostAuthenticationForLocalhost 454.It NumberOfPasswordPrompts 455.It PasswordAuthentication 456.It PermitLocalCommand 457.It PKCS11Provider 458.It Port 459.It PreferredAuthentications 460.It Protocol 461.It ProxyCommand 462.It ProxyUseFdpass 463.It PubkeyAuthentication 464.It RekeyLimit 465.It RemoteForward 466.It RequestTTY 467.It RhostsRSAAuthentication 468.It RSAAuthentication 469.It SendEnv 470.It ServerAliveInterval 471.It ServerAliveCountMax 472.It StreamLocalBindMask 473.It StreamLocalBindUnlink 474.It StrictHostKeyChecking 475.It TCPKeepAlive 476.It Tunnel 477.It TunnelDevice 478.It UsePrivilegedPort 479.It User 480.It UserKnownHostsFile 481.It VerifyHostKeyDNS 482.It VisualHostKey 483.It XAuthLocation 484.El 485.It Fl p Ar port 486Port to connect to on the remote host. 487This can be specified on a 488per-host basis in the configuration file. 489.It Fl Q Cm cipher | cipher-auth | mac | kex | key 490Queries 491.Nm 492for the algorithms supported for the specified version 2. 493The available features are: 494.Ar cipher 495(supported symmetric ciphers), 496.Ar cipher-auth 497(supported symmetric ciphers that support authenticated encryption), 498.Ar mac 499(supported message integrity codes), 500.Ar kex 501(key exchange algorithms), 502.Ar key 503(key types). 504.It Fl q 505Quiet mode. 506Causes most warning and diagnostic messages to be suppressed. 507.It Fl R Xo 508.Sm off 509.Oo Ar bind_address : Oc 510.Ar port : host : hostport 511.Sm on 512.Xc 513Specifies that the given port on the remote (server) host is to be 514forwarded to the given host and port on the local side. 515This works by allocating a socket to listen to 516.Ar port 517on the remote side, and whenever a connection is made to this port, the 518connection is forwarded over the secure channel, and a connection is 519made to 520.Ar host 521port 522.Ar hostport 523from the local machine. 524.Pp 525Port forwardings can also be specified in the configuration file. 526Privileged ports can be forwarded only when 527logging in as root on the remote machine. 528IPv6 addresses can be specified by enclosing the address in square brackets. 529.Pp 530By default, the listening socket on the server will be bound to the loopback 531interface only. 532This may be overridden by specifying a 533.Ar bind_address . 534An empty 535.Ar bind_address , 536or the address 537.Ql * , 538indicates that the remote socket should listen on all interfaces. 539Specifying a remote 540.Ar bind_address 541will only succeed if the server's 542.Cm GatewayPorts 543option is enabled (see 544.Xr sshd_config 5 ) . 545.Pp 546If the 547.Ar port 548argument is 549.Ql 0 , 550the listen port will be dynamically allocated on the server and reported 551to the client at run time. 552When used together with 553.Ic -O forward 554the allocated port will be printed to the standard output. 555.It Fl S Ar ctl_path 556Specifies the location of a control socket for connection sharing, 557or the string 558.Dq none 559to disable connection sharing. 560Refer to the description of 561.Cm ControlPath 562and 563.Cm ControlMaster 564in 565.Xr ssh_config 5 566for details. 567.It Fl s 568May be used to request invocation of a subsystem on the remote system. 569Subsystems are a feature of the SSH2 protocol which facilitate the use 570of SSH as a secure transport for other applications (eg.\& 571.Xr sftp 1 ) . 572The subsystem is specified as the remote command. 573.It Fl T 574Disable pseudo-tty allocation. 575.It Fl t 576Force pseudo-tty allocation. 577This can be used to execute arbitrary 578screen-based programs on a remote machine, which can be very useful, 579e.g. when implementing menu services. 580Multiple 581.Fl t 582options force tty allocation, even if 583.Nm 584has no local tty. 585.It Fl V 586Display the version number and exit. 587.It Fl v 588Verbose mode. 589Causes 590.Nm 591to print debugging messages about its progress. 592This is helpful in 593debugging connection, authentication, and configuration problems. 594Multiple 595.Fl v 596options increase the verbosity. 597The maximum is 3. 598.It Fl W Ar host : Ns Ar port 599Requests that standard input and output on the client be forwarded to 600.Ar host 601on 602.Ar port 603over the secure channel. 604Implies 605.Fl N , 606.Fl T , 607.Cm ExitOnForwardFailure 608and 609.Cm ClearAllForwardings . 610Works with Protocol version 2 only. 611.It Fl w Xo 612.Ar local_tun Ns Op : Ns Ar remote_tun 613.Xc 614Requests 615tunnel 616device forwarding with the specified 617.Xr tun 4 618devices between the client 619.Pq Ar local_tun 620and the server 621.Pq Ar remote_tun . 622.Pp 623The devices may be specified by numerical ID or the keyword 624.Dq any , 625which uses the next available tunnel device. 626If 627.Ar remote_tun 628is not specified, it defaults to 629.Dq any . 630See also the 631.Cm Tunnel 632and 633.Cm TunnelDevice 634directives in 635.Xr ssh_config 5 . 636If the 637.Cm Tunnel 638directive is unset, it is set to the default tunnel mode, which is 639.Dq point-to-point . 640.It Fl X 641Enables X11 forwarding. 642This can also be specified on a per-host basis in a configuration file. 643.Pp 644X11 forwarding should be enabled with caution. 645Users with the ability to bypass file permissions on the remote host 646(for the user's X authorization database) 647can access the local X11 display through the forwarded connection. 648An attacker may then be able to perform activities such as keystroke monitoring. 649.Pp 650For this reason, X11 forwarding is subjected to X11 SECURITY extension 651restrictions by default. 652Please refer to the 653.Nm 654.Fl Y 655option and the 656.Cm ForwardX11Trusted 657directive in 658.Xr ssh_config 5 659for more information. 660.It Fl x 661Disables X11 forwarding. 662.It Fl Y 663Enables trusted X11 forwarding. 664Trusted X11 forwardings are not subjected to the X11 SECURITY extension 665controls. 666.It Fl y 667Send log information using the 668.Xr syslog 3 669system module. 670By default this information is sent to stderr. 671.El 672.Pp 673.Nm 674may additionally obtain configuration data from 675a per-user configuration file and a system-wide configuration file. 676The file format and configuration options are described in 677.Xr ssh_config 5 . 678.Sh AUTHENTICATION 679The OpenSSH SSH client supports SSH protocols 1 and 2. 680The default is to use protocol 2 only, 681though this can be changed via the 682.Cm Protocol 683option in 684.Xr ssh_config 5 685or the 686.Fl 1 687and 688.Fl 2 689options (see above). 690Both protocols support similar authentication methods, 691but protocol 2 is the default since 692it provides additional mechanisms for confidentiality 693(the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) 694and integrity (hmac-md5, hmac-sha1, 695hmac-sha2-256, hmac-sha2-512, 696umac-64, umac-128, hmac-ripemd160). 697Protocol 1 lacks a strong mechanism for ensuring the 698integrity of the connection. 699.Pp 700The methods available for authentication are: 701GSSAPI-based authentication, 702host-based authentication, 703public key authentication, 704challenge-response authentication, 705and password authentication. 706Authentication methods are tried in the order specified above, 707though protocol 2 has a configuration option to change the default order: 708.Cm PreferredAuthentications . 709.Pp 710Host-based authentication works as follows: 711If the machine the user logs in from is listed in 712.Pa /etc/hosts.equiv 713or 714.Pa /etc/ssh/shosts.equiv 715on the remote machine, and the user names are 716the same on both sides, or if the files 717.Pa ~/.rhosts 718or 719.Pa ~/.shosts 720exist in the user's home directory on the 721remote machine and contain a line containing the name of the client 722machine and the name of the user on that machine, the user is 723considered for login. 724Additionally, the server 725.Em must 726be able to verify the client's 727host key (see the description of 728.Pa /etc/ssh/ssh_known_hosts 729and 730.Pa ~/.ssh/known_hosts , 731below) 732for login to be permitted. 733This authentication method closes security holes due to IP 734spoofing, DNS spoofing, and routing spoofing. 735[Note to the administrator: 736.Pa /etc/hosts.equiv , 737.Pa ~/.rhosts , 738and the rlogin/rsh protocol in general, are inherently insecure and should be 739disabled if security is desired.] 740.Pp 741Public key authentication works as follows: 742The scheme is based on public-key cryptography, 743using cryptosystems 744where encryption and decryption are done using separate keys, 745and it is unfeasible to derive the decryption key from the encryption key. 746The idea is that each user creates a public/private 747key pair for authentication purposes. 748The server knows the public key, and only the user knows the private key. 749.Nm 750implements public key authentication protocol automatically, 751using one of the DSA, ECDSA, ED25519 or RSA algorithms. 752Protocol 1 is restricted to using only RSA keys, 753but protocol 2 may use any. 754The HISTORY section of 755.Xr ssl 8 756contains a brief discussion of the DSA and RSA algorithms. 757.Pp 758The file 759.Pa ~/.ssh/authorized_keys 760lists the public keys that are permitted for logging in. 761When the user logs in, the 762.Nm 763program tells the server which key pair it would like to use for 764authentication. 765The client proves that it has access to the private key 766and the server checks that the corresponding public key 767is authorized to accept the account. 768.Pp 769The user creates his/her key pair by running 770.Xr ssh-keygen 1 . 771This stores the private key in 772.Pa ~/.ssh/identity 773(protocol 1), 774.Pa ~/.ssh/id_dsa 775(protocol 2 DSA), 776.Pa ~/.ssh/id_ecdsa 777(protocol 2 ECDSA), 778.Pa ~/.ssh/id_ed25519 779(protocol 2 ED25519), 780or 781.Pa ~/.ssh/id_rsa 782(protocol 2 RSA) 783and stores the public key in 784.Pa ~/.ssh/identity.pub 785(protocol 1), 786.Pa ~/.ssh/id_dsa.pub 787(protocol 2 DSA), 788.Pa ~/.ssh/id_ecdsa.pub 789(protocol 2 ECDSA), 790.Pa ~/.ssh/id_ed25519.pub 791(protocol 2 ED25519), 792or 793.Pa ~/.ssh/id_rsa.pub 794(protocol 2 RSA) 795in the user's home directory. 796The user should then copy the public key 797to 798.Pa ~/.ssh/authorized_keys 799in his/her home directory on the remote machine. 800The 801.Pa authorized_keys 802file corresponds to the conventional 803.Pa ~/.rhosts 804file, and has one key 805per line, though the lines can be very long. 806After this, the user can log in without giving the password. 807.Pp 808A variation on public key authentication 809is available in the form of certificate authentication: 810instead of a set of public/private keys, 811signed certificates are used. 812This has the advantage that a single trusted certification authority 813can be used in place of many public/private keys. 814See the CERTIFICATES section of 815.Xr ssh-keygen 1 816for more information. 817.Pp 818The most convenient way to use public key or certificate authentication 819may be with an authentication agent. 820See 821.Xr ssh-agent 1 822for more information. 823.Pp 824Challenge-response authentication works as follows: 825The server sends an arbitrary 826.Qq challenge 827text, and prompts for a response. 828Protocol 2 allows multiple challenges and responses; 829protocol 1 is restricted to just one challenge/response. 830Examples of challenge-response authentication include 831.Bx 832Authentication (see 833.Xr login.conf 5 ) 834and PAM (some 835.Pf non- Ox 836systems). 837.Pp 838Finally, if other authentication methods fail, 839.Nm 840prompts the user for a password. 841The password is sent to the remote 842host for checking; however, since all communications are encrypted, 843the password cannot be seen by someone listening on the network. 844.Pp 845.Nm 846automatically maintains and checks a database containing 847identification for all hosts it has ever been used with. 848Host keys are stored in 849.Pa ~/.ssh/known_hosts 850in the user's home directory. 851Additionally, the file 852.Pa /etc/ssh/ssh_known_hosts 853is automatically checked for known hosts. 854Any new hosts are automatically added to the user's file. 855If a host's identification ever changes, 856.Nm 857warns about this and disables password authentication to prevent 858server spoofing or man-in-the-middle attacks, 859which could otherwise be used to circumvent the encryption. 860The 861.Cm StrictHostKeyChecking 862option can be used to control logins to machines whose 863host key is not known or has changed. 864.Pp 865When the user's identity has been accepted by the server, the server 866either executes the given command, or logs into the machine and gives 867the user a normal shell on the remote machine. 868All communication with 869the remote command or shell will be automatically encrypted. 870.Pp 871If a pseudo-terminal has been allocated (normal login session), the 872user may use the escape characters noted below. 873.Pp 874If no pseudo-tty has been allocated, 875the session is transparent and can be used to reliably transfer binary data. 876On most systems, setting the escape character to 877.Dq none 878will also make the session transparent even if a tty is used. 879.Pp 880The session terminates when the command or shell on the remote 881machine exits and all X11 and TCP connections have been closed. 882.Sh ESCAPE CHARACTERS 883When a pseudo-terminal has been requested, 884.Nm 885supports a number of functions through the use of an escape character. 886.Pp 887A single tilde character can be sent as 888.Ic ~~ 889or by following the tilde by a character other than those described below. 890The escape character must always follow a newline to be interpreted as 891special. 892The escape character can be changed in configuration files using the 893.Cm EscapeChar 894configuration directive or on the command line by the 895.Fl e 896option. 897.Pp 898The supported escapes (assuming the default 899.Ql ~ ) 900are: 901.Bl -tag -width Ds 902.It Cm ~. 903Disconnect. 904.It Cm ~^Z 905Background 906.Nm . 907.It Cm ~# 908List forwarded connections. 909.It Cm ~& 910Background 911.Nm 912at logout when waiting for forwarded connection / X11 sessions to terminate. 913.It Cm ~? 914Display a list of escape characters. 915.It Cm ~B 916Send a BREAK to the remote system 917(only useful for SSH protocol version 2 and if the peer supports it). 918.It Cm ~C 919Open command line. 920Currently this allows the addition of port forwardings using the 921.Fl L , 922.Fl R 923and 924.Fl D 925options (see above). 926It also allows the cancellation of existing port-forwardings 927with 928.Sm off 929.Fl KL Oo Ar bind_address : Oc Ar port 930.Sm on 931for local, 932.Sm off 933.Fl KR Oo Ar bind_address : Oc Ar port 934.Sm on 935for remote and 936.Sm off 937.Fl KD Oo Ar bind_address : Oc Ar port 938.Sm on 939for dynamic port-forwardings. 940.Ic !\& Ns Ar command 941allows the user to execute a local command if the 942.Ic PermitLocalCommand 943option is enabled in 944.Xr ssh_config 5 . 945Basic help is available, using the 946.Fl h 947option. 948.It Cm ~R 949Request rekeying of the connection 950(only useful for SSH protocol version 2 and if the peer supports it). 951.It Cm ~V 952Decrease the verbosity 953.Pq Ic LogLevel 954when errors are being written to stderr. 955.It Cm ~v 956Increase the verbosity 957.Pq Ic LogLevel 958when errors are being written to stderr. 959.El 960.Sh TCP FORWARDING 961Forwarding of arbitrary TCP connections over the secure channel can 962be specified either on the command line or in a configuration file. 963One possible application of TCP forwarding is a secure connection to a 964mail server; another is going through firewalls. 965.Pp 966In the example below, we look at encrypting communication between 967an IRC client and server, even though the IRC server does not directly 968support encrypted communications. 969This works as follows: 970the user connects to the remote host using 971.Nm , 972specifying a port to be used to forward connections 973to the remote server. 974After that it is possible to start the service which is to be encrypted 975on the client machine, 976connecting to the same local port, 977and 978.Nm 979will encrypt and forward the connection. 980.Pp 981The following example tunnels an IRC session from client machine 982.Dq 127.0.0.1 983(localhost) 984to remote server 985.Dq server.example.com : 986.Bd -literal -offset 4n 987$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 988$ irc -c '#users' -p 1234 pinky 127.0.0.1 989.Ed 990.Pp 991This tunnels a connection to IRC server 992.Dq server.example.com , 993joining channel 994.Dq #users , 995nickname 996.Dq pinky , 997using port 1234. 998It doesn't matter which port is used, 999as long as it's greater than 1023 1000(remember, only root can open sockets on privileged ports) 1001and doesn't conflict with any ports already in use. 1002The connection is forwarded to port 6667 on the remote server, 1003since that's the standard port for IRC services. 1004.Pp 1005The 1006.Fl f 1007option backgrounds 1008.Nm 1009and the remote command 1010.Dq sleep 10 1011is specified to allow an amount of time 1012(10 seconds, in the example) 1013to start the service which is to be tunnelled. 1014If no connections are made within the time specified, 1015.Nm 1016will exit. 1017.Sh X11 FORWARDING 1018If the 1019.Cm ForwardX11 1020variable is set to 1021.Dq yes 1022(or see the description of the 1023.Fl X , 1024.Fl x , 1025and 1026.Fl Y 1027options above) 1028and the user is using X11 (the 1029.Ev DISPLAY 1030environment variable is set), the connection to the X11 display is 1031automatically forwarded to the remote side in such a way that any X11 1032programs started from the shell (or command) will go through the 1033encrypted channel, and the connection to the real X server will be made 1034from the local machine. 1035The user should not manually set 1036.Ev DISPLAY . 1037Forwarding of X11 connections can be 1038configured on the command line or in configuration files. 1039Take note that X11 forwarding can represent a security hazard. 1040.Pp 1041The 1042.Ev DISPLAY 1043value set by 1044.Nm 1045will point to the server machine, but with a display number greater than zero. 1046This is normal, and happens because 1047.Nm 1048creates a 1049.Dq proxy 1050X server on the server machine for forwarding the 1051connections over the encrypted channel. 1052.Pp 1053.Nm 1054will also automatically set up Xauthority data on the server machine. 1055For this purpose, it will generate a random authorization cookie, 1056store it in Xauthority on the server, and verify that any forwarded 1057connections carry this cookie and replace it by the real cookie when 1058the connection is opened. 1059The real authentication cookie is never 1060sent to the server machine (and no cookies are sent in the plain). 1061.Pp 1062If the 1063.Cm ForwardAgent 1064variable is set to 1065.Dq yes 1066(or see the description of the 1067.Fl A 1068and 1069.Fl a 1070options above) and 1071the user is using an authentication agent, the connection to the agent 1072is automatically forwarded to the remote side. 1073.Sh VERIFYING HOST KEYS 1074When connecting to a server for the first time, 1075a fingerprint of the server's public key is presented to the user 1076(unless the option 1077.Cm StrictHostKeyChecking 1078has been disabled). 1079Fingerprints can be determined using 1080.Xr ssh-keygen 1 : 1081.Pp 1082.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key 1083.Pp 1084If the fingerprint is already known, it can be matched 1085and the key can be accepted or rejected. 1086Because of the difficulty of comparing host keys 1087just by looking at hex strings, 1088there is also support to compare host keys visually, 1089using 1090.Em random art . 1091By setting the 1092.Cm VisualHostKey 1093option to 1094.Dq yes , 1095a small ASCII graphic gets displayed on every login to a server, no matter 1096if the session itself is interactive or not. 1097By learning the pattern a known server produces, a user can easily 1098find out that the host key has changed when a completely different pattern 1099is displayed. 1100Because these patterns are not unambiguous however, a pattern that looks 1101similar to the pattern remembered only gives a good probability that the 1102host key is the same, not guaranteed proof. 1103.Pp 1104To get a listing of the fingerprints along with their random art for 1105all known hosts, the following command line can be used: 1106.Pp 1107.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts 1108.Pp 1109If the fingerprint is unknown, 1110an alternative method of verification is available: 1111SSH fingerprints verified by DNS. 1112An additional resource record (RR), 1113SSHFP, 1114is added to a zonefile 1115and the connecting client is able to match the fingerprint 1116with that of the key presented. 1117.Pp 1118In this example, we are connecting a client to a server, 1119.Dq host.example.com . 1120The SSHFP resource records should first be added to the zonefile for 1121host.example.com: 1122.Bd -literal -offset indent 1123$ ssh-keygen -r host.example.com. 1124.Ed 1125.Pp 1126The output lines will have to be added to the zonefile. 1127To check that the zone is answering fingerprint queries: 1128.Pp 1129.Dl $ dig -t SSHFP host.example.com 1130.Pp 1131Finally the client connects: 1132.Bd -literal -offset indent 1133$ ssh -o "VerifyHostKeyDNS ask" host.example.com 1134[...] 1135Matching host key fingerprint found in DNS. 1136Are you sure you want to continue connecting (yes/no)? 1137.Ed 1138.Pp 1139See the 1140.Cm VerifyHostKeyDNS 1141option in 1142.Xr ssh_config 5 1143for more information. 1144.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS 1145.Nm 1146contains support for Virtual Private Network (VPN) tunnelling 1147using the 1148.Xr tun 4 1149network pseudo-device, 1150allowing two networks to be joined securely. 1151The 1152.Xr sshd_config 5 1153configuration option 1154.Cm PermitTunnel 1155controls whether the server supports this, 1156and at what level (layer 2 or 3 traffic). 1157.Pp 1158The following example would connect client network 10.0.50.0/24 1159with remote network 10.0.99.0/24 using a point-to-point connection 1160from 10.1.1.1 to 10.1.1.2, 1161provided that the SSH server running on the gateway to the remote network, 1162at 192.168.1.15, allows it. 1163.Pp 1164On the client: 1165.Bd -literal -offset indent 1166# ssh -f -w 0:1 192.168.1.15 true 1167# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252 1168# route add 10.0.99.0/24 10.1.1.2 1169.Ed 1170.Pp 1171On the server: 1172.Bd -literal -offset indent 1173# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252 1174# route add 10.0.50.0/24 10.1.1.1 1175.Ed 1176.Pp 1177Client access may be more finely tuned via the 1178.Pa /root/.ssh/authorized_keys 1179file (see below) and the 1180.Cm PermitRootLogin 1181server option. 1182The following entry would permit connections on 1183.Xr tun 4 1184device 1 from user 1185.Dq jane 1186and on tun device 2 from user 1187.Dq john , 1188if 1189.Cm PermitRootLogin 1190is set to 1191.Dq forced-commands-only : 1192.Bd -literal -offset 2n 1193tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane 1194tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john 1195.Ed 1196.Pp 1197Since an SSH-based setup entails a fair amount of overhead, 1198it may be more suited to temporary setups, 1199such as for wireless VPNs. 1200More permanent VPNs are better provided by tools such as 1201.Xr ipsecctl 8 1202and 1203.Xr isakmpd 8 . 1204.Sh ENVIRONMENT 1205.Nm 1206will normally set the following environment variables: 1207.Bl -tag -width "SSH_ORIGINAL_COMMAND" 1208.It Ev DISPLAY 1209The 1210.Ev DISPLAY 1211variable indicates the location of the X11 server. 1212It is automatically set by 1213.Nm 1214to point to a value of the form 1215.Dq hostname:n , 1216where 1217.Dq hostname 1218indicates the host where the shell runs, and 1219.Sq n 1220is an integer \*(Ge 1. 1221.Nm 1222uses this special value to forward X11 connections over the secure 1223channel. 1224The user should normally not set 1225.Ev DISPLAY 1226explicitly, as that 1227will render the X11 connection insecure (and will require the user to 1228manually copy any required authorization cookies). 1229.It Ev HOME 1230Set to the path of the user's home directory. 1231.It Ev LOGNAME 1232Synonym for 1233.Ev USER ; 1234set for compatibility with systems that use this variable. 1235.It Ev MAIL 1236Set to the path of the user's mailbox. 1237.It Ev PATH 1238Set to the default 1239.Ev PATH , 1240as specified when compiling 1241.Nm . 1242.It Ev SSH_ASKPASS 1243If 1244.Nm 1245needs a passphrase, it will read the passphrase from the current 1246terminal if it was run from a terminal. 1247If 1248.Nm 1249does not have a terminal associated with it but 1250.Ev DISPLAY 1251and 1252.Ev SSH_ASKPASS 1253are set, it will execute the program specified by 1254.Ev SSH_ASKPASS 1255and open an X11 window to read the passphrase. 1256This is particularly useful when calling 1257.Nm 1258from a 1259.Pa .xsession 1260or related script. 1261(Note that on some machines it 1262may be necessary to redirect the input from 1263.Pa /dev/null 1264to make this work.) 1265.It Ev SSH_AUTH_SOCK 1266Identifies the path of a 1267.Ux Ns -domain 1268socket used to communicate with the agent. 1269.It Ev SSH_CONNECTION 1270Identifies the client and server ends of the connection. 1271The variable contains 1272four space-separated values: client IP address, client port number, 1273server IP address, and server port number. 1274.It Ev SSH_ORIGINAL_COMMAND 1275This variable contains the original command line if a forced command 1276is executed. 1277It can be used to extract the original arguments. 1278.It Ev SSH_TTY 1279This is set to the name of the tty (path to the device) associated 1280with the current shell or command. 1281If the current session has no tty, 1282this variable is not set. 1283.It Ev TZ 1284This variable is set to indicate the present time zone if it 1285was set when the daemon was started (i.e. the daemon passes the value 1286on to new connections). 1287.It Ev USER 1288Set to the name of the user logging in. 1289.El 1290.Pp 1291Additionally, 1292.Nm 1293reads 1294.Pa ~/.ssh/environment , 1295and adds lines of the format 1296.Dq VARNAME=value 1297to the environment if the file exists and users are allowed to 1298change their environment. 1299For more information, see the 1300.Cm PermitUserEnvironment 1301option in 1302.Xr sshd_config 5 . 1303.Sh FILES 1304.Bl -tag -width Ds -compact 1305.It Pa ~/.rhosts 1306This file is used for host-based authentication (see above). 1307On some machines this file may need to be 1308world-readable if the user's home directory is on an NFS partition, 1309because 1310.Xr sshd 8 1311reads it as root. 1312Additionally, this file must be owned by the user, 1313and must not have write permissions for anyone else. 1314The recommended 1315permission for most machines is read/write for the user, and not 1316accessible by others. 1317.Pp 1318.It Pa ~/.shosts 1319This file is used in exactly the same way as 1320.Pa .rhosts , 1321but allows host-based authentication without permitting login with 1322rlogin/rsh. 1323.Pp 1324.It Pa ~/.ssh/ 1325This directory is the default location for all user-specific configuration 1326and authentication information. 1327There is no general requirement to keep the entire contents of this directory 1328secret, but the recommended permissions are read/write/execute for the user, 1329and not accessible by others. 1330.Pp 1331.It Pa ~/.ssh/authorized_keys 1332Lists the public keys (DSA, ECDSA, ED25519, RSA) 1333that can be used for logging in as this user. 1334The format of this file is described in the 1335.Xr sshd 8 1336manual page. 1337This file is not highly sensitive, but the recommended 1338permissions are read/write for the user, and not accessible by others. 1339.Pp 1340.It Pa ~/.ssh/config 1341This is the per-user configuration file. 1342The file format and configuration options are described in 1343.Xr ssh_config 5 . 1344Because of the potential for abuse, this file must have strict permissions: 1345read/write for the user, and not writable by others. 1346.Pp 1347.It Pa ~/.ssh/environment 1348Contains additional definitions for environment variables; see 1349.Sx ENVIRONMENT , 1350above. 1351.Pp 1352.It Pa ~/.ssh/identity 1353.It Pa ~/.ssh/id_dsa 1354.It Pa ~/.ssh/id_ecdsa 1355.It Pa ~/.ssh/id_ed25519 1356.It Pa ~/.ssh/id_rsa 1357Contains the private key for authentication. 1358These files 1359contain sensitive data and should be readable by the user but not 1360accessible by others (read/write/execute). 1361.Nm 1362will simply ignore a private key file if it is accessible by others. 1363It is possible to specify a passphrase when 1364generating the key which will be used to encrypt the 1365sensitive part of this file using 3DES. 1366.Pp 1367.It Pa ~/.ssh/identity.pub 1368.It Pa ~/.ssh/id_dsa.pub 1369.It Pa ~/.ssh/id_ecdsa.pub 1370.It Pa ~/.ssh/id_ed25519.pub 1371.It Pa ~/.ssh/id_rsa.pub 1372Contains the public key for authentication. 1373These files are not 1374sensitive and can (but need not) be readable by anyone. 1375.Pp 1376.It Pa ~/.ssh/known_hosts 1377Contains a list of host keys for all hosts the user has logged into 1378that are not already in the systemwide list of known host keys. 1379See 1380.Xr sshd 8 1381for further details of the format of this file. 1382.Pp 1383.It Pa ~/.ssh/rc 1384Commands in this file are executed by 1385.Nm 1386when the user logs in, just before the user's shell (or command) is 1387started. 1388See the 1389.Xr sshd 8 1390manual page for more information. 1391.Pp 1392.It Pa /etc/hosts.equiv 1393This file is for host-based authentication (see above). 1394It should only be writable by root. 1395.Pp 1396.It Pa /etc/ssh/shosts.equiv 1397This file is used in exactly the same way as 1398.Pa hosts.equiv , 1399but allows host-based authentication without permitting login with 1400rlogin/rsh. 1401.Pp 1402.It Pa /etc/ssh/ssh_config 1403Systemwide configuration file. 1404The file format and configuration options are described in 1405.Xr ssh_config 5 . 1406.Pp 1407.It Pa /etc/ssh/ssh_host_key 1408.It Pa /etc/ssh/ssh_host_dsa_key 1409.It Pa /etc/ssh/ssh_host_ecdsa_key 1410.It Pa /etc/ssh/ssh_host_ed25519_key 1411.It Pa /etc/ssh/ssh_host_rsa_key 1412These files contain the private parts of the host keys 1413and are used for host-based authentication. 1414If protocol version 1 is used, 1415.Nm 1416must be setuid root, since the host key is readable only by root. 1417For protocol version 2, 1418.Nm 1419uses 1420.Xr ssh-keysign 8 1421to access the host keys, 1422eliminating the requirement that 1423.Nm 1424be setuid root when host-based authentication is used. 1425By default 1426.Nm 1427is not setuid root. 1428.Pp 1429.It Pa /etc/ssh/ssh_known_hosts 1430Systemwide list of known host keys. 1431This file should be prepared by the 1432system administrator to contain the public host keys of all machines in the 1433organization. 1434It should be world-readable. 1435See 1436.Xr sshd 8 1437for further details of the format of this file. 1438.Pp 1439.It Pa /etc/ssh/sshrc 1440Commands in this file are executed by 1441.Nm 1442when the user logs in, just before the user's shell (or command) is started. 1443See the 1444.Xr sshd 8 1445manual page for more information. 1446.El 1447.Sh EXIT STATUS 1448.Nm 1449exits with the exit status of the remote command or with 255 1450if an error occurred. 1451.Sh SEE ALSO 1452.Xr scp 1 , 1453.Xr sftp 1 , 1454.Xr ssh-add 1 , 1455.Xr ssh-agent 1 , 1456.Xr ssh-keygen 1 , 1457.Xr ssh-keyscan 1 , 1458.Xr tun 4 , 1459.Xr ssh_config 5 , 1460.Xr ssh-keysign 8 , 1461.Xr sshd 8 1462.Sh STANDARDS 1463.Rs 1464.%A S. Lehtinen 1465.%A C. Lonvick 1466.%D January 2006 1467.%R RFC 4250 1468.%T The Secure Shell (SSH) Protocol Assigned Numbers 1469.Re 1470.Pp 1471.Rs 1472.%A T. Ylonen 1473.%A C. Lonvick 1474.%D January 2006 1475.%R RFC 4251 1476.%T The Secure Shell (SSH) Protocol Architecture 1477.Re 1478.Pp 1479.Rs 1480.%A T. Ylonen 1481.%A C. Lonvick 1482.%D January 2006 1483.%R RFC 4252 1484.%T The Secure Shell (SSH) Authentication Protocol 1485.Re 1486.Pp 1487.Rs 1488.%A T. Ylonen 1489.%A C. Lonvick 1490.%D January 2006 1491.%R RFC 4253 1492.%T The Secure Shell (SSH) Transport Layer Protocol 1493.Re 1494.Pp 1495.Rs 1496.%A T. Ylonen 1497.%A C. Lonvick 1498.%D January 2006 1499.%R RFC 4254 1500.%T The Secure Shell (SSH) Connection Protocol 1501.Re 1502.Pp 1503.Rs 1504.%A J. Schlyter 1505.%A W. Griffin 1506.%D January 2006 1507.%R RFC 4255 1508.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints 1509.Re 1510.Pp 1511.Rs 1512.%A F. Cusack 1513.%A M. Forssen 1514.%D January 2006 1515.%R RFC 4256 1516.%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH) 1517.Re 1518.Pp 1519.Rs 1520.%A J. Galbraith 1521.%A P. Remaker 1522.%D January 2006 1523.%R RFC 4335 1524.%T The Secure Shell (SSH) Session Channel Break Extension 1525.Re 1526.Pp 1527.Rs 1528.%A M. Bellare 1529.%A T. Kohno 1530.%A C. Namprempre 1531.%D January 2006 1532.%R RFC 4344 1533.%T The Secure Shell (SSH) Transport Layer Encryption Modes 1534.Re 1535.Pp 1536.Rs 1537.%A B. Harris 1538.%D January 2006 1539.%R RFC 4345 1540.%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol 1541.Re 1542.Pp 1543.Rs 1544.%A M. Friedl 1545.%A N. Provos 1546.%A W. Simpson 1547.%D March 2006 1548.%R RFC 4419 1549.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol 1550.Re 1551.Pp 1552.Rs 1553.%A J. Galbraith 1554.%A R. Thayer 1555.%D November 2006 1556.%R RFC 4716 1557.%T The Secure Shell (SSH) Public Key File Format 1558.Re 1559.Pp 1560.Rs 1561.%A D. Stebila 1562.%A J. Green 1563.%D December 2009 1564.%R RFC 5656 1565.%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer 1566.Re 1567.Pp 1568.Rs 1569.%A A. Perrig 1570.%A D. Song 1571.%D 1999 1572.%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99) 1573.%T Hash Visualization: a New Technique to improve Real-World Security 1574.Re 1575.Sh AUTHORS 1576OpenSSH is a derivative of the original and free 1577ssh 1.2.12 release by Tatu Ylonen. 1578Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 1579Theo de Raadt and Dug Song 1580removed many bugs, re-added newer features and 1581created OpenSSH. 1582Markus Friedl contributed the support for SSH 1583protocol versions 1.5 and 2.0. 1584