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.\" $FreeBSD$ 38.Dd $Mdocdate: July 24 2014 $ 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 1246AaCfgKkMNnqsTtVvXxYy 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 L Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport 57.Op Fl l Ar login_name 58.Op Fl m Ar mac_spec 59.Op Fl O Ar ctl_cmd 60.Op Fl o Ar option 61.Op Fl p Ar port 62.Op Fl Q Cm cipher | cipher-auth | mac | kex | key 63.Op Fl R Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport 64.Op Fl S Ar ctl_path 65.Op Fl W Ar host : Ns Ar port 66.Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun 67.Oo Ar user Ns @ Oc Ns Ar hostname 68.Op Ar command 69.Ek 70.Sh DESCRIPTION 71.Nm 72(SSH client) is a program for logging into a remote machine and for 73executing commands on a remote machine. 74It is intended to replace rlogin and rsh, 75and 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 89depending on the protocol version used (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.Bl -tag -width Ds 98.It Fl 1 99Forces 100.Nm 101to try protocol version 1 only. 102.It Fl 2 103Forces 104.Nm 105to try protocol version 2 only. 106.It Fl 4 107Forces 108.Nm 109to use IPv4 addresses only. 110.It Fl 6 111Forces 112.Nm 113to use IPv6 addresses only. 114.It Fl A 115Enables forwarding of the authentication agent connection. 116This can also be specified on a per-host basis in a configuration file. 117.Pp 118Agent forwarding should be enabled with caution. 119Users with the ability to bypass file permissions on the remote host 120(for the agent's 121.Ux Ns -domain 122socket) can access the local agent through the forwarded connection. 123An attacker cannot obtain key material from the agent, 124however they can perform operations on the keys that enable them to 125authenticate using the identities loaded into the agent. 126.It Fl a 127Disables forwarding of the authentication agent connection. 128.It Fl b Ar bind_address 129Use 130.Ar bind_address 131on the local machine as the source address 132of the connection. 133Only useful on systems with more than one address. 134.It Fl C 135Requests compression of all data (including stdin, stdout, stderr, and 136data for forwarded X11, TCP and 137.Ux Ns -domain 138connections). 139The compression algorithm is the same used by 140.Xr gzip 1 , 141and the 142.Dq level 143can be controlled by the 144.Cm CompressionLevel 145option for protocol version 1. 146Compression is desirable on modem lines and other 147slow connections, but will only slow down things on fast networks. 148The default value can be set on a host-by-host basis in the 149configuration files; see the 150.Cm Compression 151option. 152.It Fl c Ar cipher_spec 153Selects the cipher specification for encrypting the session. 154.Pp 155Protocol version 1 allows specification of a single cipher. 156The supported values are 157.Dq 3des , 158.Dq blowfish , 159and 160.Dq des . 161For protocol version 2, 162.Ar cipher_spec 163is a comma-separated list of ciphers 164listed in order of preference. 165See the 166.Cm Ciphers 167keyword in 168.Xr ssh_config 5 169for more information. 170.It Fl D Xo 171.Sm off 172.Oo Ar bind_address : Oc 173.Ar port 174.Sm on 175.Xc 176Specifies a local 177.Dq dynamic 178application-level port forwarding. 179This works by allocating a socket to listen to 180.Ar port 181on the local side, optionally bound to the specified 182.Ar bind_address . 183Whenever a connection is made to this port, the 184connection is forwarded over the secure channel, and the application 185protocol is then used to determine where to connect to from the 186remote machine. 187Currently the SOCKS4 and SOCKS5 protocols are supported, and 188.Nm 189will act as a SOCKS server. 190Only root can forward privileged ports. 191Dynamic port forwardings can also be specified in the configuration file. 192.Pp 193IPv6 addresses can be specified by enclosing the address in square brackets. 194Only the superuser can forward privileged ports. 195By default, the local port is bound in accordance with the 196.Cm GatewayPorts 197setting. 198However, an explicit 199.Ar bind_address 200may be used to bind the connection to a specific address. 201The 202.Ar bind_address 203of 204.Dq localhost 205indicates that the listening port be bound for local use only, while an 206empty address or 207.Sq * 208indicates that the port should be available from all interfaces. 209.It Fl E Ar log_file 210Append debug logs to 211.Ar log_file 212instead of standard error. 213.It Fl e Ar escape_char 214Sets the escape character for sessions with a pty (default: 215.Ql ~ ) . 216The escape character is only recognized at the beginning of a line. 217The escape character followed by a dot 218.Pq Ql \&. 219closes the connection; 220followed by control-Z suspends the connection; 221and followed by itself sends the escape character once. 222Setting the character to 223.Dq none 224disables any escapes and makes the session fully transparent. 225.It Fl F Ar configfile 226Specifies an alternative per-user configuration file. 227If a configuration file is given on the command line, 228the system-wide configuration file 229.Pq Pa /etc/ssh/ssh_config 230will be ignored. 231The default for the per-user configuration file is 232.Pa ~/.ssh/config . 233.It Fl f 234Requests 235.Nm 236to go to background just before command execution. 237This is useful if 238.Nm 239is going to ask for passwords or passphrases, but the user 240wants it in the background. 241This implies 242.Fl n . 243The recommended way to start X11 programs at a remote site is with 244something like 245.Ic ssh -f host xterm . 246.Pp 247If the 248.Cm ExitOnForwardFailure 249configuration option is set to 250.Dq yes , 251then a client started with 252.Fl f 253will wait for all remote port forwards to be successfully established 254before placing itself in the background. 255.It Fl g 256Allows remote hosts to connect to local forwarded ports. 257If used on a multiplexed connection, then this option must be specified 258on the master process. 259.It Fl I Ar pkcs11 260Specify the PKCS#11 shared library 261.Nm 262should use to communicate with a PKCS#11 token providing the user's 263private RSA key. 264.It Fl i Ar identity_file 265Selects a file from which the identity (private key) for 266public key authentication is read. 267The default is 268.Pa ~/.ssh/identity 269for protocol version 1, and 270.Pa ~/.ssh/id_dsa , 271.Pa ~/.ssh/id_ecdsa , 272.Pa ~/.ssh/id_ed25519 273and 274.Pa ~/.ssh/id_rsa 275for protocol version 2. 276Identity files may also be specified on 277a per-host basis in the configuration file. 278It is possible to have multiple 279.Fl i 280options (and multiple identities specified in 281configuration files). 282.Nm 283will also try to load certificate information from the filename obtained 284by appending 285.Pa -cert.pub 286to identity filenames. 287.It Fl K 288Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI 289credentials to the server. 290.It Fl k 291Disables forwarding (delegation) of GSSAPI credentials to the server. 292.It Fl L Xo 293.Sm off 294.Oo Ar bind_address : Oc 295.Ar port : host : hostport 296.Sm on 297.Xc 298Specifies that the given port on the local (client) host is to be 299forwarded to the given host and port on the remote side. 300This works by allocating a socket to listen to 301.Ar port 302on the local side, optionally bound to the specified 303.Ar bind_address . 304Whenever a connection is made to this port, the 305connection is forwarded over the secure channel, and a connection is 306made to 307.Ar host 308port 309.Ar hostport 310from the remote machine. 311Port forwardings can also be specified in the configuration file. 312IPv6 addresses can be specified by enclosing the address in square brackets. 313Only the superuser can forward privileged ports. 314By default, the local port is bound in accordance with the 315.Cm GatewayPorts 316setting. 317However, an explicit 318.Ar bind_address 319may be used to bind the connection to a specific address. 320The 321.Ar bind_address 322of 323.Dq localhost 324indicates that the listening port be bound for local use only, while an 325empty address or 326.Sq * 327indicates that the port should be available from all interfaces. 328.It Fl l Ar login_name 329Specifies the user to log in as on the remote machine. 330This also may be specified on a per-host basis in the configuration file. 331.It Fl M 332Places the 333.Nm 334client into 335.Dq master 336mode for connection sharing. 337Multiple 338.Fl M 339options places 340.Nm 341into 342.Dq master 343mode with confirmation required before slave connections are accepted. 344Refer to the description of 345.Cm ControlMaster 346in 347.Xr ssh_config 5 348for details. 349.It Fl m Ar mac_spec 350Additionally, for protocol version 2 a comma-separated list of MAC 351(message authentication code) algorithms can 352be specified in order of preference. 353See the 354.Cm MACs 355keyword for more information. 356.It Fl N 357Do not execute a remote command. 358This is useful for just forwarding ports 359(protocol version 2 only). 360.It Fl n 361Redirects stdin from 362.Pa /dev/null 363(actually, prevents reading from stdin). 364This must be used when 365.Nm 366is run in the background. 367A common trick is to use this to run X11 programs on a remote machine. 368For example, 369.Ic ssh -n shadows.cs.hut.fi emacs & 370will start an emacs on shadows.cs.hut.fi, and the X11 371connection will be automatically forwarded over an encrypted channel. 372The 373.Nm 374program will be put in the background. 375(This does not work if 376.Nm 377needs to ask for a password or passphrase; see also the 378.Fl f 379option.) 380.It Fl O Ar ctl_cmd 381Control an active connection multiplexing master process. 382When the 383.Fl O 384option is specified, the 385.Ar ctl_cmd 386argument is interpreted and passed to the master process. 387Valid commands are: 388.Dq check 389(check that the master process is running), 390.Dq forward 391(request forwardings without command execution), 392.Dq cancel 393(cancel forwardings), 394.Dq exit 395(request the master to exit), and 396.Dq stop 397(request the master to stop accepting further multiplexing requests). 398.It Fl o Ar option 399Can be used to give options in the format used in the configuration file. 400This is useful for specifying options for which there is no separate 401command-line flag. 402For full details of the options listed below, and their possible values, see 403.Xr ssh_config 5 . 404.Pp 405.Bl -tag -width Ds -offset indent -compact 406.It AddressFamily 407.It BatchMode 408.It BindAddress 409.It CanonicalDomains 410.It CanonicalizeFallbackLocal 411.It CanonicalizeHostname 412.It CanonicalizeMaxDots 413.It CanonicalizePermittedCNAMEs 414.It ChallengeResponseAuthentication 415.It CheckHostIP 416.It Cipher 417.It Ciphers 418.It ClearAllForwardings 419.It Compression 420.It CompressionLevel 421.It ConnectionAttempts 422.It ConnectTimeout 423.It ControlMaster 424.It ControlPath 425.It ControlPersist 426.It DynamicForward 427.It EscapeChar 428.It ExitOnForwardFailure 429.It ForwardAgent 430.It ForwardX11 431.It ForwardX11Timeout 432.It ForwardX11Trusted 433.It GatewayPorts 434.It GlobalKnownHostsFile 435.It GSSAPIAuthentication 436.It GSSAPIDelegateCredentials 437.It HashKnownHosts 438.It Host 439.It HostbasedAuthentication 440.It HostKeyAlgorithms 441.It HostKeyAlias 442.It HostName 443.It IdentityFile 444.It IdentitiesOnly 445.It IPQoS 446.It KbdInteractiveAuthentication 447.It KbdInteractiveDevices 448.It KexAlgorithms 449.It LocalCommand 450.It LocalForward 451.It LogLevel 452.It MACs 453.It Match 454.It NoHostAuthenticationForLocalhost 455.It NumberOfPasswordPrompts 456.It PasswordAuthentication 457.It PermitLocalCommand 458.It PKCS11Provider 459.It Port 460.It PreferredAuthentications 461.It Protocol 462.It ProxyCommand 463.It ProxyUseFdpass 464.It PubkeyAuthentication 465.It RekeyLimit 466.It RemoteForward 467.It RequestTTY 468.It RhostsRSAAuthentication 469.It RSAAuthentication 470.It SendEnv 471.It ServerAliveInterval 472.It ServerAliveCountMax 473.It StreamLocalBindMask 474.It StreamLocalBindUnlink 475.It StrictHostKeyChecking 476.It TCPKeepAlive 477.It Tunnel 478.It TunnelDevice 479.It UsePrivilegedPort 480.It User 481.It UserKnownHostsFile 482.It VerifyHostKeyDNS 483.It VersionAddendum 484.It VisualHostKey 485.It XAuthLocation 486.El 487.It Fl p Ar port 488Port to connect to on the remote host. 489This can be specified on a 490per-host basis in the configuration file. 491.It Fl Q Cm cipher | cipher-auth | mac | kex | key 492Queries 493.Nm 494for the algorithms supported for the specified version 2. 495The available features are: 496.Ar cipher 497(supported symmetric ciphers), 498.Ar cipher-auth 499(supported symmetric ciphers that support authenticated encryption), 500.Ar mac 501(supported message integrity codes), 502.Ar kex 503(key exchange algorithms), 504.Ar key 505(key types). 506.It Fl q 507Quiet mode. 508Causes most warning and diagnostic messages to be suppressed. 509.It Fl R Xo 510.Sm off 511.Oo Ar bind_address : Oc 512.Ar port : host : hostport 513.Sm on 514.Xc 515Specifies that the given port on the remote (server) host is to be 516forwarded to the given host and port on the local side. 517This works by allocating a socket to listen to 518.Ar port 519on the remote side, and whenever a connection is made to this port, the 520connection is forwarded over the secure channel, and a connection is 521made to 522.Ar host 523port 524.Ar hostport 525from the local machine. 526.Pp 527Port forwardings can also be specified in the configuration file. 528Privileged ports can be forwarded only when 529logging in as root on the remote machine. 530IPv6 addresses can be specified by enclosing the address in square brackets. 531.Pp 532By default, the listening socket on the server will be bound to the loopback 533interface only. 534This may be overridden by specifying a 535.Ar bind_address . 536An empty 537.Ar bind_address , 538or the address 539.Ql * , 540indicates that the remote socket should listen on all interfaces. 541Specifying a remote 542.Ar bind_address 543will only succeed if the server's 544.Cm GatewayPorts 545option is enabled (see 546.Xr sshd_config 5 ) . 547.Pp 548If the 549.Ar port 550argument is 551.Ql 0 , 552the listen port will be dynamically allocated on the server and reported 553to the client at run time. 554When used together with 555.Ic -O forward 556the allocated port will be printed to the standard output. 557.It Fl S Ar ctl_path 558Specifies the location of a control socket for connection sharing, 559or the string 560.Dq none 561to disable connection sharing. 562Refer to the description of 563.Cm ControlPath 564and 565.Cm ControlMaster 566in 567.Xr ssh_config 5 568for details. 569.It Fl s 570May be used to request invocation of a subsystem on the remote system. 571Subsystems are a feature of the SSH2 protocol which facilitate the use 572of SSH as a secure transport for other applications (eg.\& 573.Xr sftp 1 ) . 574The subsystem is specified as the remote command. 575.It Fl T 576Disable pseudo-tty allocation. 577.It Fl t 578Force pseudo-tty allocation. 579This can be used to execute arbitrary 580screen-based programs on a remote machine, which can be very useful, 581e.g. when implementing menu services. 582Multiple 583.Fl t 584options force tty allocation, even if 585.Nm 586has no local tty. 587.It Fl V 588Display the version number and exit. 589.It Fl v 590Verbose mode. 591Causes 592.Nm 593to print debugging messages about its progress. 594This is helpful in 595debugging connection, authentication, and configuration problems. 596Multiple 597.Fl v 598options increase the verbosity. 599The maximum is 3. 600.It Fl W Ar host : Ns Ar port 601Requests that standard input and output on the client be forwarded to 602.Ar host 603on 604.Ar port 605over the secure channel. 606Implies 607.Fl N , 608.Fl T , 609.Cm ExitOnForwardFailure 610and 611.Cm ClearAllForwardings . 612Works with Protocol version 2 only. 613.It Fl w Xo 614.Ar local_tun Ns Op : Ns Ar remote_tun 615.Xc 616Requests 617tunnel 618device forwarding with the specified 619.Xr tun 4 620devices between the client 621.Pq Ar local_tun 622and the server 623.Pq Ar remote_tun . 624.Pp 625The devices may be specified by numerical ID or the keyword 626.Dq any , 627which uses the next available tunnel device. 628If 629.Ar remote_tun 630is not specified, it defaults to 631.Dq any . 632See also the 633.Cm Tunnel 634and 635.Cm TunnelDevice 636directives in 637.Xr ssh_config 5 . 638If the 639.Cm Tunnel 640directive is unset, it is set to the default tunnel mode, which is 641.Dq point-to-point . 642.It Fl X 643Enables X11 forwarding. 644This can also be specified on a per-host basis in a configuration file. 645.Pp 646X11 forwarding should be enabled with caution. 647Users with the ability to bypass file permissions on the remote host 648(for the user's X authorization database) 649can access the local X11 display through the forwarded connection. 650An attacker may then be able to perform activities such as keystroke monitoring. 651.Pp 652For this reason, X11 forwarding is subjected to X11 SECURITY extension 653restrictions by default. 654Please refer to the 655.Nm 656.Fl Y 657option and the 658.Cm ForwardX11Trusted 659directive in 660.Xr ssh_config 5 661for more information. 662.It Fl x 663Disables X11 forwarding. 664.It Fl Y 665Enables trusted X11 forwarding. 666Trusted X11 forwardings are not subjected to the X11 SECURITY extension 667controls. 668.It Fl y 669Send log information using the 670.Xr syslog 3 671system module. 672By default this information is sent to stderr. 673.El 674.Pp 675.Nm 676may additionally obtain configuration data from 677a per-user configuration file and a system-wide configuration file. 678The file format and configuration options are described in 679.Xr ssh_config 5 . 680.Sh AUTHENTICATION 681The OpenSSH SSH client supports SSH protocols 1 and 2. 682The default is to use protocol 2 only, 683though this can be changed via the 684.Cm Protocol 685option in 686.Xr ssh_config 5 687or the 688.Fl 1 689and 690.Fl 2 691options (see above). 692Both protocols support similar authentication methods, 693but protocol 2 is the default since 694it provides additional mechanisms for confidentiality 695(the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) 696and integrity (hmac-md5, hmac-sha1, 697hmac-sha2-256, hmac-sha2-512, 698umac-64, umac-128, hmac-ripemd160). 699Protocol 1 lacks a strong mechanism for ensuring the 700integrity of the connection. 701.Pp 702The methods available for authentication are: 703GSSAPI-based authentication, 704host-based authentication, 705public key authentication, 706challenge-response authentication, 707and password authentication. 708Authentication methods are tried in the order specified above, 709though protocol 2 has a configuration option to change the default order: 710.Cm PreferredAuthentications . 711.Pp 712Host-based authentication works as follows: 713If the machine the user logs in from is listed in 714.Pa /etc/hosts.equiv 715or 716.Pa /etc/shosts.equiv 717on the remote machine, and the user names are 718the same on both sides, or if the files 719.Pa ~/.rhosts 720or 721.Pa ~/.shosts 722exist in the user's home directory on the 723remote machine and contain a line containing the name of the client 724machine and the name of the user on that machine, the user is 725considered for login. 726Additionally, the server 727.Em must 728be able to verify the client's 729host key (see the description of 730.Pa /etc/ssh/ssh_known_hosts 731and 732.Pa ~/.ssh/known_hosts , 733below) 734for login to be permitted. 735This authentication method closes security holes due to IP 736spoofing, DNS spoofing, and routing spoofing. 737[Note to the administrator: 738.Pa /etc/hosts.equiv , 739.Pa ~/.rhosts , 740and the rlogin/rsh protocol in general, are inherently insecure and should be 741disabled if security is desired.] 742.Pp 743Public key authentication works as follows: 744The scheme is based on public-key cryptography, 745using cryptosystems 746where encryption and decryption are done using separate keys, 747and it is unfeasible to derive the decryption key from the encryption key. 748The idea is that each user creates a public/private 749key pair for authentication purposes. 750The server knows the public key, and only the user knows the private key. 751.Nm 752implements public key authentication protocol automatically, 753using one of the DSA, ECDSA, ED25519 or RSA algorithms. 754Protocol 1 is restricted to using only RSA keys, 755but protocol 2 may use any. 756The HISTORY section of 757.Xr ssl 8 758contains a brief discussion of the DSA and RSA algorithms. 759.Pp 760The file 761.Pa ~/.ssh/authorized_keys 762lists the public keys that are permitted for logging in. 763When the user logs in, the 764.Nm 765program tells the server which key pair it would like to use for 766authentication. 767The client proves that it has access to the private key 768and the server checks that the corresponding public key 769is authorized to accept the account. 770.Pp 771The user creates his/her key pair by running 772.Xr ssh-keygen 1 . 773This stores the private key in 774.Pa ~/.ssh/identity 775(protocol 1), 776.Pa ~/.ssh/id_dsa 777(protocol 2 DSA), 778.Pa ~/.ssh/id_ecdsa 779(protocol 2 ECDSA), 780.Pa ~/.ssh/id_ed25519 781(protocol 2 ED25519), 782or 783.Pa ~/.ssh/id_rsa 784(protocol 2 RSA) 785and stores the public key in 786.Pa ~/.ssh/identity.pub 787(protocol 1), 788.Pa ~/.ssh/id_dsa.pub 789(protocol 2 DSA), 790.Pa ~/.ssh/id_ecdsa.pub 791(protocol 2 ECDSA), 792.Pa ~/.ssh/id_ed25519.pub 793(protocol 2 ED25519), 794or 795.Pa ~/.ssh/id_rsa.pub 796(protocol 2 RSA) 797in the user's home directory. 798The user should then copy the public key 799to 800.Pa ~/.ssh/authorized_keys 801in his/her home directory on the remote machine. 802The 803.Pa authorized_keys 804file corresponds to the conventional 805.Pa ~/.rhosts 806file, and has one key 807per line, though the lines can be very long. 808After this, the user can log in without giving the password. 809.Pp 810A variation on public key authentication 811is available in the form of certificate authentication: 812instead of a set of public/private keys, 813signed certificates are used. 814This has the advantage that a single trusted certification authority 815can be used in place of many public/private keys. 816See the CERTIFICATES section of 817.Xr ssh-keygen 1 818for more information. 819.Pp 820The most convenient way to use public key or certificate authentication 821may be with an authentication agent. 822See 823.Xr ssh-agent 1 824for more information. 825.Pp 826Challenge-response authentication works as follows: 827The server sends an arbitrary 828.Qq challenge 829text, and prompts for a response. 830Protocol 2 allows multiple challenges and responses; 831protocol 1 is restricted to just one challenge/response. 832Examples of challenge-response authentication include 833.Bx 834Authentication (see 835.Xr login.conf 5 ) 836and PAM (some 837.Pf non- Ox 838systems). 839.Pp 840Finally, if other authentication methods fail, 841.Nm 842prompts the user for a password. 843The password is sent to the remote 844host for checking; however, since all communications are encrypted, 845the password cannot be seen by someone listening on the network. 846.Pp 847.Nm 848automatically maintains and checks a database containing 849identification for all hosts it has ever been used with. 850Host keys are stored in 851.Pa ~/.ssh/known_hosts 852in the user's home directory. 853Additionally, the file 854.Pa /etc/ssh/ssh_known_hosts 855is automatically checked for known hosts. 856Any new hosts are automatically added to the user's file. 857If a host's identification ever changes, 858.Nm 859warns about this and disables password authentication to prevent 860server spoofing or man-in-the-middle attacks, 861which could otherwise be used to circumvent the encryption. 862The 863.Cm StrictHostKeyChecking 864option can be used to control logins to machines whose 865host key is not known or has changed. 866.Pp 867When the user's identity has been accepted by the server, the server 868either executes the given command, or logs into the machine and gives 869the user a normal shell on the remote machine. 870All communication with 871the remote command or shell will be automatically encrypted. 872.Pp 873If a pseudo-terminal has been allocated (normal login session), the 874user may use the escape characters noted below. 875.Pp 876If no pseudo-tty has been allocated, 877the session is transparent and can be used to reliably transfer binary data. 878On most systems, setting the escape character to 879.Dq none 880will also make the session transparent even if a tty is used. 881.Pp 882The session terminates when the command or shell on the remote 883machine exits and all X11 and TCP connections have been closed. 884.Sh ESCAPE CHARACTERS 885When a pseudo-terminal has been requested, 886.Nm 887supports a number of functions through the use of an escape character. 888.Pp 889A single tilde character can be sent as 890.Ic ~~ 891or by following the tilde by a character other than those described below. 892The escape character must always follow a newline to be interpreted as 893special. 894The escape character can be changed in configuration files using the 895.Cm EscapeChar 896configuration directive or on the command line by the 897.Fl e 898option. 899.Pp 900The supported escapes (assuming the default 901.Ql ~ ) 902are: 903.Bl -tag -width Ds 904.It Cm ~. 905Disconnect. 906.It Cm ~^Z 907Background 908.Nm . 909.It Cm ~# 910List forwarded connections. 911.It Cm ~& 912Background 913.Nm 914at logout when waiting for forwarded connection / X11 sessions to terminate. 915.It Cm ~? 916Display a list of escape characters. 917.It Cm ~B 918Send a BREAK to the remote system 919(only useful for SSH protocol version 2 and if the peer supports it). 920.It Cm ~C 921Open command line. 922Currently this allows the addition of port forwardings using the 923.Fl L , 924.Fl R 925and 926.Fl D 927options (see above). 928It also allows the cancellation of existing port-forwardings 929with 930.Sm off 931.Fl KL Oo Ar bind_address : Oc Ar port 932.Sm on 933for local, 934.Sm off 935.Fl KR Oo Ar bind_address : Oc Ar port 936.Sm on 937for remote and 938.Sm off 939.Fl KD Oo Ar bind_address : Oc Ar port 940.Sm on 941for dynamic port-forwardings. 942.Ic !\& Ns Ar command 943allows the user to execute a local command if the 944.Ic PermitLocalCommand 945option is enabled in 946.Xr ssh_config 5 . 947Basic help is available, using the 948.Fl h 949option. 950.It Cm ~R 951Request rekeying of the connection 952(only useful for SSH protocol version 2 and if the peer supports it). 953.It Cm ~V 954Decrease the verbosity 955.Pq Ic LogLevel 956when errors are being written to stderr. 957.It Cm ~v 958Increase the verbosity 959.Pq Ic LogLevel 960when errors are being written to stderr. 961.El 962.Sh TCP FORWARDING 963Forwarding of arbitrary TCP connections over the secure channel can 964be specified either on the command line or in a configuration file. 965One possible application of TCP forwarding is a secure connection to a 966mail server; another is going through firewalls. 967.Pp 968In the example below, we look at encrypting communication between 969an IRC client and server, even though the IRC server does not directly 970support encrypted communications. 971This works as follows: 972the user connects to the remote host using 973.Nm , 974specifying a port to be used to forward connections 975to the remote server. 976After that it is possible to start the service which is to be encrypted 977on the client machine, 978connecting to the same local port, 979and 980.Nm 981will encrypt and forward the connection. 982.Pp 983The following example tunnels an IRC session from client machine 984.Dq 127.0.0.1 985(localhost) 986to remote server 987.Dq server.example.com : 988.Bd -literal -offset 4n 989$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 990$ irc -c '#users' -p 1234 pinky 127.0.0.1 991.Ed 992.Pp 993This tunnels a connection to IRC server 994.Dq server.example.com , 995joining channel 996.Dq #users , 997nickname 998.Dq pinky , 999using port 1234. 1000It doesn't matter which port is used, 1001as long as it's greater than 1023 1002(remember, only root can open sockets on privileged ports) 1003and doesn't conflict with any ports already in use. 1004The connection is forwarded to port 6667 on the remote server, 1005since that's the standard port for IRC services. 1006.Pp 1007The 1008.Fl f 1009option backgrounds 1010.Nm 1011and the remote command 1012.Dq sleep 10 1013is specified to allow an amount of time 1014(10 seconds, in the example) 1015to start the service which is to be tunnelled. 1016If no connections are made within the time specified, 1017.Nm 1018will exit. 1019.Sh X11 FORWARDING 1020If the 1021.Cm ForwardX11 1022variable is set to 1023.Dq yes 1024(or see the description of the 1025.Fl X , 1026.Fl x , 1027and 1028.Fl Y 1029options above) 1030and the user is using X11 (the 1031.Ev DISPLAY 1032environment variable is set), the connection to the X11 display is 1033automatically forwarded to the remote side in such a way that any X11 1034programs started from the shell (or command) will go through the 1035encrypted channel, and the connection to the real X server will be made 1036from the local machine. 1037The user should not manually set 1038.Ev DISPLAY . 1039Forwarding of X11 connections can be 1040configured on the command line or in configuration files. 1041.Pp 1042The 1043.Ev DISPLAY 1044value set by 1045.Nm 1046will point to the server machine, but with a display number greater than zero. 1047This is normal, and happens because 1048.Nm 1049creates a 1050.Dq proxy 1051X server on the server machine for forwarding the 1052connections over the encrypted channel. 1053.Pp 1054.Nm 1055will also automatically set up Xauthority data on the server machine. 1056For this purpose, it will generate a random authorization cookie, 1057store it in Xauthority on the server, and verify that any forwarded 1058connections carry this cookie and replace it by the real cookie when 1059the connection is opened. 1060The real authentication cookie is never 1061sent to the server machine (and no cookies are sent in the plain). 1062.Pp 1063If the 1064.Cm ForwardAgent 1065variable is set to 1066.Dq yes 1067(or see the description of the 1068.Fl A 1069and 1070.Fl a 1071options above) and 1072the user is using an authentication agent, the connection to the agent 1073is automatically forwarded to the remote side. 1074.Sh VERIFYING HOST KEYS 1075When connecting to a server for the first time, 1076a fingerprint of the server's public key is presented to the user 1077(unless the option 1078.Cm StrictHostKeyChecking 1079has been disabled). 1080Fingerprints can be determined using 1081.Xr ssh-keygen 1 : 1082.Pp 1083.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key 1084.Pp 1085If the fingerprint is already known, it can be matched 1086and the key can be accepted or rejected. 1087Because of the difficulty of comparing host keys 1088just by looking at hex strings, 1089there is also support to compare host keys visually, 1090using 1091.Em random art . 1092By setting the 1093.Cm VisualHostKey 1094option to 1095.Dq yes , 1096a small ASCII graphic gets displayed on every login to a server, no matter 1097if the session itself is interactive or not. 1098By learning the pattern a known server produces, a user can easily 1099find out that the host key has changed when a completely different pattern 1100is displayed. 1101Because these patterns are not unambiguous however, a pattern that looks 1102similar to the pattern remembered only gives a good probability that the 1103host key is the same, not guaranteed proof. 1104.Pp 1105To get a listing of the fingerprints along with their random art for 1106all known hosts, the following command line can be used: 1107.Pp 1108.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts 1109.Pp 1110If the fingerprint is unknown, 1111an alternative method of verification is available: 1112SSH fingerprints verified by DNS. 1113An additional resource record (RR), 1114SSHFP, 1115is added to a zonefile 1116and the connecting client is able to match the fingerprint 1117with that of the key presented. 1118.Pp 1119In this example, we are connecting a client to a server, 1120.Dq host.example.com . 1121The SSHFP resource records should first be added to the zonefile for 1122host.example.com: 1123.Bd -literal -offset indent 1124$ ssh-keygen -r host.example.com. 1125.Ed 1126.Pp 1127The output lines will have to be added to the zonefile. 1128To check that the zone is answering fingerprint queries: 1129.Pp 1130.Dl $ dig -t SSHFP host.example.com 1131.Pp 1132Finally the client connects: 1133.Bd -literal -offset indent 1134$ ssh -o "VerifyHostKeyDNS ask" host.example.com 1135[...] 1136Matching host key fingerprint found in DNS. 1137Are you sure you want to continue connecting (yes/no)? 1138.Ed 1139.Pp 1140See the 1141.Cm VerifyHostKeyDNS 1142option in 1143.Xr ssh_config 5 1144for more information. 1145.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS 1146.Nm 1147contains support for Virtual Private Network (VPN) tunnelling 1148using the 1149.Xr tun 4 1150network pseudo-device, 1151allowing two networks to be joined securely. 1152The 1153.Xr sshd_config 5 1154configuration option 1155.Cm PermitTunnel 1156controls whether the server supports this, 1157and at what level (layer 2 or 3 traffic). 1158.Pp 1159The following example would connect client network 10.0.50.0/24 1160with remote network 10.0.99.0/24 using a point-to-point connection 1161from 10.1.1.1 to 10.1.1.2, 1162provided that the SSH server running on the gateway to the remote network, 1163at 192.168.1.15, allows it. 1164.Pp 1165On the client: 1166.Bd -literal -offset indent 1167# ssh -f -w 0:1 192.168.1.15 true 1168# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252 1169# route add 10.0.99.0/24 10.1.1.2 1170.Ed 1171.Pp 1172On the server: 1173.Bd -literal -offset indent 1174# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252 1175# route add 10.0.50.0/24 10.1.1.1 1176.Ed 1177.Pp 1178Client access may be more finely tuned via the 1179.Pa /root/.ssh/authorized_keys 1180file (see below) and the 1181.Cm PermitRootLogin 1182server option. 1183The following entry would permit connections on 1184.Xr tun 4 1185device 1 from user 1186.Dq jane 1187and on tun device 2 from user 1188.Dq john , 1189if 1190.Cm PermitRootLogin 1191is set to 1192.Dq forced-commands-only : 1193.Bd -literal -offset 2n 1194tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane 1195tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john 1196.Ed 1197.Pp 1198Since an SSH-based setup entails a fair amount of overhead, 1199it may be more suited to temporary setups, 1200such as for wireless VPNs. 1201More permanent VPNs are better provided by tools such as 1202.Xr ipsecctl 8 1203and 1204.Xr isakmpd 8 . 1205.Sh ENVIRONMENT 1206.Nm 1207will normally set the following environment variables: 1208.Bl -tag -width "SSH_ORIGINAL_COMMAND" 1209.It Ev DISPLAY 1210The 1211.Ev DISPLAY 1212variable indicates the location of the X11 server. 1213It is automatically set by 1214.Nm 1215to point to a value of the form 1216.Dq hostname:n , 1217where 1218.Dq hostname 1219indicates the host where the shell runs, and 1220.Sq n 1221is an integer \*(Ge 1. 1222.Nm 1223uses this special value to forward X11 connections over the secure 1224channel. 1225The user should normally not set 1226.Ev DISPLAY 1227explicitly, as that 1228will render the X11 connection insecure (and will require the user to 1229manually copy any required authorization cookies). 1230.It Ev HOME 1231Set to the path of the user's home directory. 1232.It Ev LOGNAME 1233Synonym for 1234.Ev USER ; 1235set for compatibility with systems that use this variable. 1236.It Ev MAIL 1237Set to the path of the user's mailbox. 1238.It Ev PATH 1239Set to the default 1240.Ev PATH , 1241as specified when compiling 1242.Nm . 1243.It Ev SSH_ASKPASS 1244If 1245.Nm 1246needs a passphrase, it will read the passphrase from the current 1247terminal if it was run from a terminal. 1248If 1249.Nm 1250does not have a terminal associated with it but 1251.Ev DISPLAY 1252and 1253.Ev SSH_ASKPASS 1254are set, it will execute the program specified by 1255.Ev SSH_ASKPASS 1256and open an X11 window to read the passphrase. 1257This is particularly useful when calling 1258.Nm 1259from a 1260.Pa .xsession 1261or related script. 1262(Note that on some machines it 1263may be necessary to redirect the input from 1264.Pa /dev/null 1265to make this work.) 1266.It Ev SSH_AUTH_SOCK 1267Identifies the path of a 1268.Ux Ns -domain 1269socket used to communicate with the agent. 1270.It Ev SSH_CONNECTION 1271Identifies the client and server ends of the connection. 1272The variable contains 1273four space-separated values: client IP address, client port number, 1274server IP address, and server port number. 1275.It Ev SSH_ORIGINAL_COMMAND 1276This variable contains the original command line if a forced command 1277is executed. 1278It can be used to extract the original arguments. 1279.It Ev SSH_TTY 1280This is set to the name of the tty (path to the device) associated 1281with the current shell or command. 1282If the current session has no tty, 1283this variable is not set. 1284.It Ev TZ 1285This variable is set to indicate the present time zone if it 1286was set when the daemon was started (i.e. the daemon passes the value 1287on to new connections). 1288.It Ev USER 1289Set to the name of the user logging in. 1290.El 1291.Pp 1292Additionally, 1293.Nm 1294reads 1295.Pa ~/.ssh/environment , 1296and adds lines of the format 1297.Dq VARNAME=value 1298to the environment if the file exists and users are allowed to 1299change their environment. 1300For more information, see the 1301.Cm PermitUserEnvironment 1302option in 1303.Xr sshd_config 5 . 1304.Sh FILES 1305.Bl -tag -width Ds -compact 1306.It Pa ~/.rhosts 1307This file is used for host-based authentication (see above). 1308On some machines this file may need to be 1309world-readable if the user's home directory is on an NFS partition, 1310because 1311.Xr sshd 8 1312reads it as root. 1313Additionally, this file must be owned by the user, 1314and must not have write permissions for anyone else. 1315The recommended 1316permission for most machines is read/write for the user, and not 1317accessible by others. 1318.Pp 1319.It Pa ~/.shosts 1320This file is used in exactly the same way as 1321.Pa .rhosts , 1322but allows host-based authentication without permitting login with 1323rlogin/rsh. 1324.Pp 1325.It Pa ~/.ssh/ 1326This directory is the default location for all user-specific configuration 1327and authentication information. 1328There is no general requirement to keep the entire contents of this directory 1329secret, but the recommended permissions are read/write/execute for the user, 1330and not accessible by others. 1331.Pp 1332.It Pa ~/.ssh/authorized_keys 1333Lists the public keys (DSA, ECDSA, ED25519, RSA) 1334that can be used for logging in as this user. 1335The format of this file is described in the 1336.Xr sshd 8 1337manual page. 1338This file is not highly sensitive, but the recommended 1339permissions are read/write for the user, and not accessible by others. 1340.Pp 1341.It Pa ~/.ssh/config 1342This is the per-user configuration file. 1343The file format and configuration options are described in 1344.Xr ssh_config 5 . 1345Because of the potential for abuse, this file must have strict permissions: 1346read/write for the user, and not writable by others. 1347.Pp 1348.It Pa ~/.ssh/environment 1349Contains additional definitions for environment variables; see 1350.Sx ENVIRONMENT , 1351above. 1352.Pp 1353.It Pa ~/.ssh/identity 1354.It Pa ~/.ssh/id_dsa 1355.It Pa ~/.ssh/id_ecdsa 1356.It Pa ~/.ssh/id_ed25519 1357.It Pa ~/.ssh/id_rsa 1358Contains the private key for authentication. 1359These files 1360contain sensitive data and should be readable by the user but not 1361accessible by others (read/write/execute). 1362.Nm 1363will simply ignore a private key file if it is accessible by others. 1364It is possible to specify a passphrase when 1365generating the key which will be used to encrypt the 1366sensitive part of this file using 3DES. 1367.Pp 1368.It Pa ~/.ssh/identity.pub 1369.It Pa ~/.ssh/id_dsa.pub 1370.It Pa ~/.ssh/id_ecdsa.pub 1371.It Pa ~/.ssh/id_ed25519.pub 1372.It Pa ~/.ssh/id_rsa.pub 1373Contains the public key for authentication. 1374These files are not 1375sensitive and can (but need not) be readable by anyone. 1376.Pp 1377.It Pa ~/.ssh/known_hosts 1378Contains a list of host keys for all hosts the user has logged into 1379that are not already in the systemwide list of known host keys. 1380See 1381.Xr sshd 8 1382for further details of the format of this file. 1383.Pp 1384.It Pa ~/.ssh/rc 1385Commands in this file are executed by 1386.Nm 1387when the user logs in, just before the user's shell (or command) is 1388started. 1389See the 1390.Xr sshd 8 1391manual page for more information. 1392.Pp 1393.It Pa /etc/hosts.equiv 1394This file is for host-based authentication (see above). 1395It should only be writable by root. 1396.Pp 1397.It Pa /etc/shosts.equiv 1398This file is used in exactly the same way as 1399.Pa hosts.equiv , 1400but allows host-based authentication without permitting login with 1401rlogin/rsh. 1402.Pp 1403.It Pa /etc/ssh/ssh_config 1404Systemwide configuration file. 1405The file format and configuration options are described in 1406.Xr ssh_config 5 . 1407.Pp 1408.It Pa /etc/ssh/ssh_host_key 1409.It Pa /etc/ssh/ssh_host_dsa_key 1410.It Pa /etc/ssh/ssh_host_ecdsa_key 1411.It Pa /etc/ssh/ssh_host_ed25519_key 1412.It Pa /etc/ssh/ssh_host_rsa_key 1413These files contain the private parts of the host keys 1414and are used for host-based authentication. 1415If protocol version 1 is used, 1416.Nm 1417must be setuid root, since the host key is readable only by root. 1418For protocol version 2, 1419.Nm 1420uses 1421.Xr ssh-keysign 8 1422to access the host keys, 1423eliminating the requirement that 1424.Nm 1425be setuid root when host-based authentication is used. 1426By default 1427.Nm 1428is not setuid root. 1429.Pp 1430.It Pa /etc/ssh/ssh_known_hosts 1431Systemwide list of known host keys. 1432This file should be prepared by the 1433system administrator to contain the public host keys of all machines in the 1434organization. 1435It should be world-readable. 1436See 1437.Xr sshd 8 1438for further details of the format of this file. 1439.Pp 1440.It Pa /etc/ssh/sshrc 1441Commands in this file are executed by 1442.Nm 1443when the user logs in, just before the user's shell (or command) is started. 1444See the 1445.Xr sshd 8 1446manual page for more information. 1447.El 1448.Sh EXIT STATUS 1449.Nm 1450exits with the exit status of the remote command or with 255 1451if an error occurred. 1452.Sh SEE ALSO 1453.Xr scp 1 , 1454.Xr sftp 1 , 1455.Xr ssh-add 1 , 1456.Xr ssh-agent 1 , 1457.Xr ssh-keygen 1 , 1458.Xr ssh-keyscan 1 , 1459.Xr tun 4 , 1460.Xr ssh_config 5 , 1461.Xr ssh-keysign 8 , 1462.Xr sshd 8 1463.Sh STANDARDS 1464.Rs 1465.%A S. Lehtinen 1466.%A C. Lonvick 1467.%D January 2006 1468.%R RFC 4250 1469.%T The Secure Shell (SSH) Protocol Assigned Numbers 1470.Re 1471.Pp 1472.Rs 1473.%A T. Ylonen 1474.%A C. Lonvick 1475.%D January 2006 1476.%R RFC 4251 1477.%T The Secure Shell (SSH) Protocol Architecture 1478.Re 1479.Pp 1480.Rs 1481.%A T. Ylonen 1482.%A C. Lonvick 1483.%D January 2006 1484.%R RFC 4252 1485.%T The Secure Shell (SSH) Authentication Protocol 1486.Re 1487.Pp 1488.Rs 1489.%A T. Ylonen 1490.%A C. Lonvick 1491.%D January 2006 1492.%R RFC 4253 1493.%T The Secure Shell (SSH) Transport Layer Protocol 1494.Re 1495.Pp 1496.Rs 1497.%A T. Ylonen 1498.%A C. Lonvick 1499.%D January 2006 1500.%R RFC 4254 1501.%T The Secure Shell (SSH) Connection Protocol 1502.Re 1503.Pp 1504.Rs 1505.%A J. Schlyter 1506.%A W. Griffin 1507.%D January 2006 1508.%R RFC 4255 1509.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints 1510.Re 1511.Pp 1512.Rs 1513.%A F. Cusack 1514.%A M. Forssen 1515.%D January 2006 1516.%R RFC 4256 1517.%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH) 1518.Re 1519.Pp 1520.Rs 1521.%A J. Galbraith 1522.%A P. Remaker 1523.%D January 2006 1524.%R RFC 4335 1525.%T The Secure Shell (SSH) Session Channel Break Extension 1526.Re 1527.Pp 1528.Rs 1529.%A M. Bellare 1530.%A T. Kohno 1531.%A C. Namprempre 1532.%D January 2006 1533.%R RFC 4344 1534.%T The Secure Shell (SSH) Transport Layer Encryption Modes 1535.Re 1536.Pp 1537.Rs 1538.%A B. Harris 1539.%D January 2006 1540.%R RFC 4345 1541.%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol 1542.Re 1543.Pp 1544.Rs 1545.%A M. Friedl 1546.%A N. Provos 1547.%A W. Simpson 1548.%D March 2006 1549.%R RFC 4419 1550.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol 1551.Re 1552.Pp 1553.Rs 1554.%A J. Galbraith 1555.%A R. Thayer 1556.%D November 2006 1557.%R RFC 4716 1558.%T The Secure Shell (SSH) Public Key File Format 1559.Re 1560.Pp 1561.Rs 1562.%A D. Stebila 1563.%A J. Green 1564.%D December 2009 1565.%R RFC 5656 1566.%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer 1567.Re 1568.Pp 1569.Rs 1570.%A A. Perrig 1571.%A D. Song 1572.%D 1999 1573.%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99) 1574.%T Hash Visualization: a New Technique to improve Real-World Security 1575.Re 1576.Sh AUTHORS 1577OpenSSH is a derivative of the original and free 1578ssh 1.2.12 release by Tatu Ylonen. 1579Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 1580Theo de Raadt and Dug Song 1581removed many bugs, re-added newer features and 1582created OpenSSH. 1583Markus Friedl contributed the support for SSH 1584protocol versions 1.5 and 2.0. 1585