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 1.356 2015/03/03 06:48:58 djm Exp $ 37.\" $FreeBSD$ 38.Dd $Mdocdate: March 3 2015 $ 39.Dt SSH 1 40.Os 41.Sh NAME 42.Nm ssh 43.Nd OpenSSH SSH client (remote login program) 44.Sh SYNOPSIS 45.Nm ssh 46.Bk -words 47.Op Fl 1246AaCfGgKkMNnqsTtVvXxYy 48.Op Fl b Ar bind_address 49.Op Fl c Ar cipher_spec 50.Op Fl D Oo Ar bind_address : Oc Ns Ar port 51.Op Fl E Ar log_file 52.Op Fl e Ar escape_char 53.Op Fl F Ar configfile 54.Op Fl I Ar pkcs11 55.Op Fl i Ar identity_file 56.Op Fl 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 | protocol-version 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 256Causes 257.Nm 258to print its configuration after evaluating 259.Cm Host 260and 261.Cm Match 262blocks and exit. 263.It Fl g 264Allows remote hosts to connect to local forwarded ports. 265If used on a multiplexed connection, then this option must be specified 266on the master process. 267.It Fl I Ar pkcs11 268Specify the PKCS#11 shared library 269.Nm 270should use to communicate with a PKCS#11 token providing the user's 271private RSA key. 272.It Fl i Ar identity_file 273Selects a file from which the identity (private key) for 274public key authentication is read. 275The default is 276.Pa ~/.ssh/identity 277for protocol version 1, and 278.Pa ~/.ssh/id_dsa , 279.Pa ~/.ssh/id_ecdsa , 280.Pa ~/.ssh/id_ed25519 281and 282.Pa ~/.ssh/id_rsa 283for protocol version 2. 284Identity files may also be specified on 285a per-host basis in the configuration file. 286It is possible to have multiple 287.Fl i 288options (and multiple identities specified in 289configuration files). 290.Nm 291will also try to load certificate information from the filename obtained 292by appending 293.Pa -cert.pub 294to identity filenames. 295.It Fl K 296Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI 297credentials to the server. 298.It Fl k 299Disables forwarding (delegation) of GSSAPI credentials to the server. 300.It Fl L Xo 301.Sm off 302.Oo Ar bind_address : Oc 303.Ar port : host : hostport 304.Sm on 305.Xc 306Specifies that the given port on the local (client) host is to be 307forwarded to the given host and port on the remote side. 308This works by allocating a socket to listen to 309.Ar port 310on the local side, optionally bound to the specified 311.Ar bind_address . 312Whenever a connection is made to this port, the 313connection is forwarded over the secure channel, and a connection is 314made to 315.Ar host 316port 317.Ar hostport 318from the remote machine. 319Port forwardings can also be specified in the configuration file. 320IPv6 addresses can be specified by enclosing the address in square brackets. 321Only the superuser can forward privileged ports. 322By default, the local port is bound in accordance with the 323.Cm GatewayPorts 324setting. 325However, an explicit 326.Ar bind_address 327may be used to bind the connection to a specific address. 328The 329.Ar bind_address 330of 331.Dq localhost 332indicates that the listening port be bound for local use only, while an 333empty address or 334.Sq * 335indicates that the port should be available from all interfaces. 336.It Fl l Ar login_name 337Specifies the user to log in as on the remote machine. 338This also may be specified on a per-host basis in the configuration file. 339.It Fl M 340Places the 341.Nm 342client into 343.Dq master 344mode for connection sharing. 345Multiple 346.Fl M 347options places 348.Nm 349into 350.Dq master 351mode with confirmation required before slave connections are accepted. 352Refer to the description of 353.Cm ControlMaster 354in 355.Xr ssh_config 5 356for details. 357.It Fl m Ar mac_spec 358Additionally, for protocol version 2 a comma-separated list of MAC 359(message authentication code) algorithms can 360be specified in order of preference. 361See the 362.Cm MACs 363keyword for more information. 364.It Fl N 365Do not execute a remote command. 366This is useful for just forwarding ports 367(protocol version 2 only). 368.It Fl n 369Redirects stdin from 370.Pa /dev/null 371(actually, prevents reading from stdin). 372This must be used when 373.Nm 374is run in the background. 375A common trick is to use this to run X11 programs on a remote machine. 376For example, 377.Ic ssh -n shadows.cs.hut.fi emacs & 378will start an emacs on shadows.cs.hut.fi, and the X11 379connection will be automatically forwarded over an encrypted channel. 380The 381.Nm 382program will be put in the background. 383(This does not work if 384.Nm 385needs to ask for a password or passphrase; see also the 386.Fl f 387option.) 388.It Fl O Ar ctl_cmd 389Control an active connection multiplexing master process. 390When the 391.Fl O 392option is specified, the 393.Ar ctl_cmd 394argument is interpreted and passed to the master process. 395Valid commands are: 396.Dq check 397(check that the master process is running), 398.Dq forward 399(request forwardings without command execution), 400.Dq cancel 401(cancel forwardings), 402.Dq exit 403(request the master to exit), and 404.Dq stop 405(request the master to stop accepting further multiplexing requests). 406.It Fl o Ar option 407Can be used to give options in the format used in the configuration file. 408This is useful for specifying options for which there is no separate 409command-line flag. 410For full details of the options listed below, and their possible values, see 411.Xr ssh_config 5 . 412.Pp 413.Bl -tag -width Ds -offset indent -compact 414.It AddressFamily 415.It BatchMode 416.It BindAddress 417.It CanonicalDomains 418.It CanonicalizeFallbackLocal 419.It CanonicalizeHostname 420.It CanonicalizeMaxDots 421.It CanonicalizePermittedCNAMEs 422.It ChallengeResponseAuthentication 423.It CheckHostIP 424.It Cipher 425.It Ciphers 426.It ClearAllForwardings 427.It Compression 428.It CompressionLevel 429.It ConnectionAttempts 430.It ConnectTimeout 431.It ControlMaster 432.It ControlPath 433.It ControlPersist 434.It DynamicForward 435.It EscapeChar 436.It ExitOnForwardFailure 437.It FingerprintHash 438.It ForwardAgent 439.It ForwardX11 440.It ForwardX11Timeout 441.It ForwardX11Trusted 442.It GatewayPorts 443.It GlobalKnownHostsFile 444.It GSSAPIAuthentication 445.It GSSAPIDelegateCredentials 446.It HashKnownHosts 447.It Host 448.It HostbasedAuthentication 449.It HostbasedKeyTypes 450.It HostKeyAlgorithms 451.It HostKeyAlias 452.It HostName 453.It IdentityFile 454.It IdentitiesOnly 455.It IPQoS 456.It KbdInteractiveAuthentication 457.It KbdInteractiveDevices 458.It KexAlgorithms 459.It LocalCommand 460.It LocalForward 461.It LogLevel 462.It MACs 463.It Match 464.It NoHostAuthenticationForLocalhost 465.It NumberOfPasswordPrompts 466.It PasswordAuthentication 467.It PermitLocalCommand 468.It PKCS11Provider 469.It Port 470.It PreferredAuthentications 471.It Protocol 472.It ProxyCommand 473.It ProxyUseFdpass 474.It PubkeyAuthentication 475.It RekeyLimit 476.It RemoteForward 477.It RequestTTY 478.It RhostsRSAAuthentication 479.It RSAAuthentication 480.It SendEnv 481.It ServerAliveInterval 482.It ServerAliveCountMax 483.It StreamLocalBindMask 484.It StreamLocalBindUnlink 485.It StrictHostKeyChecking 486.It TCPKeepAlive 487.It Tunnel 488.It TunnelDevice 489.It UpdateHostKeys 490.It UsePrivilegedPort 491.It User 492.It UserKnownHostsFile 493.It VerifyHostKeyDNS 494.It VersionAddendum 495.It VisualHostKey 496.It XAuthLocation 497.El 498.It Fl p Ar port 499Port to connect to on the remote host. 500This can be specified on a 501per-host basis in the configuration file. 502.It Fl Q Cm cipher | cipher-auth | mac | kex | key | protocol-version 503Queries 504.Nm 505for the algorithms supported for the specified version 2. 506The available features are: 507.Ar cipher 508(supported symmetric ciphers), 509.Ar cipher-auth 510(supported symmetric ciphers that support authenticated encryption), 511.Ar mac 512(supported message integrity codes), 513.Ar kex 514(key exchange algorithms), 515.Ar key 516(key types) and 517.Ar protocol-version 518(supported SSH protocol versions). 519.It Fl q 520Quiet mode. 521Causes most warning and diagnostic messages to be suppressed. 522.It Fl R Xo 523.Sm off 524.Oo Ar bind_address : Oc 525.Ar port : host : hostport 526.Sm on 527.Xc 528Specifies that the given port on the remote (server) host is to be 529forwarded to the given host and port on the local side. 530This works by allocating a socket to listen to 531.Ar port 532on the remote side, and whenever a connection is made to this port, the 533connection is forwarded over the secure channel, and a connection is 534made to 535.Ar host 536port 537.Ar hostport 538from the local machine. 539.Pp 540Port forwardings can also be specified in the configuration file. 541Privileged ports can be forwarded only when 542logging in as root on the remote machine. 543IPv6 addresses can be specified by enclosing the address in square brackets. 544.Pp 545By default, the listening socket on the server will be bound to the loopback 546interface only. 547This may be overridden by specifying a 548.Ar bind_address . 549An empty 550.Ar bind_address , 551or the address 552.Ql * , 553indicates that the remote socket should listen on all interfaces. 554Specifying a remote 555.Ar bind_address 556will only succeed if the server's 557.Cm GatewayPorts 558option is enabled (see 559.Xr sshd_config 5 ) . 560.Pp 561If the 562.Ar port 563argument is 564.Ql 0 , 565the listen port will be dynamically allocated on the server and reported 566to the client at run time. 567When used together with 568.Ic -O forward 569the allocated port will be printed to the standard output. 570.It Fl S Ar ctl_path 571Specifies the location of a control socket for connection sharing, 572or the string 573.Dq none 574to disable connection sharing. 575Refer to the description of 576.Cm ControlPath 577and 578.Cm ControlMaster 579in 580.Xr ssh_config 5 581for details. 582.It Fl s 583May be used to request invocation of a subsystem on the remote system. 584Subsystems are a feature of the SSH2 protocol which facilitate the use 585of SSH as a secure transport for other applications (eg.\& 586.Xr sftp 1 ) . 587The subsystem is specified as the remote command. 588.It Fl T 589Disable pseudo-tty allocation. 590.It Fl t 591Force pseudo-tty allocation. 592This can be used to execute arbitrary 593screen-based programs on a remote machine, which can be very useful, 594e.g. when implementing menu services. 595Multiple 596.Fl t 597options force tty allocation, even if 598.Nm 599has no local tty. 600.It Fl V 601Display the version number and exit. 602.It Fl v 603Verbose mode. 604Causes 605.Nm 606to print debugging messages about its progress. 607This is helpful in 608debugging connection, authentication, and configuration problems. 609Multiple 610.Fl v 611options increase the verbosity. 612The maximum is 3. 613.It Fl W Ar host : Ns Ar port 614Requests that standard input and output on the client be forwarded to 615.Ar host 616on 617.Ar port 618over the secure channel. 619Implies 620.Fl N , 621.Fl T , 622.Cm ExitOnForwardFailure 623and 624.Cm ClearAllForwardings . 625Works with Protocol version 2 only. 626.It Fl w Xo 627.Ar local_tun Ns Op : Ns Ar remote_tun 628.Xc 629Requests 630tunnel 631device forwarding with the specified 632.Xr tun 4 633devices between the client 634.Pq Ar local_tun 635and the server 636.Pq Ar remote_tun . 637.Pp 638The devices may be specified by numerical ID or the keyword 639.Dq any , 640which uses the next available tunnel device. 641If 642.Ar remote_tun 643is not specified, it defaults to 644.Dq any . 645See also the 646.Cm Tunnel 647and 648.Cm TunnelDevice 649directives in 650.Xr ssh_config 5 . 651If the 652.Cm Tunnel 653directive is unset, it is set to the default tunnel mode, which is 654.Dq point-to-point . 655.It Fl X 656Enables X11 forwarding. 657This can also be specified on a per-host basis in a configuration file. 658.Pp 659X11 forwarding should be enabled with caution. 660Users with the ability to bypass file permissions on the remote host 661(for the user's X authorization database) 662can access the local X11 display through the forwarded connection. 663An attacker may then be able to perform activities such as keystroke monitoring. 664.Pp 665For this reason, X11 forwarding is subjected to X11 SECURITY extension 666restrictions by default. 667Please refer to the 668.Nm 669.Fl Y 670option and the 671.Cm ForwardX11Trusted 672directive in 673.Xr ssh_config 5 674for more information. 675.It Fl x 676Disables X11 forwarding. 677.It Fl Y 678Enables trusted X11 forwarding. 679Trusted X11 forwardings are not subjected to the X11 SECURITY extension 680controls. 681.It Fl y 682Send log information using the 683.Xr syslog 3 684system module. 685By default this information is sent to stderr. 686.El 687.Pp 688.Nm 689may additionally obtain configuration data from 690a per-user configuration file and a system-wide configuration file. 691The file format and configuration options are described in 692.Xr ssh_config 5 . 693.Sh AUTHENTICATION 694The OpenSSH SSH client supports SSH protocols 1 and 2. 695The default is to use protocol 2 only, 696though this can be changed via the 697.Cm Protocol 698option in 699.Xr ssh_config 5 700or the 701.Fl 1 702and 703.Fl 2 704options (see above). 705Both protocols support similar authentication methods, 706but protocol 2 is the default since 707it provides additional mechanisms for confidentiality 708(the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) 709and integrity (hmac-md5, hmac-sha1, 710hmac-sha2-256, hmac-sha2-512, 711umac-64, umac-128, hmac-ripemd160). 712Protocol 1 lacks a strong mechanism for ensuring the 713integrity of the connection. 714.Pp 715The methods available for authentication are: 716GSSAPI-based authentication, 717host-based authentication, 718public key authentication, 719challenge-response authentication, 720and password authentication. 721Authentication methods are tried in the order specified above, 722though protocol 2 has a configuration option to change the default order: 723.Cm PreferredAuthentications . 724.Pp 725Host-based authentication works as follows: 726If the machine the user logs in from is listed in 727.Pa /etc/hosts.equiv 728or 729.Pa /etc/shosts.equiv 730on the remote machine, and the user names are 731the same on both sides, or if the files 732.Pa ~/.rhosts 733or 734.Pa ~/.shosts 735exist in the user's home directory on the 736remote machine and contain a line containing the name of the client 737machine and the name of the user on that machine, the user is 738considered for login. 739Additionally, the server 740.Em must 741be able to verify the client's 742host key (see the description of 743.Pa /etc/ssh/ssh_known_hosts 744and 745.Pa ~/.ssh/known_hosts , 746below) 747for login to be permitted. 748This authentication method closes security holes due to IP 749spoofing, DNS spoofing, and routing spoofing. 750[Note to the administrator: 751.Pa /etc/hosts.equiv , 752.Pa ~/.rhosts , 753and the rlogin/rsh protocol in general, are inherently insecure and should be 754disabled if security is desired.] 755.Pp 756Public key authentication works as follows: 757The scheme is based on public-key cryptography, 758using cryptosystems 759where encryption and decryption are done using separate keys, 760and it is unfeasible to derive the decryption key from the encryption key. 761The idea is that each user creates a public/private 762key pair for authentication purposes. 763The server knows the public key, and only the user knows the private key. 764.Nm 765implements public key authentication protocol automatically, 766using one of the DSA, ECDSA, Ed25519 or RSA algorithms. 767Protocol 1 is restricted to using only RSA keys, 768but protocol 2 may use any. 769The HISTORY section of 770.Xr ssl 8 771contains a brief discussion of the DSA and RSA algorithms. 772.Pp 773The file 774.Pa ~/.ssh/authorized_keys 775lists the public keys that are permitted for logging in. 776When the user logs in, the 777.Nm 778program tells the server which key pair it would like to use for 779authentication. 780The client proves that it has access to the private key 781and the server checks that the corresponding public key 782is authorized to accept the account. 783.Pp 784The user creates his/her key pair by running 785.Xr ssh-keygen 1 . 786This stores the private key in 787.Pa ~/.ssh/identity 788(protocol 1), 789.Pa ~/.ssh/id_dsa 790(protocol 2 DSA), 791.Pa ~/.ssh/id_ecdsa 792(protocol 2 ECDSA), 793.Pa ~/.ssh/id_ed25519 794(protocol 2 Ed25519), 795or 796.Pa ~/.ssh/id_rsa 797(protocol 2 RSA) 798and stores the public key in 799.Pa ~/.ssh/identity.pub 800(protocol 1), 801.Pa ~/.ssh/id_dsa.pub 802(protocol 2 DSA), 803.Pa ~/.ssh/id_ecdsa.pub 804(protocol 2 ECDSA), 805.Pa ~/.ssh/id_ed25519.pub 806(protocol 2 Ed25519), 807or 808.Pa ~/.ssh/id_rsa.pub 809(protocol 2 RSA) 810in the user's home directory. 811The user should then copy the public key 812to 813.Pa ~/.ssh/authorized_keys 814in his/her home directory on the remote machine. 815The 816.Pa authorized_keys 817file corresponds to the conventional 818.Pa ~/.rhosts 819file, and has one key 820per line, though the lines can be very long. 821After this, the user can log in without giving the password. 822.Pp 823A variation on public key authentication 824is available in the form of certificate authentication: 825instead of a set of public/private keys, 826signed certificates are used. 827This has the advantage that a single trusted certification authority 828can be used in place of many public/private keys. 829See the CERTIFICATES section of 830.Xr ssh-keygen 1 831for more information. 832.Pp 833The most convenient way to use public key or certificate authentication 834may be with an authentication agent. 835See 836.Xr ssh-agent 1 837for more information. 838.Pp 839Challenge-response authentication works as follows: 840The server sends an arbitrary 841.Qq challenge 842text, and prompts for a response. 843Protocol 2 allows multiple challenges and responses; 844protocol 1 is restricted to just one challenge/response. 845Examples of challenge-response authentication include 846.Bx 847Authentication (see 848.Xr login.conf 5 ) 849and PAM (some 850.Pf non- Ox 851systems). 852.Pp 853Finally, if other authentication methods fail, 854.Nm 855prompts the user for a password. 856The password is sent to the remote 857host for checking; however, since all communications are encrypted, 858the password cannot be seen by someone listening on the network. 859.Pp 860.Nm 861automatically maintains and checks a database containing 862identification for all hosts it has ever been used with. 863Host keys are stored in 864.Pa ~/.ssh/known_hosts 865in the user's home directory. 866Additionally, the file 867.Pa /etc/ssh/ssh_known_hosts 868is automatically checked for known hosts. 869Any new hosts are automatically added to the user's file. 870If a host's identification ever changes, 871.Nm 872warns about this and disables password authentication to prevent 873server spoofing or man-in-the-middle attacks, 874which could otherwise be used to circumvent the encryption. 875The 876.Cm StrictHostKeyChecking 877option can be used to control logins to machines whose 878host key is not known or has changed. 879.Pp 880When the user's identity has been accepted by the server, the server 881either executes the given command, or logs into the machine and gives 882the user a normal shell on the remote machine. 883All communication with 884the remote command or shell will be automatically encrypted. 885.Pp 886If a pseudo-terminal has been allocated (normal login session), the 887user may use the escape characters noted below. 888.Pp 889If no pseudo-tty has been allocated, 890the session is transparent and can be used to reliably transfer binary data. 891On most systems, setting the escape character to 892.Dq none 893will also make the session transparent even if a tty is used. 894.Pp 895The session terminates when the command or shell on the remote 896machine exits and all X11 and TCP connections have been closed. 897.Sh ESCAPE CHARACTERS 898When a pseudo-terminal has been requested, 899.Nm 900supports a number of functions through the use of an escape character. 901.Pp 902A single tilde character can be sent as 903.Ic ~~ 904or by following the tilde by a character other than those described below. 905The escape character must always follow a newline to be interpreted as 906special. 907The escape character can be changed in configuration files using the 908.Cm EscapeChar 909configuration directive or on the command line by the 910.Fl e 911option. 912.Pp 913The supported escapes (assuming the default 914.Ql ~ ) 915are: 916.Bl -tag -width Ds 917.It Cm ~. 918Disconnect. 919.It Cm ~^Z 920Background 921.Nm . 922.It Cm ~# 923List forwarded connections. 924.It Cm ~& 925Background 926.Nm 927at logout when waiting for forwarded connection / X11 sessions to terminate. 928.It Cm ~? 929Display a list of escape characters. 930.It Cm ~B 931Send a BREAK to the remote system 932(only useful for SSH protocol version 2 and if the peer supports it). 933.It Cm ~C 934Open command line. 935Currently this allows the addition of port forwardings using the 936.Fl L , 937.Fl R 938and 939.Fl D 940options (see above). 941It also allows the cancellation of existing port-forwardings 942with 943.Sm off 944.Fl KL Oo Ar bind_address : Oc Ar port 945.Sm on 946for local, 947.Sm off 948.Fl KR Oo Ar bind_address : Oc Ar port 949.Sm on 950for remote and 951.Sm off 952.Fl KD Oo Ar bind_address : Oc Ar port 953.Sm on 954for dynamic port-forwardings. 955.Ic !\& Ns Ar command 956allows the user to execute a local command if the 957.Ic PermitLocalCommand 958option is enabled in 959.Xr ssh_config 5 . 960Basic help is available, using the 961.Fl h 962option. 963.It Cm ~R 964Request rekeying of the connection 965(only useful for SSH protocol version 2 and if the peer supports it). 966.It Cm ~V 967Decrease the verbosity 968.Pq Ic LogLevel 969when errors are being written to stderr. 970.It Cm ~v 971Increase the verbosity 972.Pq Ic LogLevel 973when errors are being written to stderr. 974.El 975.Sh TCP FORWARDING 976Forwarding of arbitrary TCP connections over the secure channel can 977be specified either on the command line or in a configuration file. 978One possible application of TCP forwarding is a secure connection to a 979mail server; another is going through firewalls. 980.Pp 981In the example below, we look at encrypting communication between 982an IRC client and server, even though the IRC server does not directly 983support encrypted communications. 984This works as follows: 985the user connects to the remote host using 986.Nm , 987specifying a port to be used to forward connections 988to the remote server. 989After that it is possible to start the service which is to be encrypted 990on the client machine, 991connecting to the same local port, 992and 993.Nm 994will encrypt and forward the connection. 995.Pp 996The following example tunnels an IRC session from client machine 997.Dq 127.0.0.1 998(localhost) 999to remote server 1000.Dq server.example.com : 1001.Bd -literal -offset 4n 1002$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 1003$ irc -c '#users' -p 1234 pinky 127.0.0.1 1004.Ed 1005.Pp 1006This tunnels a connection to IRC server 1007.Dq server.example.com , 1008joining channel 1009.Dq #users , 1010nickname 1011.Dq pinky , 1012using port 1234. 1013It doesn't matter which port is used, 1014as long as it's greater than 1023 1015(remember, only root can open sockets on privileged ports) 1016and doesn't conflict with any ports already in use. 1017The connection is forwarded to port 6667 on the remote server, 1018since that's the standard port for IRC services. 1019.Pp 1020The 1021.Fl f 1022option backgrounds 1023.Nm 1024and the remote command 1025.Dq sleep 10 1026is specified to allow an amount of time 1027(10 seconds, in the example) 1028to start the service which is to be tunnelled. 1029If no connections are made within the time specified, 1030.Nm 1031will exit. 1032.Sh X11 FORWARDING 1033If the 1034.Cm ForwardX11 1035variable is set to 1036.Dq yes 1037(or see the description of the 1038.Fl X , 1039.Fl x , 1040and 1041.Fl Y 1042options above) 1043and the user is using X11 (the 1044.Ev DISPLAY 1045environment variable is set), the connection to the X11 display is 1046automatically forwarded to the remote side in such a way that any X11 1047programs started from the shell (or command) will go through the 1048encrypted channel, and the connection to the real X server will be made 1049from the local machine. 1050The user should not manually set 1051.Ev DISPLAY . 1052Forwarding of X11 connections can be 1053configured on the command line or in configuration files. 1054.Pp 1055The 1056.Ev DISPLAY 1057value set by 1058.Nm 1059will point to the server machine, but with a display number greater than zero. 1060This is normal, and happens because 1061.Nm 1062creates a 1063.Dq proxy 1064X server on the server machine for forwarding the 1065connections over the encrypted channel. 1066.Pp 1067.Nm 1068will also automatically set up Xauthority data on the server machine. 1069For this purpose, it will generate a random authorization cookie, 1070store it in Xauthority on the server, and verify that any forwarded 1071connections carry this cookie and replace it by the real cookie when 1072the connection is opened. 1073The real authentication cookie is never 1074sent to the server machine (and no cookies are sent in the plain). 1075.Pp 1076If the 1077.Cm ForwardAgent 1078variable is set to 1079.Dq yes 1080(or see the description of the 1081.Fl A 1082and 1083.Fl a 1084options above) and 1085the user is using an authentication agent, the connection to the agent 1086is automatically forwarded to the remote side. 1087.Sh VERIFYING HOST KEYS 1088When connecting to a server for the first time, 1089a fingerprint of the server's public key is presented to the user 1090(unless the option 1091.Cm StrictHostKeyChecking 1092has been disabled). 1093Fingerprints can be determined using 1094.Xr ssh-keygen 1 : 1095.Pp 1096.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key 1097.Pp 1098If the fingerprint is already known, it can be matched 1099and the key can be accepted or rejected. 1100Because of the difficulty of comparing host keys 1101just by looking at fingerprint strings, 1102there is also support to compare host keys visually, 1103using 1104.Em random art . 1105By setting the 1106.Cm VisualHostKey 1107option to 1108.Dq yes , 1109a small ASCII graphic gets displayed on every login to a server, no matter 1110if the session itself is interactive or not. 1111By learning the pattern a known server produces, a user can easily 1112find out that the host key has changed when a completely different pattern 1113is displayed. 1114Because these patterns are not unambiguous however, a pattern that looks 1115similar to the pattern remembered only gives a good probability that the 1116host key is the same, not guaranteed proof. 1117.Pp 1118To get a listing of the fingerprints along with their random art for 1119all known hosts, the following command line can be used: 1120.Pp 1121.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts 1122.Pp 1123If the fingerprint is unknown, 1124an alternative method of verification is available: 1125SSH fingerprints verified by DNS. 1126An additional resource record (RR), 1127SSHFP, 1128is added to a zonefile 1129and the connecting client is able to match the fingerprint 1130with that of the key presented. 1131.Pp 1132In this example, we are connecting a client to a server, 1133.Dq host.example.com . 1134The SSHFP resource records should first be added to the zonefile for 1135host.example.com: 1136.Bd -literal -offset indent 1137$ ssh-keygen -r host.example.com. 1138.Ed 1139.Pp 1140The output lines will have to be added to the zonefile. 1141To check that the zone is answering fingerprint queries: 1142.Pp 1143.Dl $ dig -t SSHFP host.example.com 1144.Pp 1145Finally the client connects: 1146.Bd -literal -offset indent 1147$ ssh -o "VerifyHostKeyDNS ask" host.example.com 1148[...] 1149Matching host key fingerprint found in DNS. 1150Are you sure you want to continue connecting (yes/no)? 1151.Ed 1152.Pp 1153See the 1154.Cm VerifyHostKeyDNS 1155option in 1156.Xr ssh_config 5 1157for more information. 1158.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS 1159.Nm 1160contains support for Virtual Private Network (VPN) tunnelling 1161using the 1162.Xr tun 4 1163network pseudo-device, 1164allowing two networks to be joined securely. 1165The 1166.Xr sshd_config 5 1167configuration option 1168.Cm PermitTunnel 1169controls whether the server supports this, 1170and at what level (layer 2 or 3 traffic). 1171.Pp 1172The following example would connect client network 10.0.50.0/24 1173with remote network 10.0.99.0/24 using a point-to-point connection 1174from 10.1.1.1 to 10.1.1.2, 1175provided that the SSH server running on the gateway to the remote network, 1176at 192.168.1.15, allows it. 1177.Pp 1178On the client: 1179.Bd -literal -offset indent 1180# ssh -f -w 0:1 192.168.1.15 true 1181# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252 1182# route add 10.0.99.0/24 10.1.1.2 1183.Ed 1184.Pp 1185On the server: 1186.Bd -literal -offset indent 1187# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252 1188# route add 10.0.50.0/24 10.1.1.1 1189.Ed 1190.Pp 1191Client access may be more finely tuned via the 1192.Pa /root/.ssh/authorized_keys 1193file (see below) and the 1194.Cm PermitRootLogin 1195server option. 1196The following entry would permit connections on 1197.Xr tun 4 1198device 1 from user 1199.Dq jane 1200and on tun device 2 from user 1201.Dq john , 1202if 1203.Cm PermitRootLogin 1204is set to 1205.Dq forced-commands-only : 1206.Bd -literal -offset 2n 1207tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane 1208tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john 1209.Ed 1210.Pp 1211Since an SSH-based setup entails a fair amount of overhead, 1212it may be more suited to temporary setups, 1213such as for wireless VPNs. 1214More permanent VPNs are better provided by tools such as 1215.Xr ipsecctl 8 1216and 1217.Xr isakmpd 8 . 1218.Sh ENVIRONMENT 1219.Nm 1220will normally set the following environment variables: 1221.Bl -tag -width "SSH_ORIGINAL_COMMAND" 1222.It Ev DISPLAY 1223The 1224.Ev DISPLAY 1225variable indicates the location of the X11 server. 1226It is automatically set by 1227.Nm 1228to point to a value of the form 1229.Dq hostname:n , 1230where 1231.Dq hostname 1232indicates the host where the shell runs, and 1233.Sq n 1234is an integer \*(Ge 1. 1235.Nm 1236uses this special value to forward X11 connections over the secure 1237channel. 1238The user should normally not set 1239.Ev DISPLAY 1240explicitly, as that 1241will render the X11 connection insecure (and will require the user to 1242manually copy any required authorization cookies). 1243.It Ev HOME 1244Set to the path of the user's home directory. 1245.It Ev LOGNAME 1246Synonym for 1247.Ev USER ; 1248set for compatibility with systems that use this variable. 1249.It Ev MAIL 1250Set to the path of the user's mailbox. 1251.It Ev PATH 1252Set to the default 1253.Ev PATH , 1254as specified when compiling 1255.Nm . 1256.It Ev SSH_ASKPASS 1257If 1258.Nm 1259needs a passphrase, it will read the passphrase from the current 1260terminal if it was run from a terminal. 1261If 1262.Nm 1263does not have a terminal associated with it but 1264.Ev DISPLAY 1265and 1266.Ev SSH_ASKPASS 1267are set, it will execute the program specified by 1268.Ev SSH_ASKPASS 1269and open an X11 window to read the passphrase. 1270This is particularly useful when calling 1271.Nm 1272from a 1273.Pa .xsession 1274or related script. 1275(Note that on some machines it 1276may be necessary to redirect the input from 1277.Pa /dev/null 1278to make this work.) 1279.It Ev SSH_AUTH_SOCK 1280Identifies the path of a 1281.Ux Ns -domain 1282socket used to communicate with the agent. 1283.It Ev SSH_CONNECTION 1284Identifies the client and server ends of the connection. 1285The variable contains 1286four space-separated values: client IP address, client port number, 1287server IP address, and server port number. 1288.It Ev SSH_ORIGINAL_COMMAND 1289This variable contains the original command line if a forced command 1290is executed. 1291It can be used to extract the original arguments. 1292.It Ev SSH_TTY 1293This is set to the name of the tty (path to the device) associated 1294with the current shell or command. 1295If the current session has no tty, 1296this variable is not set. 1297.It Ev TZ 1298This variable is set to indicate the present time zone if it 1299was set when the daemon was started (i.e. the daemon passes the value 1300on to new connections). 1301.It Ev USER 1302Set to the name of the user logging in. 1303.El 1304.Pp 1305Additionally, 1306.Nm 1307reads 1308.Pa ~/.ssh/environment , 1309and adds lines of the format 1310.Dq VARNAME=value 1311to the environment if the file exists and users are allowed to 1312change their environment. 1313For more information, see the 1314.Cm PermitUserEnvironment 1315option in 1316.Xr sshd_config 5 . 1317.Sh FILES 1318.Bl -tag -width Ds -compact 1319.It Pa ~/.rhosts 1320This file is used for host-based authentication (see above). 1321On some machines this file may need to be 1322world-readable if the user's home directory is on an NFS partition, 1323because 1324.Xr sshd 8 1325reads it as root. 1326Additionally, this file must be owned by the user, 1327and must not have write permissions for anyone else. 1328The recommended 1329permission for most machines is read/write for the user, and not 1330accessible by others. 1331.Pp 1332.It Pa ~/.shosts 1333This file is used in exactly the same way as 1334.Pa .rhosts , 1335but allows host-based authentication without permitting login with 1336rlogin/rsh. 1337.Pp 1338.It Pa ~/.ssh/ 1339This directory is the default location for all user-specific configuration 1340and authentication information. 1341There is no general requirement to keep the entire contents of this directory 1342secret, but the recommended permissions are read/write/execute for the user, 1343and not accessible by others. 1344.Pp 1345.It Pa ~/.ssh/authorized_keys 1346Lists the public keys (DSA, ECDSA, Ed25519, RSA) 1347that can be used for logging in as this user. 1348The format of this file is described in the 1349.Xr sshd 8 1350manual page. 1351This file is not highly sensitive, but the recommended 1352permissions are read/write for the user, and not accessible by others. 1353.Pp 1354.It Pa ~/.ssh/config 1355This is the per-user configuration file. 1356The file format and configuration options are described in 1357.Xr ssh_config 5 . 1358Because of the potential for abuse, this file must have strict permissions: 1359read/write for the user, and not writable by others. 1360.Pp 1361.It Pa ~/.ssh/environment 1362Contains additional definitions for environment variables; see 1363.Sx ENVIRONMENT , 1364above. 1365.Pp 1366.It Pa ~/.ssh/identity 1367.It Pa ~/.ssh/id_dsa 1368.It Pa ~/.ssh/id_ecdsa 1369.It Pa ~/.ssh/id_ed25519 1370.It Pa ~/.ssh/id_rsa 1371Contains the private key for authentication. 1372These files 1373contain sensitive data and should be readable by the user but not 1374accessible by others (read/write/execute). 1375.Nm 1376will simply ignore a private key file if it is accessible by others. 1377It is possible to specify a passphrase when 1378generating the key which will be used to encrypt the 1379sensitive part of this file using 3DES. 1380.Pp 1381.It Pa ~/.ssh/identity.pub 1382.It Pa ~/.ssh/id_dsa.pub 1383.It Pa ~/.ssh/id_ecdsa.pub 1384.It Pa ~/.ssh/id_ed25519.pub 1385.It Pa ~/.ssh/id_rsa.pub 1386Contains the public key for authentication. 1387These files are not 1388sensitive and can (but need not) be readable by anyone. 1389.Pp 1390.It Pa ~/.ssh/known_hosts 1391Contains a list of host keys for all hosts the user has logged into 1392that are not already in the systemwide list of known host keys. 1393See 1394.Xr sshd 8 1395for further details of the format of this file. 1396.Pp 1397.It Pa ~/.ssh/rc 1398Commands in this file are executed by 1399.Nm 1400when the user logs in, just before the user's shell (or command) is 1401started. 1402See the 1403.Xr sshd 8 1404manual page for more information. 1405.Pp 1406.It Pa /etc/hosts.equiv 1407This file is for host-based authentication (see above). 1408It should only be writable by root. 1409.Pp 1410.It Pa /etc/shosts.equiv 1411This file is used in exactly the same way as 1412.Pa hosts.equiv , 1413but allows host-based authentication without permitting login with 1414rlogin/rsh. 1415.Pp 1416.It Pa /etc/ssh/ssh_config 1417Systemwide configuration file. 1418The file format and configuration options are described in 1419.Xr ssh_config 5 . 1420.Pp 1421.It Pa /etc/ssh/ssh_host_key 1422.It Pa /etc/ssh/ssh_host_dsa_key 1423.It Pa /etc/ssh/ssh_host_ecdsa_key 1424.It Pa /etc/ssh/ssh_host_ed25519_key 1425.It Pa /etc/ssh/ssh_host_rsa_key 1426These files contain the private parts of the host keys 1427and are used for host-based authentication. 1428If protocol version 1 is used, 1429.Nm 1430must be setuid root, since the host key is readable only by root. 1431For protocol version 2, 1432.Nm 1433uses 1434.Xr ssh-keysign 8 1435to access the host keys, 1436eliminating the requirement that 1437.Nm 1438be setuid root when host-based authentication is used. 1439By default 1440.Nm 1441is not setuid root. 1442.Pp 1443.It Pa /etc/ssh/ssh_known_hosts 1444Systemwide list of known host keys. 1445This file should be prepared by the 1446system administrator to contain the public host keys of all machines in the 1447organization. 1448It should be world-readable. 1449See 1450.Xr sshd 8 1451for further details of the format of this file. 1452.Pp 1453.It Pa /etc/ssh/sshrc 1454Commands in this file are executed by 1455.Nm 1456when the user logs in, just before the user's shell (or command) is started. 1457See the 1458.Xr sshd 8 1459manual page for more information. 1460.El 1461.Sh EXIT STATUS 1462.Nm 1463exits with the exit status of the remote command or with 255 1464if an error occurred. 1465.Sh SEE ALSO 1466.Xr scp 1 , 1467.Xr sftp 1 , 1468.Xr ssh-add 1 , 1469.Xr ssh-agent 1 , 1470.Xr ssh-keygen 1 , 1471.Xr ssh-keyscan 1 , 1472.Xr tun 4 , 1473.Xr ssh_config 5 , 1474.Xr ssh-keysign 8 , 1475.Xr sshd 8 1476.Sh STANDARDS 1477.Rs 1478.%A S. Lehtinen 1479.%A C. Lonvick 1480.%D January 2006 1481.%R RFC 4250 1482.%T The Secure Shell (SSH) Protocol Assigned Numbers 1483.Re 1484.Pp 1485.Rs 1486.%A T. Ylonen 1487.%A C. Lonvick 1488.%D January 2006 1489.%R RFC 4251 1490.%T The Secure Shell (SSH) Protocol Architecture 1491.Re 1492.Pp 1493.Rs 1494.%A T. Ylonen 1495.%A C. Lonvick 1496.%D January 2006 1497.%R RFC 4252 1498.%T The Secure Shell (SSH) Authentication Protocol 1499.Re 1500.Pp 1501.Rs 1502.%A T. Ylonen 1503.%A C. Lonvick 1504.%D January 2006 1505.%R RFC 4253 1506.%T The Secure Shell (SSH) Transport Layer Protocol 1507.Re 1508.Pp 1509.Rs 1510.%A T. Ylonen 1511.%A C. Lonvick 1512.%D January 2006 1513.%R RFC 4254 1514.%T The Secure Shell (SSH) Connection Protocol 1515.Re 1516.Pp 1517.Rs 1518.%A J. Schlyter 1519.%A W. Griffin 1520.%D January 2006 1521.%R RFC 4255 1522.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints 1523.Re 1524.Pp 1525.Rs 1526.%A F. Cusack 1527.%A M. Forssen 1528.%D January 2006 1529.%R RFC 4256 1530.%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH) 1531.Re 1532.Pp 1533.Rs 1534.%A J. Galbraith 1535.%A P. Remaker 1536.%D January 2006 1537.%R RFC 4335 1538.%T The Secure Shell (SSH) Session Channel Break Extension 1539.Re 1540.Pp 1541.Rs 1542.%A M. Bellare 1543.%A T. Kohno 1544.%A C. Namprempre 1545.%D January 2006 1546.%R RFC 4344 1547.%T The Secure Shell (SSH) Transport Layer Encryption Modes 1548.Re 1549.Pp 1550.Rs 1551.%A B. Harris 1552.%D January 2006 1553.%R RFC 4345 1554.%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol 1555.Re 1556.Pp 1557.Rs 1558.%A M. Friedl 1559.%A N. Provos 1560.%A W. Simpson 1561.%D March 2006 1562.%R RFC 4419 1563.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol 1564.Re 1565.Pp 1566.Rs 1567.%A J. Galbraith 1568.%A R. Thayer 1569.%D November 2006 1570.%R RFC 4716 1571.%T The Secure Shell (SSH) Public Key File Format 1572.Re 1573.Pp 1574.Rs 1575.%A D. Stebila 1576.%A J. Green 1577.%D December 2009 1578.%R RFC 5656 1579.%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer 1580.Re 1581.Pp 1582.Rs 1583.%A A. Perrig 1584.%A D. Song 1585.%D 1999 1586.%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99) 1587.%T Hash Visualization: a New Technique to improve Real-World Security 1588.Re 1589.Sh AUTHORS 1590OpenSSH is a derivative of the original and free 1591ssh 1.2.12 release by Tatu Ylonen. 1592Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 1593Theo de Raadt and Dug Song 1594removed many bugs, re-added newer features and 1595created OpenSSH. 1596Markus Friedl contributed the support for SSH 1597protocol versions 1.5 and 2.0. 1598