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centos:ssh-install [13.11.2016 16:46. ]
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centos:ssh-install [20.04.2018 10:30. ] (aktuell)
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 ====== Secure Shell - ssh ====== ====== Secure Shell - ssh ======
-{{:​centos:​openssh.png?​200 |openSSH Logo}}Bei Internetdiensten wie [[centos:mail_c7:​start|eMail]] oder [[centos:web_c7:​start|Web]] haben sich verschlüsselte Datenübertragungen mit SSL/TLS ohne Eingriffe in das Originalprotokoll durchgesetzt. Bei den klassischen unverschlüsselten Unix-Diensten zum Arbeiten mit entfernten Rechnern oder zur Datenübertragung auf andere Rechner - z.B. **telnet**, **rcp** und **rsh** - erfolgt eine alternative ​Lösung ​mittels [[http://​www.openssh.org|OpenSSH]].+{{:​centos:​openssh.png?​200 |openSSH Logo}}Bei Internetdiensten wie [[centos:mailserver:​start|eMail]] oder [[centos:webserver:​start|Web]] haben sich verschlüsselte Datenübertragungen mit SSL/TLS ohne Eingriffe in das Originalprotokoll durchgesetzt. Bei den klassischen unverschlüsselten Unix-Diensten zum Arbeiten mit entfernten Rechnern oder zur Datenübertragung auf andere Rechner - z.B. **telnet**, **rcp** und **rsh** - erfolgt eine alternative ​Lösiung ​mittels [[http://​www.openssh.org|OpenSSH]].
  
 ===== openSSH - Programmsuite ===== ===== openSSH - Programmsuite =====
 Die für die **//​Secure-Shell//​** benötigten Pakete werden i.d.R. bereits bei der Erstinstallation erfolgreich ins System eingebettet. Bei Centos teilen sich die Programme der //​Programmsuite//​ auf folgende Pakete auf: Die für die **//​Secure-Shell//​** benötigten Pakete werden i.d.R. bereits bei der Erstinstallation erfolgreich ins System eingebettet. Bei Centos teilen sich die Programme der //​Programmsuite//​ auf folgende Pakete auf:
-  * openssh : Die OpenSSH-Implementierung der SSH Protokoll-Versionen ​2 (und 1) +  * openssh.i386 : Die OpenSSH-Implementierung der SSH Protokoll-Versionen 1 und 2 
-  * openssh-clients : Die OpenSSH-Client-Anwendungen +  * openssh-clients.i386 : Die OpenSSH-Client-Anwendungen 
-  * openssh-server : Der OpenSSH-Server Daemon +  * openssh-server.i386 : Der OpenSSH-Server Daemon 
-  * openssh-askpass : Passphrase-Dialog für OpenSSH und X+  * openssh-askpass.i386 : Passphrase-Dialog für OpenSSH und X
 ==== openssh ==== ==== openssh ====
-Mittels ​''​rpm ​-qil'' ​können wir überprüfen,​ welche Programme, Konfigurationsdateien und Dokumentationen ​beim Paket **openssh** ​installiert wurden.+Mittels ​**__rpm ​-iql__** ​können wir überprüfen,​ welche Programme, Konfigurationsdateien und Dokumentationen installiert wurden
 +<​code>#​ rpm -iql openssh 
 +Name        : openssh ​                     Relocations:​ (not relocatable) 
 +Version ​    : 4.3p2                             ​Vendor:​ CentOS 
 +...
  
-   # rpm -qil openssh +... 
-<​code>​Name ​       : openssh +Signature ​  : ​DSA/SHA1Mo 09 Mär 2009 02:48:50 CET, Key ID a8a447dce8562897 
-Version ​    : 6.6.1p1 +Packager ​   : Karanbir Singh <kbsingh@karan.org>
-Release ​    : 25.el7_2 +
-Architecture:​ x86_64 +
-Install Date: Wed 23 Mar 2016 07:14:52 PM CET +
-Group       : Applications/​Internet +
-Size        : 1450050 +
-License ​    : BSD +
-Signature ​  : ​RSA/SHA256Mon 21 Mar 2016 11:22:48 PM CET, Key ID 24c6a8a7f4a80eb5 +
-Source RPM  : openssh-6.6.1p1-25.el7_2.src.rpm +
-Build Date  : Mon 21 Mar 2016 11:18:48 PM CET +
-Build Host  : worker1.bsys.centos.org +
-Relocations : (not relocatable) +
-Packager ​   : CentOS BuildSystem ​<http://​bugs.centos.org> +
-Vendor ​     : CentOS+
 URL         : http://​www.openssh.com/​portable.html URL         : http://​www.openssh.com/​portable.html
-Summary ​    : ​An open source implementation of SSH protocol versions ​and 2+Summary ​    : ​Die OpenSSH-Implementierung der SSH Protokoll-Versionen ​und 2
 Description : Description :
 SSH (Secure SHell) is a program for logging into and executing SSH (Secure SHell) is a program for logging into and executing
Zeile 37: Zeile 28:
  
 OpenSSH is OpenBSD'​s version of the last free version of SSH, bringing OpenSSH is OpenBSD'​s version of the last free version of SSH, bringing
-it up to date in terms of security and features.+it up to date in terms of security and features, as well as removing 
 +all patented algorithms to separate libraries.
  
 This package includes the core files necessary for both the OpenSSH This package includes the core files necessary for both the OpenSSH
Zeile 46: Zeile 38:
 /​usr/​bin/​ssh-keygen /​usr/​bin/​ssh-keygen
 /​usr/​libexec/​openssh /​usr/​libexec/​openssh
-/​usr/​libexec/​openssh/​ctr-cavstest 
 /​usr/​libexec/​openssh/​ssh-keysign /​usr/​libexec/​openssh/​ssh-keysign
-/​usr/​share/​doc/​openssh-6.6.1p1 +/​usr/​share/​doc/​openssh-4.3p2 
-/​usr/​share/​doc/​openssh-6.6.1p1/CREDITS +/​usr/​share/​doc/​openssh-4.3p2/CREDITS 
-/​usr/​share/​doc/​openssh-6.6.1p1/​ChangeLog +/​usr/​share/​doc/​openssh-4.3p2/​ChangeLog 
-/​usr/​share/​doc/​openssh-6.6.1p1/INSTALL +/​usr/​share/​doc/​openssh-4.3p2/INSTALL 
-/​usr/​share/​doc/​openssh-6.6.1p1/OVERVIEW +/​usr/​share/​doc/​openssh-4.3p2/LICENCE 
-/​usr/​share/​doc/​openssh-6.6.1p1/PROTOCOL +/​usr/​share/​doc/​openssh-4.3p2/OVERVIEW 
-/​usr/​share/​doc/​openssh-6.6.1p1/PROTOCOL.agent +/​usr/​share/​doc/​openssh-4.3p2/README 
-/​usr/​share/​doc/​openssh-6.6.1p1/PROTOCOL.certkeys +/​usr/​share/​doc/​openssh-4.3p2/README.dns 
-/​usr/​share/​doc/​openssh-6.6.1p1/PROTOCOL.chacha20poly1305 +/​usr/​share/​doc/​openssh-4.3p2/README.nss 
-/​usr/​share/​doc/​openssh-6.6.1p1/PROTOCOL.key +/​usr/​share/​doc/​openssh-4.3p2/README.platform 
-/​usr/​share/​doc/​openssh-6.6.1p1/​PROTOCOL.krl +/​usr/​share/​doc/​openssh-4.3p2/README.privsep 
-/​usr/​share/​doc/​openssh-6.6.1p1/​PROTOCOL.mux +/​usr/​share/​doc/​openssh-4.3p2/README.smartcard 
-/​usr/​share/​doc/​openssh-6.6.1p1/README +/​usr/​share/​doc/​openssh-4.3p2/README.tun 
-/​usr/​share/​doc/​openssh-6.6.1p1/​README.dns +/​usr/​share/​doc/​openssh-4.3p2/RFC.nroff 
-/​usr/​share/​doc/​openssh-6.6.1p1/README.platform +/​usr/​share/​doc/​openssh-4.3p2/TODO 
-/​usr/​share/​doc/​openssh-6.6.1p1/README.privsep +/usr/share/doc/openssh-4.3p2/WARNING.RNG
-/​usr/​share/​doc/​openssh-6.6.1p1/README.tun +
-/​usr/​share/​doc/​openssh-6.6.1p1/TODO +
-/usr/share/licenses/openssh-6.6.1p1 +
-/usr/​share/​licenses/​openssh-6.6.1p1/​LICENCE+
 /​usr/​share/​man/​man1/​ssh-keygen.1.gz /​usr/​share/​man/​man1/​ssh-keygen.1.gz
 /​usr/​share/​man/​man8/​ssh-keysign.8.gz</​code>​ /​usr/​share/​man/​man8/​ssh-keysign.8.gz</​code>​
- 
- 
 ==== openssh-clients ==== ==== openssh-clients ====
 Beim Paket **openssh-clients** wird mitgeliefert:​ Beim Paket **openssh-clients** wird mitgeliefert:​
 +<​code>#​ rpm -iql openssh-clients
 +Name        : openssh-clients ​             Relocations:​ (not relocatable)
 +Version ​    : 4.3p2                             ​Vendor:​ CentOS
 +...
  
-   # rpm -qil openssh-clients +... 
-<​code>​Name ​       : openssh-clients +Signature ​  : ​DSA/SHA1Mo 09 Mär 2009 02:48:50 CET, Key ID a8a447dce8562897 
-Version ​    : 6.6.1p1 +Packager ​   : Karanbir Singh <kbsingh@karan.org>
-Release ​    : 25.el7_2 +
-Architecture:​ x86_64 +
-Install Date: Wed 23 Mar 2016 07:14:59 PM CET +
-Group       : Applications/​Internet +
-Size        : 2298871 +
-License ​    : BSD +
-Signature ​  : ​RSA/SHA256Mon 21 Mar 2016 11:22:58 PM CET, Key ID 24c6a8a7f4a80eb5 +
-Source RPM  : openssh-6.6.1p1-25.el7_2.src.rpm +
-Build Date  : Mon 21 Mar 2016 11:18:48 PM CET +
-Build Host  : worker1.bsys.centos.org +
-Relocations : (not relocatable) +
-Packager ​   : CentOS BuildSystem ​<http://​bugs.centos.org> +
-Vendor ​     : CentOS+
 URL         : http://​www.openssh.com/​portable.html URL         : http://​www.openssh.com/​portable.html
-Summary ​    : ​An open source SSH client applications+Summary ​    : ​Die OpenSSH-Client-Anwendungen
 Description : Description :
 OpenSSH is a free version of SSH (Secure SHell), a program for logging OpenSSH is a free version of SSH (Secure SHell), a program for logging
 into and executing commands on a remote machine. This package includes into and executing commands on a remote machine. This package includes
 the clients necessary to make encrypted connections to SSH servers. the clients necessary to make encrypted connections to SSH servers.
 +You'll also need to install the openssh package on OpenSSH clients.
 /​etc/​ssh/​ssh_config /​etc/​ssh/​ssh_config
 /​usr/​bin/​scp /​usr/​bin/​scp
Zeile 106: Zeile 83:
 /​usr/​bin/​ssh-copy-id /​usr/​bin/​ssh-copy-id
 /​usr/​bin/​ssh-keyscan /​usr/​bin/​ssh-keyscan
-/​usr/​lib64/​fipscheck/​ssh.hmac 
-/​usr/​libexec/​openssh/​ssh-pkcs11-helper 
 /​usr/​share/​man/​man1/​scp.1.gz /​usr/​share/​man/​man1/​scp.1.gz
 /​usr/​share/​man/​man1/​sftp.1.gz /​usr/​share/​man/​man1/​sftp.1.gz
Zeile 116: Zeile 91:
 /​usr/​share/​man/​man1/​ssh-keyscan.1.gz /​usr/​share/​man/​man1/​ssh-keyscan.1.gz
 /​usr/​share/​man/​man1/​ssh.1.gz /​usr/​share/​man/​man1/​ssh.1.gz
-/​usr/​share/​man/​man5/​ssh_config.5.gz +/​usr/​share/​man/​man5/​ssh_config.5.gz</​code>​
-/​usr/​share/​man/​man8/​ssh-pkcs11-helper.8.gz</​code>​+
 ==== openssh-server ==== ==== openssh-server ====
 Hingegen liefert uns **openssh-server** folgende Dateien: Hingegen liefert uns **openssh-server** folgende Dateien:
 +<​code>#​ rpm -iql openssh-server
 +Name        : openssh-server ​              ​Relocations:​ (not relocatable)
 +Version ​    : 4.3p2                             ​Vendor:​ CentOS
 +...
  
-   # rpm -qil openssh-server +... 
-<​code>​Version ​    : 6.6.1p1 +Signature ​  : ​DSA/SHA1Mo 09 Mär 2009 02:48:50 CET, Key ID a8a447dce8562897 
-Release ​    : 25.el7_2 +Packager ​   : Karanbir Singh <kbsingh@karan.org>
-Architecture:​ x86_64 +
-Install Date: Wed 23 Mar 2016 07:14:58 PM CET +
-Group       : System Environment/​Daemons +
-Size        : 943088 +
-License ​    : BSD +
-Signature ​  : ​RSA/SHA256Mon 21 Mar 2016 11:23:11 PM CET, Key ID 24c6a8a7f4a80eb5 +
-Source RPM  : openssh-6.6.1p1-25.el7_2.src.rpm +
-Build Date  : Mon 21 Mar 2016 11:18:48 PM CET +
-Build Host  : worker1.bsys.centos.org +
-Relocations : (not relocatable) +
-Packager ​   : CentOS BuildSystem ​<http://​bugs.centos.org> +
-Vendor ​     : CentOS+
 URL         : http://​www.openssh.com/​portable.html URL         : http://​www.openssh.com/​portable.html
-Summary ​    : ​An open source SSH server daemon+Summary ​    : ​Der OpenSSH-Server Daemon
 Description : Description :
 OpenSSH is a free version of SSH (Secure SHell), a program for logging OpenSSH is a free version of SSH (Secure SHell), a program for logging
 into and executing commands on a remote machine. This package contains into and executing commands on a remote machine. This package contains
 the secure shell daemon (sshd). The sshd daemon allows SSH clients to the secure shell daemon (sshd). The sshd daemon allows SSH clients to
-securely connect to your SSH server.+securely connect to your SSH server. You also need to have the openssh 
 +package installed.
 /​etc/​pam.d/​sshd /​etc/​pam.d/​sshd
 +/​etc/​rc.d/​init.d/​sshd
 +/etc/ssh
 /​etc/​ssh/​sshd_config /​etc/​ssh/​sshd_config
-/​etc/​sysconfig/​sshd 
-/​usr/​lib/​systemd/​system/​sshd-keygen.service 
-/​usr/​lib/​systemd/​system/​sshd.service 
-/​usr/​lib/​systemd/​system/​sshd.socket 
-/​usr/​lib/​systemd/​system/​sshd@.service 
-/​usr/​lib64/​fipscheck/​sshd.hmac 
 /​usr/​libexec/​openssh/​sftp-server /​usr/​libexec/​openssh/​sftp-server
 /​usr/​sbin/​sshd /​usr/​sbin/​sshd
-/​usr/​sbin/​sshd-keygen 
-/​usr/​share/​man/​man5/​moduli.5.gz 
 /​usr/​share/​man/​man5/​sshd_config.5.gz /​usr/​share/​man/​man5/​sshd_config.5.gz
 /​usr/​share/​man/​man8/​sftp-server.8.gz /​usr/​share/​man/​man8/​sftp-server.8.gz
 /​usr/​share/​man/​man8/​sshd.8.gz /​usr/​share/​man/​man8/​sshd.8.gz
-/​var/​empty/​sshd</​code>​+/​var/​empty/​sshd 
 +/​var/​empty/​sshd/​etc 
 +/​var/​empty/​sshd/​etc/​localtime</​code>​
 ==== openssh-askpass ==== ==== openssh-askpass ====
 Zu guter Letzt sehen wir uns noch das Paket **openssh-askpass** genauer an: Zu guter Letzt sehen wir uns noch das Paket **openssh-askpass** genauer an:
 +<​code>#​ rpm -iql openssh-askpass
 +Name        : openssh-askpass ​             Relocations:​ (not relocatable)
 +Version ​    : 4.3p2                             ​Vendor:​ CentOS
 +...
  
-   # rpm -qil openssh-askpass +... 
-<​code>​Name ​       : openssh-askpass +Signature ​  : ​DSA/SHA1Mo 09 Mär 2009 02:48:50 CET, Key ID a8a447dce8562897 
-Version ​    : 6.6.1p1 +Packager ​   : Karanbir Singh <kbsingh@karan.org>
-Release ​    : 25.el7_2 +
-Architecture:​ x86_64 +
-Install Date: Sat 12 Nov 2016 08:22:40 PM CET +
-Group       : Applications/​Internet +
-Size        : 15944 +
-License ​    : BSD +
-Signature ​  : ​RSA/SHA256Mon 21 Mar 2016 11:22:53 PM CET, Key ID 24c6a8a7f4a80eb5 +
-Source RPM  : openssh-6.6.1p1-25.el7_2.src.rpm +
-Build Date  : Mon 21 Mar 2016 11:18:48 PM CET +
-Build Host  : worker1.bsys.centos.org +
-Relocations : (not relocatable) +
-Packager ​   : CentOS BuildSystem ​<http://​bugs.centos.org> +
-Vendor ​     : CentOS+
 URL         : http://​www.openssh.com/​portable.html URL         : http://​www.openssh.com/​portable.html
-Summary ​    : ​A passphrase dialog for OpenSSH ​and X+Summary ​    : ​Passphrase-Dialog für OpenSSH ​und X
 Description : Description :
 OpenSSH is a free version of SSH (Secure SHell), a program for logging OpenSSH is a free version of SSH (Secure SHell), a program for logging
Zeile 188: Zeile 142:
 /​usr/​libexec/​openssh/​gnome-ssh-askpass /​usr/​libexec/​openssh/​gnome-ssh-askpass
 /​usr/​libexec/​openssh/​ssh-askpass</​code>​ /​usr/​libexec/​openssh/​ssh-askpass</​code>​
- 
-===== Dokumentation ===== 
-Wichtige Hinweise zur Absicherung von **ssh** finden sich im [[https://​access.redhat.com/​documentation/​en-US/​Red_Hat_Enterprise_Linux/​7/​html/​Security_Guide/​sec-Securing_Services.html#​sec-Securing_SSH|Kapitel 4.3.11. Securing SSH]] aus dem [[https://​access.redhat.com/​documentation/​en-US/​Red_Hat_Enterprise_Linux/​7/​html/​Security_Guide/​index.html|Red Hat Enterprise Linux Security Guide]]. 
- 
-Die Optionen rund um opennssh findet amn wie immer, in der manpage zu **ssh**. 
-<​code>​SSH(1) ​                                BSD General Commands Manual ​                               SSH(1) 
- 
-NAME 
-     ssh — OpenSSH SSH client (remote login program) 
- 
-SYNOPSIS 
-     ssh [-1246AaCfgKkMNnqsTtVvXxYy] [-b bind_address] [-c cipher_spec] [-D [bind_address:​]port] 
-         [-E log_file] [-e escape_char] [-F configfile] [-I pkcs11] [-i identity_file] 
-         [-L [bind_address:​]port:​host:​hostport] [-l login_name] [-m mac_spec] [-O ctl_cmd] [-o option] 
-         [-p port] [-Q cipher | cipher-auth | mac | kex | key] [-R [bind_address:​]port:​host:​hostport] 
-         [-S ctl_path] [-W host:port] [-w local_tun[:​remote_tun]] [user@]hostname [command] 
- 
-DESCRIPTION 
-     ssh (SSH client) is a program for logging into a remote machine and for executing commands on a 
-     ​remote machine. ​ It is intended to replace rlogin and rsh, and provide secure encrypted communica‐ 
-     tions between two untrusted hosts over an insecure network. ​ X11 connections and arbitrary TCP 
-     ports can also be forwarded over the secure channel. 
- 
-     ssh connects and logs into the specified hostname (with optional user name). ​ The user must prove 
-     ​his/​her identity to the remote machine using one of several methods depending on the protocol ver‐ 
-     sion used (see below). 
- 
-     If command is specified, it is executed on the remote host instead of a login shell. 
- 
-     The options are as follows: 
- 
-     ​-1 ​     Forces ssh to try protocol version 1 only. 
- 
-     ​-2 ​     Forces ssh to try protocol version 2 only. 
- 
-     ​-4 ​     Forces ssh to use IPv4 addresses only. 
- 
-     ​-6 ​     Forces ssh to use IPv6 addresses only. 
- 
-     ​-A ​     Enables forwarding of the authentication agent connection. ​ This can also be specified on a 
-             ​per-host basis in a configuration file. 
- 
-             Agent forwarding should be enabled with caution. ​ Users with the ability to bypass file 
-             ​permissions on the remote host (for the agent'​s UNIX-domain socket) can access the local 
-             agent through the forwarded connection. ​ An attacker cannot obtain key material from the 
-             ​agent,​ however they can perform operations on the keys that enable them to authenticate 
-             using the identities loaded into the agent. 
- 
-     ​-a ​     Disables forwarding of the authentication agent connection. 
- 
-     -b bind_address 
-             Use bind_address on the local machine as the source address of the connection. ​ Only useful 
-             on systems with more than one address. 
- 
-     ​-C ​     Requests compression of all data (including stdin, stdout, stderr, and data for forwarded 
-             X11 and TCP connections). ​ The compression algorithm is the same used by gzip(1), and the 
-             ​“level” can be controlled by the CompressionLevel option for protocol version 1.  Compres‐ 
-             sion is desirable on modem lines and other slow connections,​ but will only slow down things 
-             on fast networks. ​ The default value can be set on a host-by-host basis in the configura‐ 
-             tion files; see the Compression option. 
- 
-     -c cipher_spec 
-             ​Selects the cipher specification for encrypting the session. 
- 
-             ​Protocol version 1 allows specification of a single cipher. ​ The supported values are 
-             ​“3des”,​ “blowfish”,​ and “des”. ​ 3des (triple-des) is an encrypt-decrypt-encrypt triple with 
-             three different keys.  It is believed to be secure. ​ blowfish is a fast block cipher; it 
-             ​appears very secure and is much faster than 3des.  des is only supported in the ssh client 
-             for interoperability with legacy protocol 1 implementations that do not support the 3des 
-             ​cipher. ​ Its use is strongly discouraged due to cryptographic weaknesses. ​ The default is 
-             ​“3des”. 
- 
-             For protocol version 2, cipher_spec is a comma-separated list of ciphers listed in order of 
-             ​preference. ​ See the Ciphers keyword in ssh_config(5) for more information. 
- 
-     -D [bind_address:​]port 
-             ​Specifies a local “dynamic” application-level port forwarding. ​ This works by allocating a 
-             ​socket to listen to port on the local side, optionally bound to the specified bind_address. 
-             ​Whenever a connection is made to this port, the connection is forwarded over the secure 
-             ​channel,​ and the application protocol is then used to determine where to connect to from 
-             the remote machine. ​ Currently the SOCKS4 and SOCKS5 protocols are supported, and ssh will 
-             act as a SOCKS server. ​ Only root can forward privileged ports. ​ Dynamic port forwardings 
-             can also be specified in the configuration file. 
- 
-             IPv6 addresses can be specified by enclosing the address in square brackets. ​ Only the 
-             ​superuser can forward privileged ports. ​ By default, the local port is bound in accordance 
-             with the GatewayPorts setting. ​ However, an explicit bind_address may be used to bind the 
-             ​connection to a specific address. ​ The bind_address of “localhost” indicates that the lis‐ 
-             ​tening port be bound for local use only, while an empty address or ‘*’ indicates that the 
-             port should be available from all interfaces. 
- 
-     -E log_file 
-             ​Append debug logs to log_file instead of standard error. 
- 
-     -e escape_char 
-             Sets the escape character for sessions with a pty (default: ‘~’). ​ The escape character is 
-             only recognized at the beginning of a line.  The escape character followed by a dot (‘.’) 
-             ​closes the connection; followed by control-Z suspends the connection; and followed by 
-             ​itself sends the escape character once.  Setting the character to “none” disables any 
-             ​escapes and makes the session fully transparent. 
- 
-     -F configfile 
-             ​Specifies an alternative per-user configuration file.  If a configuration file is given on 
-             the command line, the system-wide configuration file (/​etc/​ssh/​ssh_config) will be ignored. 
-             The default for the per-user configuration file is ~/​.ssh/​config. 
- 
-     ​-f ​     Requests ssh to go to background just before command execution. ​ This is useful if ssh is 
-             going to ask for passwords or passphrases,​ but the user wants it in the background. ​ This 
-             ​implies -n.  The recommended way to start X11 programs at a remote site is with something 
-             like ssh -f host xterm. 
- 
-             If the ExitOnForwardFailure configuration option is set to “yes”, then a client started 
-             with -f will wait for all remote port forwards to be successfully established before plac‐ 
-             ing itself in the background. 
- 
-     ​-g ​     Allows remote hosts to connect to local forwarded ports. 
- 
-     -I pkcs11 
-             ​Specify the PKCS#11 shared library ssh should use to communicate with a PKCS#11 token pro‐ 
-             ​viding the user's private RSA key. 
- 
-     -i identity_file 
-             ​Selects a file from which the identity (private key) for public key authentication is read. 
-             The default is ~/​.ssh/​identity for protocol version 1, and ~/​.ssh/​id_dsa,​ ~/​.ssh/​id_ecdsa,​ 
-             ​~/​.ssh/​id_ed25519 and ~/​.ssh/​id_rsa for protocol version 2.  Identity files may also be 
-             ​specified on a per-host basis in the configuration file.  It is possible to have multiple 
-             -i options (and multiple identities specified in configuration files). ​ ssh will also try 
-             to load certificate information from the filename obtained by appending -cert.pub to iden‐ 
-             tity filenames. 
- 
-     ​-K ​     Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI credentials to 
-             the server. 
- 
-     ​-k ​     Disables forwarding (delegation) of GSSAPI credentials to the server. 
- 
-     -L [bind_address:​]port:​host:​hostport 
-             ​Specifies that the given port on the local (client) host is to be forwarded to the given 
-             host and port on the remote side.  This works by allocating a socket to listen to port on 
-             the local side, optionally bound to the specified bind_address. ​ Whenever a connection is 
-             made to this port, the connection is forwarded over the secure channel, and a connection is 
-             made to host port hostport from the remote machine. ​ Port forwardings can also be specified 
-             in the configuration file.  IPv6 addresses can be specified by enclosing the address in 
-             ​square brackets. ​ Only the superuser can forward privileged ports. ​ By default, the local 
-             port is bound in accordance with the GatewayPorts setting. ​ However, an explicit 
-             ​bind_address may be used to bind the connection to a specific address. ​ The bind_address of 
-             ​“localhost” indicates that the listening port be bound for local use only, while an empty 
-             ​address or ‘*’ indicates that the port should be available from all interfaces. 
- 
-     -l login_name 
-             ​Specifies the user to log in as on the remote machine. ​ This also may be specified on a 
-             ​per-host basis in the configuration file. 
- 
-     ​-M ​     Places the ssh client into “master” mode for connection sharing. ​ Multiple -M options 
-             ​places ssh into “master” mode with confirmation required before slave connections are 
-             ​accepted. ​ Refer to the description of ControlMaster in ssh_config(5) for details. 
- 
-     -m mac_spec 
-             ​Additionally,​ for protocol version 2 a comma-separated list of MAC (message authentication 
-             code) algorithms can be specified in order of preference. ​ See the MACs keyword for more 
-             ​information. 
- 
-     ​-N ​     Do not execute a remote command. ​ This is useful for just forwarding ports (protocol ver‐ 
-             sion 2 only). 
- 
-     ​-n ​     Redirects stdin from /dev/null (actually, prevents reading from stdin). ​ This must be used 
-             when ssh is run in the background. ​ A common trick is to use this to run X11 programs on a 
-             ​remote machine. ​ For example, ssh -n shadows.cs.hut.fi emacs & will start an emacs on shad‐ 
-             ​ows.cs.hut.fi,​ and the X11 connection will be automatically forwarded over an encrypted 
-             ​channel. ​ The ssh program will be put in the background. ​ (This does not work if ssh needs 
-             to ask for a password or passphrase; see also the -f option.) 
- 
-     -O ctl_cmd 
-             ​Control an active connection multiplexing master process. ​ When the -O option is specified, 
-             the ctl_cmd argument is interpreted and passed to the master process. ​ Valid commands are: 
-             ​“check” (check that the master process is running), “forward” (request forwardings without 
-             ​command execution), “cancel” (cancel forwardings),​ “exit” (request the master to exit), and 
-             ​“stop” (request the master to stop accepting further multiplexing requests). 
- 
-     -o option 
-             Can be used to give options in the format used in the configuration file.  This is useful 
-             for specifying options for which there is no separate command-line flag.  For full details 
-             of the options listed below, and their possible values, see ssh_config(5). 
- 
-                   ​AddressFamily 
-                   ​BatchMode 
-                   ​BindAddress 
-                   ​CanonicalDomains 
-                   ​CanonicalizeFallbackLocal 
-                   ​CanonicalizeHostname 
-                   ​CanonicalizeMaxDots 
-                   ​CanonicalizePermittedCNAMEs 
-                   ​ChallengeResponseAuthentication 
-                   ​CheckHostIP 
-                   ​Cipher 
-                   ​Ciphers 
-                   ​ClearAllForwardings 
-                   ​Compression 
-                   ​CompressionLevel 
-                   ​ConnectionAttempts 
-                   ​ConnectTimeout 
-                   ​ControlMaster 
-                   ​ControlPath 
-                   ​ControlPersist 
-                   ​DynamicForward 
-                   ​EscapeChar 
-                   ​ExitOnForwardFailure 
-                   ​ForwardAgent 
-                   ​ForwardX11 
-                   ​ForwardX11Timeout 
-                   ​ForwardX11Trusted 
-                   ​GatewayPorts 
-                   ​GlobalKnownHostsFile 
-                   ​GSSAPIAuthentication 
-                   ​GSSAPIKeyExchange 
-                   ​GSSAPIClientIdentity 
-                   ​GSSAPIDelegateCredentials 
-                   ​GSSAPIRenewalForcesRekey 
-                   ​GSSAPITrustDns 
-                   ​GSSAPIKexAlgorithms 
-                   ​HashKnownHosts 
-                   Host 
-                   ​HostbasedAuthentication 
-                   ​HostKeyAlgorithms 
-                   ​HostKeyAlias 
-                   ​HostName 
-                   ​IdentityFile 
-                   ​IdentitiesOnly 
-                   IPQoS 
-                   ​KbdInteractiveAuthentication 
-                   ​KbdInteractiveDevices 
-                   ​KexAlgorithms 
-                   ​LocalCommand 
-                   ​LocalForward 
-                   ​LogLevel 
-                   MACs 
-                   Match 
-                   ​NoHostAuthenticationForLocalhost 
-                   ​NumberOfPasswordPrompts 
-                   ​PasswordAuthentication 
-                   ​PermitLocalCommand 
-                   ​PKCS11Provider 
-                   Port 
-                   ​PreferredAuthentications 
-                   ​Protocol 
-                   ​ProxyCommand 
-                   ​ProxyUseFdpass 
-                   ​PubkeyAuthentication 
-                   ​RekeyLimit 
-                   ​RemoteForward 
-                   ​RequestTTY 
-                   ​RhostsRSAAuthentication 
-                   ​RSAAuthentication 
-                   ​SendEnv 
-                   ​ServerAliveInterval 
-                   ​ServerAliveCountMax 
-                   ​StrictHostKeyChecking 
-                   ​TCPKeepAlive 
-                   ​Tunnel 
-                   ​TunnelDevice 
-                   ​UsePrivilegedPort 
-                   User 
-                   ​UserKnownHostsFile 
-                   ​VerifyHostKeyDNS 
-                   ​VisualHostKey 
-                   ​XAuthLocation 
- 
-     -p port 
-             Port to connect to on the remote host.  This can be specified on a per-host basis in the 
-             ​configuration file. 
- 
-     -Q cipher | cipher-auth | mac | kex | key 
-             ​Queries ssh for the algorithms supported for the specified version 2.  The available fea‐ 
-             tures are: cipher (supported symmetric ciphers), cipher-auth (supported symmetric ciphers 
-             that support authenticated encryption),​ mac (supported message integrity codes), kex (key 
-             ​exchange algorithms),​ key (key types). 
- 
-     ​-q ​     Quiet mode.  Causes most warning and diagnostic messages to be suppressed. 
- 
-     -R [bind_address:​]port:​host:​hostport 
-             ​Specifies that the given port on the remote (server) host is to be forwarded to the given 
-             host and port on the local side.  This works by allocating a socket to listen to port on 
-             the remote side, and whenever a connection is made to this port, the connection is for‐ 
-             ​warded over the secure channel, and a connection is made to host port hostport from the 
-             local machine. 
- 
-             Port forwardings can also be specified in the configuration file.  Privileged ports can be 
-             ​forwarded only when logging in as root on the remote machine. ​ IPv6 addresses can be speci‐ 
-             fied by enclosing the address in square brackets. 
- 
-             By default, the listening socket on the server will be bound to the loopback interface 
-             ​only. ​ This may be overridden by specifying a bind_address. ​ An empty bind_address,​ or the 
-             ​address ‘*’, indicates that the remote socket should listen on all interfaces. ​ Specifying 
-             a remote bind_address will only succeed if the server'​s GatewayPorts option is enabled (see 
-             ​sshd_config(5)). 
- 
-             If the port argument is ‘0’, the listen port will be dynamically allocated on the server 
-             and reported to the client at run time.  When used together with -O forward the allocated 
-             port will be printed to the standard output. 
- 
-     -S ctl_path 
-             ​Specifies the location of a control socket for connection sharing, or the string “none” to 
-             ​disable connection sharing. ​ Refer to the description of ControlPath and ControlMaster in 
-             ​ssh_config(5) for details. 
- 
-     ​-s ​     May be used to request invocation of a subsystem on the remote system. ​ Subsystems are a 
-             ​feature of the SSH2 protocol which facilitate the use of SSH as a secure transport for 
-             other applications (eg. sftp(1)). ​ The subsystem is specified as the remote command. 
- 
-     ​-T ​     Disable pseudo-tty allocation. 
- 
-     ​-t ​     Force pseudo-tty allocation. ​ This can be used to execute arbitrary screen-based programs 
-             on a remote machine, which can be very useful, e.g. when implementing menu services. ​ Mul‐ 
-             tiple -t options force tty allocation, even if ssh has no local tty. 
- 
-     ​-V ​     Display the version number and exit. 
- 
-     ​-v ​     Verbose mode.  Causes ssh to print debugging messages about its progress. ​ This is helpful 
-             in debugging connection, authentication,​ and configuration problems. ​ Multiple -v options 
-             ​increase the verbosity. ​ The maximum is 3. 
- 
-     -W host:port 
-             ​Requests that standard input and output on the client be forwarded to host on port over the 
-             ​secure channel. ​ Implies -N, -T, ExitOnForwardFailure and ClearAllForwardings. ​ Works with 
-             ​Protocol version 2 only. 
- 
-     -w local_tun[:​remote_tun] 
-             ​Requests tunnel device forwarding with the specified tun(4) devices between the client 
-             ​(local_tun) and the server (remote_tun). 
- 
-             The devices may be specified by numerical ID or the keyword “any”, which uses the next 
-             ​available tunnel device. ​ If remote_tun is not specified, it defaults to “any”. ​ See also 
-             the Tunnel and TunnelDevice directives in ssh_config(5). ​ If the Tunnel directive is unset, 
-             it is set to the default tunnel mode, which is “point-to-point”. 
- 
-     ​-X ​     Enables X11 forwarding. ​ This can also be specified on a per-host basis in a configuration 
-             file. 
- 
-             X11 forwarding should be enabled with caution. ​ Users with the ability to bypass file per‐ 
-             ​missions on the remote host (for the user's X authorization database) can access the local 
-             X11 display through the forwarded connection. ​ An attacker may then be able to perform 
-             ​activities such as keystroke monitoring. 
- 
-             For this reason, X11 forwarding is subjected to X11 SECURITY extension restrictions by 
-             ​default. ​ Please refer to the ssh -Y option and the ForwardX11Trusted directive in 
-             ​ssh_config(5) for more information. 
- 
-     ​-x ​     Disables X11 forwarding. 
- 
-     ​-Y ​     Enables trusted X11 forwarding. ​ Trusted X11 forwardings are not subjected to the X11 SECU‐ 
-             RITY extension controls. 
- 
-     ​-y ​     Send log information using the syslog(3) system module. ​ By default this information is 
-             sent to stderr. 
- 
-     ssh may additionally obtain configuration data from a per-user configuration file and a system-wide 
-     ​configuration file.  The file format and configuration options are described in ssh_config(5). 
- 
-AUTHENTICATION 
-     The OpenSSH SSH client supports SSH protocols 1 and 2.  The default is to use protocol 2 only, 
-     ​though this can be changed via the Protocol option in ssh_config(5) or the -1 and -2 options (see 
-     ​above). ​ Both protocols support similar authentication methods, but protocol 2 is the default since 
-     it provides additional mechanisms for confidentiality (the traffic is encrypted using AES, 3DES, 
-     ​Blowfish,​ CAST128, or Arcfour) and integrity (hmac-md5, hmac-sha1, hmac-sha2-256,​ hmac-sha2-512,​ 
-     ​umac-64,​ umac-128, hmac-ripemd160). ​ Protocol 1 lacks a strong mechanism for ensuring the integrity 
-     of the connection. 
- 
-     The methods available for authentication are: GSSAPI-based authentication,​ host-based authentica‐ 
-     tion, public key authentication,​ challenge-response authentication,​ and password authentication. 
-     ​Authentication methods are tried in the order specified above, though protocol 2 has a configura‐ 
-     tion option to change the default order: PreferredAuthentications. 
- 
-     ​Host-based authentication works as follows: If the machine the user logs in from is listed in 
-     /​etc/​hosts.equiv or /​etc/​ssh/​shosts.equiv on the remote machine, and the user names are the same on 
-     both sides, or if the files ~/.rhosts or ~/.shosts exist in the user's home directory on the remote 
-     ​machine and contain a line containing the name of the client machine and the name of the user on 
-     that machine, the user is considered for login. ​ Additionally,​ the server must be able to verify 
-     the client'​s host key (see the description of /​etc/​ssh/​ssh_known_hosts and ~/​.ssh/​known_hosts,​ 
-     ​below) for login to be permitted. ​ This authentication method closes security holes due to IP 
-     ​spoofing,​ DNS spoofing, and routing spoofing. ​ [Note to the administrator:​ /​etc/​hosts.equiv,​ 
-     ​~/​.rhosts,​ and the rlogin/rsh protocol in general, are inherently insecure and should be disabled 
-     if security is desired.] 
- 
-     ​Public key authentication works as follows: The scheme is based on public-key cryptography,​ using 
-     ​cryptosystems where encryption and decryption are done using separate keys, and it is unfeasible to 
-     ​derive the decryption key from the encryption key.  The idea is that each user creates a pub‐ 
-     ​lic/​private key pair for authentication purposes. ​ The server knows the public key, and only the 
-     user knows the private key.  ssh implements public key authentication protocol automatically,​ using 
-     one of the DSA, ECDSA, ED25519 or RSA algorithms. ​ Protocol 1 is restricted to using only RSA keys, 
-     but protocol 2 may use any.  The HISTORY section of ssl(8) contains a brief discussion of the DSA 
-     and RSA algorithms. 
- 
-     The file ~/​.ssh/​authorized_keys lists the public keys that are permitted for logging in.  When the 
-     user logs in, the ssh program tells the server which key pair it would like to use for authentica‐ 
-     ​tion. ​ The client proves that it has access to the private key and the server checks that the cor‐ 
-     ​responding public key is authorized to accept the account. 
- 
-     The user creates his/her key pair by running ssh-keygen(1). ​ This stores the private key in 
-     ​~/​.ssh/​identity (protocol 1), ~/​.ssh/​id_dsa (protocol 2 DSA), ~/​.ssh/​id_ecdsa (protocol 2 ECDSA), 
-     ​~/​.ssh/​id_ed25519 (protocol 2 ED25519), or ~/​.ssh/​id_rsa (protocol 2 RSA) and stores the public key 
-     in ~/​.ssh/​identity.pub (protocol 1), ~/​.ssh/​id_dsa.pub (protocol 2 DSA), ~/​.ssh/​id_ecdsa.pub (pro‐ 
-     tocol 2 ECDSA), ~/​.ssh/​id_ed25519.pub (protocol 2 ED25519), or ~/​.ssh/​id_rsa.pub (protocol 2 RSA) 
-     in the user's home directory. ​ The user should then copy the public key to ~/​.ssh/​authorized_keys 
-     in his/her home directory on the remote machine. ​ The authorized_keys file corresponds to the con‐ 
-     ​ventional ~/.rhosts file, and has one key per line, though the lines can be very long.  After this, 
-     the user can log in without giving the password. 
- 
-     A variation on public key authentication is available in the form of certificate authentication:​ 
-     ​instead of a set of public/​private keys, signed certificates are used.  This has the advantage that 
-     a single trusted certification authority can be used in place of many public/​private keys.  See the 
-     ​CERTIFICATES section of ssh-keygen(1) for more information. 
- 
-     The most convenient way to use public key or certificate authentication may be with an authentica‐ 
-     tion agent. ​ See ssh-agent(1) for more information. 
- 
-     ​Challenge-response authentication works as follows: The server sends an arbitrary "​challenge"​ text, 
-     and prompts for a response. ​ Protocol 2 allows multiple challenges and responses; protocol 1 is 
-     ​restricted to just one challenge/​response. ​ Examples of challenge-response authentication include 
-     BSD Authentication (see login.conf(5)) and PAM (some non-OpenBSD systems). 
- 
-     ​Finally,​ if other authentication methods fail, ssh prompts the user for a password. ​ The password 
-     is sent to the remote host for checking; however, since all communications are encrypted, the pass‐ 
-     word cannot be seen by someone listening on the network. 
- 
-     ssh automatically maintains and checks a database containing identification for all hosts it has 
-     ever been used with.  Host keys are stored in ~/​.ssh/​known_hosts in the user's home directory. 
-     ​Additionally,​ the file /​etc/​ssh/​ssh_known_hosts is automatically checked for known hosts. ​ Any new 
-     hosts are automatically added to the user's file.  If a host's identification ever changes, ssh 
-     warns about this and disables password authentication to prevent server spoofing or man-in-the-mid‐ 
-     dle attacks, which could otherwise be used to circumvent the encryption. ​ The StrictHostKeyChecking 
-     ​option can be used to control logins to machines whose host key is not known or has changed. 
- 
-     When the user's identity has been accepted by the server, the server either executes the given com‐ 
-     mand, or logs into the machine and gives the user a normal shell on the remote machine. ​ All commu‐ 
-     ​nication with the remote command or shell will be automatically encrypted. 
- 
-     If a pseudo-terminal has been allocated (normal login session), the user may use the escape charac‐ 
-     ters noted below. 
- 
-     If no pseudo-tty has been allocated, the session is transparent and can be used to reliably trans‐ 
-     fer binary data.  On most systems, setting the escape character to “none” will also make the ses‐ 
-     sion transparent even if a tty is used. 
- 
-     The session terminates when the command or shell on the remote machine exits and all X11 and TCP 
-     ​connections have been closed. 
- 
-ESCAPE CHARACTERS 
-     When a pseudo-terminal has been requested, ssh supports a number of functions through the use of an 
-     ​escape character. 
- 
-     A single tilde character can be sent as ~~ or by following the tilde by a character other than 
-     those described below. ​ The escape character must always follow a newline to be interpreted as spe‐ 
-     ​cial. ​ The escape character can be changed in configuration files using the EscapeChar configura‐ 
-     tion directive or on the command line by the -e option. 
- 
-     The supported escapes (assuming the default ‘~’) are: 
- 
-     ​~. ​     Disconnect. 
- 
-     ​~^Z ​    ​Background ssh. 
- 
-     ​~# ​     List forwarded connections. 
- 
-     ​~& ​     Background ssh at logout when waiting for forwarded connection / X11 sessions to terminate. 
- 
-     ​~? ​     Display a list of escape characters. 
- 
-     ​~B ​     Send a BREAK to the remote system (only useful for SSH protocol version 2 and if the peer 
-             ​supports it). 
- 
-     ​~C ​     Open command line.  Currently this allows the addition of port forwardings using the -L, -R 
-             and -D options (see above). ​ It also allows the cancellation of existing port-forwardings 
-             with -KL[bind_address:​]port for local, -KR[bind_address:​]port for remote and 
-             ​-KD[bind_address:​]port for dynamic port-forwardings. ​ !command allows the user to execute a 
-             local command if the PermitLocalCommand option is enabled in ssh_config(5). ​ Basic help is 
-             ​available,​ using the -h option. 
- 
-     ​~R ​     Request rekeying of the connection (only useful for SSH protocol version 2 and if the peer 
-             ​supports it). 
- 
-     ​~V ​     Decrease the verbosity (LogLevel) when errors are being written to stderr. 
- 
-     ​~v ​     Increase the verbosity (LogLevel) when errors are being written to stderr. 
- 
-TCP FORWARDING 
-     ​Forwarding of arbitrary TCP connections over the secure channel can be specified either on the com‐ 
-     mand line or in a configuration file.  One possible application of TCP forwarding is a secure con‐ 
-     ​nection to a mail server; another is going through firewalls. 
- 
-     In the example below, we look at encrypting communication between an IRC client and server, even 
-     ​though the IRC server does not directly support encrypted communications. ​ This works as follows: 
-     the user connects to the remote host using ssh, specifying a port to be used to forward connections 
-     to the remote server. ​ After that it is possible to start the service which is to be encrypted on 
-     the client machine, connecting to the same local port, and ssh will encrypt and forward the connec‐ 
-     tion. 
- 
-     The following example tunnels an IRC session from client machine “127.0.0.1” (localhost) to remote 
-     ​server “server.example.com”:​ 
- 
-         $ ssh -f -L 1234:​localhost:​6667 server.example.com sleep 10 
-         $ irc -c '#​users'​ -p 1234 pinky 127.0.0.1 
- 
-     This tunnels a connection to IRC server “server.example.com”,​ joining channel “#​users”,​ nickname 
-     ​“pinky”,​ using port 1234.  It doesn'​t matter which port is used, as long as it's greater than 1023 
-     ​(remember,​ only root can open sockets on privileged ports) and doesn'​t conflict with any ports 
-     ​already in use.  The connection is forwarded to port 6667 on the remote server, since that's the 
-     ​standard port for IRC services. 
- 
-     The -f option backgrounds ssh and the remote command “sleep 10” is specified to allow an amount of 
-     time (10 seconds, in the example) to start the service which is to be tunnelled. ​ If no connections 
-     are made within the time specified, ssh will exit. 
- 
-X11 FORWARDING 
-     If the ForwardX11 variable is set to “yes” (or see the description of the -X, -x, and -Y options 
-     ​above) and the user is using X11 (the DISPLAY environment variable is set), the connection to the 
-     X11 display is automatically forwarded to the remote side in such a way that any X11 programs 
-     ​started from the shell (or command) will go through the encrypted channel, and the connection to 
-     the real X server will be made from the local machine. ​ The user should not manually set DISPLAY. 
-     ​Forwarding of X11 connections can be configured on the command line or in configuration files. 
- 
-     The DISPLAY value set by ssh will point to the server machine, but with a display number greater 
-     than zero.  This is normal, and happens because ssh creates a “proxy” X server on the server 
-     ​machine for forwarding the connections over the encrypted channel. 
- 
-     ssh will also automatically set up Xauthority data on the server machine. ​ For this purpose, it 
-     will generate a random authorization cookie, store it in Xauthority on the server, and verify that 
-     any forwarded connections carry this cookie and replace it by the real cookie when the connection 
-     is opened. ​ The real authentication cookie is never sent to the server machine (and no cookies are 
-     sent in the plain). 
- 
-     If the ForwardAgent variable is set to “yes” (or see the description of the -A and -a options 
-     ​above) and the user is using an authentication agent, the connection to the agent is automatically 
-     ​forwarded to the remote side. 
- 
-VERIFYING HOST KEYS 
-     When connecting to a server for the first time, a fingerprint of the server'​s public key is pre‐ 
-     ​sented to the user (unless the option StrictHostKeyChecking has been disabled). ​ Fingerprints can 
-     be determined using ssh-keygen(1):​ 
- 
-           $ ssh-keygen -l -f /​etc/​ssh/​ssh_host_rsa_key 
- 
-     If the fingerprint is already known, it can be matched and the key can be accepted or rejected. 
-     ​Because of the difficulty of comparing host keys just by looking at hex strings, there is also sup‐ 
-     port to compare host keys visually, using random art.  By setting the VisualHostKey option to 
-     ​“yes”,​ a small ASCII graphic gets displayed on every login to a server, no matter if the session 
-     ​itself is interactive or not.  By learning the pattern a known server produces, a user can easily 
-     find out that the host key has changed when a completely different pattern is displayed. ​ Because 
-     these patterns are not unambiguous however, a pattern that looks similar to the pattern remembered 
-     only gives a good probability that the host key is the same, not guaranteed proof. 
- 
-     To get a listing of the fingerprints along with their random art for all known hosts, the following 
-     ​command line can be used: 
- 
-           $ ssh-keygen -lv -f ~/​.ssh/​known_hosts 
- 
-     If the fingerprint is unknown, an alternative method of verification is available: SSH fingerprints 
-     ​verified by DNS.  An additional resource record (RR), SSHFP, is added to a zonefile and the con‐ 
-     ​necting client is able to match the fingerprint with that of the key presented. 
- 
-     In this example, we are connecting a client to a server, “host.example.com”. ​ The SSHFP resource 
-     ​records should first be added to the zonefile for host.example.com:​ 
- 
-           $ ssh-keygen -r host.example.com. 
- 
-     The output lines will have to be added to the zonefile. ​ To check that the zone is answering fin‐ 
-     ​gerprint queries: 
- 
-           $ dig -t SSHFP host.example.com 
- 
-     ​Finally the client connects: 
- 
-           $ ssh -o "​VerifyHostKeyDNS ask" host.example.com 
-           [...] 
-           ​Matching host key fingerprint found in DNS. 
-           Are you sure you want to continue connecting (yes/no)? 
- 
-     See the VerifyHostKeyDNS option in ssh_config(5) for more information. 
- 
-SSH-BASED VIRTUAL PRIVATE NETWORKS 
-     ssh contains support for Virtual Private Network (VPN) tunnelling using the tun(4) network pseudo- 
-     ​device,​ allowing two networks to be joined securely. ​ The sshd_config(5) configuration option 
-     ​PermitTunnel controls whether the server supports this, and at what level (layer 2 or 3 traffic). 
- 
-     The following example would connect client network 10.0.50.0/​24 with remote network 10.0.99.0/​24 
-     using a point-to-point connection from 10.1.1.1 to 10.1.1.2, provided that the SSH server running 
-     on the gateway to the remote network, at 192.168.1.15,​ allows it. 
- 
-     On the client: 
- 
-           # ssh -f -w 0:1 192.168.1.15 true 
-           # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252 
-           # route add 10.0.99.0/​24 10.1.1.2 
- 
-     On the server: 
- 
-           # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252 
-           # route add 10.0.50.0/​24 10.1.1.1 
- 
-     ​Client access may be more finely tuned via the /​root/​.ssh/​authorized_keys file (see below) and the 
-     ​PermitRootLogin server option. ​ The following entry would permit connections on tun(4) device 1 
-     from user “jane” and on tun device 2 from user “john”, if PermitRootLogin is set to 
-     ​“forced-commands-only”:​ 
- 
-       ​tunnel="​1",​command="​sh /​etc/​netstart tun1" ssh-rsa ... jane 
-       ​tunnel="​2",​command="​sh /​etc/​netstart tun2" ssh-rsa ... john 
- 
-     Since an SSH-based setup entails a fair amount of overhead, it may be more suited to temporary set‐ 
-     ups, such as for wireless VPNs.  More permanent VPNs are better provided by tools such as 
-     ​ipsecctl(8) and isakmpd(8). 
- 
-ENVIRONMENT 
-     ssh will normally set the following environment variables: 
- 
-     ​DISPLAY ​              The DISPLAY variable indicates the location of the X11 server. ​ It is auto‐ 
-                           ​matically set by ssh to point to a value of the form “hostname:​n”,​ where 
-                           ​“hostname” indicates the host where the shell runs, and ‘n’ is an integer ≥ 
-                           ​1. ​ ssh uses this special value to forward X11 connections over the secure 
-                           ​channel. ​ The user should normally not set DISPLAY explicitly, as that will 
-                           ​render the X11 connection insecure (and will require the user to manually 
-                           copy any required authorization cookies). 
- 
-     ​HOME ​                 Set to the path of the user's home directory. 
- 
-     ​LOGNAME ​              ​Synonym for USER; set for compatibility with systems that use this variable. 
- 
-     ​MAIL ​                 Set to the path of the user's mailbox. 
- 
-     ​PATH ​                 Set to the default PATH, as specified when compiling ssh. 
- 
-     ​SSH_ASKPASS ​          If ssh needs a passphrase, it will read the passphrase from the current ter‐ 
-                           minal if it was run from a terminal. ​ If ssh does not have a terminal associ‐ 
-                           ated with it but DISPLAY and SSH_ASKPASS are set, it will execute the program 
-                           ​specified by SSH_ASKPASS and open an X11 window to read the passphrase. ​ This 
-                           is particularly useful when calling ssh from a .xsession or related script. 
-                           (Note that on some machines it may be necessary to redirect the input from 
-                           /​dev/​null to make this work.) 
- 
-     ​SSH_AUTH_SOCK ​        ​Identifies the path of a UNIX-domain socket used to communicate with the 
-                           ​agent. 
- 
-     ​SSH_CONNECTION ​       Identifies the client and server ends of the connection. ​ The variable con‐ 
-                           tains four space-separated values: client IP address, client port number, 
-                           ​server IP address, and server port number. 
- 
-     ​SSH_ORIGINAL_COMMAND ​ This variable contains the original command line if a forced command is exe‐ 
-                           ​cuted. ​ It can be used to extract the original arguments. 
- 
-     ​SSH_TTY ​              This is set to the name of the tty (path to the device) associated with the 
-                           ​current shell or command. ​ If the current session has no tty, this variable 
-                           is not set. 
- 
-     ​TZ ​                   This variable is set to indicate the present time zone if it was set when the 
-                           ​daemon was started (i.e. the daemon passes the value on to new connections). 
- 
-     ​USER ​                 Set to the name of the user logging in. 
- 
-     ​Additionally,​ ssh reads ~/​.ssh/​environment,​ and adds lines of the format “VARNAME=value” to the 
-     ​environment if the file exists and users are allowed to change their environment. ​ For more infor‐ 
-     ​mation,​ see the PermitUserEnvironment option in sshd_config(5). 
- 
-ENVIRONMENT 
-     ​SSH_USE_STRONG_RNG 
-             The reseeding of the OpenSSL random generator is usually done from /​dev/​urandom. ​ If the 
-             ​SSH_USE_STRONG_RNG environment variable is set to value other than 0 the OpenSSL random 
-             ​generator is reseeded from /​dev/​random. ​ The number of bytes read is defined by the 
-             ​SSH_USE_STRONG_RNG value. ​ Minimum is 14 bytes. ​ This setting is not recommended on the 
-             ​computers without the hardware random generator because insufficient entropy causes the 
-             ​connection to be blocked until enough entropy is available. 
- 
-FILES 
-     ​~/​.rhosts 
-             This file is used for host-based authentication (see above). ​ On some machines this file 
-             may need to be world-readable if the user's home directory is on an NFS partition, because 
-             ​sshd(8) reads it as root.  Additionally,​ this file must be owned by the user, and must not 
-             have write permissions for anyone else.  The recommended permission for most machines is 
-             ​read/​write for the user, and not accessible by others. 
- 
-     ​~/​.shosts 
-             This file is used in exactly the same way as .rhosts, but allows host-based authentication 
-             ​without permitting login with rlogin/rsh. 
- 
-     ​~/​.ssh/​ 
-             This directory is the default location for all user-specific configuration and authentica‐ 
-             tion information. ​ There is no general requirement to keep the entire contents of this 
-             ​directory secret, but the recommended permissions are read/​write/​execute for the user, and 
-             not accessible by others. 
- 
-     ​~/​.ssh/​authorized_keys 
-             Lists the public keys (DSA, ECDSA, ED25519, RSA) that can be used for logging in as this 
-             ​user. ​ The format of this file is described in the sshd(8) manual page.  This file is not 
-             ​highly sensitive, but the recommended permissions are read/write for the user, and not 
-             ​accessible by others. 
- 
-     ​~/​.ssh/​config 
-             This is the per-user configuration file.  The file format and configuration options are 
-             ​described in ssh_config(5). ​ Because of the potential for abuse, this file must have strict 
-             ​permissions:​ read/write for the user, and not writable by others. 
- 
-     ​~/​.ssh/​environment 
-             ​Contains additional definitions for environment variables; see ENVIRONMENT,​ above. 
- 
-     ​~/​.ssh/​identity 
-     ​~/​.ssh/​id_dsa 
-     ​~/​.ssh/​id_ecdsa 
-     ​~/​.ssh/​id_ed25519 
-     ​~/​.ssh/​id_rsa 
-             ​Contains the private key for authentication. ​ These files contain sensitive data and should 
-             be readable by the user but not accessible by others (read/​write/​execute). ​ ssh will simply 
-             ​ignore a private key file if it is accessible by others. ​ It is possible to specify a 
-             ​passphrase when generating the key which will be used to encrypt the sensitive part of this 
-             file using 3DES. 
- 
-     ​~/​.ssh/​identity.pub 
-     ​~/​.ssh/​id_dsa.pub 
-     ​~/​.ssh/​id_ecdsa.pub 
-     ​~/​.ssh/​id_ed25519.pub 
-     ​~/​.ssh/​id_rsa.pub 
-             ​Contains the public key for authentication. ​ These files are not sensitive and can (but 
-             need not) be readable by anyone. 
- 
-     ​~/​.ssh/​known_hosts 
-             ​Contains a list of host keys for all hosts the user has logged into that are not already in 
-             the systemwide list of known host keys.  See sshd(8) for further details of the format of 
-             this file. 
- 
-     ​~/​.ssh/​rc 
-             ​Commands in this file are executed by ssh when the user logs in, just before the user's 
-             shell (or command) is started. ​ See the sshd(8) manual page for more information. 
- 
-     /​etc/​hosts.equiv 
-             This file is for host-based authentication (see above). ​ It should only be writable by 
-             root. 
- 
-     /​etc/​ssh/​shosts.equiv 
-             This file is used in exactly the same way as hosts.equiv,​ but allows host-based authentica‐ 
-             tion without permitting login with rlogin/rsh. 
- 
-     /​etc/​ssh/​ssh_config 
-             ​Systemwide configuration file.  The file format and configuration options are described in 
-             ​ssh_config(5). 
- 
-     /​etc/​ssh/​ssh_host_key 
-     /​etc/​ssh/​ssh_host_dsa_key 
-     /​etc/​ssh/​ssh_host_ecdsa_key 
-     /​etc/​ssh/​ssh_host_ed25519_key 
-     /​etc/​ssh/​ssh_host_rsa_key 
-             These files contain the private parts of the host keys and are used for host-based authen‐ 
-             ​tication. ​ If protocol version 1 is used, ssh must be setuid root, since the host key is 
-             ​readable only by root.  For protocol version 2, ssh uses ssh-keysign(8) to access the host 
-             keys, eliminating the requirement that ssh be setuid root when host-based authentication is 
-             ​used. ​ By default ssh is not setuid root. 
- 
-     /​etc/​ssh/​ssh_known_hosts 
-             ​Systemwide list of known host keys.  This file should be prepared by the system administra‐ 
-             tor to contain the public host keys of all machines in the organization. ​ It should be 
-             ​world-readable. ​ See sshd(8) for further details of the format of this file. 
- 
-     /​etc/​ssh/​sshrc 
-             ​Commands in this file are executed by ssh when the user logs in, just before the user's 
-             shell (or command) is started. ​ See the sshd(8) manual page for more information. 
- 
-EXIT STATUS 
-     ssh exits with the exit status of the remote command or with 255 if an error occurred. 
- 
-IPV6 
-     IPv6 address can be used everywhere where IPv4 address. In all entries must be the IPv6 address 
-     ​enclosed in square brackets. Note: The square brackets are metacharacters for the shell and must be 
-     ​escaped in shell. 
- 
-SEE ALSO 
-     ​scp(1),​ sftp(1), ssh-add(1), ssh-agent(1),​ ssh-keygen(1),​ ssh-keyscan(1),​ tun(4), hosts.equiv(5),​ 
-     ​ssh_config(5),​ ssh-keysign(8),​ sshd(8) 
- 
-STANDARDS 
-     S. Lehtinen and C. Lonvick, The Secure Shell (SSH) Protocol Assigned Numbers, RFC 4250, January 
-     2006. 
- 
-     T. Ylonen and C. Lonvick, The Secure Shell (SSH) Protocol Architecture,​ RFC 4251, January 2006. 
- 
-     T. Ylonen and C. Lonvick, The Secure Shell (SSH) Authentication Protocol, RFC 4252, January 2006. 
- 
-     T. Ylonen and C. Lonvick, The Secure Shell (SSH) Transport Layer Protocol, RFC 4253, January 2006. 
- 
-     T. Ylonen and C. Lonvick, The Secure Shell (SSH) Connection Protocol, RFC 4254, January 2006. 
- 
-     J. Schlyter and W. Griffin, Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints,​ RFC 
-     4255, January 2006. 
- 
-     F. Cusack and M. Forssen, Generic Message Exchange Authentication for the Secure Shell Protocol 
-     ​(SSH),​ RFC 4256, January 2006. 
- 
-     J. Galbraith and P. Remaker, The Secure Shell (SSH) Session Channel Break Extension, RFC 4335, 
-     ​January 2006. 
- 
-     M. Bellare, T. Kohno, and C. Namprempre, The Secure Shell (SSH) Transport Layer Encryption Modes, 
-     RFC 4344, January 2006. 
- 
-     B. Harris, Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol, RFC 4345, 
-     ​January 2006. 
- 
-     M. Friedl, N. Provos, and W. Simpson, Diffie-Hellman Group Exchange for the Secure Shell (SSH) 
-     ​Transport Layer Protocol, RFC 4419, March 2006. 
- 
-     J. Galbraith and R. Thayer, The Secure Shell (SSH) Public Key File Format, RFC 4716, November 2006. 
- 
-     D. Stebila and J. Green, Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer, 
-     RFC 5656, December 2009. 
- 
-     A. Perrig and D. Song, Hash Visualization:​ a New Technique to improve Real-World Security, 1999, 
-     ​International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99). 
- 
-AUTHORS 
-     ​OpenSSH is a derivative of the original and free ssh 1.2.12 release by Tatu Ylonen. ​ Aaron Camp‐ 
-     bell, Bob Beck, Markus Friedl, Niels Provos, Theo de Raadt and Dug Song removed many bugs, re-added 
-     newer features and created OpenSSH. ​ Markus Friedl contributed the support for SSH protocol ver‐ 
-     sions 1.5 and 2.0. 
- 
-BSD                                         ​November 12, 2016                                        BSD</​code>​ 
- 
- 
- 
- 
- 
 ===== ssh in der Praxis ===== ===== ssh in der Praxis =====
-Auch wenn Passworte ​bei **ssh** verschlüsselt übertragen ​werdenwollen wir **__zwei wesentliche Aspekte__** bei Verwendung der **ssh** berücksichtigen:​ +Auch wenn das Passwort ​bei **ssh** verschlüsselt übertragen ​wirdlohnt ein Blick auf die Alternative ​ ​**//​RSA/​DSA-Authentifizierung//**Bei dieser Variante muss gar kein Passwort über das Netz übertragen werdenNormalerweise muss der User beim Zugriff ​via ssh auf einen entfernten Rechner sein Passwort eingebenZum einen wollen wir aus Sicherheitsgründen darauf verzichten ​und zum anderen kann dies doch auf Dauer doch als etwas nervig empfunden ​werden.  
-  - Der Benutzer **root** soll sich bei unseren Systemen nicht mehr remote anmelden dürfen. Lediglich ​ein oder die berechtigten Nutzern erhalten die Erlaubnis, von entfernter Stelle sich anzumelden. Via ''​su -''​ kann dann der berechtigte Administrator,​ root-Rechte erhalten! +Einfacher geht dies über asymetrische ​Schlüssel.  
-  - Wir werden Key-basierte Anmeldungen verwenden und **__keine__** Anmeldungen mit Passwort zulassen. Somit laufen wir nicht in Gefahr, Zugänge durch Trivialpassworte angreifbar zu machen. Stattdessen werden wir uns für unsere Administratoren und berechtigten Nutzern, ein Schlüsselpaar bestehend aus privaten und öffentlichen Schlüssel erzeugen. Bei der Erzeugung dieses Schlüsselpaares werden wir eine Schlüsselpasswort (passphrase) angeben, welches Zur Nutzung des Schlüssel abgefragt wird.  +==== Erzeugung eines Schlüssel ​ ​==== 
- +Als erstes ​erzeugen wir uns einen Schlüssel für die Authentifizierung:​ 
- +<​code>​[django@host ~]$ ssh-keygen -b 4096 -t rsa 
- +Generating public/​private rsa key pair. 
-Zum Erstellen eines Schlüsselpaares nutzen wir das Programm **ssh-keygen**. Einen Überberlick über die möglichen Optionen erhalten wir beim Abruf der zugehörigen **manpage**. +Enter file in which to save the key (/​home/​django/​.ssh/​id_rsa)
-   # man ssh-keygen +
- +
-<​code>​SSH-KEYGEN(1) ​                         BSD General Commands Manual ​                        ​SSH-KEYGEN(1) +
- +
-NAME +
-     ​ssh-keygen — authentication key generation, management and conversion +
- +
-SYNOPSIS +
-     ​ssh-keygen [-q] [-b bits] [-t type] [-N new_passphrase] [-C comment] [-f output_keyfile] +
-     ​ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile] +
-     ​ssh-keygen -i [-m key_format] [-f input_keyfile] +
-     ​ssh-keygen -e [-m key_format] [-f input_keyfile] +
-     ​ssh-keygen -y [-f input_keyfile] +
-     ​ssh-keygen -c [-P passphrase] [-C comment] [-f keyfile] +
-     ​ssh-keygen -l [-f input_keyfile] +
-     ​ssh-keygen -B [-f input_keyfile] +
-     ​ssh-keygen -D pkcs11 +
-     ​ssh-keygen -F hostname [-f known_hosts_file] [-l] +
-     ​ssh-keygen -H [-f known_hosts_file] +
-     ​ssh-keygen -R hostname [-f known_hosts_file] +
-     ​ssh-keygen -r hostname [-f input_keyfile] [-g] +
-     ​ssh-keygen -G output_file [-v] [-b bits] [-M memory] [-S start_point] +
-     ​ssh-keygen -T output_file -f input_file [-v] [-a rounds] [-J num_lines] [-j start_line] +
-                [-K checkpt] [-W generator] +
-     ​ssh-keygen -s ca_key -I certificate_identity [-h] [-n principals] [-O option] +
-                [-V validity_interval] [-z serial_number] file ... +
-     ​ssh-keygen -L [-f input_keyfile] +
-     ​ssh-keygen -A +
-     ​ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number] file ... +
-     ​ssh-keygen -Q -f krl_file file ... +
- +
-DESCRIPTION +
-     ​ssh-keygen generates, manages and converts authentication keys for ssh(1). ​ ssh-keygen can create +
-     RSA keys for use by SSH protocol version 1 and DSA, ECDSA, ED25519 or RSA keys for use by SSH pro‐ +
-     tocol version 2.  The type of key to be generated is specified with the -t option. ​ If invoked +
-     ​without any arguments, ssh-keygen will generate an RSA key for use in SSH protocol 2 connections. +
- +
-     ​ssh-keygen is also used to generate groups for use in Diffie-Hellman group exchange (DH-GEX). ​ See +
-     the MODULI GENERATION section for details. +
- +
-     ​Finally,​ ssh-keygen can be used to generate and update Key Revocation Lists, and to test whether +
-     given keys have been revoked by one.  See the KEY REVOCATION LISTS section for details. +
- +
-     ​Normally each user wishing to use SSH with public key authentication runs this once to create the +
-     ​authentication key in ~/.ssh/identity, ~/​.ssh/​id_dsa,​ ~/​.ssh/​id_ecdsa,​ ~/​.ssh/​id_ed25519 or +
-     ​~/​.ssh/​id_rsa. ​ Additionally,​ the system administrator may use this to generate host keys, as seen +
-     in /etc/rc. +
- +
-     ​Normally this program generates the key and asks for a file in which to store the private key.  The +
-     ​public key is stored in a file with the same name but “.pub” appended. ​ The program also asks for a +
-     ​passphrase. ​ The passphrase may be empty to indicate no passphrase (host keys must have an empty +
-     ​passphrase),​ or it may be a string of arbitrary length. ​ A passphrase is similar to a password, +
-     ​except it can be a phrase with a series of words, punctuation,​ numbers, whitespace, or any string +
-     of characters you want.  Good passphrases are 10-30 characters long, are not simple sentences or +
-     ​otherwise easily guessable (English prose has only 1-2 bits of entropy per character, and provides +
-     very bad passphrases),​ and contain a mix of upper and lowercase letters, numbers, and non-alphanu‐ +
-     meric characters. ​ The passphrase can be changed later by using the -p option. +
- +
-     There is no way to recover a lost passphrase. ​ If the passphrase is lost or forgotten, a new key +
-     must be generated and the corresponding public key copied to other machines. +
- +
-     For RSA1 keys, there is also a comment field in the key file that is only for convenience to the +
-     user to help identify the key.  The comment can tell what the key is for, or whatever is useful. +
-     The comment is initialized to “user@host” when the key is created, but can be changed using the -c +
-     ​option. +
- +
-     After a key is generated, instructions below detail where the keys should be placed to be acti‐ +
-     ​vated. +
- +
-     The options are as follows: +
- +
-     ​-A ​     For each of the key types (rsa1, rsa, dsa, ecdsa and ed25519) for which host keys do not +
-             ​exist,​ generate the host keys with the default key file path, an empty passphrase, default +
-             bits for the key type, and default comment. ​ This is used by /etc/rc to generate new host +
-             ​keys. +
- +
-     -a rounds +
-             When saving a new-format private key (i.e. an ed25519 key or any SSH protocol 2 key when +
-             the -o flag is set), this option specifies the number of KDF (key derivation function) +
-             ​rounds used.  Higher numbers result in slower passphrase verification and increased resis‐ +
-             tance to brute-force password cracking (should the keys be stolen). +
- +
-             When screening DH-GEX candidates ( using the -T command). ​ This option specifies the number +
-             of primality tests to perform. +
- +
-     ​-B ​     Show the bubblebabble digest of specified private or public key file. +
- +
-     -b bits +
-             ​Specifies the number of bits in the key to create. ​ For RSA keys, the minimum size is 768 +
-             bits and the default is 2048 bits.  Generally, 2048 bits is considered sufficient. ​ DSA +
-             keys must be exactly 1024 bits as specified by FIPS 186-2. ​ For ECDSA keys, the -b flag +
-             ​determines the key length by selecting from one of three elliptic curve sizes: 256, 384 or +
-             521 bits.  Attempting to use bit lengths other than these three values for ECDSA keys will +
-             ​fail. ​ ED25519 keys have a fixed length and the -b flag will be ignored. +
- +
-     -C comment +
-             ​Provides a new comment. +
- +
-     ​-c ​     Requests changing the comment in the private and public key files. ​ This operation is only +
-             ​supported for RSA1 keys.  The program will prompt for the file containing the private keys, +
-             for the passphrase if the key has one, and for the new comment. +
- +
-     -D pkcs11 +
-             ​Download the RSA public keys provided by the PKCS#11 shared library pkcs11. ​ When used in +
-             ​combination with -s, this option indicates that a CA key resides in a PKCS#11 token (see +
-             the CERTIFICATES section for details). +
- +
-     ​-e ​     This option will read a private or public OpenSSH key file and print to stdout the key in +
-             one of the formats specified by the -m option. ​ The default export format is “RFC4716”. +
-             This option allows exporting OpenSSH keys for use by other programs, including several com‐ +
-             ​mercial SSH implementations. +
- +
-     -F hostname +
-             ​Search for the specified hostname in a known_hosts file, listing any occurrences found. +
-             This option is useful to find hashed host names or addresses and may also be used in con‐ +
-             ​junction with the -H option to print found keys in a hashed format. +
- +
-     -f filename +
-             ​Specifies the filename of the key file. +
- +
-     -G output_file +
-             ​Generate candidate primes for DH-GEX. ​ These primes must be screened for safety (using the +
-             -T option) before use. +
- +
-     ​-g ​     Use generic DNS format when printing fingerprint resource records using the -r command. +
- +
-     ​-H ​     Hash a known_hosts file.  This replaces all hostnames and addresses with hashed representa‐ +
-             tions within the specified file; the original content is moved to a file with a .old suf‐ +
-             ​fix. ​ These hashes may be used normally by ssh and sshd, but they do not reveal identifying +
-             ​information should the file's contents be disclosed. ​ This option will not modify existing +
-             ​hashed hostnames and is therefore safe to use on files that mix hashed and non-hashed +
-             ​names. +
- +
-     ​-h ​     When signing a key, create a host certificate instead of a user certificate. ​ Please see +
-             the CERTIFICATES section for details. +
- +
-     -I certificate_identity +
-             ​Specify the key identity when signing a public key.  Please see the CERTIFICATES section +
-             for details. +
- +
-     ​-i ​     This option will read an unencrypted private (or public) key file in the format specified +
-             by the -m option and print an OpenSSH compatible private (or public) key to stdout. +
- +
-     -J num_lines +
-             Exit after screening the specified number of lines while performing DH candidate screening +
-             using the -T option. +
- +
-     -j start_line +
-             Start screening at the specified line number while performing DH candidate screening using +
-             the -T option. +
- +
-     -K checkpt +
-             Write the last line processed to the file checkpt while performing DH candidate screening +
-             using the -T option. ​ This will be used to skip lines in the input file that have already +
-             been processed if the job is restarted. ​ This option allows importing keys from other soft‐ +
-             ware, including several commercial SSH implementations. ​ The default import format is +
-             ​“RFC4716”. +
- +
-     ​-k ​     Generate a KRL file.  In this mode, ssh-keygen will generate a KRL file at the location +
-             ​specified via the -f flag that revokes every key or certificate presented on the command +
-             ​line. ​ Keys/certificates to be revoked may be specified by public key file or using the +
-             ​format described in the KEY REVOCATION LISTS section. +
- +
-     ​-L ​     Prints the contents of a certificate. +
- +
-     ​-l ​     Show fingerprint of specified public key file.  Private RSA1 keys are also supported. ​ For +
-             RSA and DSA keys ssh-keygen tries to find the matching public key file and prints its fin‐ +
-             ​gerprint. ​ If combined with -v, an ASCII art representation of the key is supplied with the +
-             ​fingerprint. +
- +
-     -M memory +
-             ​Specify the amount of memory to use (in megabytes) when generating candidate moduli for DH- +
-             ​GEX. +
- +
-     -m key_format +
-             ​Specify a key format for the -i (import) or -e (export) conversion options. ​ The supported +
-             key formats are: “RFC4716” (RFC 4716/SSH2 public or private key), “PKCS8” (PEM PKCS8 public +
-             key) or “PEM” (PEM public key).  The default conversion format is “RFC4716”. +
- +
-     -N new_passphrase +
-             ​Provides the new passphrase. +
- +
-     -n principals +
-             ​Specify one or more principals (user or host names) to be included in a certificate when +
-             ​signing a key.  Multiple principals may be specified, separated by commas. ​ Please see the +
-             ​CERTIFICATES section for details. +
- +
-     -O option +
-             ​Specify a certificate option when signing a key.  This option may be specified multiple +
-             ​times. ​ Please see the CERTIFICATES section for details. ​ The options that are valid for +
-             user certificates are: +
- +
-             ​clear ​  Clear all enabled permissions. ​ This is useful for clearing the default set of per‐ +
-                     ​missions so permissions may be added individually. +
- +
-             ​force-command=command +
-                     ​Forces the execution of command instead of any shell or command specified by the +
-                     user when the certificate is used for authentication. +
- +
-             ​no-agent-forwarding +
-                     ​Disable ssh-agent(1) forwarding (permitted by default). +
- +
-             ​no-port-forwarding +
-                     ​Disable port forwarding (permitted by default). +
- +
-             ​no-pty ​ Disable PTY allocation (permitted by default). +
- +
-             ​no-user-rc +
-                     ​Disable execution of ~/.ssh/rc by sshd(8) (permitted by default). +
- +
-             ​no-x11-forwarding +
-                     ​Disable X11 forwarding (permitted by default). +
- +
-             ​permit-agent-forwarding +
-                     ​Allows ssh-agent(1) forwarding. +
- +
-             ​permit-port-forwarding +
-                     ​Allows port forwarding. +
- +
-             ​permit-pty +
-                     ​Allows PTY allocation. +
- +
-             ​permit-user-rc +
-                     ​Allows execution of ~/.ssh/rc by sshd(8). +
- +
-             ​permit-x11-forwarding +
-                     ​Allows X11 forwarding. +
- +
-             ​source-address=address_list +
-                     ​Restrict the source addresses from which the certificate is considered valid. ​ The +
-                     ​address_list is a comma-separated list of one or more address/​netmask pairs in CIDR +
-                     ​format. +
- +
-             At present, no options are valid for host keys. +
- +
-     ​-o ​     Causes ssh-keygen to save SSH protocol 2 private keys using the new OpenSSH format rather +
-             than the more compatible PEM format. ​ The new format has increased resistance to brute- +
-             force password cracking but is not supported by versions of OpenSSH prior to 6.5.  Ed25519 +
-             keys always use the new private key format. +
- +
-     -P passphrase +
-             ​Provides the (old) passphrase. +
- +
-     ​-p ​     Requests changing the passphrase of a private key file instead of creating a new private +
-             ​key. ​ The program will prompt for the file containing the private key, for the old +
-             ​passphrase,​ and twice for the new passphrase. +
- +
-     ​-Q ​     Test whether keys have been revoked in a KRL. +
- +
-     ​-q ​     Silence ssh-keygen. +
- +
-     -R hostname +
-             ​Removes all keys belonging to hostname from a known_hosts file.  This option is useful to +
-             ​delete hashed hosts (see the -H option above). +
- +
-     -r hostname +
-             Print the SSHFP fingerprint resource record named hostname for the specified public key +
-             ​file. +
- +
-     -S start +
-             ​Specify start point (in hex) when generating candidate moduli for DH-GEX. +
- +
-     -s ca_key +
-             ​Certify (sign) a public key using the specified CA key.  Please see the CERTIFICATES sec‐ +
-             tion for details. +
- +
-             When generating a KRL, -s specifies a path to a CA public key file used to revoke certifi‐ +
-             cates directly by key ID or serial number. ​ See the KEY REVOCATION LISTS section for +
-             ​details. +
- +
-     -T output_file +
-             Test DH group exchange candidate primes (generated using the -G option) for safety. +
- +
-     -t type +
-             ​Specifies the type of key to create. ​ The possible values are “rsa1” for protocol version 1 +
-             and “dsa”, “ecdsa”,​ “ed25519”,​ or “rsa” for protocol version 2. +
- +
-     ​-u ​     Update a KRL.  When specified with -k, keys listed via the command line are added to the +
-             ​existing KRL rather than a new KRL being created. +
- +
-     -V validity_interval +
-             ​Specify a validity interval when signing a certificate. ​ A validity interval may consist of +
-             a single time, indicating that the certificate is valid beginning now and expiring at that +
-             time, or may consist of two times separated by a colon to indicate an explicit time inter‐ +
-             ​val. ​ The start time may be specified as a date in YYYYMMDD format, a time in YYYYMMDDHH‐ +
-             MMSS format or a relative time (to the current time) consisting of a minus sign followed by +
-             a relative time in the format described in the TIME FORMATS section of sshd_config(5). ​ The +
-             end time may be specified as a YYYYMMDD date, a YYYYMMDDHHMMSS time or a relative time +
-             ​starting with a plus character. +
- +
-             For example: “+52w1d” (valid from now to 52 weeks and one day from now), “-4w:​+4w” (valid +
-             from four weeks ago to four weeks from now), “20100101123000:​20110101123000” (valid from +
-             12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011), “-1d:​20110101” (valid from +
-             ​yesterday to midnight, January 1st, 2011). +
- +
-     ​-v ​     Verbose mode.  Causes ssh-keygen to print debugging messages about its progress. ​ This is +
-             ​helpful for debugging moduli generation. ​ Multiple -v options increase the verbosity. ​ The +
-             ​maximum is 3. +
- +
-     -W generator +
-             ​Specify desired generator when testing candidate moduli for DH-GEX. +
- +
-     ​-y ​     This option will read a private OpenSSH format file and print an OpenSSH public key to std‐ +
-             ​out. +
- +
-     -z serial_number +
-             ​Specifies a serial number to be embedded in the certificate to distinguish this certificate +
-             from others from the same CA.  The default serial number is zero. +
- +
-             When generating a KRL, the -z flag is used to specify a KRL version number. +
- +
-MODULI GENERATION +
-     ​ssh-keygen may be used to generate groups for the Diffie-Hellman Group Exchange (DH-GEX) protocol. +
-     ​Generating these groups is a two-step process: first, candidate primes are generated using a fast, +
-     but memory intensive process. ​ These candidate primes are then tested for suitability (a CPU-inten‐ +
-     sive process). +
- +
-     ​Generation of primes is performed using the -G option. ​ The desired length of the primes may be +
-     ​specified by the -b option. ​ For example: +
- +
-           # ssh-keygen -G moduli-2048.candidates -b 2048 +
- +
-     By default, the search for primes begins at a random point in the desired length range. ​ This may +
-     be overridden using the -S option, which specifies a different start point (in hex). +
- +
-     Once a set of candidates have been generated, they must be screened for suitability. ​ This may be +
-     ​performed using the -T option. ​ In this mode ssh-keygen will read candidates from standard input +
-     (or a file specified using the -f option). ​ For example: +
- +
-           # ssh-keygen -T moduli-2048 -f moduli-2048.candidates +
- +
-     By default, each candidate will be subjected to 100 primality tests. ​ This may be overridden using +
-     the -a option. ​ The DH generator value will be chosen automatically for the prime under considera‐ +
-     ​tion. ​ If a specific generator is desired, it may be requested using the -W option. ​ Valid genera‐ +
-     tor values are 2, 3, and 5. +
- +
-     ​Screened DH groups may be installed in /​etc/​ssh/​moduli. ​ It is important that this file contains +
-     ​moduli of a range of bit lengths and that both ends of a connection share common moduli. +
- +
-CERTIFICATES +
-     ​ssh-keygen supports signing of keys to produce certificates that may be used for user or host +
-     ​authentication. ​ Certificates consist of a public key, some identity information,​ zero or more +
-     ​principal (user or host) names and a set of options that are signed by a Certification Authority +
-     (CA) key.  Clients or servers may then trust only the CA key and verify its signature on a certifi‐ +
-     cate rather than trusting many user/host keys.  Note that OpenSSH certificates are a different, and +
-     much simpler, format to the X.509 certificates used in ssl(8). +
- +
-     ​ssh-keygen supports two types of certificates:​ user and host.  ​User certificates authenticate users +
-     to servers, whereas host certificates authenticate server hosts to users. ​ To generate a user cer‐ +
-     ​tificate:​ +
- +
-           $ ssh-keygen -s /​path/​to/​ca_key -I key_id /​path/​to/​user_key.pub +
- +
-     The resultant certificate will be placed in /​path/​to/​user_key-cert.pub. ​ A host certificate +
-     ​requires the -h option: +
- +
-           $ ssh-keygen -s /​path/​to/​ca_key -I key_id -h /​path/​to/​host_key.pub +
- +
-     The host certificate will be output to /​path/​to/​host_key-cert.pub. +
- +
-     It is possible to sign using a CA key stored in a PKCS#11 token by providing the token library +
-     using -D and identifying the CA key by providing its public half as an argument to -s: +
- +
-           $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id host_key.pub +
- +
-     In all cases, key_id is a "key identifier"​ that is logged by the server when the certificate is +
-     used for authentication. +
- +
-     ​Certificates may be limited to be valid for a set of principal (user/host) names. ​ By default, gen‐ +
-     ​erated certificates are valid for all users or hosts. ​ To generate a certificate for a specified +
-     set of principals:​ +
- +
-           $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub +
-           $ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub +
- +
-     ​Additional limitations on the validity and use of user certificates may be specified through cer‐ +
-     ​tificate options. ​ A certificate option may disable features of the SSH session, may be valid only +
-     when presented from particular source addresses or may force the use of a specific command. ​ For a +
-     list of valid certificate options, see the documentation for the -O option above. +
- +
-     ​Finally,​ certificates may be defined with a validity lifetime. ​ The -V option allows specification +
-     of certificate start and end times. ​ A certificate that is presented at a time outside this range +
-     will not be considered valid. ​ By default, certificates are valid from UNIX Epoch to the distant +
-     ​future. +
- +
-     For certificates to be used for user or host authentication,​ the CA public key must be trusted by +
-     ​sshd(8) or ssh(1). ​ Please refer to those manual pages for details. +
- +
-KEY REVOCATION LISTS +
-     ​ssh-keygen is able to manage OpenSSH format Key Revocation Lists (KRLs). ​ These binary files spec‐ +
-     ify keys or certificates to be revoked using a compact format, taking as little as one bit per cer‐ +
-     ​tificate if they are being revoked by serial number. +
- +
-     KRLs may be generated using the -k flag.  This option reads one or more files from the command line +
-     and generates a new KRL.  The files may either contain a KRL specification (see below) or public +
-     keys, listed one per line.  Plain public keys are revoked by listing their hash or contents in the +
-     KRL and certificates revoked by serial number or key ID (if the serial is zero or not available). +
- +
-     ​Revoking keys using a KRL specification offers explicit control over the types of record used to +
-     ​revoke keys and may be used to directly revoke certificates by serial number or key ID without hav‐ +
-     ing the complete original certificate on hand.  A KRL specification consists of lines containing +
-     one of the following directives followed by a colon and some directive-specific information. +
- +
-     ​serial:​ serial_number[-serial_number] +
-             ​Revokes a certificate with the specified serial number. ​ Serial numbers are 64-bit values, +
-             not including zero and may be expressed in decimal, hex or octal. ​ If two serial numbers +
-             are specified separated by a hyphen, then the range of serial numbers including and between +
-             each is revoked. ​ The CA key must have been specified on the ssh-keygen command line using +
-             the -s option. +
- +
-     id: key_id +
-             ​Revokes a certificate with the specified key ID string. ​ The CA key must have been speci‐ +
-             fied on the ssh-keygen command line using the -s option. +
- +
-     key: public_key +
-             ​Revokes the specified key.  If a certificate is listed, then it is revoked as a plain pub‐ +
-             lic key. +
- +
-     sha1: public_key +
-             ​Revokes the specified key by its SHA1 hash. +
- +
-     KRLs may be updated using the -u flag in addition to -k.  When this option is specified, keys +
-     ​listed ​via the command line are merged into the KRL, adding to those already there. +
- +
-     It is also possible, given a KRL, to test whether it revokes a particular key (or keys). ​ The -Q +
-     flag will query an existing KRL, testing each key specified on the commandline. ​ If any key listed +
-     on the command line has been revoked (or an error encountered) then ssh-keygen will exit with a +
-     ​non-zero exit status A zero exit status will only be returned if no key was revoked. +
- +
-FILES +
-     ​~/​.ssh/​identity +
-             ​Contains the protocol version 1 RSA authentication identity of the user.  This file should +
-             not be readable by anyone but the user.  It is possible to specify a passphrase when gener‐ +
-             ating the key; that passphrase will be used to encrypt the private part of this file using +
-             ​3DES. ​ This file is not automatically accessed by ssh-keygen but it is offered as the +
-             ​default file for the private key.  ssh(1) will read this file when a login attempt is made. +
- +
-     ​~/​.ssh/​identity.pub +
-             ​Contains the protocol version 1 RSA public key for authentication. ​ The contents of this +
-             file should be added to ~/​.ssh/​authorized_keys on all machines where the user wishes to log +
-             in using RSA authentication. ​ There is no need to keep the contents of this file secret. +
- +
-     ​~/​.ssh/​id_dsa +
-     ​~/​.ssh/​id_ecdsa +
-     ​~/​.ssh/​id_ed25519 +
-     ​~/​.ssh/​id_rsa +
-             ​Contains the protocol version 2 DSA, ECDSA, ED25519 or RSA authentication identity of the +
-             ​user. ​ This file should not be readable by anyone but the user.  It is possible to specify +
-             a passphrase when generating the key; that passphrase will be used to encrypt the private +
-             part of this file using 128-bit AES.  This file is not automatically accessed by ssh-keygen +
-             but it is offered as the default file for the private key.  ssh(1) will read this file when +
-             a login attempt is made. +
- +
-     ​~/​.ssh/​id_dsa.pub +
-     ​~/​.ssh/​id_ecdsa.pub +
-     ​~/​.ssh/​id_ed25519.pub +
-     ​~/​.ssh/​id_rsa.pub +
-             ​Contains the protocol version 2 DSA, ECDSA, ED25519 or RSA public key for authentication. +
-             The contents of this file should be added to ~/​.ssh/​authorized_keys on all machines where +
-             the user wishes to log in using public key authentication. ​ There is no need to keep the +
-             ​contents of this file secret. +
-             ​default file for the private key.  ssh(1) will read this file when a login attempt is made. +
- +
-     ​~/​.ssh/​identity.pub +
-             ​Contains the protocol version 1 RSA public key for authentication. ​ The contents of this +
-             file should be added to ~/​.ssh/​authorized_keys on all machines where the user wishes to log +
-             in using RSA authentication. ​ There is no need to keep the contents of this file secret. +
- +
-     ​~/​.ssh/​id_dsa +
-     ​~/​.ssh/​id_ecdsa +
-     ​~/​.ssh/​id_ed25519 +
-     ​~/​.ssh/​id_rsa +
-             ​Contains the protocol version 2 DSA, ECDSA, ED25519 or RSA authentication identity of the +
-             ​user. ​ This file should not be readable by anyone but the user.  It is possible to specify +
-             a passphrase when generating the key; that passphrase will be used to encrypt the private +
-             part of this file using 128-bit AES.  This file is not automatically accessed by ssh-keygen +
-             but it is offered as the default file for the private key.  ssh(1) will read this file when +
-             a login attempt is made. +
- +
-     ​~/​.ssh/​id_dsa.pub +
-     ​~/​.ssh/​id_ecdsa.pub +
-     ​~/​.ssh/​id_ed25519.pub +
-     ​~/​.ssh/​id_rsa.pub +
-             ​Contains the protocol version 2 DSA, ECDSA, ED25519 or RSA public key for authentication. +
-             The contents of this file should be added to ~/​.ssh/​authorized_keys on all machines where +
-             the user wishes to log in using public key authentication. ​ There is no need to keep the +
-             ​contents of this file secret. +
- +
-     /​etc/​ssh/​moduli +
-             ​Contains Diffie-Hellman groups used for DH-GEX. ​ The file format is described in moduli(5). +
- +
-ENVIRONMENT +
-     ​SSH_USE_STRONG_RNG +
-             The reseeding of the OpenSSL random generator is usually done from /​dev/​urandom. ​ If the +
-             ​SSH_USE_STRONG_RNG environment variable is set to value other than 0 the OpenSSL random +
-             ​generator is reseeded from /​dev/​random. ​ The number of bytes read is defined by the +
-             ​SSH_USE_STRONG_RNG value. ​ Minimum is 14 bytes. ​ This setting is not recommended on the +
-             ​computers without the hardware random generator because insufficient entropy causes the +
-             ​connection to be blocked until enough entropy is available. +
- +
-SEE ALSO +
-     ​ssh(1),​ ssh-add(1), ssh-agent(1),​ moduli(5), sshd(8) +
- +
-     The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006. +
- +
-AUTHORS +
-     ​OpenSSH is a derivative of the original and free ssh 1.2.12 release by Tatu Ylonen. ​ Aaron Camp‐ +
-     bell, Bob Beck, Markus Friedl, Niels Provos, Theo de Raadt and Dug Song removed many bugs, re-added +
-     newer features and created OpenSSH. ​ Markus Friedl contributed the support for SSH protocol ver‐ +
-     sions 1.5 and 2.0. +
- +
-BSD                                         ​November 13, 2016                                        BSD +
-</​code>​ +
- +
-Bevor wir uns die Entscheidung treffen können, welchen Schlüssel-Typ wir erzeugen ​wollen, müssen wir überlegen, von welchem System ​wir aus auf unseren Linux/​CentOS-Host zugreifen wollen. Sind wir in der misslichen Lage und müssen von einem **Windows**-Rechner aus auf unseren Linux-Host zugreifen, müssen wir sicherheitstechnische Abstrichen machen, da ** putty** z.B. nicht alle aktuiellen Cipher, MAC und Schlüsselaustauschmechanismen zu Verfügung stellt, die uns z.B der CentOS 7 Zielserver ggf. anbietet. Ähnliches gilt, wenn wir z.B. von einem CentOS 6 System auf eine aktuelles CentOS 7 System via ssh zugreifen wollen. +
- +
-Hier empfiehlt es sich auf den beteiligten System zu überprüfen,​ welche Cipher, MACs, Schlüssel Typen und Key Exchange Algorithmen unterstützt ​werden. Zum Abfragen können wir den Befehl **ssh** mit der Option //**-Q**// verwenden+
- +
-=== Liste der unterstützten Cipher === +
-   # ssh -Q cipher +
-<​code>​3des-cbc +
-blowfish-cbc +
-cast128-cbc +
-arcfour +
-arcfour128 +
-arcfour256 +
-aes128-cbc +
-aes192-cbc +
-aes256-cbc +
-rijndael-cbc@lysator.liu.se +
-aes128-ctr +
-aes192-ctr +
-aes256-ctr +
-aes128-gcm@openssh.com +
-aes256-gcm@openssh.com +
-chacha20-poly1305@openssh.com</​code>​ +
- +
-=== Liste der unterstützten MACs === +
-   # ssh -Q mac +
-<​code>​hmac-sha1 +
-hmac-sha1-96 +
-hmac-sha2-256 +
-hmac-sha2-512 +
-hmac-md5 +
-hmac-md5-96 +
-hmac-ripemd160 +
-hmac-ripemd160@openssh.com +
-umac-64@openssh.com +
-umac-128@openssh.com +
-hmac-sha1-etm@openssh.com +
-hmac-sha1-96-etm@openssh.com +
-hmac-sha2-256-etm@openssh.com +
-hmac-sha2-512-etm@openssh.com +
-hmac-md5-etm@openssh.com +
-hmac-md5-96-etm@openssh.com +
-hmac-ripemd160-etm@openssh.com +
-umac-64-etm@openssh.com +
-umac-128-etm@openssh.com</​code>​ +
- +
-=== Liste der unterstützten ​Schlüssel ​Typen ==== +
-   # ssh -Q key +
-<​code>​ssh-rsa +
-ssh-dss +
-ssh-ed25519 +
-ecdsa-sha2-nistp256 +
-ecdsa-sha2-nistp384 +
-ecdsa-sha2-nistp521 +
-ssh-rsa-cert-v01@openssh.com +
-ssh-dss-cert-v01@openssh.com +
-ecdsa-sha2-nistp256-cert-v01@openssh.com +
-ecdsa-sha2-nistp384-cert-v01@openssh.com +
-ecdsa-sha2-nistp521-cert-v01@openssh.com +
-ssh-rsa-cert-v00@openssh.com +
-ssh-dss-cert-v00@openssh.com +
-ssh-ed25519-cert-v01@openssh.com +
-null</​code>​ +
- +
-=== Liste alller unterstützten Key Exchange Algorithmen === +
-   # ssh -Q kex +
-<​code>​diffie-hellman-group1-sha1 +
-diffie-hellman-group14-sha1 +
-diffie-hellman-group-exchange-sha1 +
-diffie-hellman-group-exchange-sha256 +
-ecdh-sha2-nistp256 +
-ecdh-sha2-nistp384 +
-ecdh-sha2-nistp521 +
-diffie-hellman-group1-sha1 +
-curve25519-sha256@libssh.org +
-gss-gex-sha1- +
-gss-group1-sha1- +
-gss-group14-sha1-</​code>​ +
- +
- +
-==== Erzeugung eines Schlüsselpäärchens ​ ​==== +
-=== RSA Key === +
-Im ersten Beispiel ​erzeugen wir uns einen 4096er RSA-Schlüssel für die Authentifizierung:​ +
-    $ ssh-keygen -b 4096 -t rsa -C django@nausch.org -f ~/​.ssh/​id_rsa4096_dmz +
- +
-<​code>​Generating public/​private rsa key pair. +
-Enter passphrase (empty for no passphrase):​  +
-Enter same passphrase again:  +
-Your identification has been saved in /​home/​django/​.ssh/​id_rsa4096_dmz. +
-Your public ​key has been saved in /​home/​django/​.ssh/​id_rsa4096_dmz.pub. +
-The key fingerprint is: +
-44:​8b:​1a:​4b:​87:​95:​3a:​23:​af:​65:​b7:​e6:​1a:​bf:​98:​3d django@nausch.org +
-The key's randomart image is: +
-+--[ RSA 4096]----+ +
-|      ...        | +
-|     o.o .       | +
-|    +.o o        | +
-|  ..+= .         | +
-|   ​ooo ​ S        | +
-|    + .          | +
-|   +.. .         | +
-|  .  *E          | +
-|    ++=o         | +
-+-----------------+</​code>​ +
- +
- +
-Die //​passphrase//​ die man hier angibt, wird später beim Anmelden auf dem entfernten Rechner abgefragt, oder vom //​ssh-agent//​ bei der Anmeldung mitübergeben. +
- +
-Nun liegen in dem Verzeichnis **/​home/​django/​.ssh** zwei weitere Dateien: +
-  # ll ~/​.ssh/​id_rsa+
-<​code>​-rw-------. 1 django django 3326 13. Nov 15:27 /​home/​django/​.ssh/​id_rsa4096_dmz +
--rw-r--r--. 1 django django ​ 743 13. Nov 15:27 /​home/​django/​.ssh/​id_rsa4096_dmz.pub</​code>​ +
- +
-**id_rsa4096_dmz** enthält den privaten Schlüssel und sollte auf keinen Fall weitergegeben werden und darf auch __nur__ für den Nutzer selbst lesbar sein! **id_rsa4096_dmz.pub**,​ der öffentliche Schlüssel, dagegen muss auf den Zielrechner kopiert werden.  +
- +
-=== ED25519 Key === +
-Ob man in Zeiten von Überwachungsphantasten bei einer NSA oder BND, noch solhcen Schlüssel einsetzen kann und mag, muss natürlich jeder Admin für sich sekbst entscheiden. Auf solche Schlüssel muss man aber nicht mehr zwingend zurückgreifen,​ stehen doch aktuellere und zeitgemäße Cipher, MACs, Schlüssel Typen und Key Exchange Algorithmen zur Verfügung. Als Alternative zu einem RSA-Keys wollen wir nun nun einen [[http://​ed25519.cr.yp.to/​|ed25519]] Schlüssels erzeugen. [[https://​de.wikipedia.org/​wiki/​Curve25519|Ed25519]] ist ein Elliptic Curve Signature Schema, welches beste Sicherheit bei vertretbaren Aufwand verspricht, als ECDSA oder DSA dies versprechen. Zur Auswahl sicherer kryptografischer Kurven bei der //​Elliptic-Curve Cryptography//​ findet man auf der Seite [[https://​safecurves.cr.yp.to/​|hier]] hilfreiche Erklärungen und eine Gegenüberstellung der möglichen verschiedenen Alternativen. +
-   $ ssh-keygen -t ed25519 -o -a 100 -C django@nausch.org -f ~/​.ssh/​id_ed25519_dmz +
- +
-<​code>​Generating public/​private ed25519 key pair.+
 Enter passphrase (empty for no passphrase): ​ Enter passphrase (empty for no passphrase): ​
 Enter same passphrase again: ​ Enter same passphrase again: ​
-Your identification has been saved in /​home/​django/​.ssh/​id_ed25519_dmz+Your identification has been saved in /​home/​django/​.ssh/​id_rsa
-Your public key has been saved in /​home/​django/​.ssh/​id_ed25519_dmz.pub.+Your public key has been saved in /​home/​django/​.ssh/​id_rsa.pub.
 The key fingerprint is: The key fingerprint is:
-a3:03:59:5c:1b:d3:60:2a:93:77:2a:9f:9d:fc:e8:68 django@nausch.org +2b:83:69:f2:76:e8:c9:8b:cf:34:c8:c2:ae:2b:e1:ee django@host.nausch.org</​code>​
-The key's randomart image is: +
-+--[ED25519 ​ 256--+ +
-|        *o       | +
-|     o + +.      | +
-|    + = o        | +
-|     * o         | +
-|    + . S        | +
-|     + = o       | +
-|      = +        | +
-|      Eo o       | +
-|     ...o .      | +
-+-----------------+</​code>​+
  
 Die //​passphrase//​ die man hier angibt, wird später beim Anmelden auf dem entfernten Rechner abgefragt, oder vom //​ssh-agent//​ bei der Anmeldung mitübergeben. Die //​passphrase//​ die man hier angibt, wird später beim Anmelden auf dem entfernten Rechner abgefragt, oder vom //​ssh-agent//​ bei der Anmeldung mitübergeben.
  
-Nun liegen in dem Verzeichnis **/​home/​django/​.ssh** zwei weitere ​Dateien: +Nun liegen in dem Verzeichnis **/​home/​django/​.ssh** zwei Dateien: 
-  # ll ~/.ssh/*ed25519* +<​code>​[django@host ​.ssh]$ ll 
-<​code>​-rw-------1 django django ​464  2Nov 21:43 /​home/​django/​.ssh/​id_ed25519_dmz +insgesamt 24 
--rw-r--r--1 django django  ​99  2Nov 21:43 /​home/​django/​.ssh/​id_ed25519_dmz.pub</​code>​+-rw------- 1 django django ​3311 22Apr 22:11 id_rsa 
 +-rw-r--r-- 1 django django  ​748 22Apr 22:11 id_rsa.pub</​code>​
  
-**id_ed25519_dmz** enthält den privaten Schlüssel und sollte auf keinen Fall weitergegeben werden und darf auch __nur__ für den Nutzer selbst lesbar sein! **id_ed25519_dmz.pub**, der öffentliche Schlüssel, dagegen muss auf den Zielrechner kopiert werden. ​+**id_rsa** enthält den privaten Schlüssel und sollte auf keinen Fall weitergegeben werden und darf auch __nur__ für den Nutzer selbst lesbar sein! **id_rsa.pub**, der öffentliche Schlüssel, dagegen muss auf den Zielrechner kopiert werden. ​
 ==== Zielverzeichnis anlegen und öffentlichen Schlüssel kopieren ​ ==== ==== Zielverzeichnis anlegen und öffentlichen Schlüssel kopieren ​ ====
 Auf dem Zielrechner legen wir nun das Verzeichnis **.ssh** an und schützen es entsprechend. Auf dem Zielrechner legen wir nun das Verzeichnis **.ssh** an und schützen es entsprechend.
Zeile 1684: Zeile 172:
   [django@zielhost django]$ chmod 700 .ssh   [django@zielhost django]$ chmod 700 .ssh
  
-Den öffentlichen Schlüssel kopieren wir dann wie folgt auf das Zielsystem; hatten wir uns einen RSA-key erstellt verwenden wir folgenden Aufruf+Den öffentlichen Schlüssel kopieren wir dann wie folgt auf das Zielsystem:​ 
-   $  scp /home/django/.ssh/​id_rsa4096_dmz.pub zielhost:/​home/​django/​.ssh/​key.pub +  ​[django@host .ssh]$  scp /​home/​django/​.ssh/​id_rsa.pub zielhost:/​home/​django/​.ssh/​id_rsa.pub
-bzw. bei einem ed25519 Schlüssel:​ +
-   $  scp /​home/​django/​.ssh/​id_ed25519_dmz.pub zielhost:/​home/​django/​.ssh/​key.pub+
  
-Anschliessend ​wird der Schlüssel in die Datei authorized_keys kopiert. Diese Datei kann mehrere Schlüssel enthalten, daher ist das doppelte Umleitungszeichen wichtig, um eine evt. existierende Datei nicht versehentlich zu überschreiben. Somit wird der neue Schlüssel in die Datei hinzugefügt:​ +Anschließend ​wird der Schlüssel in die Datei authorized_keys kopiert. Diese Datei kann mehrere Schlüssel enthalten, daher ist das doppelte Umleitungszeichen wichtig, um eine evt. existierende Datei nicht versehentlich zu überschreiben. Somit wird der neue Schlüssel in die Datei hinzugefügt:​ 
-   ​$ cat key.pub >> authorized_keys+  ​[django@zielhost .ssh]$ cat id_rsa.pub >> authorized_keys
 Zu guter Letzt passen wir noch die Berechtigungen an und löschen die nicht mehr benötigte **id_rsa.pub** Zu guter Letzt passen wir noch die Berechtigungen an und löschen die nicht mehr benötigte **id_rsa.pub**
-   $ chmod 600 authorized_keys +  [django@zielhost .ssh]$ chmod 600 authorized_keys 
-   ​$ rm key.pub+  ​[django@zielhost .ssh]$ rm id_rsa.pub
  
 <WRAP round info>Das Kopieren des Public-Keys auf unseren Zielhost mit Anpassen der Dateiberechtigungen kann man natürlich auch einfacher vornehmen. Man benutzt hierzu einfach den Befehl **ssh-copy-id** aus dem Paket //​**openssh-clients**//​. <WRAP round info>Das Kopieren des Public-Keys auf unseren Zielhost mit Anpassen der Dateiberechtigungen kann man natürlich auch einfacher vornehmen. Man benutzt hierzu einfach den Befehl **ssh-copy-id** aus dem Paket //​**openssh-clients**//​.
  
-  * RSA-Key <​code> ​$ ssh-copy-id -i ~/​.ssh/​id_rsa.pub testhost.intra.nausch.org</​code>​ +   $ ssh-copy-id -i ~/​.ssh/​id_rsa.pub testhost.intra.nausch.org
-  * ed25519-Key <​code>​ $ ssh-copy-id -i ~/​.ssh/​id_ed25519_dmz testhost.intra.nausch.org</​code>​+
  
-Mit der Angabe ''​~/​.ssh/​id_rsa4096_dmz''​ bzw. ''​~/​.ssh/​id_ed25519_dmz''​ kopiert dann der Befehl **ssh-copy-id** den zugehörigen öffentlichen Schlüssel auf den Zielhost ​''​testhost.intra.nausch.org''​.+Die Angabe ''​~/​.ssh/​id_rsa.pub'' ​entspricht dabei dem Public-Key und ''​testhost.intra.nausch.org 
 +'' ​dem gewünschten Zielhost.
 </​WRAP>​ </​WRAP>​
 ==== authorized_keys vs. authorized_keys2 ==== ==== authorized_keys vs. authorized_keys2 ====
-<WRAP round tip>Bei der Einführung von SSH Version 2 kam die Datei ''​authorized_keys2''​ zum Einsatz. Seit OpenSSH 3.0 wird nun wiederum neben der ''​authorized_keys2''​ wieder die ''​authorized_keys''​ verwendet. In unserem Fall nutzen wir in unserem obigen Beispiel daher nur noch die Schlüsseldatei ''​authorized_keys''​.</​WRAP>​ +<WRAP round info>Bei der Einführung von SSH Version 2 kam die Datei ''​authorized_keys2''​ zum Einsatz. Seit OpenSSH 3.0 wird nun wiederum neben der ''​authorized_keys2''​ wieder die ''​authorized_keys''​ verwendet. In unserem Fall nutzen wir in unserem obigen Beispiel daher nur noch die Schlüsseldatei ''​authorized_keys''​.</​WRAP>​
  
 ===== ssh-Daemon ===== ===== ssh-Daemon =====
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   }   }
   state Workstation {   state Workstation {
-    Workstation : Gerät: ​Djangos ​Admin-Workstation+    Workstation : Gerät: ​Django'​s ​Admin-Workstation
     Workstation : Hostname: pml010040     Workstation : Hostname: pml010040
     Workstation : CNAME: office-work     Workstation : CNAME: office-work
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 Host daxie Host daxie
     Hostname <​was-das-auch-immer-für-ein geiler-FQDN-sein-mag>​     Hostname <​was-das-auch-immer-für-ein geiler-FQDN-sein-mag>​
-    ProxyCommand ​ ssh -l root -i ~/​.ssh/​id_rsa_daxie -2 -4 fwa nc -w 120 %h %p+    ProxyCommand ​ ssh -l root -i ~/​.ssh/​id_rsa_daxie -2 -4 fwa nc -w 120 %h
 </​file>​ </​file>​
  
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   * **[[http://​dokuwiki.nausch.org/​doku.php/​|Zurück zur Startseite]]**   * **[[http://​dokuwiki.nausch.org/​doku.php/​|Zurück zur Startseite]]**
  
-~~DISCUSSION~~+
  • centos/ssh-install.txt
  • Zuletzt geändert: 20.04.2018 10:30.
  • (Externe Bearbeitung)