centos:ssh-install

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centos:ssh-install [12.11.2016 21:04. ] – [Erzeugung eines Schlüssel] djangocentos:ssh-install [13.11.2016 16:46. ] – [Zielverzeichnis anlegen und öffentlichen Schlüssel kopieren] django
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 ====== Secure Shell - ssh ====== ====== Secure Shell - ssh ======
-{{: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 Lösung mittels [[http://www.openssh.org|OpenSSH]].+{{: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]].
  
 ===== openSSH - Programmsuite ===== ===== openSSH - Programmsuite =====
Zeile 1011: Zeile 1011:
  
 ===== ssh in der Praxis ===== ===== ssh in der Praxis =====
-Auch wenn das Passwort bei **ssh** verschlüsselt übertragen wird, lohnt ein Blick auf die Alternative  **//RSA/DSA-Authentifizierung//**. Bei dieser Variante muss gar kein Passwort über das Netz übertragen werden. Normalerweise muss der User beim Zugriff via ssh auf einen entfernten Rechner sein Passwort eingeben. Zum einen wollen wir aus Sicherheitsgründen darauf verzichten und zum anderen kann dies doch auf Dauer doch als etwas nervig empfunden werden.  +Auch wenn Passworte bei **ssh** verschlüsselt übertragen werden, wollen wir **__zwei wesentliche Aspekte__** bei Verwendung der **ssh** berücksichtigen: 
-Einfacher geht dies über asymetrische Schlüssel.  +  - 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! 
-==== Erzeugung eines 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. 
-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. +
-Enter file in which to save the key (/home/django/.ssh/id_rsa):  +
-Enter passphrase (empty for no passphrase):  +
-Enter same passphrase again:  +
-Your identification has been saved in /home/django/.ssh/id_rsa. +
-Your public key has been saved in /home/django/.ssh/id_rsa.pub. +
-The key fingerprint is: +
-2b:83:69:f2:76:e8:c9:8b:cf:34:c8:c2:ae:2b:e1:ee django@host.nausch.org</code>+
  
-Oder die Erstellung eines [[http://ed25519.cr.yp.to/|ed25519]] Schlüssels. [[https://de.wikipedia.org/wiki/Curve25519|Ed25519]] ist ein Elliptic Curve Signature Schema, welches beste Sicherheit bei vertretbatren Aufwand verspricht, als ECDSA oder DSA dies versprechen. 
-   $ ssh-keygen -t ed25519 -o -a 100 -C django@nausch.org -f ~/.ssh/id_ed25519_dmz 
  
  
 +Zum Erstellen eines Schlüsselpaares nutzen wir das Programm **ssh-keygen**. Einen Überberlick über die möglichen Optionen erhalten wir beim Abruf der zugehörigen **manpage**.
 +   # man ssh-keygen
  
-Die //passphrase// die man hier angibt, wird später beim Anmelden auf dem entfernten Rechner abgefragt, oder vom //ssh-agent// bei der Anmeldung mitübergeben.+<code>SSH-KEYGEN(1)                          BSD General Commands Manual                         SSH-KEYGEN(1)
  
-Nun liegen in dem Verzeichnis **/home/django/.ssh** zwei Dateien: +NAME 
-<code>[django@host .ssh]$ ll +     ssh-keygen — authentication key generation, management and conversion
-insgesamt 24 +
--rw------- 1 django django 3311 22. Apr 22:11 id_rsa +
--rw-r--r-- 1 django django  748 22. Apr 22:11 id_rsa.pub</code>+
  
-**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.  +SYNOPSIS 
-==== Zielverzeichnis anlegen und öffentlichen Schlüssel kopieren  ==== +     ssh-keygen [-q] [-b bits] [-t type] [-N new_passphrase] [-C comment] [-f output_keyfile] 
-Auf dem Zielrechner legen wir nun das Verzeichnis **.ssh** an und schützen es entsprechend.+     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 ...
  
-  [django@zielhost django]$ mkdir .ssh +DESCRIPTION 
-  [django@zielhost django]$ chmod 700 .ssh+     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.
  
-Den öffentlichen Schlüssel kopieren wir dann wie folgt auf das Zielsystem: +     ssh-keygen is also used to generate groups for use in Diffie-Hellman group exchange (DH-GEX).  See 
-  [django@host .ssh]$  scp /home/django/.ssh/id_rsa.pub zielhost:/home/django/.ssh/id_rsa.pub+     the MODULI GENERATION section for details.
  
-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: +     Finally, ssh-keygen can be used to generate and update Key Revocation Lists, and to test whether 
-  [django@zielhost .ssh]$ cat id_rsa.pub >> authorized_keys +     given keys have been revoked by one.  See the KEY REVOCATION LISTS section for details.
-Zu guter Letzt passen wir noch die Berechtigungen an und löschen die nicht mehr benötigte **id_rsa.pub** +
-  [django@zielhost .ssh]$ chmod 600 authorized_keys +
-  [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**//.+     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.
  
-   $ ssh-copy-id -i ~/.ssh/id_rsa.pub testhost.intra.nausch.org+     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.
  
-Die Angabe ''~/.ssh/id_rsa.pub'' entspricht dabei dem Public-Key und ''testhost.intra.nausch.org +     There is no way to recover a lost passphrase.  If the passphrase is lost or forgotten, a new key 
-'' dem gewünschten Zielhost. +     must be generated and the corresponding public key copied to other machines. 
-</WRAP> + 
-==== authorized_keys vs. authorized_keys2 ==== +     For RSA1 keys, there is also a comment field in the key file that is only for convenience to the 
-<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>+     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.
  
-==== Interoperabilität ==== 
 === Liste der unterstützten Cipher === === Liste der unterstützten Cipher ===
    # ssh -Q cipher    # ssh -Q cipher
Zeile 1106: Zeile 1577:
 umac-128-etm@openssh.com</code> umac-128-etm@openssh.com</code>
  
-=== Liste der unterstütznen Schlüssel Typen ====+=== Liste der unterstützten Schlüssel Typen ====
    # ssh -Q key    # ssh -Q key
 <code>ssh-rsa <code>ssh-rsa
Zeile 1138: Zeile 1609:
 gss-group1-sha1- gss-group1-sha1-
 gss-group14-sha1-</code> 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 same passphrase again: 
 +Your identification has been saved in /home/django/.ssh/id_ed25519_dmz.
 +Your public key has been saved in /home/django/.ssh/id_ed25519_dmz.pub.
 +The key fingerprint is:
 +a3:03:59:5c:1b:d3:60:2a:93:77:2a:9f:9d:fc:e8:68 django@nausch.org
 +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.
 +
 +Nun liegen in dem Verzeichnis **/home/django/.ssh** zwei weitere Dateien:
 +  # ll ~/.ssh/*ed25519*
 +<code>-rw-------. 1 django django 464  2. Nov 21:43 /home/django/.ssh/id_ed25519_dmz
 +-rw-r--r--. 1 django django  99  2. Nov 21:43 /home/django/.ssh/id_ed25519_dmz.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. 
 +==== Zielverzeichnis anlegen und öffentlichen Schlüssel kopieren  ====
 +Auf dem Zielrechner legen wir nun das Verzeichnis **.ssh** an und schützen es entsprechend.
 +
 +  [django@zielhost django]$ mkdir .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:
 +   $  scp /home/django/.ssh/id_rsa4096_dmz.pub zielhost:/home/django/.ssh/key.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:
 +   $ cat key.pub >> authorized_keys
 +Zu guter Letzt passen wir noch die Berechtigungen an und löschen die nicht mehr benötigte **id_rsa.pub**
 +   $ chmod 600 authorized_keys
 +   $ rm key.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**//.
 +
 +  * RSA-Key <code> $ ssh-copy-id -i ~/.ssh/id_rsa.pub testhost.intra.nausch.org</code>
 +  * 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''.
 +</WRAP>
 +==== 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>
 +
  
 ===== ssh-Daemon ===== ===== ssh-Daemon =====
  • centos/ssh-install.txt
  • Zuletzt geändert: 20.05.2021 07:50.
  • von 127.0.0.1