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SSH-KEYGEN(1)							 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  num_trials]  [-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

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 or RSA keys for use by SSH protocol  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.

       Normally	 each  user  wishing to use SSH with public key authentication
       runs this once to create the  authentication  key  in  ~/.ssh/identity,
       ~/.ssh/id_ecdsa,	 ~/.ssh/id_dsa	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 char‐
       acters  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 let‐
       ters, numbers, and non-alphanumeric 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 activated.

       The options are as follows:

       -A     For each of the key types (rsa1, rsa, dsa and ecdsa)  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 trials
	      Specifies the number of primality tests to perform when  screen‐
	      ing DH-GEX candidates using the -T command.

       -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.

       -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 CER‐
	      TIFICATES 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 commercial 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 conjunction 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 representations within the specified file;
	      the original content is moved to a  file	with  a	 .old  suffix.
	      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 host‐
	      names 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.

       -K checkpt
	      Write the last line processed to the file checkpt while perform‐
	      ing DH candidate screening using the -T option.	This  will  be
	      used to skip lines in the input file that have already been pro‐
	      cessed if the job is restarted.  This  option  allows  importing
	      keys  from  other	 software,  including  several	commercial SSH
	      implementations.	The default import format is ``RFC4716''.

       -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 fingerprint.
	      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 generat‐
	      ing candidate moduli for DH-GEX.

       -m key_format
	      Specify  a key format for the -i (import) or -e (export) conver‐
	      sion 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  princi‐
	      pals may be specified, separated by commas.  Please see the CER‐
	      TIFICATES 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  cer‐
	      tificates are:

       clear  Clear  all enabled permissions.  This is useful for clearing the
	      default set of permissions so permissions may be added individu‐
	      ally.

       force-command Ns = Ns command
	      Forces  the execution of command instead of any shell or command
	      specified by the user when the certificate is used for authenti‐
	      cation.

       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 Ns = Ns address_list
	      Restrict the source addresses from which the certificate is con‐
	      sidered  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.

       -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     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 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''  or
	      ``rsa'' for protocol version 2.

       -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	 indi‐
	      cate an explicit time interval.  The start time may be specified
	      as a date in YYYYMMDD format, a time in YYYYMMDDHHMMSS 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 speci‐
	      fied 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 gener‐
	      ation.  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 stdout.

       -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.

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	 suit‐
       ability (a CPU-intensive 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:

       Dl # 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  tested  for
       suitability.   This may be performed using the -T option.  In this mode
       ssh-keygen will read candidates from standard input (or a  file	speci‐
       fied using the -f option).  For example:

       Dl # 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 consideration.  If a
       specific generator is desired, it may be requested using the -W option.
       Valid generator values are 2, 3, and 5.

       Screened	 DH  groups may be installed in /boot/common/settings/ssh/mod‐
       uli.  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 certificate  rather  than  trusting  many  user/host
       keys.   Note  that  OpenSSH certificates are a different, and much sim‐
       pler, 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 certificate:

       Dl $ 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:

       Dl $ 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 pro‐
       viding the token library using -D and identifying the CA key by provid‐
       ing its public half as an argument to -s :

       Dl $ 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, generated certificates are valid for
       all users or hosts.  To generate a certificate for a specified  set  of
       principals:

       Dl  $  ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub Dl "$
       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  certificate  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  documenta‐
       tion 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 cer‐
       tificate	 that  is  presented  at a time outside this range will not be
       considered valid.  By default, certificates  have  a  maximum  validity
       interval.

       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.

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 generating
	      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  authentica‐
	      tion.    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_rsa
	      Contains the protocol version 2 DSA, ECDSA or RSA authentication
	      identity	of the user.  This file should not be readable by any‐
	      one 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_rsa.pub
	      Contains the protocol version 2 DSA, ECDSA 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.

       /boot/common/settings/ssh/moduli
	      Contains Diffie-Hellman groups used for DH-GEX.  The file format
	      is described in moduli(5).

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  Campbell, 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 versions 1.5 and 2.0.

			       October 16 2011			 SSH-KEYGEN(1)
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