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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 [-f input_keyfile]
       ssh-keygen -e [-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] [-W gener‐
       ator]
       ssh-keygen  -s  ca_key -I certificate_identity [-h] [-n principals] [-O
       constraint] [-V validity_interval] file ...
       ssh-keygen -L [-f input_keyfile]

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 RSA or DSA keys for use by SSH protocol version 2.	 The  type  of
       key  to be generated is specified with the -t option.  If invoked with‐
       out 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 RSA or DSA authentication
       runs this once to create the  authentication  key  in  ~/.ssh/identity,
       ~/.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 copied to the corre‐
       sponding public key 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 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.

       -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.

       -e     This option will read a private or public OpenSSH key  file  and
	      print  the key in RFC 4716 SSH Public Key File Format to stdout.
	      This option allows exporting keys for use by 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 SSH2-compatible format and print an  OpenSSH  compatible
	      private  (or  public)  key to stdout.  ssh-keygen also reads the
	      RFC 4716 SSH Public Key File Format.  This option allows import‐
	      ing keys from several commercial SSH implementations.

       -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.

       -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 constraint
	      Specify  a  certificate  constraint  when	 signing  a key.  This
	      option may be specified multiple times.  Please see the CERTIFI‐
	      CATES  section  for details.  The constraints that are valid for
	      user certificates 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 constraints 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.  Used by /etc/rc when creating a new key.

       -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 ``rsa'' or ``dsa'' for pro‐
	      tocol 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.

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 /usr/pkg/usr/pkg/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 an optional set of constraints that are signed by a Certifi‐
       cation 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 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 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.   In
       both  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 constraints.	A constrained certifi‐
       cate 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 constraints, 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 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 128-bit AES.  This file is not automati‐
	      cally 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
	      Contains the protocol version 2 DSA 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 automati‐
	      cally  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
	      Contains	the  protocol version 2 DSA 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 public key authentication.  There  is  no  need  to
	      keep the contents of this file secret.

       ~/.ssh/id_rsa
	      Contains	the  protocol version 2 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 automati‐
	      cally 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_rsa.pub
	      Contains the protocol version 2 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  public  key authentication.  There is no need to
	      keep the contents of this file secret.

       /usr/pkg/usr/pkg/etc/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.

				March 13 2010			 SSH-KEYGEN(1)
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