$ ssh-keygen [option]
-f [file] : 出力ファイルを指定
-t [type] : 暗号化方式 (rsa , dsa)
$ ssh-keygen -t [type] -N [new-password] -c [comment] -f [file]
$ ssh-keygen -P [old-password] -N [new-password] -f [file]
$ ssh-keygen -i -f [file]
$ ssh-keygen -l -f [file]
ssh-keygen -- authentication key generation, management and conversion
ssh-keygen [-q] [-b bits] -t type [-N new_passphrase] [-C comment]
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] [-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 -k -f krl_file [-u] [-s ca_public] [-z version_number] file ...
ssh-keygen -Q -f krl_file file ...
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 argu-
ments, ssh-keygen will generate an RSA key for use in SSH protocol 2 connec-
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and to test whether given keys have been revoked by one.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_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 characters long, are not simple sentences or oth-
erwise 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-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
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.
Specifies the number of primality tests to perform when screening
DH-GEX candidates using the -T command.
-B Show the bubblebabble digest of specified private or public key
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. Gener-
ally, 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.
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.
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 sec-
tion 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.
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.
Specifies the filename of the key 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 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 cer-
tificate. Please see the CERTIFICATES section for details.
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 compati-
ble private (or public) key to stdout.
Exit after screening the specified number of lines while performing
DH candidate screening using the -T option.
Start screening at the specified line number while performing DH
candidate screening using the -T option.
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
software, 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 for-
mat 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 fingerprint. If com-
bined with -v, an ASCII art representation of the key is supplied
with the fingerprint.
Specify the amount of memory to use (in megabytes) when generating
candidate moduli for DH-GEX.
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''.
Provides the new passphrase.
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
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 permissions so permissions may be added
Forces the execution of command instead of any shell or com-
mand specified by the user when the certificate is used for
Disable ssh-agent(1) forwarding (permitted by default).
Disable port forwarding (permitted by default).
no-pty Disable PTY allocation (permitted by default).
Disable execution of ~/.ssh/rc by sshd(8) (permitted by
Disable X11 forwarding (permitted by default).
Allows ssh-agent(1) forwarding.
Allows port forwarding.
Allows PTY allocation.
Allows execution of ~/.ssh/rc by sshd(8).
Allows X11 forwarding.
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.
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.
Removes all keys belonging to hostname from a known_hosts file.
This option is useful to delete hashed hosts (see the -H option
Print the SSHFP fingerprint resource record named hostname for the
specified public key file.
Specify start point (in hex) when generating candidate moduli for
Certify (sign) a public key using the specified CA key. Please see
the CERTIFICATES section for details.
When generating a KRL, -s specifies a path to a CA public key file
used to revoke certificates directly by key ID or serial number.
See the KEY REVOCATION LISTS section for details.
Test DH group exchange candidate primes (generated using the -G
option) for safety.
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.
-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 cre-
Specify a validity interval when signing a certificate. A validity
interval may consist of a single time, indicating that the certifi-
cate is valid beginning now and expiring at that time, or may con-
sist of two times separated by a colon to indicate 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 specified as a YYYYMMDD date, a
YYYYMMDDHHMMSS time or a relative time starting with a plus charac-
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, Jan-
uary 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.
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.
Specifies a serial number to be embedded in the certificate to dis-
tinguish 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
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-
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 cho-
sen automatically for the prime under consideration. If a specific genera-
tor 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 /etc/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.
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 cer-
tificate rather than trusting many user/host keys. Note that OpenSSH cer-
tificates are a different, and much simpler, format to the X.509 certifi-
cates used in ssl(8).
ssh-keygen supports two types of certificates: user and host. User certifi-
cates authenticate users to servers, whereas host certificates authenticate
server hosts to users. To generate a user certificate:
$ 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 pub-
lic 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, generated 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 certificate options. A certificate option may disable
features of the SSH session, may be valid only when presented from particu-
lar 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 certifi-
cate 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
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 specify keys or certificates to be revoked using a com-
pact format, taking as little a one bit per certificate 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 cer-
tificates by serial number or key ID without having 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
Revokes a certificate with the specified serial number. Serial num-
bers are 64-bit values, not including zero and may be expressed in
decimal, hex or octal. If two serial numbers are specified sepa-
rated 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.
Revokes a certificate with the specified key ID string. The CA key
must have been specified on the ssh-keygen command line using the -s
Revokes the specified key. If a certificate is listed, then it is
revoked as a plain 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
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.
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 authenti-
cation. There is no need to keep the contents of this file secret.
Contains the protocol version 2 DSA, ECDSA 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 generat-
ing 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
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.
Contains Diffie-Hellman groups used for DH-GEX. The file format is
described in moduli(5).
ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)
The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006.
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.