SSH-KEYGEN linux command manual
SSH-KEYGEN(1) BSD General Commands Manual SSH-KEYGEN(1)
NAME
ssh-keygen - authentication key generation, management and conversion
SYNOPSIS
ssh-keygen [-q] [-b bits] -t type [-N new_passphrase] [-C comment]
[-f output_keyfile]
ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile]
ssh-keygen -i [-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 reader
ssh-keygen -U reader [-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.
Normally each user wishing to use SSH with RSA or DSA authentication
runs this once to create the authentication key in $HOME/.ssh/identity,
$HOME/.ssh/id_dsa or $HOME/.ssh/id_rsa. Additionally, the system admin-
istrator may use this to generate host keys, as seen in /etc/rc.
Normally this program generates the key and asks for a file in which to
store the private key. The public key is stored in a file with the same
name but ".pub" appended. The program also asks for a passphrase. The
passphrase may be empty to indicate no passphrase (host keys must have
an empty passphrase), or it may be a string of arbitrary length. A
passphrase is similar to a password, except it can be a phrase with a
series of words, punctuation, numbers, whitespace, or any string of
characters you want. Good passphrases are 10-30 characters long, are
not simple sentences or otherwise easily guessable (English prose has
only 1-2 bits of entropy per character, and provides very bad
passphrases), and contain a mix of upper and lowercase letters, numbers,
and non-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 correspond-
ing 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:
-b bits
Specifies the number of bits in the key to create. Minimum is
512 bits. Generally, 1024 bits is considered sufficient. The
default is 1024 bits.
-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.
-e This option will read a private or public OpenSSH key file and
print the key in a 'SECSH Public Key File Format' to stdout.
This option allows exporting keys for use by several commercial
SSH implementations.
-f filename
Specifies the filename of the key file.
-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
'SECSH Public Key File Format'. This option allows importing
keys from several commercial SSH implementations.
-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.
-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.
-y This option will read a private OpenSSH format file and print an
OpenSSH public key to stdout.
-t type
Specifies the type of the key to create. The possible values
are "rsa1" for protocol version 1 and "rsa" or "dsa" for proto-
col version 2.
-B Show the bubblebabble digest of specified private or public key
file.
-C comment
Provides the new comment.
-D reader
Download the RSA public key stored in the smartcard in reader.
-N new_passphrase
Provides the new passphrase.
-P passphrase
Provides the (old) passphrase.
-U reader
Upload an existing RSA private key into the smartcard in reader.
FILES
$HOME/.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.
$HOME/.ssh/identity.pub
Contains the protocol version 1 RSA public key for authentica-
tion. The contents of this file should be added to
$HOME/.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.
$HOME/.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 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.
$HOME/.ssh/id_dsa.pub
Contains the protocol version 2 DSA public key for authentica-
tion. The contents of this file should be added to
$HOME/.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.
$HOME/.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 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.
$HOME/.ssh/id_rsa.pub
Contains the protocol version 2 RSA public key for authentica-
tion. The contents of this file should be added to
$HOME/.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.
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 pro-
tocol versions 1.5 and 2.0.
SEE ALSO
ssh(1), ssh-add(1), ssh-agent(1), sshd(8)
J. Galbraith and R. Thayer, SECSH Public Key File Format, draft-ietf-
secsh-publickeyfile-01.txt, March 2001, work in progress material.
BSD September 25, 1999 BSD