User Commands ssh-keygen(1)
NAME
ssh-keygen - authentication key generation
SYNOPSIS
ssh-keygen [-q] [-b bits ] -t type [-N newpassphrase]
[-C comment] [-f outputkeyfile]
ssh-keygen -p [-P oldpassphrase] [-N newpassphrase]
[-f keyfile]
ssh-keygen -i [-f inputkeyfile]
ssh-keygen -e [-f inputkeyfile]
ssh-keygen -y [-f inputkeyfile]
ssh-keygen -c [-P passphrase] [-C comment] [-f keyfile]
ssh-keygen -l [-f inputkeyfile]
ssh-keygen -B [-f inputkeyfile]
ssh-keygen -F hostname [-f knownhostsfile]
ssh-keygen -H [-f knownhostsfile]
ssh-keygen -R hostname [-f knownhostsfile]
DESCRIPTION
The ssh-keygen utility generates, manages, and converts
authentication keys for ssh(1). ssh-keygen can create RSA
keys for use by SH protocol version 1 and RSA or DSA keys
for use by SH protocol version 2. The type of key to be
generated is specified with the -t option.
Normally, each user wishing to use SH with RSA or DSA
authentication runs this once to create the authentication
key in $HOME/.ssh/identity, $HOME/.ssh/iddsa, or
$HOME/.ssh/idrsa. The system administrator can also use
this to generate host keys..
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User Commands ssh-keygen(1)
Ordinarily, 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 with the ``.pub''
extension appended. The program also asks for a passphrase.
The passphrase can be empty to indicate no passphrase (host
keys must have empty passphrases), or it can be a string of
arbitrary length. Good passphrases are 10-30 characters
long, are not simple sentences or otherwise easy to guess,
and contain a mix of uppercase and lowercase letters,
numbers, and non-alphanumeric characters. (English prose has
only 1-2 bits of entropy per word and provides very poor
passphrases.) If a passphrase is set, it must be at least 4
characters long.
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, you have to generate a new
key and copy the corresponding public key to other machines.
For RSA, 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 to
place the keys to activate them.
OPTIONS
The following options are supported:
-b bits Specifies the number of bits in the key
to create. The minimum number is 512
bits. Generally, 1024 bits is con-
sidered sufficient. Key sizes above
that no longer improve security but
make things slower. The default is 1024
bits.
-B Shows the bubblebabble digest of the
specified private or public key file.
-c Requests changing the comment in the
private and public key files. The pro-
gram prompts for the file containing
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User Commands ssh-keygen(1)
the private keys, for the passphrase if
the key has one, and for the new com-
ment.
This option only applies to rsa1
(SHv1) keys.
-C comment Provides the new comment.
-e This option reads a private or public
OpenSH key file and prints the key in
a "SECSH" Public Key File Format to
stdout. This option allows exporting
keys for use by several other SH
implementations.
-f Specifies the filename of the key file.
-F Search for the specified hostname in a
knownhosts file, listing any
occurrences found. This option is use-
ful to find hashed host names or
addresses and can also be used in con-
junction with the -H option to print
found keys in a hashed format.
-H Hash a knownhosts file. This replaces
all host names 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 does not modify existing hashed
host names and is therefore safe to use
on files that mix hashed and non-hashed
names.
-i This option reads an unencrypted
private (or public) key file in SH2-
compatible format and prints an OpenSH
compatible private (or public) key to
stdout. ssh-keygen also reads the
"SECSH" Public Key File Format. This
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User Commands ssh-keygen(1)
option allows importing keys from
several other SH implementations.
-l Shows the fingerprint of the specified
private or public key file.
-N newpassphrase Provides the new passphrase.
-p Requests changing the passphrase of a
private key file instead of creating a
new private key. The program prompts
for the file containing the private
key, for the old passphrase, and
prompts twice for the new passphrase.
-P passphrase Provides the (old) passphrase.
-q Silences ssh-keygen.
-t type Specifies the algorithm used for the
key, where type is one of rsa, dsa, and
rsa1. Type rsa1 is used only for the
SHv1 protocol.
-R hostname Removes all keys belonging to hostname
from a knownhosts file. This option is
useful to delete hashed hosts. See -H.
-x Obsolete. Replaced by the -e option.
-X Obsolete. Replaced by the -i option.
-y This option reads a private OpenSH
format file and prints an OpenSH pub-
lic key to stdout.
EXIT STATUS
The following exit values are returned:
0 Successful completion.
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User Commands ssh-keygen(1)
1 An error occurred.
FILES
$HOME/.ssh/identity This file contains the RSA
private key for the SHv1 proto-
col. This file should not be
readable by anyone but the user.
It is possible to specify a
passphrase when generating the
key; that passphrase is 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.
sshd(1M) reads this file when a
login attempt is made.
$HOME/.ssh/identity.pub This file contains the RSA public
key for the SHv1 protocol. The
contents of this file should be
added to
$HOME/.ssh/authorizedkeys on all
machines where you wish to log in
using RSA authentication. There
is no need to keep the contents
of this file secret.
$HOME/.ssh/iddsa These files contain, respec-
$HOME/.ssh/idrsa tively, the DSA or RSA private
key for the SHv2 protocol. These
files should not be readable by
anyone but the user. It is possi-
ble to specify a passphrase when
generating the key; that
passphrase is used to encrypt the
private part of the file using
3DES. Neither of these files is
automatically accessed by ssh-
keygen but is offered as the
default file for the private key.
sshd(1M) reads this file when a
login attempt is made.
$HOME/.ssh/iddsa.pub These files contain, respec-
$HOME/.ssh/idrsa.pub tively, the DSA or RSA public key
for the SHv2 protocol. The con-
tents of these files should be
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User Commands ssh-keygen(1)
added, respectively, to
$HOME/.ssh/authorizedkeys on all
machines where you wish to log in
using DSA or RSA authentication.
There is no need to keep the con-
tents of these files secret.
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWsshcu
Interface Stability Committed
SEE ALSO
ssh(1), ssh-add(1), ssh-agent(1), sshd(1M), attributes(5)
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