SSH-KEYGEN(1)SSH-KEYGEN(1)NAMEssh-keygen - authentication key generation
SYNOPSISssh-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-F hostname [-f known_hosts_file]
ssh-keygen-H [-f known_hosts_file]
ssh-keygen-R hostname [-f known_hosts_file]
DESCRIPTION
The ssh-keygen utility 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. The system administrator can
also use this to generate host keys..
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 char‐
acters. (English prose has only 1-2 bits of entropy per word and pro‐
vides 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 considered 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 program prompts for the file
containing the private keys, for the passphrase if
the key has one, and for the new comment.
This option only applies to rsa1 (SSHv1) keys.
-C comment
Provides the new comment.
-e
This option reads a private or public OpenSSH key
file and prints the key in a "SECSH" Public Key
File Format to stdout. This option allows export‐
ing keys for use by several other SSH implementa‐
tions.
-f
Specifies the filename of the key file.
-F
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 can also be used in conjunction with the -H
option to print found keys in a hashed format.
-H
Hash a known_hosts 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 pub‐
lic) key file in SSH2-compatible format and prints
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 other SSH implementations.
-l
Shows the fingerprint of the specified private or
public key file.
-N new_passphrase
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 pri‐
vate 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 SSHv1 protocol.
-R hostname
Removes all keys belonging to hostname from a
known_hosts 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 OpenSSH format file
and prints an OpenSSH public key to stdout.
EXIT STATUS
The following exit values are returned:
0
Successful completion.
1
An error occurred.
FILES
$HOME/.ssh/identity
This file contains the RSA private key for
the SSHv1 protocol. This file should not be
readable by anyone but the user. It is pos‐
sible to specify a passphrase when generat‐
ing 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 SSHv1 protocol. The contents of this
file should be added to $HOME/.ssh/autho‐
rized_keys 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/id_dsa
$HOME/.ssh/id_rsa
These files contain, respectively, the DSA
or RSA private key for the SSHv2 protocol.
These files 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 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/id_dsa.pub
$HOME/.ssh/id_rsa.pub
These files contain, respectively, the DSA
or RSA public key for the SSHv2 protocol.
The contents of these files should be added,
respectively, to $HOME/.ssh/authorized_keys
on all machines where you wish to log in
using DSA or RSA authentication. There is no
need to keep the contents of these files
secret.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬─────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼─────────────────┤
│Interface Stability │ Committed │
└────────────────────┴─────────────────┘
SEE ALSOssh(1), ssh-add(1), ssh-agent(1), sshd(1M), attributes(5)
Feb 17, 2009 SSH-KEYGEN(1)
