SSH-KEYGEN(1) SSH SSH-KEYGEN(1)NAMEssh-keygen - authentication key pair generation
SYNOPSISssh-keygen [-b bits] [-f file] [-N new_passphrase] [-C comment]
ssh-keygen-p [-P old_passphrase] [-N new_passphrase]
ssh-keygen-c [-P passphrase] [-C comment]
ssh-keygen-u [-f file] [-P passphrase]
DESCRIPTION
Ssh-keygen generates and manages authentication keys for ssh(1). Nor‐
mally each user wishing to use ssh with RSA authentication runs this
once to create the authentication key in $HOME/.ssh/identity. Addi‐
tionally, the system administrator may use this to generate host keys.
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 empty passphrase), or it may be a string of arbitrary length.
Good passphrases are 10-30 characters long and are not simple sentences
or otherwise easily guessable (English prose has only 1-2 bits of
entropy per word, and provides very bad passphrases). 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 will have to generate a new key and copy the
corresponding public key to other machines.
USING GOOD, UNGUESSABLE PASSPHRASES IS STRONGLY RECOMMENDED. EMPTY
PASSPHRASES SHOULD NOT BE USED UNLESS YOU UNDERSTAND WHAT YOU ARE
DOING.
There is also a comment field in the key file that is only for conve‐
nience 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.
The cipher to be used when encrypting keys with a passphrase is defined
in ssh.h. Using the -u option, keys encrypted in any supported cipher
can be updated to use this default cipher.
OPTIONS-b bits
Specifies the number of bits in the key to create. Minimum is
512 bits. Generally 1024 bits is considered sufficient, and key
sizes above that no longer improve security but make things
slower. The default is 1024 bits.
-c Requests changing the comment in the private and public key
files. The program will prompt for the file containing the pri‐
vate keys, for passphrase if the key has one, and for the new
comment.
-f Specifies the file name in which to load/store the key.
-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.
-u Requests that the key's cipher is changed to the current default
cipher (determined at compile-time - currently 3DES).
-C Provides the new comment.
-N Provides the new passphrase.
-P Provides the (old) passphrase.
FILES
$HOME/.ssh/random_seed
Used for seeding the random number generator. This file should
not be readable by anyone but the user. This file is created the
first time the program is run, and is updated every time.
$HOME/.ssh/identity
Contains the 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.
$HOME/.ssh/identity.pub
Contains the public key for authentication. The contents of this
file should be added to $HOME/.ssh/authorized_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.
AUTHOR
Tatu Ylonen <ylo@ssh.fi>
SEE ALSOssh(1), sshd(8), ssh-agent(1), ssh-add(1)SSH November 8, 1995 SSH-KEYGEN(1)
