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 -F hostname [-f known_hosts_file]
ssh-keygen -H [-f known_hosts_file]
ssh-keygen -R hostname [-f known_hosts_file]
ssh-keygen -U reader [-f input_keyfile]
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]
[-W
generator]
DESCRIPTION
ssh-keygen generates, manages and converts authentication
keys for
ssh(1). ssh-keygen can create RSA keys for use by SSH pro-
tocol 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.
ssh-keygen is also used to generate groups for use in
Diffie-Hellman
group exchange (DH-GEX). See the MODULI GENERATION section
for details.
Normally each user wishing to use SSH with RSA or DSA au-
thentication runs
this once to create the authentication key in ~/.ssh/identi-
ty,
~/.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
contain a mix of upper and lowercase letters, numbers, and
non-alphanu-
meric 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
corresponding
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 com-
ment is initial-
ized 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:
-a trials
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
file.
-b bits
Specifies the number of bits in the key to create.
Minimum is
512 bits. Generally, 2048 bits is considered suffi-
cient. The
default is 2048 bits.
-C comment
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 pro-
gram will prompt for the file containing the private
SSH implementations.
-F hostname
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 conjunc-
tion with the
-H option to print found keys in a hashed format.
-f filename
Specifies the filename of the key file.
-G output_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 re-
source records
using the -r command.
-H Hash a known_hosts file. This replaces all host-
names and ad-
dresses with hashed representations within the spec-
ified 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.
-i This option will read an unencrypted private (or
public) key file
in SSH2-compatible format and print an OpenSSH com-
patible private
(or public) key to stdout. ssh-keygen also reads
the `SECSH
Public Key File Format'. This option allows import-
ing keys from
several commercial SSH implementations.
-l Show fingerprint of specified public key file. Pri-
vate RSA1 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 Silence ssh-keygen. Used by /etc/rc when creating a
new key.
-R hostname
Removes all keys belonging to hostname from a
known_hosts file.
This option is useful to delete hashed hosts (see
the -H option
above).
-r hostname
Print the SSHFP fingerprint resource record named
hostname for
the specified public key file.
-S start
Specify start point (in hex) when generating candi-
date moduli for
DH-GEX.
-T output_file
Test DH group exchange candidate primes (generated
using the -G
option) for safety.
-t type
Specifies the type of key to create. The possible
values are
``rsa1'' for protocol version 1 and ``rsa'' or
``dsa'' for proto-
col version 2.
-U reader
Upload an existing RSA private key into the smart-
card in reader.
-v Verbose mode. Causes ssh-keygen to print debugging
messages
about its progress. This is helpful for debugging
moduli genera-
tion. Multiple -v options increase the verbosity.
The maximum
Exchange (DH-GEX) protocol. Generating these groups is a
two-step pro-
cess: first, candidate primes are generated using a fast,
but memory in-
tensive process. These candidate primes are then tested for
suitability
(a CPU-intensive process).
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 speci-
fies a different start point (in hex).
Once a set of candidates have been generated, they must be
tested 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 primali-
ty tests.
This may be overridden using the -a option. The DH genera-
tor value will
be chosen automatically for the prime under consideration.
If a specific
generator is desired, it may be requested using the -W op-
tion. 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.
FILES
~/.ssh/identity
Contains the protocol version 1 RSA authentication
identity of
the user. This file should not be readable by any-
authentica-
tion. The contents of this file should be added to
~/.ssh/authorized_keys on all machines where the us-
er wishes to
log in using RSA authentication. There is no need
to keep the
contents of this file secret.
~/.ssh/id_dsa
Contains the protocol version 2 DSA authentication
identity of
the user. This file should not be readable by any-
one but the us-
er. 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 automatical-
ly 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 at-
tempt is made.
~/.ssh/id_dsa.pub
Contains the protocol version 2 DSA public key for
authentica-
tion. The contents of this file should be added to
~/.ssh/authorized_keys on all machines where the us-
er wishes to
log in using public key authentication. There is no
need to keep
the contents of this file secret.
~/.ssh/id_rsa
Contains the protocol version 2 RSA authentication
identity of
the user. This file should not be readable by any-
one but the us-
er. 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 automatical-
ly 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 at-
tempt is made.
~/.ssh/id_rsa.pub
Contains the protocol version 2 RSA public key for
ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)
J. Galbraith and R. Thayer, SECSH Public Key File Format,
draft-ietf-
secsh-publickeyfile-01.txt, March 2001, work in progress ma-
terial.
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 fea-
tures and
created OpenSSH. Markus Friedl contributed the support for
SSH protocol
versions 1.5 and 2.0.
OpenBSD 3.8 September 25, 1999
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