[gssapi-openssh.git] / openssh / ssh-keygen.0

SSH-KEYGEN(1)              OpenBSD Reference 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 -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 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.  If invoked without any
     arguments, ssh-keygen will generate an RSA key for use in SSH protocol 2
     connections.

     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 authentication runs
     this once to create the authentication key in ~/.ssh/identity,
     ~/.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
     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 se-
     ries of words, punctuation, numbers, whitespace, or any string of charac-
     ters you want.  Good passphrases are 10-30 characters long, are not sim-
     ple 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-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 comment 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.  For RSA keys,
             the minimum size is 768 bits and the default is 2048 bits.  Gen-
             erally, 2048 bits is considered sufficient.  DSA keys must be ex-
             actly 1024 bits as specified by FIPS 186-2.

     -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 keys, for
             the passphrase if the key has one, and for the new comment.

     -D reader
             Download the RSA public key stored in the smartcard in reader.

     -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 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 conjunction 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 resource records
             using the -r command.

     -H      Hash a known_hosts file.  This replaces all hostnames and ad-
             dresses 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 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 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.

     -M memory
             Specify the amount of memory to use (in megabytes) when generat-
             ing candidate moduli for DH-GEX.

     -N new_passphrase
             Provides the new passphrase.

     -P passphrase
             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 candidate 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 smartcard 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
             is 3.

     -W generator
             Specify desired generator when testing candidate moduli for DH-
             GEX.

     -y      This option will read a private OpenSSH format file and print an
             OpenSSH public key to stdout.

MODULI GENERATION
     ssh-keygen may be used to generate groups for the Diffie-Hellman Group
     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 primality tests.
     This may be overridden using the -a option.  The DH generator value will
     be chosen automatically for the prime under consideration.  If a specific
     generator is desired, it may be requested using the -W option.  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 anyone 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 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.

     ~/.ssh/identity.pub
             Contains the protocol version 1 RSA public key for authentica-
             tion.  The contents of this file should be added to
             ~/.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.

     ~/.ssh/id_dsa
             Contains the protocol version 2 DSA authentication identity of
             the user.  This file should not be readable by anyone 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 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.

     ~/.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 user 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 anyone 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 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.

     ~/.ssh/id_rsa.pub
             Contains the protocol version 2 RSA public key for authentica-
             tion.  The contents of this file should be added to
             ~/.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.

     /etc/moduli
             Contains Diffie-Hellman groups used for DH-GEX.  The file format
             is described in moduli(5).

SEE ALSO
     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 material.

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 protocol
     versions 1.5 and 2.0.

OpenBSD 4.0                   September 25, 1999                             5
Commit	Line	Data
9108f8d9	1	SSH-KEYGEN(1) OpenBSD Reference Manual SSH-KEYGEN(1)
	2
	3	NAME
	4	ssh-keygen - authentication key generation, management and conversion
	5
	6	SYNOPSIS
	7	ssh-keygen [-q] [-b bits] -t type [-N new_passphrase] [-C comment]
	8	[-f output_keyfile]
	9	ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile]
	10	ssh-keygen -i [-f input_keyfile]
	11	ssh-keygen -e [-f input_keyfile]
	12	ssh-keygen -y [-f input_keyfile]
	13	ssh-keygen -c [-P passphrase] [-C comment] [-f keyfile]
	14	ssh-keygen -l [-f input_keyfile]
	15	ssh-keygen -B [-f input_keyfile]
	16	ssh-keygen -D reader
	17	ssh-keygen -F hostname [-f known_hosts_file]
	18	ssh-keygen -H [-f known_hosts_file]
	19	ssh-keygen -R hostname [-f known_hosts_file]
	20	ssh-keygen -U reader [-f input_keyfile]
	21	ssh-keygen -r hostname [-f input_keyfile] [-g]
	22	ssh-keygen -G output_file [-v] [-b bits] [-M memory] [-S start_point]
	23	ssh-keygen -T output_file -f input_file [-v] [-a num_trials] [-W
	24	generator]
	25
	26	DESCRIPTION
	27	ssh-keygen generates, manages and converts authentication keys for
	28	ssh(1). ssh-keygen can create RSA keys for use by SSH protocol version 1
	29	and RSA or DSA keys for use by SSH protocol version 2. The type of key
	30	to be generated is specified with the -t option. If invoked without any
	31	arguments, ssh-keygen will generate an RSA key for use in SSH protocol 2
	32	connections.
	33
	34	ssh-keygen is also used to generate groups for use in Diffie-Hellman
	35	group exchange (DH-GEX). See the MODULI GENERATION section for details.
	36
	37	Normally each user wishing to use SSH with RSA or DSA authentication runs
	38	this once to create the authentication key in ~/.ssh/identity,
	39	~/.ssh/id_dsa or ~/.ssh/id_rsa. Additionally, the system administrator
	40	may use this to generate host keys, as seen in /etc/rc.
	41
	42	Normally this program generates the key and asks for a file in which to
	43	store the private key. The public key is stored in a file with the same
	44	name but ``.pub'' appended. The program also asks for a passphrase. The
	45	passphrase may be empty to indicate no passphrase (host keys must have an
	46	empty passphrase), or it may be a string of arbitrary length. A
	47	passphrase is similar to a password, except it can be a phrase with a se-
	48	ries of words, punctuation, numbers, whitespace, or any string of charac-
	49	ters you want. Good passphrases are 10-30 characters long, are not sim-
	50	ple sentences or otherwise easily guessable (English prose has only 1-2
	51	bits of entropy per character, and provides very bad passphrases), and
	52	contain a mix of upper and lowercase letters, numbers, and non-alphanu-
	53	meric characters. The passphrase can be changed later by using the -p
	54	option.
	55
	56	There is no way to recover a lost passphrase. If the passphrase is lost
	57	or forgotten, a new key must be generated and copied to the corresponding
	58	public key to other machines.
	59
	60	For RSA1 keys, there is also a comment field in the key file that is only
	61	for convenience to the user to help identify the key. The comment can
	62	tell what the key is for, or whatever is useful. The comment is initial-
	63	ized to ``user@host'' when the key is created, but can be changed using
	64	the -c option.
65
66	After a key is generated, instructions below detail where the keys should
67	be placed to be activated.
68
69	The options are as follows:
70
71	-a trials
72	Specifies the number of primality tests to perform when screening
73	DH-GEX candidates using the -T command.
74
75	-B Show the bubblebabble digest of specified private or public key
76	file.
77
78	-b bits
79	Specifies the number of bits in the key to create. For RSA keys,
80	the minimum size is 768 bits and the default is 2048 bits. Gen-
81	erally, 2048 bits is considered sufficient. DSA keys must be ex-
82	actly 1024 bits as specified by FIPS 186-2.
83
84	-C comment
85	Provides a new comment.
86
87	-c Requests changing the comment in the private and public key
88	files. This operation is only supported for RSA1 keys. The pro-
89	gram will prompt for the file containing the private keys, for
90	the passphrase if the key has one, and for the new comment.
91
92	-D reader
93	Download the RSA public key stored in the smartcard in reader.
94
95	-e This option will read a private or public OpenSSH key file and
96	print the key in a `SECSH Public Key File Format' to stdout.
97	This option allows exporting keys for use by several commercial
98	SSH implementations.
99
100	-F hostname
101	Search for the specified hostname in a known_hosts file, listing
102	any occurrences found. This option is useful to find hashed host
103	names or addresses and may also be used in conjunction with the
104	-H option to print found keys in a hashed format.
105
106	-f filename
107	Specifies the filename of the key file.
108
109	-G output_file
110	Generate candidate primes for DH-GEX. These primes must be
111	screened for safety (using the -T option) before use.
112
113	-g Use generic DNS format when printing fingerprint resource records
114	using the -r command.
115
116	-H Hash a known_hosts file. This replaces all hostnames and ad-
117	dresses with hashed representations within the specified file;
118	the original content is moved to a file with a .old suffix.
119	These hashes may be used normally by ssh and sshd, but they do
120	not reveal identifying information should the file's contents be
121	disclosed. This option will not modify existing hashed hostnames
122	and is therefore safe to use on files that mix hashed and non-
123	hashed names.
124
125	-i This option will read an unencrypted private (or public) key file
126	in SSH2-compatible format and print an OpenSSH compatible private
127	(or public) key to stdout. ssh-keygen also reads the `SECSH
128	Public Key File Format'. This option allows importing keys from
129	several commercial SSH implementations.
130
131	-l Show fingerprint of specified public key file. Private RSA1 keys
132	are also supported. For RSA and DSA keys ssh-keygen tries to
133	find the matching public key file and prints its fingerprint.
134
135	-M memory
136	Specify the amount of memory to use (in megabytes) when generat-
137	ing candidate moduli for DH-GEX.
138
139	-N new_passphrase
140	Provides the new passphrase.
141
142	-P passphrase
143	Provides the (old) passphrase.
144
145	-p Requests changing the passphrase of a private key file instead of
146	creating a new private key. The program will prompt for the file
147	containing the private key, for the old passphrase, and twice for
148	the new passphrase.
149
150	-q Silence ssh-keygen. Used by /etc/rc when creating a new key.
151
152	-R hostname
153	Removes all keys belonging to hostname from a known_hosts file.
154	This option is useful to delete hashed hosts (see the -H option
155	above).
156
157	-r hostname
158	Print the SSHFP fingerprint resource record named hostname for
159	the specified public key file.
160
161	-S start
162	Specify start point (in hex) when generating candidate moduli for
163	DH-GEX.
164
165	-T output_file
166	Test DH group exchange candidate primes (generated using the -G
167	option) for safety.
168
169	-t type
170	Specifies the type of key to create. The possible values are
171	``rsa1'' for protocol version 1 and ``rsa'' or ``dsa'' for proto-
172	col version 2.
173
174	-U reader
175	Upload an existing RSA private key into the smartcard in reader.
176
177	-v Verbose mode. Causes ssh-keygen to print debugging messages
178	about its progress. This is helpful for debugging moduli genera-
179	tion. Multiple -v options increase the verbosity. The maximum
180	is 3.
181
182	-W generator
183	Specify desired generator when testing candidate moduli for DH-
184	GEX.
185
186	-y This option will read a private OpenSSH format file and print an
187	OpenSSH public key to stdout.
188
189	MODULI GENERATION
190	ssh-keygen may be used to generate groups for the Diffie-Hellman Group
191	Exchange (DH-GEX) protocol. Generating these groups is a two-step pro-
192	cess: first, candidate primes are generated using a fast, but memory in-
193	tensive process. These candidate primes are then tested for suitability
194	(a CPU-intensive process).
195
196	Generation of primes is performed using the -G option. The desired
197	length of the primes may be specified by the -b option. For example:
198
199	# ssh-keygen -G moduli-2048.candidates -b 2048
200
201	By default, the search for primes begins at a random point in the desired
202	length range. This may be overridden using the -S option, which speci-
203	fies a different start point (in hex).
204
205	Once a set of candidates have been generated, they must be tested for
206	suitability. This may be performed using the -T option. In this mode
207	ssh-keygen will read candidates from standard input (or a file specified
208	using the -f option). For example:
209
210	# ssh-keygen -T moduli-2048 -f moduli-2048.candidates
211
212	By default, each candidate will be subjected to 100 primality tests.
213	This may be overridden using the -a option. The DH generator value will
214	be chosen automatically for the prime under consideration. If a specific
215	generator is desired, it may be requested using the -W option. Valid
216	generator values are 2, 3, and 5.
217
218	Screened DH groups may be installed in /etc/moduli. It is important that
219	this file contains moduli of a range of bit lengths and that both ends of
220	a connection share common moduli.
221
222	FILES
223	~/.ssh/identity
224	Contains the protocol version 1 RSA authentication identity of
225	the user. This file should not be readable by anyone but the us-
226	er. It is possible to specify a passphrase when generating the
227	key; that passphrase will be used to encrypt the private part of
228	this file using 3DES. This file is not automatically accessed by
229	ssh-keygen but it is offered as the default file for the private
230	key. ssh(1) will read this file when a login attempt is made.
231
232	~/.ssh/identity.pub
233	Contains the protocol version 1 RSA public key for authentica-
234	tion. The contents of this file should be added to
235	~/.ssh/authorized_keys on all machines where the user wishes to
236	log in using RSA authentication. There is no need to keep the
237	contents of this file secret.
238
239	~/.ssh/id_dsa
240	Contains the protocol version 2 DSA authentication identity of
241	the user. This file should not be readable by anyone but the us-
242	er. It is possible to specify a passphrase when generating the
243	key; that passphrase will be used to encrypt the private part of
244	this file using 3DES. This file is not automatically accessed by
245	ssh-keygen but it is offered as the default file for the private
246	key. ssh(1) will read this file when a login attempt is made.
247
248	~/.ssh/id_dsa.pub
249	Contains the protocol version 2 DSA public key for authentica-
250	tion. The contents of this file should be added to
251	~/.ssh/authorized_keys on all machines where the user wishes to
252	log in using public key authentication. There is no need to keep
253	the contents of this file secret.
254
255	~/.ssh/id_rsa
256	Contains the protocol version 2 RSA authentication identity of
257	the user. This file should not be readable by anyone but the us-
258	er. It is possible to specify a passphrase when generating the
259	key; that passphrase will be used to encrypt the private part of
260	this file using 3DES. This file is not automatically accessed by
261	ssh-keygen but it is offered as the default file for the private
262	key. ssh(1) will read this file when a login attempt is made.
263
264	~/.ssh/id_rsa.pub
265	Contains the protocol version 2 RSA public key for authentica-
266	tion. The contents of this file should be added to
267	~/.ssh/authorized_keys on all machines where the user wishes to
268	log in using public key authentication. There is no need to keep
269	the contents of this file secret.
270
271	/etc/moduli
272	Contains Diffie-Hellman groups used for DH-GEX. The file format
273	is described in moduli(5).
274
275	SEE ALSO
276	ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)
277
278	J. Galbraith and R. Thayer, SECSH Public Key File Format, draft-ietf-
279	secsh-publickeyfile-01.txt, March 2001, work in progress material.
280
281	AUTHORS
282	OpenSSH is a derivative of the original and free ssh 1.2.12 release by
283	Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
284	de Raadt and Dug Song removed many bugs, re-added newer features and
285	created OpenSSH. Markus Friedl contributed the support for SSH protocol
286	versions 1.5 and 2.0.
287
288	OpenBSD 4.0 September 25, 1999 5