1puttygen(1) PuTTY tool suite puttygen(1)
2
6 puttygen - public-key generator for the PuTTY tools
7
9 puttygen ( keyfile | -t keytype [ -b bits ] [ --primes method ] [ -q ] )
10 [ -C new-comment ] [ -P ] [ --reencrypt ]
11 [ --certificate cert-file | --remove-certificate ]
12 [ -O output-type | -l | -L | -p | --dump | --cert-info ]
13 [ --ppk-param key=value,... | -E fptype ]
14 [ -o output-file ]
15
17 puttygen is a tool to generate and manipulate SSH public and private
18 key pairs. It is part of the PuTTY suite, although it can also interop‐
19 erate with the key formats used by some other SSH clients.
20 When you run puttygen, it does three things. Firstly, it either loads
22 an existing key file (if you specified keyfile), or generates a new key
23 (if you specified keytype). Then, it optionally makes modifications to
24 the key (such as changing the comment and/or the passphrase); finally,
25 it outputs the key, or some information about the key, to a file.
26 All three of these phases are controlled by the options described in
28 the following section.
29
31 In the first phase, puttygen either loads or generates a key. Note that
32 generating a key requires random data, which can cause puttygen to
33 pause, possibly for some time if your system does not have much random‐
34 ness available.
35 The options to control this phase are:
37 keyfile
39 Specify a key file to be loaded. (Use `-' to read a key file
40 from standard input.)
41 Usually this will be a private key, which can be in the (de
43 facto standard) SSH-1 key format, or in PuTTY's SSH-2 key for‐
44 mat, or in either of the SSH-2 private key formats used by
45 OpenSSH and ssh.com's implementation.
46 You can also specify a file containing only a public key here.
48 The operations you can do are limited to outputting another pub‐
49 lic key format (possibly removing an attached certificate
50 first), or a fingerprint. Public keys can be in RFC 4716 or
51 OpenSSH format, or the standard SSH-1 format.
52 -t keytype
54 Specify a type of key to generate. The acceptable values here
55 are rsa, dsa, ecdsa, eddsa, ed25519, and ed448 (to generate
56 SSH-2 keys), and rsa1 (to generate SSH-1 keys).
57 -b bits
59 Specify the size of the key to generate, in bits. Default for
60 rsa and dsa keys is 2048.
61 --primes method
63 Method for generating prime numbers. The acceptable values here
64 are probable (the default), proven, and proven-even; the later
65 methods are slower. (Various synonyms for these method names are
66 also accepted.)
67 The `probable primes' method sounds unsafe, but it's the most
69 commonly used prime-generation strategy. There is in theory a
70 possibility that it might accidentally generate a number that
71 isn't prime, but the software does enough checking to make that
72 probability vanishingly small (less than 1 in 2^80, or 1 in
73 10^24). So, in practice, nobody worries about it very much.
74 The other methods cause PuTTYgen to use numbers that it is sure
76 are prime, because it generates the output number together with
77 a proof of its primality. This takes more effort, but it elimi‐
78 nates that theoretical risk in the probabilistic method.
79 You might choose to switch from probable to proven primes if you
81 have a local security standard that demands it, or if you don't
82 trust the probabilistic argument for the safety of the usual
83 method.
84 --strong-rsa
86 When generating an RSA key, make sure the prime factors of the
87 key modulus are `strong primes'. A strong prime is a prime num‐
88 ber chosen to have a particular structure that makes certain
89 factoring algorithms more difficult to apply, so some security
90 standards recommend their use. However, the most modern factor‐
91 ing algorithms are unaffected, so this option is probably not
92 worth turning on unless you have a local standard that recom‐
93 mends it.
94 -q Suppress the progress display when generating a new key.
96 --old-passphrase file
98 Specify a file name; the first line will be read from this file
99 (removing any trailing newline) and used as the old passphrase.
100 CAUTION: If the passphrase is important, the file should be
101 stored on a temporary filesystem or else securely erased after
102 use.
103 --random-device device
105 Specify device to read entropy from. By default, puttygen uses
106 /dev/urandom, falling back to /dev/random if it has to.
107 In the second phase, puttygen optionally alters properties of the key
109 it has loaded or generated. The options to control this are:
110 -C new-comment
112 Specify a comment string to describe the key. This comment
113 string will be used by PuTTY to identify the key to you (when
114 asking you to enter the passphrase, for example, so that you
115 know which passphrase to type).
116 -P Indicate that you want to change the key's passphrase. This is
118 automatic when you are generating a new key, but not when you
119 are modifying an existing key.
120 --certificate certificate-file
122 Adds an OpenSSH-style certificate to the public half of the key,
123 so that the output file contains a certified public key with the
124 same private key. If the input file already contained a certifi‐
125 cate, it will be replaced with the new one. (Use `-' to read a
126 certificate from standard input.)
127 --remove-certificate
129 Removes any certificate that was part of the key, to recover the
130 uncertified version of the underlying key.
131 --reencrypt
133 For an existing private key saved with a passphrase, refresh the
134 encryption without changing the passphrase.
135 This is most likely to be useful with the --ppk-param option, to
137 change some aspect of the key file's format or encryption.
138 --ppk-param key=value,...
140 When saving a PPK file (the default private output type for
141 SSH-2 keys), adjust details of the on-disk format.
142 Aspects to change are specified as a series of key=value pairs
144 separated by commas. The keys are:
145 version
147 The PPK format version. Possible values are 3 (the de‐
148 fault) and 2 (which is less resistant to brute-force de‐
149 cryption, but which you might need if your key needs to
150 be used by old versions of PuTTY tools, or other PPK con‐
151 sumers).
152 The following keys only affect PPK version 3 files.
154 kdf The variant of the Argon2 key derivation function to use.
156 Options are argon2id (default, and recommended), argon2i,
157 and argon2d.
158 You might change this if you consider your exposure to
160 side-channel attacks to be different to the norm.
161 memory The amount of memory needed to decrypt the key, in Kbyte.
163 Default is 8192 (i.e., 8 Mbyte).
164 time Approximate time, on this machine, required to attempt
166 decrypting the key, in milliseconds. Default is 100 (ms).
167 passes Alternative to time: explicitly specify the number of
169 hash passes required to attempt decrypting the key.
170 parallelism
172 Number of parallelisable threads that can be used to de‐
173 crypt the key. Default is 1 (force decryption to run sin‐
174 gle-threaded).
175 In the third phase, puttygen saves the key or information about it. The
177 options to control this are:
178 -O output-type
180 Specify the type of output you want puttygen to produce. Accept‐
181 able options are:
182 private
184 Save the private key in a format usable by PuTTY. This
185 will either be the standard SSH-1 key format, or PuTTY's
186 own SSH-2 key format (`PPK'). This is the default.
187 public Save the public key only. For SSH-1 keys, the standard
189 public key format will be used (`1024 37 5698745...').
190 For SSH-2 keys, the public key will be output in the for‐
191 mat specified by RFC 4716, which is a multi-line text
192 file beginning with the line `---- BEGIN SSH2 PUBLIC KEY
193 ----'.
194 public-openssh
196 Save the public key only, in a format usable by OpenSSH.
197 For SSH-1 keys, this output format behaves identically to
198 public. For SSH-2 keys, the public key will be output in
199 the OpenSSH format, which is a single line (`ssh-rsa
200 AAAAB3NzaC1yc2...').
201 fingerprint
203 Print a fingerprint of the public key. The -E option lets
204 you specify which fingerprinting algorithm to use. All
205 algorithms are believed compatible with OpenSSH.
206 private-openssh
208 Save an SSH-2 private key in OpenSSH's format, using the
209 oldest format available to maximise backward compatibil‐
210 ity. This option is not permitted for SSH-1 keys.
211 private-openssh-new
213 As private-openssh, except that it forces the use of
214 OpenSSH's newer format even for RSA, DSA, and ECDSA keys.
215 private-sshcom
217 Save an SSH-2 private key in ssh.com's format. This op‐
218 tion is not permitted for SSH-1 keys.
219 cert-info
221 Save a textual dump of information about the certificate
222 on the key, if any: whether it's a host or a user cer‐
223 tificate, what host(s) or user(s) it's certified to be,
224 its validity period, ID and serial number, and the fin‐
225 gerprint of the signing CA.
226 text Save a textual dump of the numeric components comprising
228 the key (both the public and private parts, if present).
229 Useful for debugging, or for using PuTTYgen as a key gen‐
230 erator for applications other than SSH.
231 The output consists of a series of name=value lines,
233 where each value is either a C-like string literal in
234 double quotes, a hexadecimal number starting with 0x...,
235 or a binary blob encoded with base64, denoted by
236 b64("...").
237 If no output type is specified, the default is private.
239 -o output-file
241 Specify the file where puttygen should write its output. If this
242 option is not specified, puttygen will assume you want to over‐
243 write the original file if the input and output file types are
244 the same (changing a comment or passphrase), and will assume you
245 want to output to stdout if you are asking for a public key,
246 fingerprint, or one of the textual dump types. Otherwise, the -o
247 option is required.
248 -l Synonym for `-O fingerprint'.
250 -L Synonym for `-O public-openssh'.
252 -p Synonym for `-O public'.
254 --cert-info
256 Synonym for `-O cert-info'.
257 --dump Synonym for `-O text'.
259 -E fptype
261 Specify the algorithm to use if generating a fingerprint. The
262 available algorithms are are sha256 (the default) and md5.
263 By default, when showing the fingerprint of a public key that
265 includes a certificate, puttygen will not include the certifi‐
266 cate, so that the fingerprint shown will be the same as the un‐
267 derlying public key. If you want the fingerprint including the
268 certificate (for example, so as to tell two certified keys
269 apart), you can specify sha256-cert or md5-cert as the finger‐
270 print type.
271 --new-passphrase file
273 Specify a file name; the first line will be read from this file
274 (removing any trailing newline) and used as the new passphrase.
275 If the file is empty then the saved key will be unencrypted.
276 CAUTION: If the passphrase is important, the file should be
277 stored on a temporary filesystem or else securely erased after
278 use.
279 The following options do not run PuTTYgen as normal, but print informa‐
281 tional messages and then quit:
282 -h, --help
284 Display a message summarizing the available options.
285 -V, --version
287 Display the version of PuTTYgen.
288 --pgpfp
290 Display the fingerprints of the PuTTY PGP Master Keys, to aid in
291 verifying new files released by the PuTTY team.
292
294 To generate an SSH-2 RSA key pair and save it in PuTTY's own format
295 (you will be prompted for the passphrase):
296 puttygen -t rsa -C "my home key" -o mykey.ppk
298 To generate a larger (4096-bit) key:
300 puttygen -t rsa -b 4096 -C "my home key" -o mykey.ppk
302 To change the passphrase on a key (you will be prompted for the old and
304 new passphrases):
305 puttygen -P mykey.ppk
307 To change the comment on a key:
309 puttygen -C "new comment" mykey.ppk
311 To convert a key into OpenSSH's private key format:
313 puttygen mykey.ppk -O private-openssh -o my-openssh-key
315 To convert a key from another format (puttygen will automatically de‐
317 tect the input key type):
318 puttygen my-ssh.com-key -o mykey.ppk
320 To display the SHA-256 fingerprint of a key (some key types require a
322 passphrase to extract even this much information):
323 puttygen -l mykey.ppk
325 To add the OpenSSH-format public half of a key to your authorised keys
327 file:
328 puttygen -L mykey.ppk >> $HOME/.ssh/authorized_keys
330PuTTY tool suite 2004‐03‐24 puttygen(1)