puttygen - public-key generator for the PuTTY tools
puttygen ( keyfile | -t keytype [ -b bits ] )
[ -C new-comment ] [ -P ] [ -q ]
[ -O output-type | -l | -L | -p ]
[ -o output-file ]
puttygen is a tool to generate and manipulate SSH public
and private key pairs. It is part of the PuTTY suite, although it can also
interoperate with the key formats used by some other SSH clients.
When you run puttygen, it does three things. Firstly, it
either loads an existing key file (if you specified keyfile), or
generates a new key (if you specified keytype). Then, it optionally
makes modifications to the key (changing the comment and/or the passphrase);
finally, it outputs the key, or some information about the key, to a
file.
All three of these phases are controlled by the options described
in the following section.
In the first phase, puttygen either loads or generates a
key. Note that generating a key requires random data, which can cause
puttygen to pause, possibly for some time if your system does not
have much randomness available.
The options to control this phase are:
- keyfile
- Specify a key file to be loaded.
Usually this will be a private key, which can be in the (de facto
standard) SSH-1 key format, or in PuTTY's SSH-2 key format, or in either of
the SSH-2 private key formats used by OpenSSH and ssh.com's
implementation.
You can also specify a file containing only a public key
here. The operations you can do are limited to outputting another public key
format or a fingerprint. Public keys can be in RFC 4716 or OpenSSH format,
or the standard SSH-1 format.
- -t keytype
- Specify a type of key to generate. The acceptable values here are
rsa, dsa, ecdsa, and ed25519 (to generate
SSH-2 keys), and rsa1 (to generate SSH-1 keys).
- -b bits
- Specify the size of the key to generate, in bits. Default is 2048.
- -q
- Suppress the progress display when generating a new key.
- --old-passphrase
file
- Specify a file name; the first line will be read from this file (removing
any trailing newline) and used as the old passphrase. CAUTION: If
the passphrase is important, the file should be stored on a temporary
filesystem or else securely erased after use.
- --random-device
device
- Specify device to read entropy from. By default, puttygen uses
/dev/urandom, falling back to /dev/random if it has to.
In the second phase, puttygen optionally alters properties
of the key it has loaded or generated. The options to control this are:
- -C
new-comment
- Specify a comment string to describe the key. This comment string will be
used by PuTTY to identify the key to you (when asking you to enter the
passphrase, for example, so that you know which passphrase to type).
- -P
- Indicate that you want to change the key's passphrase. This is automatic
when you are generating a new key, but not when you are modifying an
existing key.
In the third phase, puttygen saves the key or information
about it. The options to control this are:
- -O
output-type
- Specify the type of output you want puttygen to produce. Acceptable
options are:
- private
- Save the private key in a format usable by PuTTY. This will either be the
standard SSH-1 key format, or PuTTY's own SSH-2 key format.
- public
- Save the public key only. For SSH-1 keys, the standard public key format
will be used (`1024 37 5698745...'). For SSH-2 keys, the public key
will be output in the format specified by RFC 4716, which is a multi-line
text file beginning with the line `---- BEGIN SSH2 PUBLIC KEY
----'.
- public-openssh
- Save the public key only, in a format usable by OpenSSH. For SSH-1 keys,
this output format behaves identically to public. For SSH-2 keys,
the public key will be output in the OpenSSH format, which is a single
line (`ssh-rsa AAAAB3NzaC1yc2...').
- fingerprint
- Print the fingerprint of the public key. All fingerprinting algorithms are
believed compatible with OpenSSH.
- private-openssh
- Save an SSH-2 private key in OpenSSH's format, using the oldest format
available to maximise backward compatibility. This option is not permitted
for SSH-1 keys.
- private-openssh-new
- As private-openssh, except that it forces the use of OpenSSH's
newer format even for RSA, DSA, and ECDSA keys.
- private-sshcom
- Save an SSH-2 private key in ssh.com's format. This option is not
permitted for SSH-1 keys.
If no output type is specified, the default is private.
- -o
output-file
- Specify the file where puttygen should write its output. If this
option is not specified, puttygen will assume you want to overwrite
the original file if the input and output file types are the same
(changing a comment or passphrase), and will assume you want to output to
stdout if you are asking for a public key or fingerprint. Otherwise, the
-o option is required.
- -l
- Synonym for `-O fingerprint'.
- -L
- Synonym for `-O public-openssh'.
- -p
- Synonym for `-O public'.
- --new-passphrase
file
- Specify a file name; the first line will be read from this file (removing
any trailing newline) and used as the new passphrase. If the file is empty
then the saved key will be unencrypted. CAUTION: If the passphrase
is important, the file should be stored on a temporary filesystem or else
securely erased after use.
The following options do not run PuTTYgen as normal, but print
informational messages and then quit:
- -h, --help
- Display a message summarizing the available options.
- -V, --version
- Display the version of PuTTYgen.
- --pgpfp
- Display the fingerprints of the PuTTY PGP Master Keys, to aid in verifying
new files released by the PuTTY team.
To generate an SSH-2 RSA key pair and save it in PuTTY's own
format (you will be prompted for the passphrase):
puttygen -t rsa -C "my home key" -o mykey.ppk
To generate a larger (4096-bit) key:
puttygen -t rsa -b 4096 -C "my home key" -o mykey.ppk
To change the passphrase on a key (you will be prompted for the
old and new passphrases):
puttygen -P mykey.ppk
To change the comment on a key:
puttygen -C "new comment" mykey.ppk
To convert a key into OpenSSH's private key format:
puttygen mykey.ppk -O private-openssh -o my-openssh-key
To convert a key from another format (puttygen will
automatically detect the input key type):
puttygen my-ssh.com-key -o mykey.ppk
To display the fingerprint of a key (some key types require a
passphrase to extract even this much information):
puttygen -l mykey.ppk
To add the OpenSSH-format public half of a key to your authorised
keys file:
puttygen -L mykey.ppk >> $HOME/.ssh/authorized_keys