Provided by: putty-tools_0.77-1_amd64 
NAME
puttygen - public-key generator for the PuTTY tools
SYNOPSIS
puttygen ( keyfile | -t keytype [ -b bits ] [ --primes method ] [ -q ] )
[ -C new-comment ] [ -P ] [ --reencrypt ]
[ -O output-type | -l | -L | -p | --dump ] [ -E fptype ]
[ --ppk-param key=value,... ]
[ -o output-file ]
DESCRIPTION
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 (such as 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.
OPTIONS
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. (Use `-' to read a key file from standard input.)
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,
eddsa, ed25519, and ed448 (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 for rsa and dsa keys is
2048.
--primes method
Method for generating prime numbers. The acceptable values here are probable (the
default), proven, and proven-even; the later methods are slower. (Various synonyms
for these method names are also accepted.)
The `probable primes' method sounds unsafe, but it's the most commonly used prime-
generation strategy. There is in theory a possibility that it might accidentally
generate a number that isn't prime, but the software does enough checking to make
that probability vanishingly small (less than 1 in 2^80, or 1 in 10^24). So, in
practice, nobody worries about it very much.
The other methods cause PuTTYgen to use numbers that it is sure are prime, because
it generates the output number together with a proof of its primality. This takes
more effort, but it eliminates that theoretical risk in the probabilistic method.
You might choose to switch from probable to proven primes if you have a local
security standard that demands it, or if you don't trust the probabilistic argument
for the safety of the usual method.
--strong-rsa
When generating an RSA key, make sure the prime factors of the key modulus are
`strong primes'. A strong prime is a prime number chosen to have a particular
structure that makes certain factoring algorithms more difficult to apply, so some
security standards recommend their use. However, the most modern factoring
algorithms are unaffected, so this option is probably not worth turning on unless
you have a local standard that recommends it.
-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.
--reencrypt
For an existing private key saved with a passphrase, refresh the encryption without
changing the passphrase.
This is most likely to be useful with the --ppk-param option, to change some aspect
of the key file's format or encryption.
--ppk-param key=value,...
When saving a PPK file (the default private output type for SSH-2 keys), adjust
details of the on-disk format.
Aspects to change are specified as a series of key=value pairs separated by commas.
The keys are:
version
The PPK format version. Possible values are 3 (the default) and 2 (which is
less resistant to brute-force decryption, but which you might need if your
key needs to be used by old versions of PuTTY tools, or other PPK
consumers).
The following keys only affect PPK version 3 files.
kdf The variant of the Argon2 key derivation function to use. Options are
argon2id (default, and recommended), argon2i, and argon2d.
You might change this if you consider your exposure to side-channel attacks
to be different to the norm.
memory The amount of memory needed to decrypt the key, in Kbyte. Default is 8192
(i.e., 8 Mbyte).
time Approximate time, on this machine, required to attempt decrypting the key,
in milliseconds. Default is 100 (ms).
passes Alternative to time: explicitly specify the number of hash passes required
to attempt decrypting the key.
parallelism
Number of parallelisable threads that can be used to decrypt the key.
Default is 1 (force decryption to run single-threaded).
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 (`PPK'). This is
the default.
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 a fingerprint of the public key. The -E option lets you specify which
fingerprinting algorithm to use. All 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.
text Save a textual dump of the numeric components comprising the key (both the
public and private parts, if present). Useful for debugging, or for using
PuTTYgen as a key generator for applications other than SSH.
The output consists of a series of name=value lines, where each value is
either a C-like string literal in double quotes, or a hexadecimal number
starting with 0x...
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'.
--dump Synonym for `-O text'.
-E fptype
Specify the algorithm to use if generating a fingerprint. The options are sha256
(the default) and md5.
--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.
EXAMPLES
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 SHA-256 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