puttygen(1)

  NAME

puttygen - public-key generator for the PuTTY tools

  SYNOPSIS

puttygen ( keyfile | -t keytype [ -b bits ] )
         [ -C new-comment ] [ -P ]
         [ -O output-type | -l | -L | -p ]
         [ -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 private 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.

  OPTIONS

In the first phase, puttygen either loads or generates a key. The options to control this are:

keyfile
    Specify a private key file to be loaded. This private key file can be in the (de facto standard) SSH1 key format, or in PuTTY's SSH2 key format, or in either of the SSH2 private key formats used by OpenSSH and ssh.com's implementation.

-t keytype
    Specify a type of key to generate. The acceptable values here are rsa and dsa (to generate SSH2 keys), and rsa1 (to generate SSH1 keys).

-b bits
    Specify the size of the key to generate, in bits. Default is 1024.

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 SSH1 key format, or PuTTY's own SSH2 key format.

    public
        Save the public key only. For SSH1 keys, the standard public key format will be used ("1024 37 5698745..."). For SSH2 keys, the public key will be output in the format specified in the IETF drafts, 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 SSH1 keys, this output format behaves identically to public. For SSH2 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 SSH2 private key in OpenSSH's format. This option is not permitted for SSH1 keys.

    private-sshcom
        Save an SSH2 private key in ssh.com's format. This option is not permitted for SSH1 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".

  EXAMPLES

To generate an SSH2 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 (2048-bit) key:

puttygen -t rsa -b 2048 -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

  BUGS

There's currently no way to supply passphrases in batch mode, or even just to specify that you don't want a passphrase at all.