fzputtygen

fzputtygen [options] [-o output-file] [input-file]

-t type
    Specifies the type of key to generate.
Supported types are rsa, dsa, ecdsa, ed25519.

-b bits
    Specifies the number of bits in the key. The allowed values depend on the key type.

-C comment
    Specifies a comment to embed in the key file.

-o output-file
    Specifies the output file to write the key to.

input-file
    Specifies an input file to convert.

-O type
    Type of key to output. Can be private, public, ssh1, ssh2

-P
    Prompt for passphrase to encrypt the private key.

-v
    Verbose output. Shows more information about the key generation/conversion process.

fzputtygen is a command-line utility included with FileZilla that generates and converts SSH private keys for use with the FileZilla client and other applications that support PuTTY's key format.

It allows you to create new RSA, DSA, or ECDSA/Ed25519 keys, or convert existing keys from other formats (like OpenSSH) to the .ppk format used by PuTTY. This is essential for secure, passwordless authentication using SSH keys with SFTP connections in FileZilla. The generated or converted keys can then be loaded into FileZilla's site manager to establish secure connections to remote servers.

The tool is particularly useful in automated environments or when you need to generate or manipulate SSH keys programmatically. While the graphical PuTTYgen offers a visual interface, fzputtygen offers a command-line equivalent, streamlining key management tasks within scripts and workflows.

Passphrase protection is highly recommended for private keys. Losing or compromising the private key will compromise the security of the SSH authentication.

To generate a new 2048-bit RSA key and save it to 'mykey.ppk':
fzputtygen -t rsa -b 2048 -o mykey.ppk

To convert an OpenSSH key named 'id_rsa' to PuTTY format:
fzputtygen id_rsa -o mykey.ppk

ssh-keygen(1), ssh(1), sftp(1)