Ruby

Convert a PuTTY Private Key (.ppk) to OpenSSH (.pem)

Demonstrates converting a PuTTY format private key to OpenSSH format. The .ppk is imported with FromPuttyPrivateKey and re-exported with ToOpenSshPrivateKey, both unencrypted and encrypted.

Note: The file paths are relative to the application's current working directory. Supply the paths to your own files.

Background: PuTTY and OpenSSH store the same underlying key material in different container formats, so converting between them is a re-encoding rather than a new key — the corresponding public key, and therefore the server-side authorized_keys entry, is unchanged. This matters when moving between Windows tooling built around PuTTY and Unix tooling that expects PEM. Note that the Password property serves double duty: it decrypts the key on import and encrypts it on export, so set it appropriately for each step.

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Ruby

require 'chilkat'

success = false

#  Demonstrates converting a PuTTY format private key (.ppk) to OpenSSH (.pem) format.

key = Chilkat::CkSshKey.new()

#  Set the password before importing an encrypted PuTTY key.  If the key is not encrypted it
#  makes no difference whether Password is set.  This should come from a secure source rather
#  than being hard-coded.
key.put_Password("myKeyPassword")

#  LoadText is a convenience method that reads any text file into a string.  It does not itself
#  load the key.
keyStr = key.loadText("qa_data/putty_private_key.ppk")
if (key.get_LastMethodSuccess() == false)
    print key.lastErrorText() + "\n";
    exit
end

success = key.FromPuttyPrivateKey(keyStr)
if (success == false)
    print key.lastErrorText() + "\n";
    exit
end

#  Export to an unencrypted OpenSSH key.
bEncrypt = false
unencryptedKeyStr = key.toOpenSshPrivateKey(bEncrypt)
if (key.get_LastMethodSuccess() == false)
    print key.lastErrorText() + "\n";
    exit
end

success = key.SaveText(unencryptedKeyStr,"qa_output/unencrypted_openssh.pem")
if (success == false)
    print key.lastErrorText() + "\n";
    exit
end

#  Export to an encrypted OpenSSH key.  The Password property supplies the passphrase used to
#  encrypt the output.
bEncrypt = true
key.put_Password("myExportPassword")
encryptedKeyStr = key.toOpenSshPrivateKey(bEncrypt)
if (key.get_LastMethodSuccess() == false)
    print key.lastErrorText() + "\n";
    exit
end

success = key.SaveText(encryptedKeyStr,"qa_output/encrypted_openssh.pem")
if (success == false)
    print key.lastErrorText() + "\n";
    exit
end

print "Done!" + "\n";