Dart

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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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // Demonstrates converting a PuTTY format private key (.ppk) to OpenSSH (.pem) format.

  final key = CkSshKey();

  // 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.password = 'myKeyPassword';

  // LoadText is a convenience method that reads any text file into a string.  It does not itself
  // load the key.
  final String keyStr;
  try {
    keyStr = key.loadText('qa_data/putty_private_key.ppk');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    key.fromPuttyPrivateKey(keyStr);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Export to an unencrypted OpenSSH key.
  var bEncrypt = false;
  final String unencryptedKeyStr;
  try {
    unencryptedKeyStr = key.toOpenSshPrivateKey(bEncrypt);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    key.saveText(unencryptedKeyStr, 'qa_output/unencrypted_openssh.pem');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Export to an encrypted OpenSSH key.  The Password property supplies the passphrase used to
  // encrypt the output.
  bEncrypt = true;
  key.password = 'myExportPassword';
  final String encryptedKeyStr;
  try {
    encryptedKeyStr = key.toOpenSshPrivateKey(bEncrypt);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    key.saveText(encryptedKeyStr, 'qa_output/encrypted_openssh.pem');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('Done!');
}