Java

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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import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.SshKey;

public class ChilkatExample {

    public static void main(String[] args) {
        // Demonstrates converting a PuTTY format private key (.ppk) to OpenSSH (.pem) format.

        SshKey key = new SshKey();

        // 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.setPassword("myKeyPassword");

        // LoadText is a convenience method that reads any text file into a string.  It does not itself
        // load the key.
        String keyStr;
        try {
            keyStr = key.loadText("qa_data/putty_private_key.ppk");

            key.fromPuttyPrivateKey(keyStr);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // Export to an unencrypted OpenSSH key.
        boolean bEncrypt = false;
        String unencryptedKeyStr;
        String encryptedKeyStr;
        try {
            unencryptedKeyStr = key.toOpenSshPrivateKey(bEncrypt);

            key.saveText(unencryptedKeyStr, "qa_output/unencrypted_openssh.pem");

            // Export to an encrypted OpenSSH key.  The Password property supplies the passphrase used to
            // encrypt the output.
            bEncrypt = true;
            key.setPassword("myExportPassword");
            encryptedKeyStr = key.toOpenSshPrivateKey(bEncrypt);

            key.saveText(encryptedKeyStr, "qa_output/encrypted_openssh.pem");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        System.out.println("Done!");
    }
}