(Chilkat for Android™ API)
Convert PuTTY Private Key (ppk) to OpenSSH (pem)

Convert a PuTTY format private key file (.ppk) to OpenSSH (.pem).

Download: Chilkat for Android™ Java Libraries

// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {
  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    TextView tv = new TextView(this);
    String outStr = "";

    CkSshKey key = new CkSshKey();

    boolean success;

    //  Load an unencrypted or encrypted PuTTY private key.

    //  If  your PuTTY private key is encrypted, set the Password
    //  property before calling FromPuttyPrivateKey.
    //  If your PuTTY private key is not encrypted, it makes no diffference
    //  if Password is set or not set.
    key.put_Password("secret");

    //  First load the .ppk file into a string:
    String keyStr;
    keyStr = key.loadText("putty_private_key.ppk");

    //  Import into the SSH key object:
    success = key.FromPuttyPrivateKey(keyStr);
    if (success != true) {
        outStr += key.lastErrorText() + "\n";
        tv.setText(outStr);
        setContentView(tv);
        return;
    }

    //  Convert to an encrypted or unencrypted OpenSSH key.

    //  First demonstrate converting to an unencrypted OpenSSH key
    String unencryptedKeyStr;
    boolean bEncrypt;
    bEncrypt = false;
    unencryptedKeyStr = key.toOpenSshPrivateKey(bEncrypt);
    success = key.SaveText(unencryptedKeyStr,"unencrypted_openssh.pem");
    if (success != true) {
        outStr += key.lastErrorText() + "\n";
        tv.setText(outStr);
        setContentView(tv);
        return;
    }

    //  Save to an encrypted OpenSSH PEM file:
    String encryptedKeyStr;
    bEncrypt = true;
    key.put_Password("myPassword");
    encryptedKeyStr = key.toOpenSshPrivateKey(bEncrypt);
    success = key.SaveText(encryptedKeyStr,"encrypted_openssh.pem");
    if (success != true) {
        outStr += key.lastErrorText() + "\n";
        tv.setText(outStr);
        setContentView(tv);
        return;
    }

    outStr += "Done!" + "\n";
    tv.setText(outStr);
    setContentView(tv);
  }

  static {
      // Important: Make sure the name passed to loadLibrary matches the shared library
      // found in your project's libs/armeabi directory.
      //  for "libchilkat.so", pass "chilkat" to loadLibrary
      //  for "libchilkatemail.so", pass "chilkatemail" to loadLibrary
      //  etc.
      // 
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}