import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.security.Key;
import java.security.KeyPair;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.UnrecoverableKeyException;
import java.security.cert.Certificate;
import sun.misc.BASE64Encoder;
public class ExportPrivateKey {
	private File keystoreFile;
	private String keyStoreType;
	private char[] password;
	private String alias;
	private File exportedFile;
	public static KeyPair getPrivateKey(KeyStore keystore, String alias, char[] password) {
		try {
			Key key=keystore.getKey(alias,password);
			if(key instanceof PrivateKey) {
				Certificate cert=keystore.getCertificate(alias);
				PublicKey publicKey=cert.getPublicKey();
				return new KeyPair(publicKey,(PrivateKey)key);
			}
		} catch (UnrecoverableKeyException e) {
		} catch (NoSuchAlgorithmException e) {
		} catch (KeyStoreException e) {
		}
		return null;
	}
	public void export() throws Exception {
		KeyStore keystore=KeyStore.getInstance(keyStoreType);
		BASE64Encoder encoder=new BASE64Encoder();
		keystore.load(new FileInputStream(keystoreFile),password);
		KeyPair keyPair=getPrivateKey(keystore,alias,password);
		PrivateKey privateKey=keyPair.getPrivate();
		String encoded=encoder.encode(privateKey.getEncoded());
		FileWriter fw=new FileWriter(exportedFile);
		fw.write("-----BEGIN PRIVATE KEY-----\n");
		fw.write(encoded);
		fw.write("\n");
		fw.write("-----END PRIVATE KEY-----\n");
		fw.close();
	}
	public static void main(String args[]) throws Exception {
		if(args.length != 5) {
			System.err.println("Usage:java -cp /path/bin ExportPrivateKey JKS|PKCS12|JCEKS keystoreFile storePWD alias pemFile");
			System.exit(1);
		}
		ExportPrivateKey export=new ExportPrivateKey();
		export.keyStoreType=args[0];
		export.keystoreFile=new File(args[1]);
		export.password=args[2].toCharArray();
		export.alias=args[3];
		export.exportedFile=new File(args[4]);
		export.export();
	}
}