import java.io.FileInputStream;
import java.security.Key;
import java.security.KeyStore;

import sun.misc.BASE64Encoder;

/****
* This is an utility program that reads the keystore file specified in the
* parameter and dumps to the standard output the private key encoded in Base64
*
*/
public class DumpPrivateKey {
/****
* Main method. Invoked from command line. This method open the jks file
* specified in the parameter to get the private key, transforms it in
* Base64 format and write it to the standard output. `Usage`:
* java DumpPrivateKey keystore.jks alias storepassword keypassword
*
* @param args
* List of strings containing the input parameters.
*/
static public void main(String[] args) {
try {
if (args.length != 4) {
System.err
.println("Usage java DumpPrivateKey keystore.jks alias storepassword keypassword");
System.exit(1);
}
KeyStore ks = KeyStore.getInstance("jks");
String keystore = args[0];
String alias = args[1];
String storepass = args[2];
String keypass = args[3];

ks.load(new FileInputStream(keystore), storepass.toCharArray());
Key key = ks.getKey(alias, keypass.toCharArray());
if (key == null) {
System.err.println("No key found for alias:" + alias
+ " and keypass:" + keypass);
System.exit(1);
}

BASE64Encoder myB64 = new BASE64Encoder();
String b64 = myB64.encode(key.getEncoded());

System.out.println("----~~BEGIN PRIVATE KEY----~~");
System.out.println(b64);
System.out.println("----~~END PRIVATE KEY----~~");
} catch (Exception e) {
e.printStackTrace();
}
}
}