Android：如何更改公钥和私钥？

Question

我想创建一个简单的RSA加密程序，我找到了这个教程https://sites.google.com/site/androidstem/computinglabware/module-9/2-lav-activity/lab1。我想知道是否可以预先定义公钥和私钥的值

公钥：Hello

私钥：再见

MainActivity.java

public class MainActivity extends Activity {

/** Called when the activity is first created. */
@Override

public void onCreate(Bundle savedInstanceState) {
    try {
        generateKey();
    } catch (Exception e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    final Button enButton=(Button)findViewById(R.id.enbutton);
    final Button deButton=(Button)findViewById(R.id.debutton);
    final EditText input=(EditText)findViewById(R.id.input);
    final EditText Raw=(EditText)findViewById(R.id.raw);
    final EditText output=(EditText)findViewById(R.id.originText);
    enButton.setOnClickListener(new OnClickListener()
    {
        public void onClick(View v)
        {
            try {
                Raw.setText(encrypt(input.getText().toString()));
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        };
    });
    deButton.setOnClickListener(new OnClickListener()
    {
        public void onClick(View v)
        {
            try {
                output.setText(String.valueOf(decrypt(Raw.getText().toString())));
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    });
}

private final static String RSA = "RSA";
public static PublicKey uk;
public static PrivateKey rk;

public static void generateKey() throws Exception
{
    KeyPairGenerator gen = KeyPairGenerator.getInstance(RSA);
    gen.initialize(512, new SecureRandom());
    KeyPair keyPair = gen.generateKeyPair();
    uk = keyPair.getPublic();
    rk = keyPair.getPrivate();
}
private static byte[] encrypt(String text, PublicKey pubRSA) throws Exception
{
    Cipher cipher = Cipher.getInstance(RSA);
    cipher.init(Cipher.ENCRYPT_MODE, pubRSA);
    return cipher.doFinal(text.getBytes());
}
public final static String encrypt(String text)
{
    try {
        return byte2hex(encrypt(text, uk));
    }
    catch(Exception e)
    {
        e.printStackTrace();
    }
    return null;
}

public final static String decrypt(String data)
{
    try{
        return new String(decrypt(hex2byte(data.getBytes())));
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
    return null;
}

private static byte[] decrypt(byte[] src) throws Exception
{
    Cipher cipher = Cipher.getInstance(RSA);
    cipher.init(Cipher.DECRYPT_MODE, rk);
    return cipher.doFinal(src);
}

public static String byte2hex(byte[] b)
{
    String hs = "";
    String stmp = "";
    for (int n = 0; n < b.length; n ++)
    {
        stmp = Integer.toHexString(b[n] & 0xFF);
        if (stmp.length() == 1)
            hs += ("0" + stmp);
        else
            hs += stmp;
    }
    return hs.toUpperCase();
}

public static byte[] hex2byte(byte[] b)
{
    if ((b.length % 2) != 0)
        throw new IllegalArgumentException("hello");

    byte[] b2 = new byte[b.length / 2];

    for (int n = 0; n < b.length; n += 2)
    {
        String item = new String(b, n, 2);
        b2[n/2] = (byte)Integer.parseInt(item, 16);
    }
    return b2;
}
}