RSA加密解密Android

Question

I have a settings screen where I want the user to fill personal details. I want to keep them in sharedpreferences. I would like to encrypt the data before saving in Sharedpreferences. Only when it is used, it's in another application activity decrypt what exists in sharedpreferences and use it. For this purpose I encrypted the information in the settings screen and save the string that was encrypted in to sharedpreferences. In order to Decrypt I need the same privateKey and I do not know how to move it to the other activity. I tried using sharedpreferences but the program was flying.

Would appreciate help

Code:

 try{
     SharedPreferences.Editor editor =getActivity().getSharedPreferences(MY_PREFS_NAME, MODE_PRIVATE).edit();
     afterEncryptCvv = Encrypt((String) newValue,editor);
     editor.putString("cvvValue", afterEncryptCvv);
     editor.commit(); 
    }
     catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
     } catch (NoSuchPaddingException e) {
            e.printStackTrace();
     } catch (InvalidKeyException e) {
            e.printStackTrace();
     } catch (IllegalBlockSizeException e) {
            e.printStackTrace();
     } catch (BadPaddingException e) {
            e.printStackTrace();
     }

The Encrypt Function:

   public static String Encrypt(String plain, SharedPreferences.Editor editor)        
   throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException,    
   IllegalBlockSizeException, BadPaddingException
    {
        kpg = KeyPairGenerator.getInstance("RSA");
        kpg.initialize(1024);
        kp = kpg.genKeyPair();
        publicKey = kp.getPublic();


        privateKey = kp.getPrivate();
        Gson gson4 = new Gson();
        String json4 = gson4.toJson(privateKey);
        editor.putString("privateKey", json4);

        cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        encryptedBytes = cipher.doFinal(plain.getBytes());
        encrypted = bytesToString(encryptedBytes);


        return encrypted;

    }

In The second activity:

 SharedPreferences prefs = getSharedPreferences(MY_PREFS_NAME, MODE_PRIVATE);

    try {
        Gson gson4 = new Gson();
        String json4 = prefs.getString("privateKey", "");
        privateKey = gson4.fromJson(json4, PrivateKey.class);
        cvvValue = prefs.getString(Cvv, "");
        String temp = Decrypt(cvvValue);
        cvvValue =temp;
    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
    } catch (NoSuchPaddingException e) {
        e.printStackTrace();
    } catch (InvalidKeyException e) {
        e.printStackTrace();
    } catch (IllegalBlockSizeException e) {
        e.printStackTrace();
    } catch (BadPaddingException e) {
        e.printStackTrace();
    }

The Decrypt Function:

 public String Decrypt (String result) throws NoSuchAlgorithmException,          
 NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, 
 BadPaddingException
{

    cipher1= Cipher.getInstance("RSA");
    cipher1.init(Cipher.DECRYPT_MODE, privateKey);
    decryptedBytes = cipher1.doFinal(stringToBytes(result));
    decrypted = new String(decryptedBytes);
    return decrypted;

}

Answer 1

You should not store the secret key on the internal storage. Someone with a rooted device can extract it easily.

Instead, after generating the key pair, you can save it in Android Key Store (see here: http://developer.android.com/training/articles/keystore.html ) and use it when needed.

For example:

KeyStore ks = KeyStore.getInstance("AndroidKeyStore");
ks.load(null);
KeyStore.Entry entry = ks.getEntry(alias, null);