文件加密Java

Question

我正在制作一个系统，其中包含一些数据，我希望它能够接受这些数据( XML格式)，并将其保存为txt文件中的加密字符串，然后当软件再次打开时，解密该文件并将其正常读取。我已经有了将xml转换成字符串的所有代码，我已经有了保存它的代码，我只需要一些加密/解密代码的帮助吗？

注意:我确实找到了一些可以加密/解密的代码，但是我似乎不能将代码分成两个方法。

以下是我的尝试：

    public class AesEncrDec
{

public static String encrypt(String Data)
{
    byte[] byteCipherText = null;
    try {
        String plainData=Data,cipherText,decryptedText;
        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
        keyGen.init(128);
        SecureRandom rnd = new SecureRandom();
        SecretKey secretKey = keyGen.generateKey();
        IvParameterSpec iv;
        iv = new IvParameterSpec(rnd.generateSeed(16));
        Cipher aesCipher = Cipher.getInstance("AES");
        aesCipher.init(Cipher.ENCRYPT_MODE,secretKey,iv); 
        byte[] byteDataToEncrypt = plainData.getBytes();
        byteCipherText = aesCipher.doFinal(byteDataToEncrypt);
        cipherText = new BASE64Encoder().encode(byteCipherText);
        return new String(byteCipherText);
    } catch (InvalidKeyException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    } catch (NoSuchAlgorithmException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    } catch (NoSuchPaddingException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IllegalBlockSizeException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    } catch (BadPaddingException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    } catch (InvalidAlgorithmParameterException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    }
    return new String(byteCipherText);
}

public static String dencrypt(String Data)
{
    byte[] byteDecryptedText = null;
    try {
        KeyGenerator keyGen = KeyGenerator.getInstance("AES");
        keyGen.init(128);
        IvParameterSpec iv;
        SecureRandom rnd = new SecureRandom();
        iv = new IvParameterSpec(rnd.generateSeed(16));
        Cipher aesCipher = Cipher.getInstance("AES");
        SecretKey secretKey = keyGen.generateKey();
        aesCipher.init(Cipher.ENCRYPT_MODE,secretKey,iv);
        byteDecryptedText = aesCipher.doFinal(Data.getBytes());
    } catch (NoSuchAlgorithmException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    } catch (NoSuchPaddingException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    } catch (InvalidKeyException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    } catch (InvalidAlgorithmParameterException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IllegalBlockSizeException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    } catch (BadPaddingException ex) {
        Logger.getLogger(AesEncrDec.class.getName()).log(Level.SEVERE, null, ex);
    }
    return new String(byteDecryptedText);
}
}

编辑:在对@Libin的响应中，这里是错误

Mar 24, 2014 6:27:42 PM PrefsReadAndWrite.AesEncrDec decrypt
SEVERE: null
javax.crypto.BadPaddingException: Given final block not properly padded
    at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:966)
    at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:824)
    at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:436)
    at javax.crypto.Cipher.doFinal(Cipher.java:2121)
    at PrefsReadAndWrite.AesEncrDec.decrypt(AesEncrDec.java:61)
    at PrefsReadAndWrite.AesEncrDec.decryptedString(AesEncrDec.java:104)
    at smarthouse.SmartHouse.main(SmartHouse.java:12)

Exception in thread "main" java.lang.NullPointerException
    at java.lang.String.<init>(String.java:554)
    at PrefsReadAndWrite.AesEncrDec.decryptedString(AesEncrDec.java:105)
    at smarthouse.SmartHouse.main(SmartHouse.java:12)
Java Result: 1

Answer 1

您必须只生成一次密钥，并将其用于加密和解密。用这个代码..。

应该使用AppSecurity类来生成新密钥和加密/解密

public class AppSecurity{
private AppSecurity() {}

public static byte[] encrypt(byte[] key , byte[] data) {
    SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
    try {
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE,keySpec);
        return cipher.doFinal(data);
    }
    catch (NoSuchAlgorithmException e){ }
    catch (NoSuchPaddingException e){ }
    catch (InvalidKeyException e){ }
    catch (BadPaddingException e){ }
    catch (IllegalBlockSizeException e) {}
    return null;
}

public static byte[] decrypt(byte[] key , byte[] encryptedData) {
    SecretKeySpec keySpec = new SecretKeySpec(key ,"AES");
    try {
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, keySpec);
        return cipher.doFinal(encryptedData);
    }
    catch (NoSuchAlgorithmException e) {}
    catch (NoSuchPaddingException e) { }
    catch (InvalidKeyException e) { }
    catch (BadPaddingException e) {}
    catch (IllegalBlockSizeException e) {}
    return null;
}

/**
 * method to generate a secure key. call this when app starts
 * @return
 */
public static byte[] generateKey(){
    try{
        // create an AES algorithm instance.
        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
        SecureRandom secureRandom = SecureRandom.getInstance("SHA1PRNG");
        keyGenerator.init(128,secureRandom);
        SecretKey secretKey = keyGenerator.generateKey();
        return secretKey.getEncoded();
    }
    catch (NoSuchAlgorithmException e){
        return null;
    }
  }
}

方法对字符串进行加密。

 private static byte[] encryptedByte(String s) {
    return AppSecurity.encrypt(YourApplication.getSecretKey(),toBytes(s));
 }

方法来解密字节。

  private static String decryptedString(byte[] blob) {
    // here getSecretKey() should be the one used on encryption
    byte[] decrypted =  AppSecurity.decrypt(YourApplication.getSecretKey(),blob);
    return toString(decrypted);

}

方法将字节转换为字符串。

public static String toString(byte[] bytes) {
  try {
    String s = new String(bytes ,"UTF-8");
     return s;
     } catch (UnsupportedEncodingException e) {
      return null;
     }
  }

方法将字符串转换为Byte。

 public static byte[] toBytes(String s) {
   try {
       return s.getBytes("UTF-8");
    } catch (UnsupportedEncodingException e) {return null;}
   }

详细介绍了如何在应用程序中使用此方法:初始化应用程序/applet类上的initSecurity()方法，并将返回键存储到变量中，并在运行时使用该方法。

假设类名为YourApplication.java

 // initialize it on your app startup
 String mSecretKey = initSecurity()

 // call this method when you encrypt /decrypt
 public static byte[] getSecretKey() { return mSecretKey; } 

//添加此方法以从文件中读取或生成一个新键

 private void initSecurity() {
    final String secretFile = "secure_file";
    boolean keyExists = false;
    //check if secret key exist in secure file
    try {
        FileInputStream inputStream = openFileInput(secretFile);
        mSecretKey = new byte[16];
        int result = inputStream.read(mSecretKey);
        if(result >0) {
            keyExists = true;
        }
        inputStream.close();
    }
    catch (FileNotFoundException e) {}
    catch (IOException e){}
    if(!keyExists) {
        // generate a key
        mSecretKey = AppSecurity.generateKey();
        if(mSecretKey != null) {
            // write in a secure file inside the app
            try {
                // MODE_PRIVATE will create the file (or replace a file of the same name)
                // and make it private to the application.
                FileOutputStream outputStream = openFileOutput(secretFile,Context.MODE_PRIVATE);
                outputStream.write(mSecretKey);
                outputStream.close();
            }
            catch (FileNotFoundException e){}
            catch (IOException e) {}
        }
    }
}

Answer 2

您没有定义要使用的填充，因此使用了实现定义的填充。根据您的错误，在您的情况下，这可能是"NoPadding“。指定填充和操作方式，例如AES/CBC/PKCS5Padding。由于您现在将使用CBC，您还需要一个初始化向量：

IvParameterSpec iv = new IvParameterSpec(rnd.generateSeed(16));
aesCipher.init(Cipher.ENCRYPT_MODE,secretKey,iv);

其中rnd是一个SecureRandom实例。同样，将数据作为字符串返回也是个坏主意，直接使用字节。当然，按照Libin的建议使用相同的密钥进行加密和解密。