每次執行的AES加密密鑰生成是否一致？

Question

我發現這篇寫得很好的關於如何使用AES加密的例子，我承認一些更高級的方面超出了我。如果我使用同一個實例對象，該類可以正常工作。如果我創建另一個對象，使用相同的確切passPhrase - 該對象不能再正確解碼任何類型的字符串或前一個對象創建的數據。我只能得出結論，因爲這段代碼採用了相當弱的passPhrase字符串，將SALT混合在一起，並且構建了一個更強大的128位密鑰 - 這個密鑰構建過程每次都以某種方式隨機化。存在的意義：

new AESEncrypter("MyPassword") <> new AESEncrypter("MyPassword") 

有人能幫助我修改下面的類來獲得所需的行爲：

AESEncrypter a = new AESEncrypter("MyPassword") 
String encoded = a.encrypt("my message") 

AESEncrypter b = new AESEncrypter("MyPassword") 
b.decrypt(encoded) == "my message" 

import java.security.spec.KeySpec; 
import javax.crypto.Cipher; 
import javax.crypto.SecretKey; 
import javax.crypto.SecretKeyFactory; 
import javax.crypto.spec.IvParameterSpec; 
import javax.crypto.spec.PBEKeySpec; 
import javax.crypto.spec.SecretKeySpec; 
import sun.misc.BASE64Decoder; 
import sun.misc.BASE64Encoder; 

public class AESEncrypter { 

    private static final byte[] SALT = { 
      (byte) 0xA9, (byte) 0x9B, (byte) 0xC8, (byte) 0x32, 
      (byte) 0x56, (byte) 0x35, (byte) 0xE3, (byte) 0x03 
    }; 
    private static final int ITERATION_COUNT = 65536; 
    private static final int KEY_LENGTH = 128; 
    public Cipher ecipher; 
    public Cipher dcipher; 

    AESEncrypter(String passPhrase) throws Exception { 

    SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1"); 
     KeySpec spec = new PBEKeySpec(passPhrase.toCharArray(), SALT, ITERATION_COUNT, KEY_LENGTH); 
     SecretKey tmp = factory.generateSecret(spec); 

     // I Think the problem is here??? 

     SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES"); 

     ecipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); 
     ecipher.init(Cipher.ENCRYPT_MODE, secret); 

     dcipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); 
     byte[] iv = ecipher.getParameters().getParameterSpec(IvParameterSpec.class).getIV(); 
     dcipher.init(Cipher.DECRYPT_MODE, secret, new IvParameterSpec(iv)); 
    } 

    public String encrypt(String encrypt) throws Exception { 
     byte[] bytes = encrypt.getBytes("UTF8"); 
     byte[] encrypted = encrypt(bytes); 
     return new BASE64Encoder().encode(encrypted); 
    } 

    public byte[] encrypt(byte[] plain) throws Exception { 
     return ecipher.doFinal(plain); 
    } 

    public String decrypt(String encrypt) throws Exception { 
     byte[] bytes = new BASE64Decoder().decodeBuffer(encrypt); 
     byte[] decrypted = decrypt(bytes); 
     return new String(decrypted, "UTF8"); 
    } 

    public byte[] decrypt(byte[] encrypt) throws Exception { 
     return dcipher.doFinal(encrypt); 
    } 

    public static void main(String[] args) throws Exception { 

     String message = "MESSAGE"; 
     String password = "PASSWORD"; 

     AESEncrypter encrypter1 = new AESEncrypter(password); 
     AESEncrypter encrypter2 = new AESEncrypter(password); 

     String encrypted1 = encrypter1.encrypt(message); 
     String encrypted2 = encrypter2.encrypt(message); 

     System.out.println("Display Encrypted from object 1 and 2..why do they differ?"); 

     System.out.println(encrypted1) ; 
     System.out.println(encrypted2) ; 

     System.out.println("Display Each object decrypting its own encrypted msg. Works as expected"); 

     System.out.println(encrypter1.decrypt(encrypted1)) ; 
     System.out.println(encrypter2.decrypt(encrypted2)) ; 

     System.out.println("Attempt to decrypt the each others msg.. will fail"); 

     System.out.println(encrypter1.decrypt(encrypted2)) ; 
     System.out.println(encrypter2.decrypt(encrypted1)) ; 

    } 

} 

顯示從對象1和2..why加密它們有什麼不同？

 
drGy+BNSHPy34NWkkcNqLQ== 

9p06VfBgTuh7TizZSbvKjw== 

顯示每個對象解密自己的加密信息。按預期工作

 
MESSAGE 

MESSAGE 

嘗試解密每個人的味精..將失敗

錯誤：

Exception in thread "main" 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:2165) 

Answer 1

的問題是，當你初始化CBC模式中的新Cipher，它產生一個新鮮和隨機的IV給你。這個初始化向量不一定是保密的，但它必須是不可預知的，才能提供語義安全性。您可以簡單地將IV放在密文前面並將其用於解密。

public byte[] encrypt(byte[] plain) throws Exception { 
    byte[] iv = ecipher.getParameters().getParameterSpec(IvParameterSpec.class).getIV(); 
    byte[] ct = ecipher.doFinal(plain); 
    byte[] result = new byte[ct.length + iv.length]; 
    System.arraycopy(iv, 0, result, 0, iv.length); 
    System.arraycopy(ct, 0, result, iv.length, ct.length); 
    return result; 
} 

public byte[] decrypt(byte[] encrypt) throws Exception { 
    byte[] iv = new byte[dcipher.getBlockSize()]; 
    byte[] ct = new byte[encrypt.length - dcipher.getBlockSize()]; 
    System.arraycopy(encrypt, 0, iv, 0, dcipher.getBlockSize()); 
    System.arraycopy(encrypt, dcipher.getBlockSize(), ct, 0, ct.length); 

    dcipher.init(Cipher.DECRYPT_MODE, secret, new IvParameterSpec(iv)); 
    return dcipher.doFinal(ct); 
} 

則需要在一個私有變量的解密工作的初始化步驟來存儲secret。

---

請記住，PBDKF2的鹽也應該是隨機的，長度爲16個字節。你可以將它存儲在IV的旁邊。