Java AES加密和解密

Question

我想使用128位AES加密和16字节密钥对密码进行加密和解密。javax.crypto.BadPaddingException解密值时出现错误。解密时我丢失任何内容吗？

public static void main(String args[]) {
    Test t = new Test();
    String encrypt = new String(t.encrypt("mypassword"));
    System.out.println("decrypted value:" + t.decrypt("ThisIsASecretKey", encrypt));
}

public String encrypt(String value) {
    try {
        byte[] raw = new byte[]{'T', 'h', 'i', 's', 'I', 's', 'A', 'S', 'e', 'c', 'r', 'e', 't', 'K', 'e', 'y'};
        SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
        byte[] encrypted = cipher.doFinal(value.getBytes());
        System.out.println("encrypted string:" + (new String(encrypted)));
        return new String(skeySpec.getEncoded());
    } catch (NoSuchAlgorithmException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IllegalBlockSizeException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (BadPaddingException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (InvalidKeyException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (NoSuchPaddingException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    }
    return null;
}

public String decrypt(String key, String encrypted) {
    try {
        SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(skeySpec.getEncoded(), "AES"));
        //getting error here
        byte[] original = cipher.doFinal(encrypted.getBytes());
        return new String(original);
    } catch (IllegalBlockSizeException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (BadPaddingException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (InvalidKeyException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (NoSuchAlgorithmException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (NoSuchPaddingException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    }
    return null;
}

错误信息

encrypted string:�Bj�.�Ntk�F�`�
encrypted key:ThisIsASecretKey
decrypted value:null
May 25, 2012 12:54:02 PM bean.Test decrypt
SEVERE: null
javax.crypto.BadPaddingException: Given final block not properly padded
at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)
at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)
at com.sun.crypto.provider.AESCipher.engineDoFinal(DashoA13*..)
at javax.crypto.Cipher.doFinal(DashoA13*..)
at bean.Test.decrypt(Test.java:55)
at bean.Test.main(Test.java:24)

最后我基于@QuantumMechanic答案使用以下解决方案

public class Test {

public String encryptionKey;

public static void main(String args[]) {
    Test t = new Test();
    String encrypt = t.encrypt("mypassword");
    System.out.println("decrypted value:" + t.decrypt(t.encryptionKey, encrypt));
}

public String encrypt(String value) {
    try {
        // Get the KeyGenerator
        KeyGenerator kgen = KeyGenerator.getInstance("AES");
        kgen.init(256);
        // Generate the secret key specs.
        SecretKey skey = kgen.generateKey();
        byte[] raw = skey.getEncoded();
        String key = new Base64().encodeAsString(raw);
        this.encryptionKey = key;
        System.out.println("------------------Key------------------");
        System.out.println(key);
        System.out.println("--------------End of Key---------------");
        SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
        String encrypt = (new Base64()).encodeAsString(cipher.doFinal(value.getBytes()));
        System.out.println("encrypted string:" + encrypt);
        return encrypt;
    } catch (NoSuchAlgorithmException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IllegalBlockSizeException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (BadPaddingException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (InvalidKeyException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (NoSuchPaddingException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    }
    return null;
}

public String decrypt(String key, String encrypted) {
    try {
        Key k = new SecretKeySpec(Base64.getDecoder().decode(key), "AES");
        Cipher c = Cipher.getInstance("AES");
        c.init(Cipher.DECRYPT_MODE, k);
        byte[] decodedValue = Base64.getDecoder().decode(encrypted);
        byte[] decValue = c.doFinal(decodedValue);
        String decryptedValue = new String(decValue);
        return decryptedValue;
    } catch (IllegalBlockSizeException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (BadPaddingException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (InvalidKeyException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (NoSuchAlgorithmException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    } catch (NoSuchPaddingException ex) {
        Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
    }
    return null;
}

}

Answer 1

如果对于块密码，您将不使用Cipher包含填充方案的转换，则需要使明文中的字节数为该密码的块大小的整数倍。

因此，要么将纯文本填充到16字节的倍数（即AES块大小），要么在创建Cipher对象时指定填充方案。例如，您可以使用：

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

除非您有充分的理由不这样做，否则请使用JCE实现中已包含的填充方案。他们考虑了许多微妙和极端的情况，否则您将不得不自己意识到和应对这些情况。

好的，您的第二个问题是您String用来保存密文。

一般来说，

String s = new String(someBytes);
byte[] retrievedBytes = s.getBytes();

会 不会 有someBytes和retrievedBytes是相同的。

如果您希望/必须将密文保存在中String，请先对密文字节进行base64编码，然后String从base64编码的字节中构造。然后，当您解密时，将从getBytes()中获取base64编码的字节String，然后对它们进行base64解码以获取真实的密文，然后对其进行解密。

出现此问题的原因是，大多数（全部？）字符编码都无法将任意字节映射到有效字符。因此，当您String从密文创建密码时，String构造函数（使用字符编码将字节转换为字符）本质上必须丢弃一些字节，因为它对它们毫无意义。因此，当您从字符串中获取字节时，它们与您放入字符串中的字节不同。

在Java（以及通常在现代编程中）中，除非绝对知道要处理ASCII，否则不能假定一个字符=一个字节。这就是为什么要从任意字节构建字符串时需要使用base64（或类似的东西）的原因。