使用 Java 加密和解密：无法获得相同的输出

Question

我正在尝试学习和测试 java 1.6 加密/解密 API。我想知道我做错了什么以及我在知识方面缺少什么。

在下面的代码中，我创建了两个密码：一个用于加密，另一个用于解密。当我使用这些密码时，我用不同的 SecretKey 初始化它们，但我仍然能够得到相同的值。这是为什么呢？

    String algorithm = "DES";
    SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(algorithm);

    byte[] encBytes = "12345678".getBytes("UTF8");
    byte[] decBytes = "56781234".getBytes("UTF8");

    DESKeySpec keySpecEncrypt = new DESKeySpec(encBytes);
    DESKeySpec keySpecDecrypt = new DESKeySpec(decBytes);


    SecretKey keyEncrypt = keyFactory.generateSecret(keySpecEncrypt);
    SecretKey keyDecrypt = keyFactory.generateSecret(keySpecDecrypt);

    Cipher cipherEncrypt = Cipher.getInstance(algorithm);
    Cipher cipherDecrypt = Cipher.getInstance(algorithm);

    String input = "john doe";

    cipherEncrypt.init(Cipher.ENCRYPT_MODE, keyEncrypt);
    byte[] inputBytes = cipherEncrypt.doFinal(input.getBytes());
    System.out.println("inputBytes: " + new String(inputBytes));

    cipherDecrypt.init(Cipher.DECRYPT_MODE, keyDecrypt);
    byte[] outputBytes = cipherDecrypt.doFinal(inputBytes);
    System.out.println("outputBytes: " + new String(outputBytes));

Answer 1

欢迎使用加密！如前所述，DES 是对称的，需要与解密相同的密钥进行加密。该密钥必须是您正在使用的密码的正确位数。对于 56 位的 DES。不过，在你走得太远之前，你可能需要考虑以下几点：

1. 您应该使用更强的加密标准，例如AES。现在可以破解DES 加密。
2. 如果您想使用字符串作为键，那么您应该针对该键字符串使用像SHA-256 这样的强哈希函数。然后从该哈希输出中获取所需的加密密钥所需的位数，对于 AES，128 位就足够了。您的密钥字符串应该和您一样长。
3. 最好使用分组密码模式，这种模式不会每次为相同的输入生成相同的输出。请参阅block cipher modes of operation 了解有关 ECB 模式为何不好的信息和可视化。

这是一个在 CBC 模式下使用 128 位 AES 加密和 PKCS #5 填充的工作示例：

import java.security.MessageDigest;
import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class EncryptDecrypt {
    public static void main(String[] args) throws Exception {
        // here are your inputs
        String keyString = "averylongtext!@$@#$#@$#*&(*&}{23432432432dsfsdf";
        String input = "john doe";

        // setup AES cipher in CBC mode with PKCS #5 padding
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

        // setup an IV (initialization vector) that should be
        // randomly generated for each input that's encrypted
        byte[] iv = new byte[cipher.getBlockSize()];
        new SecureRandom().nextBytes(iv);
        IvParameterSpec ivSpec = new IvParameterSpec(iv);

        // hash keyString with SHA-256 and crop the output to 128-bit for key
        MessageDigest digest = MessageDigest.getInstance("SHA-256");
        digest.update(keyString.getBytes());
        byte[] key = new byte[16];
        System.arraycopy(digest.digest(), 0, key, 0, key.length);
        SecretKeySpec keySpec = new SecretKeySpec(key, "AES");

        // encrypt
        cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivSpec);
        byte[] encrypted = cipher.doFinal(input.getBytes("UTF-8"));
        System.out.println("encrypted: " + new String(encrypted));

        // include the IV with the encrypted bytes for transport, you'll
        // need the same IV when decrypting (it's safe to send unencrypted)

        // decrypt
        cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);
        byte[] decrypted = cipher.doFinal(encrypted);
        System.out.println("decrypted: " + new String(decrypted, "UTF-8"));
    }
}

Answer 2

这是来自 JDK 文档的描述：

DESKeySpec 公共 DESKeySpec（字节 [] 密钥） 抛出 InvalidKeyException 使用 key 中的前 8 个字节作为 DES 密钥的密钥材料创建一个 DESKeySpec 对象。 构成 DES 密钥的字节是介于 key[0] 和 key[7] 之间的字节。

DESKeySpec 仅使用 byte[] 的前 8 个字节作为密钥。因此，在您的示例中使用的实际键是相同的。

Answer 3

这是一个使用 56 位 DES 加密的工作示例。

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

public class CipherHelper {

    // Algorithm used
    private final static String ALGORITHM = "DES";

    /**
     * Encrypt data
     * @param secretKey -   a secret key used for encryption
     * @param data      -   data to encrypt
     * @return  Encrypted data
     * @throws Exception
     */
    public static String cipher(String secretKey, String data) throws Exception {
        // Key has to be of length 8
        if (secretKey == null || secretKey.length() != 8)
            throw new Exception("Invalid key length - 8 bytes key needed!");

        SecretKey key = new SecretKeySpec(secretKey.getBytes(), ALGORITHM);
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.ENCRYPT_MODE, key);

        return toHex(cipher.doFinal(data.getBytes()));
    }

    /**
     * Decrypt data
     * @param secretKey -   a secret key used for decryption
     * @param data      -   data to decrypt
     * @return  Decrypted data
     * @throws Exception
     */
    public static String decipher(String secretKey, String data) throws Exception {
        // Key has to be of length 8
        if (secretKey == null || secretKey.length() != 8)
            throw new Exception("Invalid key length - 8 bytes key needed!");

        SecretKey key = new SecretKeySpec(secretKey.getBytes(), ALGORITHM);
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(Cipher.DECRYPT_MODE, key);

        return new String(cipher.doFinal(toByte(data)));
    }

    // Helper methods

    private static byte[] toByte(String hexString) {
        int len = hexString.length()/2;

        byte[] result = new byte[len];

        for (int i = 0; i < len; i++)
            result[i] = Integer.valueOf(hexString.substring(2*i, 2*i+2), 16).byteValue();
        return result;
    }

    public static String toHex(byte[] stringBytes) {
        StringBuffer result = new StringBuffer(2*stringBytes.length);

        for (int i = 0; i < stringBytes.length; i++) {
            result.append(HEX.charAt((stringBytes[i]>>4)&0x0f)).append(HEX.charAt(stringBytes[i]&0x0f));
        }

        return result.toString();
    }

    private final static String HEX = "0123456789ABCDEF";

    // Helper methods - end

    /**
     * Quick test
     * @param args
     */
    public static void main(String[] args) {
        try {

            String secretKey    = "01234567";
            String data="test";
            String encryptedData = cipher(secretKey, data);

            System.out.println("encryptedData: " + encryptedData);

            String decryptedData = decipher(secretKey, encryptedData);

            System.out.println("decryptedData: " + decryptedData);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}