将 .Net 解密转换为 Java

Question

目前我正在做一个项目，他们使用 AES 加密和 RFC2898 派生字节。这是我提供的解密方法。现在我需要在 java.

中实现它

private string Decrypt(string cipherText)
    {
        string EncryptionKey = "MAKV2SPBNI657328B";
        cipherText = cipherText.Replace(" ", "+");
        byte[] cipherBytes = Convert.FromBase64String(cipherText);
        using (Aes encryptor = Aes.Create())
        {
            Rfc2898DeriveBytes pdb = new Rfc2898DeriveBytes(EncryptionKey, new byte[] {
                0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 
                });
            encryptor.Key = pdb.GetBytes(32);
            encryptor.IV = pdb.GetBytes(16);
            using (MemoryStream ms = new MemoryStream())
            {
                using (CryptoStream cs = new CryptoStream(ms, encryptor.CreateDecryptor(), CryptoStreamMode.Write))
                {
                    cs.Write(cipherBytes, 0, cipherBytes.Length);
                    cs.Close();
                }
                cipherText = Encoding.Unicode.GetString(ms.ToArray());
            }
        }
        return cipherText;
    }

这就是我到目前为止所做的：

   String EncryptionKey = "MAKV2SPBNI657328B";
   String userName="5L9p7pXPxc1N7ey6tpJOla8n10dfCNaSJFs%2bp5U0srs0GdH3OcMWs%2fDxMW69BQb7"; 
   byte[] salt =  new byte[] {0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76};
   try {
        userName = java.net.URLDecoder.decode(userName, StandardCharsets.UTF_8.name());
        SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
        PBEKeySpec pbeKeySpec = new PBEKeySpec(EncryptionKey.toCharArray(), salt, 1000);
        Key secretKey = factory.generateSecret(pbeKeySpec);
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        cipher.init(Cipher.DECRYPT_MODE, secretKey);
        byte[] result = cipher.doFinal(userName.getBytes("UTF-8"));
        System.out.println(result.toString());
   } catch (Exception e) {
        System.out.println(e.getMessage());
   }

但是我收到如下错误：

Key length not found java.security.spec.InvalidKeySpecException: Key length not found

Answer 1

Java代码中存在一些问题：必须指定要生成的位数，除了必须导出IV的密钥外，还必须申请IV进行解密，密文必须是解码明文必须使用Base64解码和Utf-16LE。详细：

实例化PBEKeySpec时，必须在第4个参数中指定要生成的位数。由于密钥（256 位）和 IV（128 位）都是在 C# 代码中派生的，因此必须应用 384（= 256 + 128）：
```
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
PBEKeySpec pbeKeySpec = new PBEKeySpec(encryptionKey.toCharArray(), salt, 1000, 384);   
```

前256位是密钥，后面128位是IV：

byte[] derivedData = factory.generateSecret(pbeKeySpec).getEncoded();
byte[] key = new byte[32];
byte[] iv = new byte[16];
System.arraycopy(derivedData, 0, key, 0, key.length);
System.arraycopy(derivedData, key.length, iv, 0, iv.length);

IV 必须在 Cipher#init-call using an IvParameterSpec 实例的第三个参数中传递：

SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
IvParameterSpec ivSpec = new IvParameterSpec(iv);
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, ivSpec);

密文必须经过Base64解码才能解密：

byte[] result = cipher.doFinal(Base64.getDecoder().decode(userName));

必须使用 Utf-16LE 编码（对应于 C# 中的 Encoding.Unicode）从解密的字节数组创建一个字符串：
```
System.out.println(new String(result, StandardCharsets.UTF_16LE)); // Output: Mohammad Al Mamun
```

注意 CBC mode, it's important that a key/IV combination is only used once for security reasons. For the C# (or Java) code here, this means that for the same password, different salts must be used for each encryption, see here.

将 .Net 解密转换为 Java

Converting .Net decryption to Java

java

.net

encryption

aes

rfc2898