序列化我的对象时如何加密选定的属性？

Question

我正在使用 JSON 在我的应用程序中存储某些设置。一些设置包含敏感信息（例如密码），而其他设置则不敏感。理想情况下，我希望能够序列化我的对象，其中敏感属性自动加密，同时保持非敏感设置可读。有没有办法使用 Json.Net 来做到这一点？我没有看到任何与加密相关的设置。

Answer 1

Json.Net 没有内置加密。如果您希望能够在序列化过程中进行加密和解密，您将需要编写一些自定义代码。一种方法是使用自定义 IContractResolver in conjunction with an IValueProvider。值提供者为您提供了一个挂钩，您可以在其中转换序列化过程中的值，而契约解析器让您可以控制何时何地应用值提供者。他们可以一起为您提供您正在寻找的解决方案。

下面是您需要的代码示例。首先，您会注意到我定义了一个新的 [JsonEncrypt] 属性；这将用于指示您要加密的属性。 EncryptedStringPropertyResolver class 扩展了 Json.Net 提供的 DefaultContractResolver。我已经覆盖了 CreateProperties() 方法，这样我就可以检查由基本解析器创建的 JsonProperty 对象，并将我的自定义 EncryptedStringValueProvider 的实例附加到具有 [=16] 的任何字符串属性=] 属性应用。 EncryptedStringValueProvider 稍后通过相应的 GetValue() 和 SetValue() 方法处理目标字符串属性的实际 encryption/decryption。

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Security.Cryptography;
using System.Text;
using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;

[AttributeUsage(AttributeTargets.Property)]
public class JsonEncryptAttribute : Attribute
{
}

public class EncryptedStringPropertyResolver : DefaultContractResolver
{
    private byte[] encryptionKeyBytes;

    public EncryptedStringPropertyResolver(string encryptionKey)
    {
        if (encryptionKey == null)
            throw new ArgumentNullException("encryptionKey");

        // Hash the key to ensure it is exactly 256 bits long, as required by AES-256
        using (SHA256Managed sha = new SHA256Managed())
        {
            this.encryptionKeyBytes = 
                sha.ComputeHash(Encoding.UTF8.GetBytes(encryptionKey));
        }
    }

    protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
    {
        IList<JsonProperty> props = base.CreateProperties(type, memberSerialization);

        // Find all string properties that have a [JsonEncrypt] attribute applied
        // and attach an EncryptedStringValueProvider instance to them
        foreach (JsonProperty prop in props.Where(p => p.PropertyType == typeof(string)))
        {
            PropertyInfo pi = type.GetProperty(prop.UnderlyingName);
            if (pi != null && pi.GetCustomAttribute(typeof(JsonEncryptAttribute), true) != null)
            {
                prop.ValueProvider = 
                    new EncryptedStringValueProvider(pi, encryptionKeyBytes);
            }
        }

        return props;
    }

    class EncryptedStringValueProvider : IValueProvider
    {
        PropertyInfo targetProperty;
        private byte[] encryptionKey;

        public EncryptedStringValueProvider(PropertyInfo targetProperty, byte[] encryptionKey)
        {
            this.targetProperty = targetProperty;
            this.encryptionKey = encryptionKey;
        }

        // GetValue is called by Json.Net during serialization.
        // The target parameter has the object from which to read the unencrypted string;
        // the return value is an encrypted string that gets written to the JSON
        public object GetValue(object target)
        {
            string value = (string)targetProperty.GetValue(target);
            byte[] buffer = Encoding.UTF8.GetBytes(value);

            using (MemoryStream inputStream = new MemoryStream(buffer, false))
            using (MemoryStream outputStream = new MemoryStream())
            using (AesManaged aes = new AesManaged { Key = encryptionKey })
            {
                byte[] iv = aes.IV;  // first access generates a new IV
                outputStream.Write(iv, 0, iv.Length);
                outputStream.Flush();

                ICryptoTransform encryptor = aes.CreateEncryptor(encryptionKey, iv);
                using (CryptoStream cryptoStream = new CryptoStream(outputStream, encryptor, CryptoStreamMode.Write))
                {
                    inputStream.CopyTo(cryptoStream);
                }

                return Convert.ToBase64String(outputStream.ToArray());
            }
        }

        // SetValue gets called by Json.Net during deserialization.
        // The value parameter has the encrypted value read from the JSON;
        // target is the object on which to set the decrypted value.
        public void SetValue(object target, object value)
        {
            byte[] buffer = Convert.FromBase64String((string)value);

            using (MemoryStream inputStream = new MemoryStream(buffer, false))
            using (MemoryStream outputStream = new MemoryStream())
            using (AesManaged aes = new AesManaged { Key = encryptionKey })
            {
                byte[] iv = new byte[16];
                int bytesRead = inputStream.Read(iv, 0, 16);
                if (bytesRead < 16)
                {
                    throw new CryptographicException("IV is missing or invalid.");
                }

                ICryptoTransform decryptor = aes.CreateDecryptor(encryptionKey, iv);
                using (CryptoStream cryptoStream = new CryptoStream(inputStream, decryptor, CryptoStreamMode.Read))
                {
                    cryptoStream.CopyTo(outputStream);
                }

                string decryptedValue = Encoding.UTF8.GetString(outputStream.ToArray());
                targetProperty.SetValue(target, decryptedValue);
            }
        }

    }
}

解析器就位后，下一步是将自定义 [JsonEncrypt] 属性应用于 class 中您希望在序列化期间加密的字符串属性。例如，这里是一个人为的 class 可能代表一个用户：

public class UserInfo
{
    public string UserName { get; set; }

    [JsonEncrypt]
    public string UserPassword { get; set; }

    public string FavoriteColor { get; set; }

    [JsonEncrypt]
    public string CreditCardNumber { get; set; }
}

最后一步是将自定义解析器注入序列化过程。为此，创建一个新的 JsonSerializerSettings 实例，然后将 ContractResolver 属性设置为自定义解析器的新实例。将设置传递给 JsonConvert.SerializeObject() 或 DeserializeObject() 方法，一切都应该正常工作。

这是一个往返演示：

public class Program
{
    public static void Main(string[] args)
    {
        try
        {
            UserInfo user = new UserInfo
            {
                UserName = "jschmoe",
                UserPassword = "Hunter2",
                FavoriteColor = "atomic tangerine",
                CreditCardNumber = "1234567898765432",
            };

            // Note: in production code you should not hardcode the encryption
            // key into the application-- instead, consider using the Data Protection 
            // API (DPAPI) to store the key.  .Net provides access to this API via
            // the ProtectedData class.

            JsonSerializerSettings settings = new JsonSerializerSettings();
            settings.Formatting = Formatting.Indented;
            settings.ContractResolver = new EncryptedStringPropertyResolver("My-Sup3r-Secr3t-Key");

            Console.WriteLine("----- Serialize -----");
            string json = JsonConvert.SerializeObject(user, settings);
            Console.WriteLine(json);
            Console.WriteLine();

            Console.WriteLine("----- Deserialize -----");
            UserInfo user2 = JsonConvert.DeserializeObject<UserInfo>(json, settings);

            Console.WriteLine("UserName: " + user2.UserName);
            Console.WriteLine("UserPassword: " + user2.UserPassword);
            Console.WriteLine("FavoriteColor: " + user2.FavoriteColor);
            Console.WriteLine("CreditCardNumber: " + user2.CreditCardNumber);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.GetType().Name + ": " + ex.Message);
        }
    }
}

输出：

----- Serialize -----
{
  "UserName": "jschmoe",
  "UserPassword": "sK2RvqT6F61Oib1ZittGBlv8xgylMEHoZ+1TuOeYhXQ=",
  "FavoriteColor": "atomic tangerine",
  "CreditCardNumber": "qz44JVAoJEFsBIGntHuPIgF1sYJ0uyYSCKdYbMzrmfkGorxgZMx3Uiv+VNbIrbPR"
}

----- Deserialize -----
UserName: jschmoe
UserPassword: Hunter2
FavoriteColor: atomic tangerine
CreditCardNumber: 1234567898765432

Fiddle: https://dotnetfiddle.net/trsiQc

Answer 2

我的解决方案：

    public string PasswordEncrypted { get; set; }

    [JsonIgnore]
    public string Password
    {
        get
        {
            var encrypted = Convert.FromBase64String(PasswordEncrypted);
            var data = ProtectedData.Unprotect(encrypted, AdditionalEntropy, DataProtectionScope.LocalMachine);
            var res = Encoding.UTF8.GetString(data);
            return res;
        }
        set
        {
            var data = Encoding.UTF8.GetBytes(value);
            var encrypted = ProtectedData.Protect(data, AdditionalEntropy, DataProtectionScope.LocalMachine);
            PasswordEncrypted = Convert.ToBase64String(encrypted);
        }

（可以变得不那么冗长）

Answer 3

虽然@Brian 的解决方案非常聪明，但我不喜欢自定义的复杂性ContractResolver。我将 Brian 的代码转换为 JsonConverter，因此您的代码将变为

public class UserInfo
{
    public string UserName { get; set; }

    [JsonConverter(typeof(EncryptingJsonConverter), "My-Sup3r-Secr3t-Key")]
    public string UserPassword { get; set; }

    public string FavoriteColor { get; set; }

    [JsonConverter(typeof(EncryptingJsonConverter), "My-Sup3r-Secr3t-Key")]
    public string CreditCardNumber { get; set; }
}

我已经将（相当冗长的）EncryptingJsonConverter 发布为 Gist and also blogged about it。

序列化我的对象时如何加密选定的属性？

How can I encrypt selected properties when serializing my objects?

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