using System;

using System.Globalization;

using System.IO;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        var input = JObject.Parse(@"

            {

                a: {

                    type: 'encrypted',

                    name: 'some-name',

                    data: 'should NOT see this',

                    b: {

                        type: 'not encrypted',

                        name: 'some-name',

                        data: 'should be visible'

                    }

                },

                d: [

                    {

                        type: 'encrypted',

                        name: 'some-name',

                        data: 'should NOT see this'

                    }

                ]

            }");

​

        var output1 = JsonConvert.SerializeObject(input, Formatting.Indented, new RemoveEncryptedDataConverter());

        var output2 = input.ToString(Formatting.Indented, new RemoveEncryptedDataConverter());

        string output3;

        using (StringWriter stringWriter = new StringWriter((IFormatProvider)CultureInfo.InvariantCulture))

        {

            JsonTextWriter jsonTextWriter = new JsonTextWriter((TextWriter)stringWriter);

            jsonTextWriter.Formatting = Formatting.Indented;

            input.WriteTo(jsonTextWriter, new RemoveEncryptedDataConverter());

            output3 = stringWriter.ToString();

        }

        Console.WriteLine("SerializeObject (CORRECT):");

        Console.WriteLine(output1);

        Console.WriteLine("ToString (INCORRECT):");

        Console.WriteLine(output2);

        Console.WriteLine("WriteTo (INCORRECT):");

        Console.WriteLine(output3);

    }

}

​

public class RemoveEncryptedDataConverter : JsonConverter

{

    public override bool CanConvert(Type objectType)

    {

        return typeof(JToken).IsAssignableFrom(objectType);

    }

​

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)

    {

        throw new NotImplementedException();

    }

​

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

    {

        JToken token = (JToken)value;

        if (token.Type == JTokenType.Object)

        {

            bool omitDataProperty = token.Value<string>("type") == "encrypted";

​

            writer.WriteStartObject();

            foreach (var prop in token.Children<JProperty>())

            {

                if (omitDataProperty && prop.Name == "data")

                    continue;

​

                writer.WritePropertyName(prop.Name);

                serializer.Serialize(writer, prop.Value);  // recurse

            }

            writer.WriteEndObject();

        }

        else if (token.Type == JTokenType.Array)

        {

            writer.WriteStartArray();

            foreach (var item in token.Children())

            {

                serializer.Serialize(writer, item);  // recurse

            }

            writer.WriteEndArray();

        }

        else // JValue

        {

            token.WriteTo(writer);

        }

    }

}

​