Search for embedded object with custom serialization of QR-Code signatures

/// <summary>
/// Creates class that implements IDataSerializer interface
/// This implementation is using json library to provide serialization and deserialization
/// </summary>

public class CustomSerializationAttribute : Attribute, IDataSerializer
{
    public T Deserialize<T>(string source) where T : class
    {
        return JsonConvert.DeserializeObject<T>(source);
    }
    public string Serialize(object data)
    {
        var serializerSettings = new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore };
        return JsonConvert.SerializeObject(data, serializerSettings);
    }
}

// Define class that implements IDataEncryption interface
// Class could inherits Attribute to use it with class definition

public class CustomXOREncryption : IDataEncryption
{
    /// <summary>
    /// Gets or sets non empty key for encryption (at least one character)
    /// </summary>
    public int Key { get; set; }
    /// <summary>
    /// Encode method to encrypt string.
    /// </summary>
    /// <param name="source">Source string to encode.</param>
    /// <returns>Returns enccrypted string</returns>
    public string Encode(string source)
    {
        return Process(source);
    }
    /// <summary>
    /// Decode method to obtain decrypted string.
    /// </summary>
    /// <param name="source">Source string to decode.</param>
    /// <returns>Returns decrypted string</returns>
    public string Decode(string source)
    {
        return Process(source);
    }
    /// <summary>
    /// Using XOR operation get encoded / decoded string
    /// </summary>
    /// <param name="source"></param>
    /// <returns></returns>
    private string Process(string source)
    {
        StringBuilder src = new StringBuilder(source);
        StringBuilder dst = new StringBuilder(src.Length);
        char chTmp;
        for (int index = 0; index < src.Length; ++index)
        {
            chTmp = src[index];
            chTmp = (char)(chTmp ^ this.Key);
            dst.Append(chTmp);
        }
        return dst.ToString();
    }
}

// define class with custom serialization attribute
[CustomSerialization]
public class DocumentSignatureData
{
    [Format("SignID")]
    public string ID { get; set; }
    [Format("SAuth")]
    public string Author { get; set; }
    [Format("SDate", "yyyy-MM-dd")]
    public DateTime Signed { get; set; }
    [Format("SDFact", "N2")]
    public decimal DataFactor { get; set; }
    [SkipSerialization]
    public string Comments { get; set; }
}

using (Signature signature = new Signature("QRCodeCustomSerializationObject.pdf"))
{
    // create data encryption
    IDataEncryption encryption = new CustomXOREncryption();
    QrCodeSearchOptions options = new QrCodeSearchOptions()
    {
        // specify special pages to search on
        AllPages = true,
        DataEncryption = encryption
    };
    // search for signatures in document
    List<QrCodeSignature> signatures = signature.Search<QrCodeSignature>(options);
    Console.WriteLine("\nSource document contains following signatures:");
    foreach (var qrCodeSignature in signatures)
    {
        Console.WriteLine("QRCode signature found at page {0} with type {1}.", qrCodeSignature.PageNumber, qrCodeSignature.EncodeType);
        DocumentSignatureData documentSignatureData = qrCodeSignature.GetData<DocumentSignatureData>();
        if (documentSignatureData != null)
        {
            Console.WriteLine("QRCode signature has DocumentSignatureData object:\n ID = {0}, Author = {1}, Signed = {2}, DataFactor {3}",
                documentSignatureData.ID, documentSignatureData.Author, documentSignatureData.Signed.ToShortDateString(), documentSignatureData.DataFactor);
        }
    }
}