Search for embedded object with custom encryption of QR Code signatures Leave feedback

// 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();
    }
}

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; }
}

// instantiating the signature object
using (Signature signature = new Signature("signed.pdf"))
{
    // setup search options
    QrCodeSearchOptions searchOptions = new QrCodeSearchOptions();
    // specify as true to search all pages of a document
    searchOptions.AllPages = true;
    searchOptions.DataEncryption = new CustomXOREncryptionAttribute();
    // search document
    List<QrCodeSignature> signatures = signature.Search<QrCodeSignature>(searchOptions);
    // output signatures
    foreach (QrCodeSignature qrCodeSignature in signatures)
    {
        if (qrCodeSignature != null)
        {
            DocumentSignatureData docSignature = qrCodeSignature.GetData<DocumentSignatureData>();
            if (docSignature != null)
            {
                Console.WriteLine("Found DocumentSignature: #{0} by {1} from {2} DataFactor = {3}", docSignature.ID,
                    docSignature.Author, docSignature.Signed, docSignature.DataFactor.ToString("N2"));
            }
        }
    }
}