Implement custom encryption with QR-Code signatures

GroupDocs.Signature provides ability to embed into QR-code signature custom objects. This feature is implemented over object serialization to string and further encryption. There is ability to provide custom encryption. This procedure requires implementation of interface IDataEncryption with two methods to encrypt and decrypt data.

Here are the steps to embed into QR-code text with custom encryption with GroupDocs.Signature: 

  • Define custom data encryption class that implements IDataEncryption interface. By default GroupDocs.Signature has several encryption implementation you can use but allows user to customize it.
  • Implement class with properties and specify if needed class attributes (like custom serialization attribute, custom encryption attribute), specify attributes for properties like FormatAttribute attribute to specify serialization name and display format, same as SkipSerializationAttribute to mark property of class as not serialize
  • Create new instance of Signature class and pass source document path as a constructor parameter.
  • Create one or several objects of QrCodeSignOptions object with Data value
  • Instantiate the QrCodeSignOptions object according to your requirements and custom object to Data property.
  • Call Sign method of  Signature  class instance and pass QrCodeSignOptions to it.

This example shows how to specify custom serialization class. This class could be implemented also as Attribute (optional) to specify as class attribute.

// Define class that implements IDataEncryption interface
private 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);
        return dst.ToString();

Definition of class

This example shows how to define custom class with serialization and encryption properties and setup Format attributes for properties.

public class DocumentSignatureData
    public string ID { get; set; }
    public string Author { get; set; }
    [Format("SDate", "yyyy-MM-dd")]
    public DateTime Signed { get; set; }
    [Format("SDFact", "N2")]
    public decimal DataFactor { get; set; }
    public string Comments { get; set; }

Sign documents with custom encrypted objects and values into QR-code signatures

This example shows how to add custom object into metadata signature to Image document.

using (Signature signature = new Signature("sample.pdf"))
    // create data encryption
    IDataEncryption encryption = new CustomXOREncryption();
    // create custom object
    DocumentSignatureData documentSignatureData = new DocumentSignatureData()
        ID = Guid.NewGuid().ToString(),
        Author = Environment.UserName,
        Signed = DateTime.Now,
        DataFactor = 11.22M
    // setup QR-Code options
    QrCodeSignOptions options = new QrCodeSignOptions()
        // set custom object to serialize to QR Code
        Data = documentSignatureData,
        // QR-code type
        EncodeType = QrCodeTypes.QR,
        // specify serialization encryption
        DataEncryption = encryption,
        // locate and aligh signature
        Height = 100,
        Width = 100,
        VerticalAlignment = VerticalAlignment.Bottom,
        HorizontalAlignment = HorizontalAlignment.Right,
        Margin = new Padding() { Right = 10, Bottom = 10 }
    // sign document to file
    signature.Sign("QRCodeCustomEncryption.pdf", options);

More resources

GitHub Examples

You may easily run the code above and see the feature in action in our GitHub examples:

Free Online App 

Along with full-featured .NET library we provide simple, but powerful free Apps.
You are welcome to eSign PDF, Word, Excel, PowerPoint documents with free to use online GroupDocs Signature App.