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 setData value 
  • Instantiate the QrCodeSignOptions object according to your requirements and custom object to setData 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.

public class CustomXOREncryption implements IDataEncryption
     * <p>
     * Gets or sets non empty key for encryption (at least one character)
     * </p>
    public final int getKey(){ return auto_Key; }
     * <p>
     * Gets or sets non empty key for encryption (at least one character)
     * </p>
    public final void setKey(int value){ auto_Key = value; }
    private int auto_Key;
     * <p>
     * Encode method to encrypt string.
     * </p>
     * @return Returns enccrypted string
     * @param source Source string to encode.
    public final String encode(String source)
        return process(source);
     * <p>
     * Decode method to obtain decrypted string.
     * </p>
     * @return Returns decrypted string
     * @param source Source string to decode.
    public final String decode(String source)
        return process(source);
     * <p>
     * Using XOR operation get encoded / decoded string
     * </p>
     * @return
     * @param source
    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.charAt(index);
            chTmp = (char)(chTmp ^ this.getKey());
        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 getID(){ return ID; }
    public void setID(String value){ ID = value; }
    @FormatAttribute(propertyName = "SignID")
    public String ID;
    public final String getAuthor(){ return Author; }
    public final void setAuthor(String value){ Author = value; }
    @FormatAttribute(propertyName = "SAuth")
    public String Author;
    //JAVA-added public wrapper for internalized property accessor
    public final java.util.Date getSigned() {  return Signed; }
    public final void setSigned(java.util.Date value) { Signed = value; }
    @FormatAttribute (propertyName = "SDate",propertyFormat = "yyyy-MM-dd")
    public java.util.Date Signed = new java.util.Date();
    public final java.math.BigDecimal getDataFactor() { return DataFactor; }
    public final void setDataFactor(java.math.BigDecimal value) { DataFactor = value; }
    @FormatAttribute (propertyName = "SDFact",propertyFormat = "N2")
    public java.math.BigDecimal DataFactor = new java.math.BigDecimal(0.01);

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.

Signature signature = new Signature("sample.pdf");
// create data encryption
IDataEncryption encryption = new CustomXOREncryption();
// create custom object
DocumentSignatureData documentSignature = new DocumentSignatureData();
documentSignature.setSigned(new java.util.Date());
documentSignature.setDataFactor(new java.math.BigDecimal("11.22"));
// setup QR-Code options
QrCodeSignOptions options = new QrCodeSignOptions();
// set custom object to serialize to QR Code
// QR-code type
// specify serialization encryption
// locate and aligh signature
Padding padding = new Padding() ;
// 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.