How to use Reference in an XML signature?

Question

Doubts about System.Security.Cryptography.Xml.Reference:

1. What exactly is it for?
2. How should I use Reference? What to assign to it?
3. I need to use this in signing an XML Pq?
4. And how to use?

What to do here?

Dim reference As New Reference()
reference.Uri = ???

Answer 1

1. Reference represents the element of a digital XML signature defined by the digital signature specification (www.W3.org/TR/xmldsig-core/).

2. Some properties available font: MSDN:
   Digestmethod: Obtain or define the method Digest URI Uniform Resource Identifier of Reference.
   Digestvalue: Get or set the value of Digest of the current Reference.
   Id: Obtains or defines the identification of the current Reference.
   Transformchain Get the current transformation chain Reference.
   Type: Get or define the type of object being signed.
   Uri: Obtains or defines the Uri of the current Reference.

3. Yes together other class, for example SignedXml. Because unsigned Nfe is simply not accepted by SEFAZ.

4. Example:

   ' Create a new XML document.
   Dim doc As New XmlDocument()
   
   ' Format the document to ignore white spaces.
   doc.PreserveWhitespace = False
   
   ' Load the passed XML file using it’s name.
   doc.LoadXml(xmlString)
   
   Dim tagAss = "infNFe"
   Dim ref As New Reference()
   Dim _Uri As XmlAttributeCollection = doc.GetElementsByTagName(tagAss).Item(0).Attributes
   For Each atributo As XmlAttribute In _Uri
     If atributo.Name = "Id" Then
         ref.Uri = "#" & atributo.InnerText
     End If
   Next
   
   ' Add an enveloped transformation to the reference.
   Dim Envelope As New XmlDsigEnvelopedSignatureTransform()
   Referencia.AddTransform(Envelope)
   
   Dim c14 As New XmlDsigC14NTransform()
   ref.AddTransform(c14)
   
   ' Add the reference to the SignedXml object.
   signedXml.AddReference(ref)
   
   ' Create a new KeyInfo object
   Dim keyInfo As New KeyInfo()
   
   ' Load the certificate into a KeyInfoX509Data object
   ' and add it to the KeyInfo object.
   keyInfo.AddClause(New KeyInfoX509Data(_X509Cert))
   
   ' Add the KeyInfo object to the SignedXml object.
   signedXml.KeyInfo = keyInfo
   signedXml.ComputeSignature()
   
   ' Get the XML representation of the signature and save
   ' it to an XmlElement object.
   Dim xmlDigitalSignature As XmlElement = signedXml.GetXml()
   
   ' Gravar assinatura no documento XML
   doc.DocumentElement.AppendChild(doc.ImportNode(xmlDigitalSignature,True))
   XMLDoc = New XmlDocument()
   XMLDoc.PreserveWhitespace = False
   XMLDoc = doc 
   dim xmlAssinado = XMLDoc.OuterXml