XML : Digitally sign xml document on android xamarin

I have been trying to create an app that digitally signs an XML document. It has to be signed with certificate because i have to send said docuemnt to tax administration servers. I used certificates as assets, but now i have a problem with signing the document. Xamarin doesn't support the System.Security.Cryptography.Xml and System.Deployment library (at least as far as i know). Even if i include them in the references as a separate file (coppied to the bin folder with apk file), i don't seem to get it to work. i get errors like "can't implicitly convert System.Xml.XmlElement to System.Xml.XmlElement".

The code for signing the file is as follows:

  CryptoConfig.AddAlgorithm (typeof(RSAPKCS1SHA256SignatureDescription), "http://www.w3.org/2001/04/xmldsig-more#rsa-sha256");    System.Xml.XmlDocument xmlDoc = new System.Xml.XmlDocument ();  xmlDoc.Load (filename);    // Create a SignedXml object.  System.Security.Cryptography.Xml.SignedXml signedXml = new System.Security.Cryptography.Xml.SignedXml (xmlDoc);  byte[] data = cert.GetPublicKey ();  string base64 = Convert.ToBase64String (data);    RSACryptoServiceProvider rsaCSP = (RSACryptoServiceProvider)cert.PrivateKey;    CspParameters cspParameters = new CspParameters ();  cspParameters.KeyContainerName = rsaCSP.CspKeyContainerInfo.KeyContainerName;  cspParameters.KeyNumber = rsaCSP.CspKeyContainerInfo.KeyNumber == KeyNumber.Exchange ? 1 : 2;    RSACryptoServiceProvider rsaAesCSP = new RSACryptoServiceProvider (cspParameters);  signedXml.SigningKey = rsaAesCSP; //newKey;    System.Security.Cryptography.Xml.KeyInfo keyInfo = new System.Security.Cryptography.Xml.KeyInfo ();  System.Security.Cryptography.Xml.KeyInfoX509Data keyInfoData = new System.Security.Cryptography.Xml.KeyInfoX509Data ();  keyInfoData.AddIssuerSerial (cert.Issuer, cert.SerialNumber);  X509Extension extension = cert.Extensions [1];  AsnEncodedData asndata = new AsnEncodedData (extension.Oid, extension.RawData);  keyInfoData.AddSubjectName (cert.SubjectName.Name);    // Create a reference to be signed.  System.Security.Cryptography.Xml.Reference reference = new System.Security.Cryptography.Xml.Reference ();  reference.Uri = "#test";  reference.DigestMethod = @"http://www.w3.org/2001/04/xmlenc#sha256";    // Add an enveloped transformation to the reference.  System.Security.Cryptography.Xml.XmlDsigEnvelopedSignatureTransform env = new System.Security.Cryptography.Xml.XmlDsigEnvelopedSignatureTransform ();  reference.AddTransform (env);    // Add the reference to the SignedXml object.  signedXml.AddReference (reference);  keyInfo.AddClause (keyInfoData);    signedXml.KeyInfo = keyInfo;  signedXml.SignedInfo.SignatureMethod = "http://www.w3.org/2001/04/xmldsig-more#rsa-sha256";    // Compute the signature.              signedXml.ComputeSignature ();    // Get the XML representation of the signature and save   // it to an XmlElement object.  System.Xml.XmlElement xmlDigitalSignature = (System.Xml.XmlElement)signedXml.GetXml ();    // Append the element to the XML document.  XmlNode element;  element = xmlDoc.GetElementsByTagName ("fu:InvoiceRequest") [0];  element.AppendChild (xmlDigitalSignature);    

Is there any other way you can digitally sign XML document with certificates?