using System;

using System.Xml;

using System.IO;

using System.Text;

public class Program

{

    public static void Main()

    {   

        XmlWriterSettings settings = new XmlWriterSettings();

        settings.Indent = true;

        using (var ms = new MemoryStream())

        {           

            // default: utf-8

            using (XmlWriter writer = XmlWriter.Create(ms, settings)) 

            {               

                writer.WriteStartElement("Amt");

                writer.WriteAttributeString("xmlns", "cbc", null, "urn:ejemplo");

                writer.WriteAttributeString("xmlns", "ds", null, "urn:ejemplo2");

                writer.WriteStartElement("cbc", "price", "urn:ejemplo");

                writer.WriteString("340.00");

                writer.WriteEndElement();       

                writer.WriteStartElement("ds", "SignatureMethod", "urn:ejemplo2");              

                writer.WriteAttributeString("Algorithm", "w3.org/2000/09/xmldsig#dsa-sha1");

                writer.WriteEndElement();                

            }

            Console.WriteLine(new UTF8Encoding().GetString(ms.ToArray()));

        }

    }

}