Szyfrowanie XML

Question

Cześć,

piszę sobie program, który ma m.im. zapisywać dane do pliku XML i chciałbym zaszyfrować niektóre klucze w tym pliku. W tym celu użyłem  klasy w System.Security.Cryptography.Xml, a konkretnie przykładu z tej strony:

https://msdn.microsoft.com/pl-pl/library/ms229746(v=vs.110).aspx

Zmodyfikowałem funkcję Encrypt, tak by jako drugi argument przyjmowała zamiast nazwy klucza gotowy XmlElement:

public void Encrypt(XmlDocument Doc, XmlElement ElementToEncrypt, string EncryptionElementID, RSA Alg, string KeyName)
        {
            // Check the arguments.
            if (Doc == null)
                throw new ArgumentNullException("Doc");
            if (ElementToEncrypt == null)
                throw new ArgumentNullException("ElementToEncrypt");
            if (EncryptionElementID == null)
                throw new ArgumentNullException("EncryptionElementID");
            if (Alg == null)
                throw new ArgumentNullException("Alg");
            if (KeyName == null)
                throw new ArgumentNullException("KeyName");

            ////////////////////////////////////////////////
            // Find the specified element in the XmlDocument
            // object and create a new XmlElemnt object.
            ////////////////////////////////////////////////
           // XmlElement elementToEncrypt = Doc.GetElementsByTagName(ElementToEncrypt)[0] as XmlElement;
            XmlElement elementToEncrypt = ElementToEncrypt;

            // Throw an XmlException if the element was not found.
            if (elementToEncrypt == null)
            {
                throw new XmlException("The specified element was not found");

            }
            RijndaelManaged sessionKey = null;
           
           // MessageBox.Show(Doc.GetElementsByTagName(ElementToEncrypt).Count.ToString());
           
                try
                {

                   
                    //////////////////////////////////////////////////
                    // Create a new instance of the EncryptedXml class
                    // and use it to encrypt the XmlElement with the
                    // a new random symmetric key.
                    //////////////////////////////////////////////////

                    // Create a 256 bit Rijndael key.
                    sessionKey = new RijndaelManaged();
                    sessionKey.KeySize = 256;

                    EncryptedXml eXml = new EncryptedXml();

                    byte[] encryptedElement = eXml.EncryptData(elementToEncrypt, sessionKey, false);
                    ////////////////////////////////////////////////
                    // Construct an EncryptedData object and populate
                    // it with the desired encryption information.
                    ////////////////////////////////////////////////

                    EncryptedData edElement = new EncryptedData();
                    edElement.Type = EncryptedXml.XmlEncElementUrl;
                    edElement.Id = EncryptionElementID;
                    // Create an EncryptionMethod element so that the
                    // receiver knows which algorithm to use for decryption.

                    edElement.EncryptionMethod = new EncryptionMethod(EncryptedXml.XmlEncAES256Url);
                    // Encrypt the session key and add it to an EncryptedKey element.
                    EncryptedKey ek = new EncryptedKey();

                    byte[] encryptedKey = EncryptedXml.EncryptKey(sessionKey.Key, Alg, false);

                    ek.CipherData = new CipherData(encryptedKey);

                    ek.EncryptionMethod = new EncryptionMethod(EncryptedXml.XmlEncRSA15Url);

                    // Create a new DataReference element
                    // for the KeyInfo element.  This optional
                    // element specifies which EncryptedData
                    // uses this key.  An XML document can have
                    // multiple EncryptedData elements that use
                    // different keys.
                    DataReference dRef = new DataReference();

                    // Specify the EncryptedData URI.
                    dRef.Uri = "#" + EncryptionElementID;

                    // Add the DataReference to the EncryptedKey.
                    ek.AddReference(dRef);
                    // Add the encrypted key to the
                    // EncryptedData object.

                    edElement.KeyInfo.AddClause(new KeyInfoEncryptedKey(ek));
                    // Set the KeyInfo element to specify the
                    // name of the RSA key.


                    // Create a new KeyInfoName element.
                    KeyInfoName kin = new KeyInfoName();

                    // Specify a name for the key.
                    kin.Value = KeyName;

                    // Add the KeyInfoName element to the
                    // EncryptedKey object.
                    ek.KeyInfo.AddClause(kin);
                    // Add the encrypted element data to the
                    // EncryptedData object.
                    edElement.CipherData.CipherValue = encryptedElement;
                    ////////////////////////////////////////////////////
                    // Replace the element from the original XmlDocument
                    // object with the EncryptedData element.
                    ////////////////////////////////////////////////////
                    EncryptedXml.ReplaceElement(elementToEncrypt, edElement, false);  

                }
                catch (Exception e)
                {
                    // re-throw the exception.
                    throw e;
                }
                finally
                {
                    if (sessionKey != null)
                    {
                        sessionKey.Clear();
                    }

                }
        }

i dalej mam pętlę foreach 

XmlNodeList pass = XmlDoc.GetElementsByTagName("pass");

            foreach (XmlNode node in pass)
            {
               
                XmlElement elementToEncrypt = node as XmlElement;
                try
                {
                    // XmlElement pass = XmlDoc.GetElementsByTagName("pas")[listBox1.SelectedIndex] as XmlElement;

                    Encrypt(XmlDoc, elementToEncrypt, "EncryptedElement2", rsaKey, "rsaKey");
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
                finally
                {
                    // Clear the RSA key.
                    rsaKey.Clear();
                }
            }
            XmlDoc.Save("hosts.xml");

po uruchomieniu kody pojawia się błąd: "Lista elementów zmieniła się. Nie można kontynuować operacji wyliczenia." Próbowałem to zrobić na pętli for i while, ale zawsze szyfruje się tylko pierwszy, albo ostatni klucz w pliku XML

Answer 1

Rozwiązanie

  XmlNodeList pass = XmlDoc.GetElementsByTagName("pass");
            int x = XmlDoc.GetElementsByTagName("pass").Count;
           // foreach (XmlNode node in pass)
           for(int i=0; i<x;i++)
            {   XmlElement elementToEncrypt = pass[0] as XmlElement;
                Encrypt(XmlDoc, elementToEncrypt, "EncryptedElement2", rsaKey, "rsaKey");
            }