Problem with decrypting xml document

Question

Hi,

I have written some code that has encrypted an XML config file containing user credentials, and also the code to decrypt that file. When I run the encryption and decryption together on my local machine it works as expected. However, when I deploy the program, with only the decrypt code, the xml file will not decrypt. I get a cryptographic Exception: Bad Data? Here is my code:

    public static void Encrypt(XmlDocument Doc, string ElementToEncrypt, string EncryptionElementID, RSA Alg, string Keyname)
    {
        if (Doc == null)
            throw new ArgumentNullException("Doc");
        if (ElementToEncrypt == null)
            throw new ArgumentNullException("Element to Encrypt");
        if (EncryptionElementID == null)
            throw new ArgumentNullException("EncryptionElementID");
        if (Alg == null)
            throw new ArgumentNullException("ALG");
        //specify which xml elements to encrypt
        XmlElement elementToEncrypt = Doc.GetElementsByTagName(ElementToEncrypt)[0] as XmlElement;

        if (elementToEncrypt == null)
            throw new XmlException("The specified element was not found");
        try
        {
            //create session key
            RijndaelManaged sessionkey = new RijndaelManaged();
            sessionkey.KeySize = 256;

            //encrypt using Encrypted exml object and hold in byte array
            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;

            edElement.EncryptionMethod = new EncryptionMethod(EncryptedXml.XmlEncAES256Url);
            //encrypt the session key and add it encrypted key 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 data reference to encrypted key

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

            edElement.KeyInfo.AddClause(new KeyInfoEncryptedKey(ek));

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



        // 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)
        {
            throw e;
        }
    }


    public static string Decrypt()
    {
            //create XML documentobject and load config file
            XmlDocument xmlDoc = new XmlDocument();

            try
            {
                xmlDoc.Load("config.xml");
            }
            catch (FileNotFoundException e)
            {
                Console.WriteLine(e.Message);
                Console.ReadLine();

            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
                Console.ReadLine();
            }

            //create container for key
            CspParameters cspParam = new CspParameters();
            cspParam.KeyContainerName = "XML_RSA_FTP_KEY";
            cspParam.Flags = CspProviderFlags.UseMachineKeyStore;
            //create key and store in container
            RSACryptoServiceProvider ftpkey = new RSACryptoServiceProvider(cspParam);


            //add keyname mapping qnd decrypt the document
            EncryptedXml exml = new EncryptedXml(xmlDoc);
            exml.AddKeyNameMapping("ftpkey", ftpkey);
            exml.DecryptDocument();

            //pass decrypted document to extract credentials method
            string details =  Extract_Credentials(xmlDoc);

            //return decrypted log in details
            return details;

    }

Any help would be appreciated. Thanks, Darren

Answer 1

The obvious question is how you moved the XML_RSA_FTP_KEY private key to the server.

If you did not do anything, the decrypt()-method will have generated a new keypair in the XML_RSA_FTP_KEY-container. This key will fail to decrypt the data which was encrypted with a different key and give the "Bad data"-exception.