C#

private void encrypt_msgxml()
        {
            XmlDocument xmldoc = new XmlDocument();
            XmlElement element_to_enc;
            Rijndael sessionkey;
            EncryptedXml enxml = new EncryptedXml();
            byte[] encryp_bytes;
            byte[] encrypt_keyarray;
            EncryptedData encrypt_element;

            xmldoc.PreserveWhitespace = true;
            xmldoc.Load("ser.xml");

            element_to_enc = xmldoc.GetElementsByTagName("message")[0] as XmlElement;

            sessionkey = new RijndaelManaged();
            sessionkey.KeySize = 256;

            encryp_bytes = enxml.EncryptData(element_to_enc, sessionkey, false);

            encrypt_element = new EncryptedData();
            encrypt_element.Type = EncryptedXml.XmlEncElementUrl;

            encrypt_element.EncryptionMethod = new EncryptionMethod(EncryptedXml.XmlEncAES256Url);

            EncryptedKey encrypt_key = new EncryptedKey();
            encrypt_keyarray = EncryptedXml.EncryptKey(sessionkey.Key, rrsa, false);
            encrypt_key.CipherData = new CipherData(encrypt_keyarray);
            encrypt_key.EncryptionMethod = new EncryptionMethodEncryptedXml.XmlEncRSA15Url);

            encrypt_element.KeyInfo = new KeyInfo();
            KeyInfoName kin = new KeyInfoName();
            kin.Value = "cli_ser_pub_key";
            encrypt_element.KeyInfo.AddClause(kin);

            encrypt_element.KeyInfo.AddClause(new KeyInfoEncryptedKey(encrypt_key));

            encrypt_element.CipherData.CipherValue = encryp_bytes;
            EncryptedXml.ReplaceElement(element_to_enc, encrypt_element, false);
            xmldoc.Save("test.xml");
        }

public void decrypt_msgxml()
        {

            XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.PreserveWhitespace = true;
            xmlDoc.Load("test.xml");
            EncryptedXml exml = new EncryptedXml(xmlDoc);
            exml.AddKeyNameMapping("cli_ser_pub_key", rsa);
            exml.DecryptDocument();
        }