public  void  EncryptConnectionString()

         {

             Configuration  configuration = WebConfigurationManager .OpenWebConfiguration("~" );

             ConfigurationSection  configurationSection = configuration.GetSection("connectionstrings" );

             if (configurationSection != null  && !configurationSection.SectionInformation.IsLocked && !configurationSection.SectionInformation.IsProtected

                 && !configurationSection.IsReadOnly())

             {

                 configurationSection.SectionInformation.ProtectSection("RsaProtectedConfigurationProvider" );

                 configurationSection.SectionInformation.ForceSave = true ;

                 configuration.Save(ConfigurationSaveMode .Full);

             }

             else 

             {

                 if  (configurationSection != null )

                 {

                     configurationSection.SectionInformation.UnprotectSection();

                     configurationSection.SectionInformation.ForceSave = true ;

                 }

                 configuration.Save(ConfigurationSaveMode .Full);

             }

         }

Encryption and decryption is performed using the Windows Data Protection API  (DPAPI). Because

DPAPI does not allow the exporting of keys, this provider  should be used in situations where

the deployed solution is limited to a single  server.

if you want to encrypt any section of configuration file in non- programmatic way. Doing this

means that the configuration section can be encrypted before use and  then, as suggested

earlier, it is decrypted transparently at run time only for  use by the server. This can all

be achieved at the command prompt using the  Aspnet_regiis utility.

Keep, this in your mind ...> It should be noted that the encryption of configuration sections

can cause  problems. If the section is encrypted using DataProtectionConfigurationProvider and

the config file is  moved to a different machine, this new location cannot decrypt the value. With  RSAProtectedConfigurationProvider, however, the key can be  exported to a different machine along with the configuration file; this means  decryption can take place using the same exported key.