Web Forms :: How To Read Encrypted Connection String In Role Manager

i don't know how to use a Encrypted ConnectionString with RoleManager in ASP.NET This is code in Web.config. 

<connectionStrings>
<add name="strConnectionString" connectionString="eF8w9r2UJOsk0Ps3pxmV7/Fy/xPR2hN2S7BrC1iOYNnAUaI8AqkSm5bw7r+ta4sePWSV9t/3Spnpz6wsFpvMmcppNpqM5Zk7iiDqWVgIV4k="/>
</connectionStrings>
<roleManager enabled="true" defaultProvider="CustomizedRoleProvider">

[Code] ....

And in project I create a library to read web config

 private const string ConnectionStringKey = "strConnectionString";
private readonly string SQLConnectionString =
Security.DecryptString(ConfigurationManager.ConnectionStrings[ConnectionStringKey].ConnectionString);

if I change my ConnectionString like this, it's working: 

<add name="strConnectionString" connectionString="server=My-PCMSSQL2008; database=MyDB; uid=sa; pwd=passw0rd;"/>

But I want my ConnectionString Encrypted so i use

 <add name="strConnectionString" connectionString="eF8w9r2UJOsk0Ps3pxmV7/Fy/xPR2hN2S7BrC1iOYNnAUaI8AqkSm5bw7r+ta4sePWSV9t/3Spnpz6wsFpvMmcppNpqM5Zk7iiDqWVgIV4k="/>

So when i running website it throw error:

System.ArgumentException:Keyword not supported: 'eF8w9r2UJOsk0Ps3pxmV7/Fy/xPR2hN2S7BrC1iOYNnAUaI8AqkSm5bw7r+ta4sePWSV9t/3Spnpz6wsFpvMmcppNpqM5Zk7iiDqWVgIV4k='.

Line 46: string[] roleNames;
Line 47: roleNames = Roles.GetAllRoles();