Microsoft.SharePoint.Security namespace missing

I am making a custom timer service in VS 2012 target .Net Framework 4.5.

I am using namespace Microsoft.SharePoint andMicrosoft.SharePoint.Security but problem is it is showing following error:

The type or namespace name 'Security' does not exist in the namespace 'Microsoft.SharePoint' (are you missing an assembly reference?)

Could it be because of .Net Framework 4.5 and that I have to target .Net Framework 3.5? But then this is another problem because even though .Net Framework 3.5.1 is installed (I can see it in Windows Features) but it is not available in VS 2012.