NSDictionary To JASON

How to Convert NSDictionary into JASON ?

i have posted a dictionary into server using jason. And in the time receiving the data from the server using GET method. the data cant be accessed using normal key calling method like

" _secretanswer.text=[[NSString alloc]initWithFormat:@"%@",[customfield objectForKey:@"secanswer"]]; "

the server returning a NCFString as the result.