The 30th Reconnaissance Squadron, which is based at Tonopah Test Range Airport, operates RQ-170 Sentinels. This squadron was activated on September 1, 2005. RQ-170 Sentinels have been deployed to Afghanistan, where one was sighted at Kandahar International Airport in late 2007.[1]
So, the Air Force can keep a secret when it wants to.
A stealth aircraft is not needed in Afghanistan. A stealth aircraft in Afghanistan which can overfly Iran next door WOULD be quite useful.