Why would that level of security clearance be necessary?
My understanding of the purpose of the special master is to identify any evidence which is protected by attorney-client privilege or otherwise inadmissible in a criminal case. Why would anything requiring that level of security qualify for AC privilege or otherwise be inadmissible?
I don't typically subscribe to slippery-slope arguments, but if the special master needs highest clearance wouldn't the rest of the actors in the case?