Can't do an Extranet?
The "intelligence community" can't manage to cobble together an Extranet?
I mean, how secure does it need to be? What'd be wrong with running SSL on top of an IPsec VPN or something? Lots of companies run well-configured and administered IPsec VPNs, surely its a a good beginning for the netowrk security part. Then make sure any PCs are made tamper-proof, put a good network architecture with clean seperation between accesible and inacessible, Host material on a system that can account for who sees each document and when. This would be good enough for sharing analysts' output, certainly against any non-governmental attack, certainly more secure than the people involved.
Back to the paper age for them!