Have you looked at Arcot's WebFort? (Score 1)

Their site is at: http://www.arcot.com It uses a PIN to protect downloadable keys on the client side. They way it works is like having thousands of keys under your doormat out of which only one key is the correct key but you have to try the key to find out if it is the right key. Use of SSL is required. Only real downside is that WebFort requires client-side software. Good luck. Don Park FYI - I used to be a consultant to Arcot.