could As I think about it more, the "anonymous video on demand" problem can be solved with an oblivious transfer protocol. Here's how I see it working: (The following is adapted from the oblivious transfer protocol described in "Applied Cryptography" on page 98.) Say Alice is the Video Vendor and Bob is the customer... Alice generates a public/private key pair for each movie in her video database and publishes the public keys in an electronic catalog. Each public key would be paired with a movie description and a catalog index number. Bob downloads Alice's catalog and browses through it offline. Bob makes a selection, and also randomly picks 99 (or any large number) other catalog numbers Bob generates a random DES key and encrypts this key with the public key associated with his selection. Bob sends the encrypted DES key and the list of 100 catalog numbers to Alice. Alice decrypts the DES key with the private key associated each catalog number received from Bob. In only one case will Alice successfully recover Bob's DES key, only she doesn't know which case. Alice encrypts each movie selection with the resulting DES keys from the previous step and sends all 100 encrypted movies to Bob. Bob will only be able to decrypt and view the movie he selected and Alice wont know which of the 100 movies Bob selected. Ta Da! The nice thing about this protocol is that it doesn't really have anything to do with videos. It could be used for an electronic library, or any warehouse of digital information where the Vendor wishes to charge for a download, yet the Customer doesn't want the Vendor to know which item is selected. Also, the Vendor still can use statistical analysis to determine which items are more popular and which items are less popular. The Vendor could keep track of how many times an item was mentioned in a Customer selection list. The more popular items would appear in more lists. Unpopular items would have different statistics. This analysis breaks down if all items are equally popular, or Customers don't chose the other 99 items randomly. Jim_Miller@suite.com