A web based system for sending encrypted files

We have created a very basic prototype of the web applicaiton we need. You can take a look at www.launchbag.com

We would like you to build it using ASP.NET and to have the following features:

1. "Bags" are one or several files sent or received by any of our users
2. When a Bag is sent, it is first encrypted using a unique key, generated each time by the site. The key is not kept anywhere and is not accesible even by us (only a hash should be kept).
3. A passcode based on this key is sent seperately via SMS (Text message) or fax to the recepient.
4. The passcode is required to download the Bag by the receipeint
5. No registration is required, however, a cockie is created and next time the user (both sender and receiver) is offered to open an account.
6. As part of the account data users can see their bags, including what they have ever sent, received and also the files themsevles and a log of their activity, status of bags sent (accepted / wrong pass code/ rejected/ etc.)
7. Service should be at most secured. Data should be encrypted before being uploaded so all data on the server should be encrypted, so even our staff can't access the files which makes it secured for our end users.
8. We will register a VPS hosting service to meet your requirements, and you will upload the code and database to it.
9. We will buy the SSL certificates according to your recomendations.
10. We will provide graphic elements designed by our graphic designer, however we expect your work to look professional and modern.
11. Additional features should be included and paid for by the end user (connecting the site to a shopping cart and a billing feature which can based on PayPal):
11.1 Delayed Bag- setup a date in the future that only after it occours, the files can be viewed / downloaded.
11.2 Other features as described in the attached document