Desktop.google.com 'Local stored data for offline website search '

We need an application like [login to view URL] We would like the ability for data, from our website, to be stored on local client computers so they can search/view the data while offline, via their browser. To give an example understanding of what we're doing; we have a database of Fraternity's all across the US which a person can search(by state and/or city) when logged onto our website. From the search results they are able to get more specific information about the Fraternity (name, address, phone number, contact person, etc.). The jist of the project is that we are looking to take our online search and make it available offline through a desktop version. The front end will be HTML and the data will mostly likely be stored in XML files. The HTML is no trouble, the installer is no trouble to put together either. The hard part of this project is three fold - first, we need to be able to auto-update the XML on a regular basis while the user is online and the user also needs to have the ability to update the data manually. Secondly, we want to encrypt the locally stored data so that it can't be read outside the program. Thirdly the back end needs to run in the browser while offline so it needs a small webserver on the localhost on an unused port. Please suggest code language.