TUF support for legacy applications

Goal:Incorporate The Update Framework (TUF) into legacy applications. TUF provides a secure approach for software updaters to contact servers and mirrors and perform updates. For more information about TUF, go to : https://www.updateframework.com

 Integrating TUF onto software updaters require some level of coding of the  
 updater (recomplilation and redeployment). We propose a mechanism to minimize
 (or remove) the additional code of integrating TUF in software updaters.

Scenario: An application x has a built-in software updater that (from time to time) polls its server to see if any of its files need to be updated. If so, the software updater contacts available mirrors(s) and perform the necessary updates. As discussed in updateframerwork.com/wiki/Docs/Security, there are numerous security flaws with this current approach. TUF reduces many of these security flaws through various checks. However, adding TUF to application x requires modification to x codebase; this may be cumbersome for software developers, as well as users of legacy applications. Our work provides a layer that works between aplication x and TUF to provide the security features of TUF, without the need to modify x.

Approach: The main idea behind our approach is to intercept ALL network calls of the application x, forward the ones not related to software updating, and process the ones related to software updating through TUF api. This MUST be done in transparent fashion.

Mechanism:

	- Intercept network calls of legacy-application
		- Use LD_PRELOAD to load a modified subsection of libc (socket functions)
		- Make the modified libc trap network calls of legacy application

	- Translate relevant network calls to TUF API
		- Forward network calls that are not for software update purposes
		- Wrap the ones that are for software update with tuf-related calls 
		  for security checks and download requested  file(s)

	- Return requested updated transparently to software updater

For more details on testing this project, read the README file in the application dir

LIMITATIONS: (When running client without TUF-support) The repository maintains the files to be updated in server-resources/legacy-app/lib. If the admin modifies any of files in that dir, we provide make_manifest.py (in server-resources) to update the MANIFEST file to illustrate changes made to the file. However, we haven't figured out an efficient way to push the changed files (and manifest) to the mirrors. We are investigating how to resolve this situation.

We also are investigating how to resolve this situation with TUF-enabled
Along with updating the mirrors with the updated files, we must  update many of the metadata 
that TUF uses (using through TUF/src/quickstart.py) and pushing the updated metadata
(in client/ dir) to the legacy-client