Question

Consider a system where a data files (F_i, and i denotes the file ID) is distributed over a cloud. A data file is generated by an author (AU_k, and k, denotes the author ID) and stored on a distribution server (DS). Only authorized users (US_1, and denotes the user ID) previously registered on the system using their private keys (KPR_1) are allowed to download the data. Users' public certificates (KPU_1) and revocation lists (CRL) are available on a trusted Certificate Authority (CA). Authentication is done using an authentication server (AS) on a challenge response PKI based authentication. The files are to be encrypted (for each user on delivery) and the decryption key for file (i) to user (l) (K_a) is delivered securely to the user from a data rights management server (DRMS). Using (RSA) public key cryptography whenever possible and (AES) for encrypting data for the sake of performance, and any required hashing and MAC algorithms a. Show the contents of exchanged messages between each entity and the others in the system in the case of uploading a new file on the system, downloading a file, and accessing the contents of a file. All other messages required for authentication are also required. Number your messages (1, 2, 3, ...) b. Draw a simplified diagram with all the entities as vertices and the message as a between the entities and put on each are the message(s) number(s). c. The system is vulnerable to re-distribution of decrypted files (an authenticated user can make a new copy of the plain text file and post it over Facebook for example). Suggest a mechanism to prevent such a problem. d. Knowing that the file is stored on the local user storage after downloading, suggest a mode of operation that can be used to allow the player software to decrypt only the needed part of the file in memory, other parts of the file should remain encrypted on the storage. Take into consideration that access to the file content will be on the byte level and in a random access fashion (A byte from the middle of the file can be read then 4 bytes from the beginning of the file then the last 6 bytes and so on)

Answer 1

Customer Experience Mapping if your flow chart focuses on customer service, so that you can gain a better understanding of the process. Step 2: Organize and Document Tasks Next, start your flow chart by drawing the elongated circle shape and labeling it "Start." Then, work through your whole process, and show the actions and decisions in the order that they happen. Link them with arrows to illustrate the flow of the process. Where you need to make a decision, draw arrows from the decision diamond to each possible solution, and then label each arrow with the decision made. Remember to show the end of the process by using an elongated circle labeled "Finish."

Tip: If your process or project involves several people or teams, you might find it more useful to use a Swim Lane Diagram rather than a flow chart this helps you to show process flows between people and teams. How to Create a Flow Chart Follow these four steps: Step 1: Identify Tasks Begin by listing all of the tasks in a process in chronological order. Ask questions such as, "What happens next in the process?" or, "Do you need to make a decision before the next step?" or, "What approvals are required before you move on to the next task?" Put yourself in the shoes of the person using the process, possibly for the first time. Talk to team members who work with the process directly, and get their opinions on where improvements could be made. Better yet, take a hands-on approach and go through the procedure yourself, and think about the practicalities of each stage. Use Customer Experience Mapping if your flow chart focuses on customer service, so

For example, software developers can use them to work out how the automated and manual parts of a process join up. Inexperienced team members might follow a flow chart to help them to complete activities in the right order. A manufacturer could ensure that it keeps to its values by applying a quality-control flow chart that presents questions and decision points. And an HR department might combine a flow chart with an organogram o to show people who to contact about issues and when. Why Use Flow Charts? This tool's simplicity makes communicating and documenting a process quick and clear, so that the process will more likely be understood and applied correctly and consistently. It can also help you to estimate the timescale of the process, as you're better able to gauge the time needed for each task oalong the way. And you'll more likely identify who you should involve and at what stage, such as senior management or a compliance authority ou canho bentth prce gowhs syou buta it step by step. You'll be able to focus on the detail of each individual stage, without feeling overwhelmed by the rest of the process, and then "zoom out" again to see the wider picture.

Tip: You can use many other symbols in a flow chart but remember that these diagrams are used for communication o. If you use symbols that only a few people understand, you may fail to get your message across. So, be sure to keep things simple o! When to Use a Flow Chart All manner of organizations use flow charts to: Define a process. Standardize o a process. Communicate a process. . Identify bottlenecks or waste in a process. Solve a problem o. Improve a process.

3. Diamonds, which highlight where you must make a decision. No Example Decision Yes 4. Parallelograms, which show input and output. This can include materials, services or people. Example Input and Output

What Is a Flow Chart? Flow charts are easy-to-understand diagrams that show how the steps of a process fit together. American engineer Frank Gilbreth is widely believed to be the first person to document a process flow, having introduced the concept of a "Process Chart" to the American Society of Mechanical Engineers in 1921 Flow charts tend to consist of four main symbols, linked with arrows that show the direction of flow: 1. Elongated circles, which signify the start or end of a process. Start 2. Rectangles, which show instructions or actions. Example Task