File and network security lab

Lab partners for today.

Note: most of these exercises will only work correctly on the Macs in the Tome building.

Homework exercise 23.0: Who is your lab partner?

Part 1: Processes

  1. Examine running processes: Log in to one of the lab machines, and examine the processes running.

    Homework exercise 23.1: (a) How many processes are owned by the root user? (b) How many processes are owned by a user other than you or root?

  2. Launch multiple browsers with multiple windows each: Firefox and Safari are two different web browsers installed on our lab machines. Open both of these browsers, and use them to open multiple websites, using multiple tabs and windows.

    Homework exercise 23.2: (a) How many processes is Firefox using? (b) How many processes is Safari using?

  3. Launch a process owned by one user while another user is logged in: To describe this exercise, we will assume that the usernames of you and your lab partner are userA and userB respectively. In practice, you will of course use your own usernames. Let us assume that userA has logged into one of the lab machines. Our objective is for userB to launch the TextEdit program in a process owned by userB, without first logging out of userA's session. To do this, please execute the following instructions:
    1. Open a terminal window.
    2. Change the active user of the terminal window by using the su command (su is an abbreviation for "set user"). Specifically, type su userB, hit Enter, then type in userB's password as requested.

      Homework exercise 23.3: How many processes are currently owned by userB? List the name of each such process.

      Homework exercise 23.4: (a) Are you currently in the home directory of userA or userB? (b) What happens when you execute the "ls" command in the current directory? (c) Give a brief explanation of the result.

    3. Change directory to the location of the TextEdit program, which happens to be stored in the directory /Applications/TextEdit.app/Contents/MacOS.
    4. Run TextEdit by typing the command "./TextEdit"

      Homework exercise 23.5: List any additional processes that are now owned by userB.

    5. Exit from the terminal window.

Part 2: Files

  1. Examine the permissions of a file stored on the file server: Create a new Microsoft Word document and save it as a file named "test.docx". Locate your test.docx file in the Finder, control-click on it, choose "get info", then open up the bottom tab called "sharing and permissions". Take a look at what you see here. This is an access control list (ACL), as discussed in class. Unfortunately, the permissions you see here are complicated by the fact that this file is stored on a separate computer, known as a file server. To avoid this complexity, the rest of this part of the lab will deal only with files stored on your machine's local hard drive.
  2. Copy test.docx into /tmp: There is a special directory on the local hard drive of the machine for storing temporary files; this directory is called "/tmp". Navigate to /tmp in the Finder now. To do this, choose "go to folder" from the "Go" menu and enter "/tmp". Copy your test.docx into the /tmp folder.
  3. Examine the permissions of a file stored on the local hard drive: Examine the permissions on the new copy of test.docx. Ignore the user group "wheel" which you might encounter here; we won't be using groups in this lab.

    Homework exercise 23.6: What are the current permissions of test.docx? i.e. who can read the file? Who can write the file?

  4. Experiment with global read-only permissions: Alter the permissions of test.docx so that it is read-only for everyone, including you. Verify that you succeeded by opening the file in Word, editing it, then attempting to save it.

    Homework exercise 23.7: What error message does Word produce when you attempt to save the edited file?

  5. Experiment with private permissions: Alter the permissions of test.docx so that no one other than you can read it. Verify that you succeeded by logging out and allowing your partner to log in. Your partner should then navigate to /tmp and attempt to open test.docx by double-clicking on it.

    Homework exercise 23.8: What error message does Word produce when someone without read permission attempts to open a file?

Part 3: Network security

This part of the lab involves using some web research to investigate the security of Dropbox. As with any other academic work, you should state your sources when answering, and use quotation marks if appropriate. You are of course permitted to work on these questions with your partner, and you and your partner may submit identical solutions. Try to give a detailed and specific answer to each question. 2-3 sentences should be sufficient for each question.

Homework exercise 23.9: What security features does Dropbox offer?

Homework exercise 23.10: (a) What company owns the data centers where Dropbox stores its users' backups? (b) What country is the data stored in?

Homework exercise 23.11: What security features are offered by the relevant services of the company you named in the previous question?

Homework exercise 23.12: In your opinion, is the security of Dropbox adequate for sensitive information, such as medical records, or student grades?