File permissions and access control in Cybersecurity - Mini Project: Build & Apply

Understanding File Permissions and Access Control

📖 Scenario: You are managing files on a computer system. To keep files safe, you need to set who can read, write, or execute each file. This is called file permissions and access control.Imagine you have a folder with important documents. You want to decide who can open, change, or run these files.

🎯 Goal: Build a simple representation of file permissions using a dictionary. Then, add a rule to check if a user has permission to perform an action on a file.

📋 What You'll Learn

Create a dictionary named files with file names as keys and their permissions as values.

Add a variable named user_action to represent the action a user wants to perform.

Write a loop to check if the user has permission for the action on each file.

Add a final statement that shows which files the user can access based on their action.

💡 Why This Matters

🌍 Real World

File permissions control who can read, write, or execute files on computers, protecting data and system security.

💼 Career

Understanding access control is essential for cybersecurity roles, system administration, and software development to ensure safe data handling.

1

Create the initial file permissions dictionary

Create a dictionary called files with these exact entries: 'report.txt': 'read', 'data.csv': 'write', 'script.sh': 'execute'.

Cybersecurity

# Create the dictionary files with the given file names and permissions
# Your code here

Hint

Use curly braces {} to create a dictionary. Each key is a file name string, and each value is a permission string.

2

Add a variable for the user's desired action

Add a variable called user_action and set it to the string 'read'.

Cybersecurity

files = {'report.txt': 'read', 'data.csv': 'write', 'script.sh': 'execute'}
# Set user_action to 'read'
# Your code here

Hint

Assign the string 'read' to the variable user_action.

3

Check permissions for each file

Use a for loop with variables file and permission to iterate over files.items(). Inside the loop, write an if statement to check if permission == user_action.

Cybersecurity

files = {'report.txt': 'read', 'data.csv': 'write', 'script.sh': 'execute'}
user_action = 'read'
# Loop over files and check permissions
# Your code here

Hint

Use files.items() to get file and permission pairs. Compare permission with user_action inside the loop.

4

Complete by listing accessible files

Inside the if block, add the file name to a list called accessible_files. Before the loop, create accessible_files as an empty list.

Cybersecurity

files = {'report.txt': 'read', 'data.csv': 'write', 'script.sh': 'execute'}
user_action = 'read'
accessible_files = []
for file, permission in files.items():
    if permission == user_action:
        # Add file to accessible_files
        # Your code here

Hint

Create an empty list before the loop. Use append() to add files inside the if block.

Practice

1. What does the read permission allow a user to do with a file?

easy

A. Modify the contents of the file

B. View the contents of the file

C. Execute the file as a program

D. Delete the file

Solution

1. Step 1: Understand the meaning of read permission

   The read permission allows a user to open and see the contents of a file without changing it.

2. Step 2: Compare with other permissions

   Write permission allows changes, execute allows running the file, and delete is a separate action.

3. Final Answer:

   View the contents of the file -> Option B

4. Quick Check:

   Read permission = View file contents [OK]

Hint: Read means viewing file contents only [OK]

Common Mistakes:

• Confusing read with write permission
• Thinking read allows file execution
• Assuming read allows file deletion

2. Which of the following is the correct symbolic notation for giving the owner execute permission on a file in Unix/Linux?

easy

A. u+x

B. g+x

C. o+x

D. a+x

Solution

1. Step 1: Understand symbolic notation for permissions

   In Unix/Linux, 'u' stands for user (owner), 'g' for group, 'o' for others, and 'a' for all.

2. Step 2: Identify execute permission addition

   Adding execute permission is done with '+x'. So 'u+x' means add execute for owner.

3. Final Answer:

   u+x -> Option A

4. Quick Check:

   Owner execute permission = u+x [OK]

Hint: u means owner; +x adds execute permission [OK]

Common Mistakes:

• Using g+x or o+x for owner permissions
• Confusing a+x with owner only
• Misunderstanding symbolic letters

3. Given the file permission string -rwxr-x---, which users can execute the file?

medium

A. Owner and group members

B. Only the owner

C. Everyone

D. Only others

Solution

1. Step 1: Break down the permission string

   The string '-rwxr-x---' means: owner has read, write, execute; group has read and execute; others have no permissions.

2. Step 2: Identify who can execute

   Owner (rwx) can execute, group (r-x) can execute, others (---) cannot.

3. Final Answer:

   Owner and group members -> Option A

4. Quick Check:

   Execute permission for owner and group [OK]

Hint: Look for 'x' in owner and group parts [OK]

Common Mistakes:

• Ignoring group execute permission
• Assuming others have execute
• Misreading permission string

4. A user tries to write to a file but gets a 'Permission denied' error. The file permissions are -rw-r--r--. What is the most likely cause?

medium

A. User has execute permission but not write

B. File is read-only for everyone

C. User is not the owner and has no write permission

D. File is locked by another process

Solution

1. Step 1: Analyze the permission string

   '-rw-r--r--' means owner can read and write; group and others can only read.

2. Step 2: Understand user's permission

   If the user is not the owner, they only have read permission, so writing is denied.

3. Final Answer:

   User is not the owner and has no write permission -> Option C

4. Quick Check:

   Write denied if not owner with write permission [OK]

Hint: Write permission only for owner here [OK]

Common Mistakes:

• Assuming read means write allowed
• Confusing execute with write permission
• Ignoring ownership in permissions

5. You want to allow a group of users to read and execute a script but prevent them from modifying it. Which permission setting should you apply?

hard

A. Set group permissions to ---

B. Set group permissions to rw-

C. Set group permissions to rwx

D. Set group permissions to r-x

Solution

1. Step 1: Understand required permissions

   Users need to read and execute but not write (modify) the script.

2. Step 2: Match permissions to requirements

   'r-x' means read and execute allowed, write denied. 'rw-' allows write, 'rwx' allows all, '---' denies all.

3. Final Answer:

   Set group permissions to r-x -> Option D

4. Quick Check:

   Read + execute, no write = r-x [OK]

Hint: r-x means read and execute, no write [OK]

Common Mistakes:

• Choosing rw- which allows writing
• Choosing rwx which allows all permissions
• Choosing --- which denies access