File permissions and access control in Cybersecurity - Step-by-Step Execution

Concept Flow - File permissions and access control

User tries to access file

↓

Check file permissions

↓

Does user have permission?

No→Access Denied

Yes↓

Allow access to file

↓

Log access event

When a user tries to access a file, the system checks the file's permissions. If the user has the right permissions, access is granted; otherwise, it is denied.

Execution Sample

Cybersecurity

User: Alice
File: report.txt
Permissions: rw-r-----
Action: Read file

Alice tries to read a file with read and write permissions for owner, read for group, none for others.

Analysis Table

Step	User	File Permissions	Action	Permission Check	Result
1	Alice	rw-r-----	Read	Is Alice owner? Yes	Access Granted
2	Bob	rw-r-----	Read	Is Bob owner? No; Is Bob in group? No	Access Denied
3	Charlie	rw-r-----	Write	Is Charlie owner? No; Is Charlie in group? Yes; Write permission for group? No	Access Denied
4	Alice	rw-r-----	Write	Is Alice owner? Yes; Write permission for owner? Yes	Access Granted
5	Dave	rw-r-----	Read	Is Dave owner? No; Is Dave in group? No	Access Denied

💡 Access decisions are based on user identity and file permission bits.

State Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
User	None	Alice	Bob	Charlie	Alice	Dave
Action	None	Read	Read	Write	Write	Read
Access Result	None	Granted	Denied	Denied	Granted	Denied

Key Insights - 2 Insights

Why does Bob get denied access even though the file has read permission for the group?

Bob is neither the owner nor a member of the file's group, so group permissions do not apply to him. This is shown in execution_table row 2.

Why can Alice write to the file but Charlie cannot, even though Charlie is in the group?

The group does not have write permission (only read), so Charlie cannot write. Alice is the owner and has write permission. See execution_table rows 3 and 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the access result for Charlie when trying to write?

A Access Granted

B Access Denied

C Access Pending

D Access Unknown

💡 Hint

Check execution_table row 3 under 'Result' column.

At which step does the user have both ownership and write permission?

A Step 3

B Step 2

C Step 4

D Step 5

💡 Hint

Look at execution_table rows for 'User' and 'Permission Check' columns.

If Dave was added to the file's group, what would change in step 5?

A Access would be granted for read

B Access would be granted for write

C Access would still be denied

D No change in access

💡 Hint

Refer to execution_table row 5 and group permissions in 'File Permissions'.

Concept Snapshot

File permissions control who can read, write, or execute a file.
Permissions are set for owner, group, and others.
Access is granted only if the user matches owner or group and has the needed permission.
If not, access is denied.
This protects files from unauthorized use.

Full Transcript

File permissions and access control determine who can use a file and how. When a user tries to access a file, the system checks if the user is the owner, belongs to the file's group, or is others. Then it checks if the requested action (read, write, execute) is allowed for that category. If yes, access is granted; if no, access is denied. For example, a file with permissions rw-r----- means the owner can read and write, the group can read, and others have no access. If Alice is the owner, she can read and write. If Bob is not in the group, he cannot read. This system helps keep files safe and private.