Chapter 4 - Access Control Flashcards
Acess Control Definition
Define Access Control
The prevention of unauthorized access of a resource (or entering into physical facility)
also prevent legitimate users from using in unauthorize way
RFC Definition (of computer security)
Define Access Control
Process by which use of system** resources** is regulated according to a security policy and permitted only by authorized entities
Difference between User Authentication and Access Control
Define Access Control
Authentication establishes **who **you are and Access control establishes what you can do within a system
Relationship to other security functions
Define Access Control
“Broader Context of Access Control”
- Authentication: first verifies credentials of user are valid
- Access Control: Grants permissions to a system resource
- Auditing: Independent review of system records and activities to test adequacy, ensure compliance, and detect breaches
Access control policies should dictate:
Access Control Principles
- Who can access a resource
- What type of access is allowed
- Under what conditions
Access Control Basic Elements
Access Control Basic Elements
- Subject (entity capable of accessing objects)
- Object (Resource to be accessed)
- Access Rights (What subject can do with object)
Subjects held accountable for actions they initiate!!!
Classes of Subject (3)
Access Control Basic Elements
- Owner
- Group
- World
Examples of Access Rights
Access Control Basic Elements
- read
- write
- execute
- delete
- create
- search
What are the three main Access Control Policies?
Access Control Principles
- Discretionary Access Control (DAC): Based on identity of requestor
- Mandatory Access Control (MAC): Based on labels and security clearances
- Role-based Access Control (RBAC): Based on roles that users have in system
Not mutually exclusive, we can implement multiple at once!!!
DAC definition
DAC
Scheme in which an entity may enable another entity to access some resource
How is DAC often implemented?
DAC
An access matrix where:
- Rows = subjects
- Columns = objects
- Each cell = access rights
(That subject has to an object)
The value of cell password file:Eric = read
*From these we make access control lists and capability lists
Why use ACLs or Capability Lists?
DAC
- Access matrix can become huge
- most of the cells are empty which wastes space
- changing permissions requires modifying matrix, more cumbersome than list
What are Access Control Lists (ACLs)
DAC
List of subjects that can acccess a particular object
What are capability lists?
DAC
List of objects that a particular subject can access
ACL
Pro vs Con
DAC
Pro:
* Object owner can easily control who can access their resource
Con:
* Takes up too much space/search overhead (Many more objects in system compared to subjects)
good for managing permissions from perspective of objects (unix)
Capability List
Pro vs Con
DAC
Pro:
* Easy to see what a user is allowed to access
* More flexible, subjects can access many objects and its easier to control that with capability lists
Con:
* Harder to manage by object (see all subjects that can access specific object)
Good for user-focused resource control
How are UNIX files managed?
DAC
inodes
What is an inode (index node) in Unix
DAC
A data structure in Unix that stores key information about a file for operating systemsto provide efficient hierarchical organization and access control
Does not contain file name or file contents
- File Attributes
- File permissions
- File control information
remember directory = file with list of file names and their respective inodes
inode table
stored in disk, contains inodes of all files in filesystem
What happens when a Unix file is opened
DAC
Its inode is brought into main memory (in memory-resistant inode table)
Inode table contains inodes of all files in the file system
- System checks:
* UID (unique user ID)
* GID (Group ID)
* Protection bits (Specify access permissions) - System grants either owner (UID), group (GID) or other class permissions
How are the 12 protection bits used to show permissions?
DAC
Here’s a clearer version you can update your flashcard with:
Q: How are the 12 protection bits used to show permissions?
A:
1. 3 bits – Owner (rwx)
2. 3 bits – Group (rwx)
3. 3 bits – Other (rwx)
4. 3 bits – Special permissions:
• SUID (Set User ID): • s – Execute bit is set (rwsr-xr-x) • S – Execute bit is not set (rwSrw-r--) • SGID (Set Group ID): • s – Execute bit is set (rwxr-sr-x) • S – Execute bit is not set (rwxrwS--) • Sticky Bit: • t – Execute bit is set (rwxr-xr-t) • T – Execute bit is not set (rwxr-xr-T)
Special bits explanation:
• Lowercase (s or t) – Execute permission is present.
• Uppercase (S or T) – Execute permission is not present, but the special permission still applies
what happens when stickybit is applied to directory
only owners of files in directory can rename, move or delete users
What does this 12 bit permission structure imply?
rwxr-x—
DAC
- Owner can read, write and execute (all permissions)
- Group can read and execute but not write
- Other classes have no permission
- No special permissions
What does this 12 bit permission structure imply?
rwxr-sr–T
DAC
- Owner can read, write, and execute
- Group can read and execute with owner permissions
- Others can only read
- Only owner can delete/rename files