Access Control - Integrated Computer Security - Lecture Slides, Slides of Computer Security

Download Access Control - Integrated Computer Security - Lecture Slides and more Slides Computer Security in PDF only on Docsity!

Lecture 7

Access Control

Access Control

• ITU-T Recommendation X.800 definition:
  • “The prevention of unauthorized use of a resource, including the prevention of use of a resource in an unauthorized manner.”
• RFC 2828 defines computer security as:
  • “Measures that implement and assure security services in a computer system, particularly those that assure access control service”.

Access Control Policies

• dictates
  • what types of access are permitted,
  • under what circumstances,
  • by whom. based on the identity of the requestor and on access rules

based on comparing security labels with clearances

based on the roles and their accesses

Access Control Requirements

• reliable input
• support for fine and coarse specifications
• least privilege
• separation of duty
• open and closed policies
• policy combinations and conflict resolution
• administrative policies
• dual control

Discretionary Access Control

• scheme in which an entity may enable

another entity to access some resource

• often provided using an access matrix
  • one dimension consists of identified subjects that may attempt data access to the resources
  • the other dimension lists the objects that may be accessed
• each entry in the matrix indicates the access rights of a particular subject for a particular object

Access Matrix

Authorization

Table

Extended Access Control Matrix

Access Control System Commands

UNIX File Access Control

• control structures with key information needed for a particular file
• several file names may be associated with a single inode
• an active inode is associated with exactly one file
• file attributes, permissions and control information are sorted in the inode
• on the disk there is an inode table, or inode list, that contains the inodes of all the files in the file system
• when a file is opened its inode is brought into main memory and stored in a memory resident inode table

UNIX files are administered using inodes (index nodes)

• may contain files and/or other directories
• contains file names plus pointers to associated inodes

directories are structured in a hierarchical tree

Traditional UNIX File Access Control

• “set user ID”(SetUID)
• “set group ID”(SetGID)
  • system temporarily uses rights of the file owner / group in addition to the real user’s rights when making access control decisions
  • enables privileged programs to access files / resources not generally accessible

Traditional UNIX File Access Control

• sticky bit
  • when applied to a directory it specifies that only the owner of any file in the directory can rename, move, or delete that file
• superuser
  • is exempt from usual access control restrictions
  • has system-wide access

Access Control Lists (ACLs) in UNIX

• when a process requests access to a file

system object two steps are performed:

• step 1 : selects the most appropriate ACL
  • owner, named users, owning / named groups, others
• step 2 : checks if the matching entry contains sufficient permissions