Protection

Introduction

• Protection: a general term for all the mechanisms which control the access of a program to other things in the system.

• What is the Main goal of the paper?

• Why Protection?

Abstraction

• What is an object?
  • the things in the system which have to be protected
  • processes, domains, files, segments and terminals.
• What is a key attribute of an object?
  • ?
• Are domain objects have to be protected?
  • Yes.
• What is an access matrix?
  • rows are labeled by domain names.
  • columns by objects names (so, also could be domain names).

Implementation

• The access matrix is sparse, it is not practical to store the entire matrix.

Two approaches

1. Capability method - Attach the d'th row of access matrix A to the domain d. Domain is defined by capability list, C-list. (info on domain)
2. Access Control List (ACL) method - Attach the protection information to the object rather than the domain. (info on object)
   • Easier to revoke access
   • Likely to be more expensive.
3. A hybrid version, an object can be accessed by access key to obtain a capability, which is then used for subsequent accesses. This process when applied to files is open a file -> file descriptor.