Access Control

Passwords

• Directory : User/Owner checked at the Master File Directory level (password verification at login)
• File : allow sharing by giving password

Password protection is an all or nothing protection - i.e. not flexible - Passwords MUST be encrypted

Access Privileges

Specify type of access allowed to others (in increasing order of privilege) :

1. No Access (N)
2. Execute only (X)
3. Read only (R)
4. Append only (e.g. log files) (A)
5. Read/Write (update) (W)
6. Change Protection (C)
7. Delete (D)

Access privileges can be encoded hierarchically - i.e. each access right includes those below it (therefore, ability to write implies ability to read and execute also) - alternately, encode in a key with one but for each access mode.
Owner must always be able to change protection mode - WHY ?

 
• Specifying permitted Users