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Monday, April 6, 2020

File Protection

File Protection

Files must be kept safe for reliability ( against accidental damage ), and protection ( against deliberate malicious access. ) The former is usually managed with backup copies. For later simple protection scheme is to remove all access to a file. However this makes the file unusable, so some sort of controlled access must be arranged.

Types of Access

·         The following low-level operations are often controlled:

o    Read - View the contents of the file

o    Write - Change the contents of the file.

o    Execute - Load the file onto the CPU and follow the instructions contained therein.

o    Append - Add to the end of an existing file.

o    Delete - Remove a file from the system.

o    List -View the name and other attributes of files on the system.

·         Higher-level operations, such as copy, can generally be performed through combinations of the above.

Access Control

One approach is to have complicated Access Control Lists, ACL, which specify exactly what access is allowed or denied for specific users or groups.

·         The AFS uses this system for distributed access.

·         Control is very finely adjustable, but may be complicated, particularly when the specific users involved are unknown. 

UNIX uses a set of 9 access control bits, in three groups of three. These correspond to R, W, and X permissions for each of the Owner, Group, and Others. The RWX bits control the following privileges for ordinary files and directories:

bit

Files

Directories

R

Read ( view ) file contents.

Read directory contents. Required to get a listing of the directory.

W

Write ( change ) file contents.

Change directory contents. Required to create or delete files.

X

Execute file contents as a program.

Access detailed directory information. Required to get a long listing, or to access any specific file in the directory. Note that if a user has X but not R permissions on a directory, they can still access specific files, but only if they already know the name of the file they are trying to access.

Windows adjusts files access through a simple GUI.

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