HP OpenVMS Guide to System Security: OpenVMS Version 8.4 > Chapter 4 Protecting Data

Security Profile of Objects

Definition of a Protected Object

The objects of the OpenVMS operating system that require protection are all passive repositories that either contain or receive information. These objects are protected because once you have access to the object, you have access to the information it holds. Some examples of protected objects include:

  • A file in memory or on a storage device

  • A hardware device or a virtual device

  • A data structure, such as a common event flag cluster or a logical name table

“Specifying an Object's Class” lists the classes of objects that OpenVMS protects; see the “Descriptions of Object Classes” for an in-depth description of each class.

Contents of an Object's Profile

The security elements of any object comprise its security profile. An object's security profile contains the following types of information:

  • The owner of the object. The system uses this element in interpreting the protection code.

  • The protection code defining access to objects based on the categories of system, owner, group, and world. This protection code controls broad categories of users.

  • The access control list (ACL) controlling access to objects by individual users or groups of users.

With the exception of files, a new object inherits its security elements from a system-supplied template profile, which the site security administrator may modify. Files have a more complicated inheritance mechanism, one that affords greater control over the security elements of new objects. In all cases, you can assign security elements during object creation rather than using the operating system defaults.

This section gives an overview of protection codes and ACLs. “Controlling Access with ACLs” and “Controlling Access with Protection Codes” explore these protection mechanisms in greater detail. See the “Descriptions of Object Classes” for a description of individual object classes.


The first element of an object's security profile is the UIC of its owner.

In most cases, if you create an object, you are its owner. As the owner, you can modify its security profile. The system automatically assigns your UIC to the object and uses it in making access decisions.

There are some exceptions to the ownership rule. Files owned by resource identifiers do not have a UIC. When a user creates a file in the directory of a resource identifier, the file may be owned by the resource identifier and not the user who created the file (see “Profile Assignment”). See the “Descriptions of Object Classes” for an explanation of the ownership rules for each object class.

The owner of any object except a file can reassign ownership to another user with the SET SECURITY/OWNER command, as described in “Modifying a Security Profile”. Changing the owner of a file usually requires privilege (see “Types of Access”).

Protection Code

The second element of an object's security profile is the object's protection code.

The system automatically assigns a protection code to each new object. The protection code associated with an object determines the type of access allowed to a user, based on the relationship between the user UIC and the owner UIC. With the exception of files and pseudo-terminal (FT) devices, the code a protected object receives is derived from a template profile for the class. (A file's protection code originates from another source, described in “Files”.)

Typically, you rely on the protection code to protect an object if the object is to be accessed by: (a) only the owner, (b) all users on the system, or (c) a specific UIC-based group of users. If you want to grant access to specific groups of users outside the UIC group but not to all users on the system, then you need to add an ACL (see “Access Control List (ACL)”).

Interpreting a Protection Code

A protection code defines the access rights for four categories of users: (a) the owner, (b) the users who share the same group UIC as the owner (the group category), (c) all users on the system (the world category), and (d) those with system privileges or rights (the system category). A code lists access rights in a fixed order: the system category (S), then owner (O), then group (G), and then world (W). It has the following syntax:

[user category: access allowed (,user category: access allowed,...)]

When the operating system processes a request to use a protected object, it compares the user's UIC to the UIC of the object's owner. If the user's UIC is the same as the UIC of the object's owner, the user is granted the access of the owner protection field. Failing a match of UICs, the system progresses through the other user categories. The system tries to find a match of the group fields to determine if there is a common group membership. The system may also evaluate whether the UIC group number indicates the user belongs to the system category of users. The world category applies to all users.

For example, user Jones has a UIC of [14,1], and he tries to read a file that is owned by UIC [14,5]. Because Jones is in the same group (14), the system might grant access to the file. The final decision depends on the access rights specified in the protection code.

See “Controlling Access with Protection Codes” for a complete description of how to interpret and create protection codes.

Access Control List (ACL)

The third (optional) element of an object's security profile is the object's access control list.

An access control list (ACL) is a collection of entries that define the access rights a user or group of users has to a particular protected object, such as a file, directory, or device.

ACLs may be created by default when an object is created, they may be created by the security administrator, or they may be created by users for objects to which they have control access (see “Using Control Access to Modify an Object Profile”).

Because security administrators can set up default ACLs, some users may be unaware that their objects have ACLs and may never change ACLs themselves. (You can use the DCL command DIRECTORY/SECURITY or SHOW SECURITY to see if there are ACLs on your files.) Other users are actively involved in creating and maintaining their own ACLs.

Using ACLs is optional. Although ACLs can enhance the security of objects in any installation through a more detailed definition of who is allowed what kind of access, users have to spend time creating and maintaining the ACLs.

You use the DCL commands SET SECURITY and SHOW SECURITY for creating and displaying ACLs, although the access control list editor (ACL editor) is an important utility for more extensive work.

“Controlling Access with ACLs” continues the discussion of ACLs and how to use them.