• Exit from the terminal emulator by pressing the backslash (\) key and the Ctrl key simultaneously on your OpenVMS system.
• Enter the following command to switch your terminal line to a DECnet line manually:

  $ SET TERMINAL/PROTOCOL=DDCMP TTA0:

  
  TTA0 is the name of the terminal port on the local node.

• Enter NCP commands to turn on the line and circuit connected to your terminal port TTA0 manually, as in the following example:

  $ RUN SYS$SYSTEM:NCP NCP> SET LINE TT-0-0 RECEIVE BUFFERS 4 - _ LINE SPEED 2400 STATE ON NCP> EXIT

  
  Asynchronous DECnet is then started on the local OpenVMS node.

• Break the telephone connection.
• Run NCP and turn off either the asynchronous line or circuit. The two commands you can use are as follows:

  $ RUN SYS$SYSTEM:NCP NCP> SET LINE dev-c-u STATE OFF NCP> SET CIRCUIT dev-c-u STATE OFF NCP> EXIT

  
  If either of the above NCP commands is entered at the remote node, the line returns to terminal mode immediately. If the command is entered at the local (originating) OpenVMS node, the remote line and circuit remain on for approximately four minutes and then the line returns to terminal mode.

Figure 12-2 shows the establishment of a dynamic asynchronous connection. The commands that must be entered at each end of the connection are shown in Example 12-3.

Figure 12-2 A Typical Dynamic Asynchronous Connection

Example 12-3 Sample Commands for a Dynamic Asynchronous Connection

Commands issued at both the local OpenVMS node (LOCALA) and the remote OpenVMS node (REMOTC):

$ RUN SYS$SYSTEM:SYSGEN SYSGEN> CONNECT NOA0/NOADAPTER SYSGEN> EXIT $ INSTALL:=$SYS$SYSTEM:INSTALL $ INSTALL/COMMAND INSTALL> CREATE SYS$LIBRARY:DYNSWITCH/SHARE/PROTECT/HEADER/OPEN INSTALL> EXIT

Commands issued at the remote node (REMOTC):

$ RUN SYS$SYSTEM:SYSGEN SYSGEN> CONNECT VTA0/NOADAPTER/DRIVER=TTDRIVER SYSGEN> EXIT $ SET TERMINAL/EIGHT_BIT/PERMANENT/MODEM/DIALUP/DISCONNECT TTB0: $ RUN SYS$SYSTEM:NCP NCP> DEFINE NODE LOCALA RECEIVE PASSWORD PASSA INBOUND ENDNODE NCP> SET NODE LOCALA ALL NCP> EXIT

Commands issued at the local node (LOCALA):

$ RUN SYS$SYSTEM:NCP NCP> DEFINE NODE REMOTC TRANSMIT PASSWORD PASSA NCP> SET NODE REMOTC ALL NCP> EXIT $ SET HOST/DTE/DIAL=8556543 TTA0:

! After dialing in automatically to REMOTC, log in to your account on REMOTC.

$ SET TERMINAL/PROTOCOL=DDCMP/SWITCH=DECNET %REM-S-END - control returned to LOCALA: $

12.6 Sharing Files in a Network

Discourage users from sharing passwords and changing file and directory protection codes to grant the world category read or execute access. Grant BYPASS or READALL privilege cautiously.

The easiest way to share files on an occasional basis in a network environment is through the Mail utility. You mail the file to the intended recipient; there is no exposure of passwords, and the file is not made accessible to other users. However, there is the disadvantage of having to ask the file owner and wait for their response every time you want access. For an ongoing activity involving frequent access to shared files, it is better to set up proxy accounts and ACLs on the directories and files.

12.6.1 Using the Mail Utility

The easiest way for a user to transfer a text file to another user is to invoke the Mail utility (MAIL) and to send the user a copy of the file. This method is reasonably secure, because passwords need not be revealed and the original protection of the file is not changed. The receiving user simply includes a new file name with the MAIL command EXTRACT/NOHEADER to place a copy in the user's own directory. The copy automatically acquires the user's default protection. The user then uses the MAIL command DELETE to remove the copy from the mail file.

12.6.2 Setting Up Accounts for Local and Remote Users

A network manager may need to admit a number of users from outside nodes into a directory on the local node for a specific task. Therefore, you create a proxy account and add the proxy access to admit the outsiders into that one account (see Section 12.3.2.3). If there are local users who need to share the files in this account's directory, then you provide that access and protect the files from outsiders by placing ACLs on the directory and files.

Consider a situation where a corporation needs a central repository for sales update information that is accessible to employees throughout the corporation.

1. The security administrator at the node where the files will reside (BNORD) creates the special account SALES_READER. The SALES_READER account is set up as a captive account with mail disabled. The default directory is [SALESINFO], which has the following default protection code:

   (S:RWED,O:RWED,G:R,W)

   
   Note that this protection code permits users in the same group as SALES_READER on the home node BNORD to read the files. Furthermore, only the users in the system category or the owner category, or those who have privileges that give them such access, can update the files in the directory. ACLs are used to further define the access, as described in step 3.

2. The security administrator uses the AUTHORIZE command ADD/PROXY to add the proxy access for the outside users. For example, to extend proxy access to user Jackson on node DEXTER and user Goodwin on node BANGOR, the commands would be as follows:

   UAF> ADD/PROXY DEXTER::JACKSON SALES_READER/DEFAULT UAF> ADD/PROXY BANGOR::GOODWIN SALES_READER/DEFAULT

3. If later it becomes clear that other users at the home node BNORD need access and they do not belong to the same group as SALES_READER, ACLs could be added to the files in the directory [SALESINFO]. For example, suppose R. Grant needs control access to all the files and J. Martinez needs read access to all the files. The following two DCL commands would define the ACL for the directory and then propagate it to all existing files:

   $ SET SECURITY/ACL=- _$ ((IDENTIFIER=R_GRANT,ACCESS=CONTROL),- _$ (IDENTIFIER=J_MARTINEZ,ACCESS=READ))- _$ ((IDENTIFIER=R_GRANT,OPTIONS=DEFAULT,ACCESS=CONTROL),- _$ (IDENTIFIER=J_MARTINEZ,OPTIONS=DEFAULT,ACCESS=READ))- _$ [000000]SALESINFO.DIR $ SET SECURITY/DEFAULT *.*;*

When a small number of outside users need access, for differing reasons, to files requiring special protection, set up access to multiple proxy accounts, and apply extensive ACLs.

For example, a large corporation with many branch offices might choose to establish several proxy accounts for specific file-sharing purposes. Assume the central office wants to grant two key users from its two nodes in the eastern region read and write access to the project files for code name LEVIGRAY and read-only access to the BETSEYHARLOW project files. At the same time, there are three users from the western region who need read access to those LEVIGRAY files and require read and write access to the BETSEYHARLOW files. Only two users from the central office will have full access rights to the LEVIGRAY files, and two other users from headquarters will have full access rights to the BETSEYHARLOW files. For working purposes, the situation could be represented in tabular form, as shown in Example 12-4.

Example 12-4 Protected File Sharing in a Network

Access Requirements to CENTRL::PROJ:[DESGN_PROJECTS] Owned by [DESIGNERS,MGR] Users & Nodes Subdirectory LEVI Subdirectory BETSEY Project Files Project Files LEVIGRAY*.* BETSEYHARLOW*.* FRISCO::ALBION R RW FRISCO::ELTON R RW LA::IRVING R RW CENTRL::DIANTHA RWED NONE CENTRL::BRITTANIA RWED NONE CENTRL::ALBERT NONE RWED CENTRL::DELIA NONE RWED BOS::AYLMER RW R WASH::LAVINA RW R

The following solution uses five proxy accounts in addition to the four local accounts on node CENTRL, plus ACLs on the directory, subdirectories, and files:

1. The security administrator at headquarters uses AUTHORIZE to create new proxy accounts on node CENTRL for the remote users Albion, Elton, Irving, Aylmer, and Lavina. These accounts should be captive, disallow mail, and be restricted to network access only. The accounts are even restricted to a subset of DCL through CLI tables. The default directory should be [DESGN_PROJECTS] for each user. The manager decides it makes sense to put them into the DESIGNERS group to match their proposed uses of the files.
   Presumably, accounts already exist for users Diantha, Brittania, Albert, and Delia. They need not necessarily belong to the same group. They will be informed which device and directory to use for their work.
2. The next step is to add the proxy records to the network proxy authorization file with the following AUTHORIZE commands:

   UAF> ADD/PROXY FRISCO::ALBION ALBION/DEFAULT UAF> ADD/PROXY FRISCO::ELTON ELTON/DEFAULT UAF> ADD/PROXY LA::IRVING IRVING/DEFAULT UAF> ADD/PROXY BOS::AYLMER AYLMER/DEFAULT UAF> ADD/PROXY WASH::LAVINA LAVINA/DEFAULT

3. The security administrator at node CENTRL places an ACL on the top-level directory for [DESGN_PROJECTS] with the following DCL command:

   $ SET SECURITY/ACL=(DEFAULT_PROTECTION,S:RWED,O,G,W) - _$ [000000]DESGN_PROJECTS.DIR

   
   This ensures that no one outside of the system category of users can gain any UIC-based access to the files in the directory or any of the subdirectories unless they possess the BYPASS privilege. In fact, this restriction applies to those five users in the group DESIGNERS as well. The plan is for all files to possess ACLs that will admit the select group of users. It is desirable to propagate this protection code to all the files in this directory and its subdirectories. (The ACLs that will be placed on the files for further protection will take precedence when one of these users actually seeks access to a file.)

4. Two subdirectories are created in [DESGN_PROJECTS]:
   • [DESGN_PROJECTS.LEVI]
   • [DESGN_PROJECTS.BETSEY]
5. The security administrator uses the ACL editor to place the following additional ACEs in the ACL for the top-level directory:

   DESGN_PROJECTS.DIR (IDENTIFIER=DIANTHA,OPTIONS=PROTECTED,ACCESS=EXECUTE) (IDENTIFIER=BRITTANIA,OPTIONS=PROTECTED,ACCESS=EXECUTE) (IDENTIFIER=ALBERT,OPTIONS=PROTECTED,ACCESS=EXECUTE) (IDENTIFIER=DELIA,OPTIONS=PROTECTED,ACCESS=EXECUTE) (IDENTIFIER=AYLMER,OPTIONS=PROTECTED,ACESS=EXECUTE) (IDENTIFIER=LAVINA,OPTIONS=PROTECTED,ACCESS=EXECUTE) (IDENTIFIER=ALBION,OPTIONS=PROTECTED,ACCESS=EXECUTE) (IDENTIFIER=ELTON,OPTIONS=PROTECTED,ACCESS=EXECUTE) (IDENTIFIER=IRVING,OPTIONS=PROTECTED,ACCESS=EXECUTE)

   
   These protected ACEs ensure that only the select nine users can access the top-level directory. Because no one receives write or delete access to the top directory through the ACL, the directory and subdirectories are generally protected from deletion and renaming of files. (Of course, the system category of user obtains write and delete access through the UIC-based protection.)

6. Next, the security administrator creates ACLs on the subdirectories. The ACEs that are required are shown for their respective subdirectories:

   [DESGN_PROJECTS]LEVI.DIR (IDENTIFIER=DIANTHA,OPTIONS=PROTECTED,ACCESS=READ+WRITE+EXECUTE+CONTROL) (IDENTIFIER=DIANTHA,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ+WRITE+EXECUTE+DELETE+CONTROL) (IDENTIFIER=BRITTANIA,OPTIONS=PROTECTED,ACCESS=READ+WRITE+EXECUTE+CONTROL) (IDENTIFIER=BRITTANIA,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ+WRITE+EXECUTE+DELETE+CONTROL) (IDENTIFIER=AYLMER,OPTIONS=PROTECTED,ACCESS=READ+WRITE) (IDENTIFIER=AYLMER,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ+WRITE) (IDENTIFIER=LAVINA,OPTIONS=PROTECTED,ACCESS=READ+WRITE) (IDENTIFIER=LAVINA,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ+WRITE) (IDENTIFIER=ALBION,OPTIONS=PROTECTED,ACCESS=READ) (IDENTIFIER=ALBION,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ) (IDENTIFIER=ELTON,OPTIONS=PROTECTED,ACCESS=READ) (IDENTIFIER=ELTON,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ) (IDENTIFIER=IRVING,OPTIONS=PROTECTED,ACCESS=READ) (IDENTIFIER=IRVING,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ) [DESGN_PROJECTS]BETSEY.DIR (IDENTIFIER=ALBERT,OPTIONS=PROTECTED,ACCESS=READ+WRITE+EXECUTE+CONTROL) (IDENTIFIER=ALBERT,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ+WRITE+EXECUTE+DELETE+CONTROL) (IDENTIFIER=DELIA,OPTIONS=PROTECTED,ACCESS=READ+WRITE+EXECUTE+CONTROL) (IDENTIFIER=DELIA,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ+WRITE+EXECUTE+DELETE+CONTROL) (IDENTIFIER=ALBION,OPTIONS=PROTECTED,ACCESS=READ+WRITE) (IDENTIFIER=ALBION,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ+WRITE) (IDENTIFIER=ELTON,OPTIONS=PROTECTED,ACCESS=READ+WRITE) (IDENTIFIER=ELTON,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ+WRITE) (IDENTIFIER=IRVING,OPTIONS=PROTECTED,ACCESS=READ+WRITE) (IDENTIFIER=IRVING,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ+WRITE) (IDENTIFIER=AYLMER,OPTIONS=PROTECTED,ACCESS=READ) (IDENTIFIER=AYLMER,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ) (IDENTIFIER=LAVINA,OPTIONS=PROTECTED,ACCESS=READ) (IDENTIFIER=LAVINA,OPTIONS=DEFAULT+PROTECTED,ACCESS=READ)

   
   Note that both preceding ACLs include two ACEs for each identifier. The first ACE controls the access to the subdirectory. It denies delete access for the protection of the subdirectory and is not propagated to all the files created in the subdirectory. The second ACE for each identifier will automatically propagate to all files added to their respective subdirectories because of the inclusion of the Default attribute. Furthermore, the Protected attribute ensures that all the ACEs are protected from deletion except by specific action.

At this point, all the groundwork has been completed. Over time, files are added to the subdirectories. Thus, when the user Lavina in Washington enters the following DCL command, the file LEVIGRAYMEM3.MEM is printed at node WASH:

$ COPY CENTRL::LEVIGRAYMEM3.MEM LP:

However, if user Lavina tries to edit this file, the attempt fails because user Lavina is denied write access through the ACL.

If there were many users involved in this scheme, it would soon become worthwhile to grant additional identifiers to the users. For example, each user who would be allowed read access to the files in the LEVI subdirectory might be given the identifier LEVI_READER, and so forth. The ACLs could then be shortened.

For the most part, the OpenVMS operating system bases its security controls on user identity. Protected objects, such as files and devices, are accessible to individual users or groups of users. If an object's ACL or protection code allows a user the necessary access, then the user can make use of that object by using any available software. (See Chapter 4 for a description of OpenVMS object protection.)

In a protected subsystem, an application protected by normal access controls serves as a gatekeeper to objects belonging to the subsystem. Users have no access to the subsystem's objects unless they execute the application serving as gatekeeper. Once users run the application, their process rights list acquires identifiers giving them access to objects owned by the subsystem. As soon as they exit from the application, these identifiers and, therefore, the users' access rights to objects are taken away.

This chapter describes protected subsystems and explains how to build them.

13.1 Advantages of Protected Subsystems

Using protected subsystems offers several advantages:

• With protected subsystems, you have a mechanism to provide conditional access to data that is not available with traditional OpenVMS access controls. Traditionally, you give users privileges to bypass protection codes or access control lists (ACLs). In giving these privileges, however, you grant users a wide class of access. (Refer to Appendix A for information on the power different privileges carry.) Protected subsystems avoid extensive privilege use by individual users.
• Protected subsystems give you an alternative to installing images with privilege. Writing a secure privileged image requires skill, and failures can compromise system security.
• Protected subsystems give you an alternative to creating protected shareable images (also called user-written system services).
• Protected subsystems make system management easier because unprivileged users can manage them without much assistance from you. See Section 13.5 for details on system management requirements.

Protected subsystems have many applications, from databases to common system management situations.

One use for a protected subsystem might be a group membership list that you want to make available to all group members. The list contains the names, addresses, personnel numbers, and interests of group members. When the membership list is set up as a protected subsystem, all members of the group can read selected information and update specific types of information.

A protected subsystem might also solve the problem of confidential information being sent to printers in public areas. You could write an application to filter data for sensitive information. Confidential files would be sent to printers in restricted areas, while public files would be sent to any available printer. Any user with execute access to the application could use the restricted printers, but only through the protected subsystem.

13.3 How Protected Subsystems Work

A protected subsystem is an application that, when run, causes the process running the application to be granted one or more identifiers. For as long as a user runs the subsystem, the user's process rights list carries these additional identifiers. Figure 13-1 shows how a protected subsystem adds a second level of access control to traditional controls.

Figure 13-1 How Protected Subsystems Differ from Normal Access Control

Users with execute access to the application gain access to the subsystem. Once in the subsystem, users can work with the data files and other resources of the subsystem.

A subsystem can have several identifiers because the resources consumed by the subsystem (the files, printers, and so forth) can be protected differently.

Possession of subsystem identifiers is limited to the period users are executing the application. Once the users exit from the application, the identifiers are removed from their process rights lists. Subsystem identifiers are also removed from the rights list whenever users enter a Ctrl/Y sequence or attempt to create a subprocess with the DCL command SPAWN. (In this respect, use of the subsystem identifiers is identical to the operation of images installed with privileges.)

The following identifiers are reserved for use in the security subsystem and should not be granted to any user:

• SECSRV$CLIENT
• SECSRV$COMMUNICATION
• SECSRV$OBJECT

Someone developing an application for a protected subsystem must link the application images without the /DEBUG or /TRACEBACK qualifiers.

Although this kind of subsystem often precludes the need for privilege, applications can be installed with privilege. For example, some applications may need the PRMGBL privilege to create permanent global sections, or they may need the AUDIT privilege to send security audit records to the system security audit log file. Compaq does discourage the installation of a protected subsystem application with privileges in the All category. This category includes such privileges as BYPASS, CMKRNL, and SYSPRV---privileges that allow a user to subvert OpenVMS access controls. See Table 8-2 for a list of OpenVMS privileges and Appendix A for a description of the privileges.

Subsystem designers need to generate a list of identifiers that are necessary for it to operate as intended. Then the designers approach you, as the security administrator, to make the preparations described in Section 13.5.

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