7.0 Software Disk Write Protection

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7.1 Software Disk Protect Background

Specifying the use of a removable hard drive for computer systems which only occasionally process classified information represents an expense that may not always be necessary. Other possible solutions should be considered before making a final decision on how to implement processing security measures.

Certain application programs are readily available which are intended to block writing attempts to the system hard disk. The intent when using these programs is to place emphasis on procedural requirements and the user rather than the equipment. Procedural measures assume that normal system users do not intentionally try to circumvent their own security protection measures. When used correctly these programs work very well, and are now becoming widely accepted for stand alone computer systems.

The two common programs that are used to prevent writing to hard disks are PROTECT.COM and WPHD.COM. Both programs are similar. Each trap interrupt number 13, the normal interrupt used for writing to the hard disk. This interrupt is also commonly used by other interrupts for disk writes. Most (but not all) applications use this interrupt for hard disk writing.

PROTECT.COM and WPHD.COM will NOT protect the hard disk against a Virus or a low level format. In addition, if somehow a classified file is written to the fixed disk, disk removal and control will be required. The ADP Security Office will follow the same procedures as employed for other classified storage media when de-classifying the hard disk.

7.2 Determination of Program is Applicability

Placing control and operational constraints on classified processing activities is not as complicated as it sounds. When using the protection program, the IS may be operated in both an unclassified and a classified security mode as needed without changing equipment. However, during classified operation the system will need to operate in a stand alone dedicated mode. This means it must not connected to a network, and be limited to one user at any given time (no concurrent processing by more than one user). This approach for security emphasizes the users consciences and active part in the classified processing operation.

7.2.1 Standard Operating Procedures (Security Supplement)

The Security Supplement is intended for use by Naval Research Laboratory (NRL) personnel who have occasional need to perform classified data processing or similar activities. Its purpose is to serve as an example and to set forth standard practice procedures for safeguarding classified data processed by Microcomputer Data Processing Systems.

The generic standard practice and procedures were developed in accordance with the requirements of DoD Directive 5200.28 and SECNAV Instruction 5239.2. IS System Managers use the document as the basis to generate their own operating procedures. Once the procedure for a specific system is approved, no deviations are authorized without prior approval by the NRL ADP Security Office.

7.3 Floppy Boot Disk Preparation Procedures

Each system boot disk is unique, and must be prepared directly from the DOS system installed on the computer. System files can be transferred to the floppy by typing sys a: at the DOS prompt. The boot disk will be treated as classified material and will be kept in authorized secure storage when not is use.

In addition to the system boot program files, the following files must be copied directly from the computer that will be used for the boot disk to work correctly. Since some computers also need HDRIVE.SYS and EGA.SYS, it is best to copy all .SYS files from the DOS and C: directory to the new boot disk.


NOTE: Some machines also require SETVER.EXE

On some machines, the A: drive will not recognize the boot disk unless its write protect is removed. When installing, each new boot disk must be tested in an individual machine before it is deemed workable.

The PROTECT program can be executed manually or stored in the AUTOEXEC.BAT file on the controlled system boot floppy disk. The best approach is to have the PROTECT.COM program execute automatically during boot-up of the computer. Otherwise, the user must remember to manually execute the program before classified processing starts.

7.3.1 Installing and Executing The Program

The NRL IS Security Group will supply a controlled disk containing the copy of PROTECT.COM software. After the program is stored on the system the program is executed by typing in the file name PROTECT, prior to starting any classified processing. The message "Hard Disk Protection On" will be displayed on the CRT screen. From that point on any requests for DOS to write on Drive C: or above, should be prevented by this hard disk write protect program. The PROTECT program can be turned off by typing in the program name again. When this is done, a "Hard Disk Protection Off" message will be displayed on the screen.