Access Control Principles and Objectives

{LANG_NAVORIGIN} Certifications CISSP
Paul Gurgul 12/14/2004



Security is generally defined as the freedom from danger or as the condition of safety. Computer security, specifically, is the protection of data in a system against unauthorized disclosure, modification, or destruction and protection of the computer system itself against unauthorized use, modification, or denial of service. Because certain computer security controls inhibit productivity, security is typically a compromise toward which security practitioners, system users, and system operations and administrative personnel work to achieve a satisfactory balance between security and productivity.

Controls for providing information security can be physical, technical, or administrative. These three categories of controls can be further classified as either preventive or detective. Preventive controls attempt to avoid the occurrence of unwanted events, whereas detective controls attempt to identify unwanted events after they have occurred. Preventive controls inhibit the free use of computing resources and therefore can be applied only to the degree that the users are willing to accept. Effective security awareness programs can help increase users’ level of tolerance for preventive controls by helping them understand how such controls enable them to trust their computing systems. Common detective controls include audit trails, intrusion detection methods, and checksums.

Three other types of controls supplement preventive and detective controls. They are usually described as deterrent, corrective, and recovery. Deterrent controls are intended to discourage individuals from intentionally violating information security policies or procedures. These usually take the form of constraints that make it difficult or undesirable to perform unauthorized activities or threats of consequences that influence a potential intruder to not violate security (e.g., threats ranging from embarrassment to severe punishment).

Corrective controls either remedy the circumstances that allowed the unauthorized activity or return conditions to what they were before the violation. Execution of corrective controls could result in changes to existing physical, technical, and administrative controls. Recovery controls restore lost computing resources or capabilities and help the organization recover monetary losses caused by a security violation.

Deterrent, corrective, and recovery controls are considered to be special cases within the major categories of physical, technical, and administrative controls; they do not clearly belong in either preventive or detective categories. For example, it could be argued that deterrence is a form of prevention because it can cause an intruder to turn away; however, deterrence also involves detecting violations, which may be what the intruder fears most. Corrective controls, on the other hand, are not preventive or detective, but they are clearly linked with technical controls when antiviral software eradicates a virus or with administrative controls when backup procedures enable restoring a damaged database.

Finally, recovery controls are neither preventive nor detective but are included in administrative controls as disaster recovery or contingency plans.

Because of these overlaps with physical, technical, and administrative controls, the deterrent, corrective, and recovery controls are not discussed further in this chapter. Instead, the preventive and detective controls within the three major categories are examined.


Physical Controls

Physical security is the use of locks, security guards, badges, alarms, and similar measures to control access to computers, related equipment (including utilities), and the processing facility itself. In addition, measures are required for protecting computers, related equipment, and their contents from espionage, theft, and destruction or damage by accident, fire, or natural disaster (e.g., floods and earthquakes).

Preventive Physical Controls
Preventive physical controls are employed to prevent unauthorized personnel from entering computing facilities (i.e., locations housing computing resources, supporting utilities, computer hard copy, and input data media) and to help protect against natural disasters. Examples of these controls include:

• Backup files and documentation
• Fences
• Security guards
• Badge systems
• Double door systems
• Locks and keys
• Backup power
• Biometric access controls
• Site selection
• Fire extinguishers

Backup Files and Documentation
Should an accident or intruder destroy active data files or documentation, it is essential that backup copies be readily available. Backup files should be stored far enough away from the active data or documentation to avoid destruction by the same incident that destroyed the original. Backup material should be stored in a secure location constructed of noncombustible materials, including two-hour-rated fire walls. Backups of sensitive information should have the same level of protection as the active files of this information; it is senseless to provide tight security for data on the system but lax security for the same data in a backup location.

Fences
Although fences around the perimeter of the building do not provide much protection against a determined intruder, they do establish a formal no trespassing line and can dissuade the simply curious person. Fences should have alarms or should be under continuous surveillance by guards, dogs, or TV monitors.

Security Guards
Security guards are often stationed at the entrances of facilities to intercept intruders and ensure that only authorized persons are allowed to enter. Guards are effective in inspecting packages or other hand-carried items to ensure that only authorized, properly described articles are taken into or out of the facility. The effectiveness of stationary guards can be greatly enhanced if the building is wired with appropriate electronic detectors with alarms or other warning indicators terminating at the guard station. In addition, guards are often used to patrol unattended spaces inside buildings after normal working hours to deter intruders from obtaining or profiting from unauthorized access.

Badge Systems
Physical access to computing areas can be effectively controlled using a badge system. With this method of control, employees and visitors must wear appropriate badges whenever they are in access-controlled areas. Badge-reading systems programmed to allow entrance only to authorized persons can then easily identify intruders.

Double Door Systems
Double door systems can be used at entrances to restricted areas (e.g., computing facilities) to force people to identify themselves to the guard before they can be released into the secured area. Double doors are an excellent way to prevent intruders from following closely behind authorized persons and slipping into restricted areas.

Locks and Keys
Locks and keys are commonly used for controlling access to restricted areas. Because it is difficult to control copying of keys, many installations use cipher locks (i.e., combination locks containing buttons that open the lock when pushed in the proper sequence). With cipher locks, care must be taken to conceal which buttons are being pushed to avoid a compromise of the combination.

Backup Power
Backup power is necessary to ensure that computer services are in a constant state of readiness and to help avoid damage to equipment if normal power is lost. For short periods of power loss, backup power is usually provided by batteries. In areas susceptible to outages of more than 15–30 min., diesel generators are usually recommended.

Biometric Access Controls
Biometric identification is a more sophisticated method of controlling access to computing facilities than badge readers, but the two methods operate in much the same way. Biometrics used for identification include fingerprints, handprints, voice patterns, signature samples, and retinal scans. Because biometrics cannot be lost, stolen, or shared, they provide a higher level of security than badges. Biometric identification is recommended for high-security, low-traffic entrance control.

Site Selection
The site for the building that houses the computing facilities should be carefully chosen to avoid obvious risks. For example, wooded areas can pose a fire hazard, areas on or adjacent to an earthquake fault can be dangerous and sites located in a flood plain are susceptible to water damage. In addition, locations under an aircraft approach or departure route are risky, and locations adjacent to railroad tracks can be susceptible to vibrations that can precipitate equipment problems.

Fire Extinguishers
The control of fire is important to prevent an emergency from turning into a disaster that seriously interrupts data processing. Computing facilities should be located far from potential fire sources (e.g., kitchens or cafeterias) and should be constructed of noncombustible materials. Furnishings should also be noncombustible. It is important that appropriate types of fire extinguishers be conveniently located for easy access. Employees must be trained in the proper use of fire extinguishers and in the procedures to follow should a fire break out.

Automatic sprinklers are essential in computer rooms and surrounding spaces and when expensive equipment is located on raised floors. Sprinklers are usually specified by insurance companies for the protection of any computer room that contains combustible materials. However, the risk of water damage to computing equipment is often greater than the risk of fire damage. Therefore, carbon dioxide extinguishing systems were developed; these systems flood an area threatened by fire with carbon dioxide, which suppresses fire by removing oxygen from the air. Although carbon dioxide does not cause water damage, it is potentially lethal to people in the area and is now used only in unattended areas.

Current extinguishing systems flood the area with Halon, which is usually harmless to equipment and less dangerous to personnel than carbon dioxide. At a concentration of about 10%, Halon extinguishes fire and can be safely breathed by humans. However, higher concentrations can eventually be a health hazard. In addition, the blast from releasing Halon under pressure can blow loose objects around and can be a danger to equipment and personnel. For these reasons and because of the high cost of Halon, it is typically used only under raised floors in computer rooms. Because it contains chlorofluorocarbons, it will soon be phased out in favor of a gas that is less hazardous to the environment.

Detective Physical Controls
Detective physical controls warn protective services personnel that physical security measures are being violated. Examples of these controls include:

• Motion detectors
• Smoke and fire detectors
• Closed-circuit television monitors
• Sensors and alarms

Motion Detectors
In computing facilities that usually do not have people in them, motion detectors are useful for calling attention to potential intrusions. Motion detectors must be constantly monitored by guards.

Fire and Smoke Detectors
Fire and smoke detectors should be strategically located to provide early warning of a fire. All fire detection equipment should be tested periodically to ensure that it is in working condition.

Closed-Circuit Television Monitors
Closed-circuit televisions can be used to monitor the activities in computing areas where users or operators are frequently absent. This method helps detect individuals behaving suspiciously.

Sensors and Alarms
Sensors and alarms monitor the environment surrounding the equipment to ensure that air and cooling water temperatures remain within the levels specified by equipment design. If proper conditions are not maintained, the alarms summon operations and maintenance personnel to correct the situation before a business interruption occurs.


Technical Controls

Technical security involves the use of safeguards incorporated in computer hardware, operations or applications software, communications hardware and software, and related devices. Technical controls are sometimes referred to as logical controls.

Preventive Technical Controls
Preventive technical controls are used to prevent unauthorized personnel or programs from gaining remote access to computing resources. Examples of these controls include:

• Access control software
• Anti-virus software
• Library control systems
• Passwords
• Smart cards
• Encryption
• Dial-up access control and callback systems

Access Control Software
The purpose of access control software is to control sharing of data and programs between users. In many computer systems, access to data and programs is implemented by access control lists that designate which users are allowed access. Access control software provides the ability to control access to the system by establishing that only registered users with an authorized log-on ID and password can gain access to the computer system.

After access to the system has been granted, the next step is to control access to the data and programs residing in the system. The data or program owner can establish rules that designate who is authorized to use the data or program.

Anti-virus Software
Viruses have reached epidemic proportions throughout the computing world and can cause processing disruptions and loss of data as well as significant loss of productivity while cleanup is conducted. In addition, new viruses are emerging at an ever-increasing rate — currently about one every 48 hours. It is recommended that anti-virus software be installed on all microcomputers to detect, identify, isolate, and eradicate viruses. This software must be updated frequently to help fight new viruses. In addition, to help ensure that viruses are intercepted as early as possible, anti-virus software should be kept active on a system, not used intermittently at the discretion of users.

Library Control Systems
These systems require that all changes to production programs be implemented by library control personnel instead of the programmers who created the changes. This practice ensures separation of duties, which helps prevent unauthorized changes to production programs.

Passwords
Passwords are used to verify that the user of an ID is the owner of the ID. The ID-password combination is unique to each user and therefore provides a means of holding users accountable for their activity on the system. Fixed passwords that are used for a defined period of time are often easy for hackers to compromise; therefore, great care must be exercised to ensure that these passwords do not appear in any dictionary. Fixed passwords are often used to control access to specific data bases. In this use, however, all persons who have authorized access to the data base use the same password; therefore, no accountability can be achieved.

Currently, dynamic or one-time passwords, which are different for each log-on, are preferred over fixed passwords. Dynamic passwords are created by a token that is programmed to generate passwords randomly.

Smart Cards
Smart cards are usually about the size of a credit card and contain a chip with logic functions and information that can be read at a remote terminal to identify a specific user’s privileges. Smart cards now carry prerecorded, usually encrypted access control information that is compared with data that the user provides (e.g., a personal ID number or biometric data) to verify authorization to access the computer or network.

Encryption
Encryption is defined as the transformation of plaintext (i.e., readable data) into ciphertext (i.e., unreadable data) by cryptographic techniques. Encryption is currently considered to be the only sure way of protecting data from disclosure during network transmissions.

Encryption can be implemented with either hardware or software. Software-based encryption is the least expensive method and is suitable for applications involving low-volume transmissions; the use of software for large volumes of data results in an unacceptable increase in processing costs. Because there is no overhead associated with hardware encryption, this method is preferred when large volumes of data are involved.

Dial-Up Access Control and Callback Systems
Dial-up access to a computer system increases the risk of intrusion by hackers. In networks that contain personal computers or are connected to other networks, it is difficult to determine whether dial-up access is available or not because of the ease with which a modem can be added to a personal computer to turn it into a dial-up access point. Known dial-up access points should be controlled so that only authorized dial-up users can get through.

Currently, the best dial-up access controls use a microcomputer to intercept calls, verify the identity of the caller (using a dynamic password mechanism), and switch the user to authorized computing resources as requested. Previously, call-back systems intercepted dial-up callers, verified their authorization and called them back at their registered number, which at first proved effective; however, sophisticated hackers have learned how to defeat this control using call-forwarding techniques.

Detective Technical Controls
Detective technical controls warn personnel of violations or attempted violations of preventive technical controls. Examples of these include audit trails and intrusion detection expert systems, which are discussed in the following sections.

Audit Trails
An audit trail is a record of system activities that enables the reconstruction and examination of the sequence of events of a transaction, from its inception to output of final results. Violation reports present significant, security-oriented events that may indicate either actual or attempted policy transgressions reflected in the audit trail. Violation reports should be frequently and regularly reviewed by security officers and data base owners to identify and investigate successful or unsuccessful unauthorized accesses.

Intrusion Detection Systems
These expert systems track users (on the basis of their personal profiles) while they are using the system to determine whether their current activities are consistent with an established norm. If not, the user’s session can be terminated or a security officer can be called to investigate. Intrusion detection can be especially effective in cases in which intruders are pretending to be authorized users or when authorized users are involved in unauthorized activities.


Administrative Controls

Administrative, or personnel, security consists of management constraints, operational procedures, accountability procedures, and supplemental administrative controls established to provide an acceptable level of protection for computing resources. In addition, administrative controls include procedures established to ensure that all personnel who have access to computing resources have the required authorizations and appropriate security clearances.

Preventive Administrative Controls
Preventive administrative controls are personnel-oriented techniques for controlling people’s behavior to ensure the confidentiality, integrity, and availability of computing data and programs. Examples of preventive administrative controls include:

• Security awareness and technical training
• Separation of duties
• Procedures for recruiting and terminating employees
• Security policies and procedures
• Supervision
• Disaster recovery, contingency, and emergency plans
• User registration for computer access

Security Awareness and Technical Training
Security awareness training is a preventive measure that helps users to understand the benefits of security practices. If employees do not understand the need for the controls being imposed, they may eventually circumvent them and thereby weaken the security program or render it ineffective.

Technical training can help users prevent the most common security problem — errors and omissions — as well as ensure that they understand how to make appropriate backup files and detect and control viruses. Technical training in the form of emergency and fire drills for operations personnel can ensure that proper action will be taken to prevent such events from escalating into disasters.

Separation of Duties
This administrative control separates a process into component parts, with different users responsible for different parts of the process. Judicious separation of duties prevents one individual from obtaining control of an entire process and forces collusion with others in order to manipulate the process for personal gain.

Recruitment and Termination Procedures
Appropriate recruitment procedures can prevent the hiring of people who are likely to violate security policies. A thorough background investigation should be conducted, including checking on the applicant’s criminal history and references. Although this does not necessarily screen individuals for honesty and integrity, it can help identify areas that should be investigated further.

Three types of references should be obtained: (1) employment, (2) character, and (3) credit. Employment references can help estimate an individual’s competence to perform, or be trained to perform, the tasks required on the job. Character references can help determine such qualities as trustworthiness, reliability, and ability to get along with others. Credit references can indicate a person’s financial habits, which in turn can be an indication of maturity and willingness to assume responsibility for one’s own actions.

In addition, certain procedures should be followed when any employee leaves the company, regardless of the conditions of termination. Any employee being involuntarily terminated should be asked to leave the premises immediately upon notification, to prevent further access to computing resources. Voluntary terminations may be handled differently, depending on the judgment of the employee’s supervisors, to enable the employee to complete work in process or train a replacement.

All authorizations that have been granted to an employee should be revoked upon departure. If the departing employee has the authority to grant authorizations to others, these other authorizations should also be reviewed. All keys, badges, and other devices used to gain access to premises, information, or equipment should be retrieved from the departing employee. The combinations of all locks known to a departing employee should be changed immediately. In addition, the employee’s log-on IDs and passwords should be canceled, and the related active and backup files should be either deleted or reassigned to a replacement employee.

Any special conditions to the termination (e.g., denial of the right to use certain information) should be reviewed with the departing employee; in addition, a document stating these conditions should be signed by the employee. All terminations should be routed through the computer security representative for the facility where the terminated employee works to ensure that all information system access authority has been revoked.

Security Policies and Procedures
Appropriate policies and procedures are key to the establishment of an effective information security program. Policies and procedures should reflect the general policies of the organization as regards the protection of information and computing resources. Policies should cover the use of computing resources, marking of sensitive information, movement of computing resources outside the facility, introduction of personal computing equipment and media into the facility, disposal of sensitive waste, and computer and data security incident reporting. Enforcement of these policies is essential to their effectiveness.

Supervision
Often, an alert supervisor is the first person to notice a change in an employee’s attitude. Early signs of job dissatisfaction or personal distress should prompt supervisors to consider subtly moving the employee out of a critical or sensitive position.

Supervisors must be thoroughly familiar with the policies and procedures related to the responsibilities of their department. Supervisors should require that their staff members comply with pertinent policies and procedures and should observe the effectiveness of these guidelines. If the objectives of the policies and procedures can be accomplished more effectively, the supervisor should recommend appropriate improvements. Job assignments should be reviewed regularly to ensure that an appropriate separation of duties is maintained, that employees in sensitive positions are occasionally removed from a complete processing cycle without prior announcement, and that critical or sensitive jobs are rotated periodically among qualified personnel.

Disaster Recovery, Contingency, and Emergency Plans
The disaster recovery plan is a document containing procedures for emergency response, extended backup operations, and recovery should a computer installation experience a partial or total loss of computing resources or physical facilities (or of access to such facilities). The primary objective of this plan, used in conjunction with the contingency plans, is to provide reasonable assurance that a computing installation can recover from disasters, continue to process critical applications in a degraded mode, and return to a normal mode of operation within a reasonable time. A key part of disaster recovery planning is to provide for processing at an alternative site during the time that the original facility is unavailable. Contingency and emergency plans establish recovery procedures that address specific threats. These plans help prevent minor incidents from escalating into disasters. For example, a contingency plan might provide a set of procedures that defines the condition and response required to return a computing capability to nominal operation; an emergency plan might be a specific procedure for shutting down equipment in the event of a fire or for evacuating a facility in the event of an earthquake.

User Registration for Computer Access
Formal user registration ensures that all users are properly authorized for system and service access. In addition, it provides the opportunity to acquaint users with their responsibilities for the security of computing resources and to obtain their agreement to comply with related policies and procedures.

Detective Administrative Controls
Detective administrative controls are used to determine how well security policies and procedures are complied with, to detect fraud, and to avoid employing persons that represent an unacceptable security risk. This type of control includes:

• Security reviews and audits
• Performance evaluations
• Required vacations
• Background investigations
• Rotation of duties

Security Reviews and Audits
Reviews and audits can identify instances in which policies and procedures are not being followed satisfactorily. Management involvement in correcting deficiencies can be a significant factor in obtaining user support for the computer security program.

Performance Evaluations
Regularly conducted performance evaluations are an important element in encouraging quality performance. In addition, they can be an effective forum for reinforcing management’s support of information security principles.

Required Vacations
Tense employees are more likely to have accidents or make errors and omissions while performing their duties. Vacations contribute to the health of employees by relieving the tensions and anxieties that typically develop from long periods of work. In addition, if all employees in critical or sensitive positions are forced to take vacations, there will be less opportunity for an employee to set up a fraudulent scheme that depends on the employee’s presence (e.g., to maintain the fraud’s continuity or secrecy). Even if the employee’s presence is not necessary to the scheme, required vacations can be a deterrent to embezzlement because the employee may fear discovery during his or her absence.

Background Investigations
Background investigations may disclose past performances that might indicate the potential risks of future performance. Background investigations should be conducted on all employees being considered for promotion or transfer into a position of trust; such investigations should be completed before the employee is actually placed in a sensitive position. Job applicants being considered for sensitive positions should also be investigated for potential problems. Companies involved in government-classified projects should conduct these investigations while obtaining the required security clearance for the employee.

Rotation of Duties
Like required vacations, rotation of duties (i.e., moving employees from one job to another at random intervals) helps deter fraud. An additional benefit is that as a result of rotating duties, employees are cross-trained to perform each other’s functions in case of illness, vacation, or termination.

The organization’s security policy should be reviewed to determine the confidentiality, integrity, and availability needs of the organization. The appropriate physical, technical, and administrative controls can then be selected to provide the required level of information protection, as stated in the security policy.

A careful balance between preventive and detective control measures is needed to ensure that users consider the security controls reasonable and to ensure that the controls do not overly inhibit productivity. The combination of physical, technical, and administrative controls best suited for a specific computing environment can be identified by completing a quantitative risk analysis. Because this is usually an expensive, tedious, and subjective process, however, an alternative approach — referred to as meeting the standard of due care — is often used. Controls that meet a standard of due care are those that would be considered prudent by most organizations in similar circumstances or environments. Controls that meet the standard of due care generally are readily available for a reasonable cost and support the security policy of the organization; they include, at the least, controls that provide individual accountability, audit ability, and separation of duties.

Need-to-Know Access
Users should be granted access only to those files and programs that they need in order to perform their assigned job functions. User access to production data or source code should be further restricted through use of well-formed transactions, which ensure that users can change data only in controlled ways that maintain the integrity of data. A common element of well-formed transactions is the recording of data modifications in a log that can be reviewed later to ensure that only authorized and correct changes were made. To be effective, well-formed transactions must ensure that data can be manipulated only by a specific set of programs. These programs must be inspected for proper construction, installation, and controls to prevent unauthorized modification.

Because users must be able to work efficiently, access privileges should be judiciously granted to allow sufficient operational flexibility; need-to-know access should enable maximum control with minimum restrictions on users. The security program must employ a careful balance between ideal security and practical productivity.


Author Note: The following document is for reference purposes only.














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