COMPUTER SYSTEM SECURITY AND ACCESS CONTROLS Section A: Computer system security
Computer System Security is defined as Control of access to a computer system's resources, specially its data and operating system files . System security ensures that information is only onl y read, heard, changed, broadcast and otherwise used by people who have the right to do so. In the most basic sense, computer system securit y ensures that your computer does what it's supposed to do – even even if its users don't do what they're the y're supposed to do. It protects the information stored in it from being lost, changed changed either maliciously or accidentally, or read or modified by those not authorized to access it.
WHAT CAN GO WRONG? Data and information in any information system is at risk from: 1. Human error: e.g. entering incorrect transactions; failing to spot and correct errors; processing the wrong information; accidentally deleting data 2. Technical errors: e.g. hardware that fails or software that crashes during transaction processing 3. Accidents and disasters : e.g. floods, fire 4. Fraud - deliberate attempts to corrupt c orrupt or amend previously legitimate data and information 5. Commercial espionage (intelligence) (intelligence): e.g. competitors deliberately gaining access to commercially-sensitive data (e.g. customer details; pricing and profit margin data, designs) 6. Malicious damage: where an employee or other person deliberately sets out to destroy or damage data and systems (e.g. hackers, creators of viruses)
Based on the above, Information systems need to be secure if they are to be reliable. Since many businesses are critically criticall y reliant on their information systems for key business processes (e.g. webs sites, production scheduling, transaction processing), security can be seen to be a very important area for management to get right. How Can Computer Information Systems be Made More Secure? There is no such thing as failsafe security s ecurity for information systems. When designing security controls, a business needs to address the following factors; Prevention: What can be done to prevent security accidents, er rors and breaches? Physical security controls are a key part of prevention te chniques, as are controls designing to ensure the integrity of data. Detection: Spotting when things have gone wrong is crucial; detection needs to be done as soon as possible - particularly if the information i nformation is commercially sensitive. Detection controls are often combined with prevention controls. Deterrence: deterrence controls are about discouraging potential security breaches. Data recovery - If something goes wrong (e.g. data is corrupted or hardware breaks down) it is important to be able to recover lost data and information.
How does computer system security provide protection? There are four primary methods: 1. System Access Controls . Ensuring that unauthorized users don't get into the system, and by encouraging (and sometimes forcing) authorized users to be se curity-conscious – for for
example, by changing their passwords on a regular basis. The system also protects password data and keeps track of who's doing what in the system, especially if what they're doing is security-related (e.g., logging in, trying to open a file, using special privileges). 2. Data Access Controls . Monitoring who can access what data, and for what purpose. Your system might support discretionary access controls; with these, you determine whether other people can read or change your data. Your system might also support mandatory access controls; with these, the system determines access rules based on the security levels of the people, the files, and the other objects in your system.
3. System and Security Administration . Performing the offline procedures that make or break a secure system – by clearly delineating system administrator responsibilities, by training users appropriately, and by monitoring users to make sure that security policies are observed. This category also involves more global security management; for example, figuring out what security threats face your system and what it will cost to protect against them.
4. System Design. Taking advantage of basic hardware and software security characteristics; for example, using a system architecture that's able to segment memory, thus isolating privileged processes from nonprivileged processes.
The 10 physical security measures Physical security is the foundation for our overall strategy. These measures ensure that the network and its components have been protected at the physical level.
#1: Lock up the server room Even before you lock down the servers, in fact, before you even turn them on for the first time, you should ensure that there are good locks on the server room door. Of course, the best lock in the world does no good if it isn’t used, so you also need poli cies requiring that those doors be locked any time the room is unoccupied, and the policies should set out who has the key or keycode to get in. The server room is the heart of your physical network, and someone with physical access to the servers, switches, routers, cables and other devices in that room can do enormous damage.
#2: Set up surveillance Locking the door to the server room is a good first step, but s omeone could break in, or someone who has authorized access could misuse that authority. You need a way to know who goes in and out and when. A log book for signing in and out is the most elemental way to accomplish this, but it has a lot of drawbacks. A person with malicious intent is likely to just bypass it. A better solution than the log book is an authentication system incorporated into the locking devices, so that a smart card, token, or biometric scan is required to unlock the doors, and a record is made of the identity of each person who enters.
A video surveillance camera, placed in a location that makes it difficult to tamper with or disable (or even to find) but gives a good view of persons entering and leaving should supplement the log book or electronic access system. Surveillance cams can monitor continuously, or they can use motion detection technology to record only when someone i s moving about. They can even be set up to send e-mail or cell phone notification if motion is detected when it shouldn’t be (such as after hours).
#3: Make sure the most vulnerable devices are in that locked room Remember, it’s not just the servers you have to worry about. A hacker can plug a laptop into a hub and use sniffer software to capture data traveling across the network. Make sure that as many of your network devices as possible are in that locked room, or if they need to be in a different area, in a locked closet elsewhere in the building.
#4: Use rack mount servers Rack mount servers not only take up less server room real estate; they are also easier to secure. Although smaller and arguably lighter than (some) tower s ystems, they can easily be locked into closed racks that, once loaded with several servers, can then be bolted to the floor, making the entire package almost impossible to move, much less to steal.
#5: Don’t forget the workstations Hackers can use any unsecured computer that’s connected to the network to acces s or delete information that’s important to your business. Workstations at unoccupied desks or in empty offices (such as those used by employees who are on vacation or have left the company and not yet been replaced) or at locations easil y accessible to outsiders, such as the front receptionist’s desk, are particularly vulnerable. Disconnect and/or remove computers that aren’t being used and/or lock the doors of empty offices, including those that are temporarily empty while an employee is at lunch or out sick. Equip computers that must remain in open areas, sometimes out of view of employees, with smart card or biometric readers so that it’s more difficult for unauthorized persons to log on.
#6: Keep intruders from opening the case Both servers and workstations should be protected from thieves who can open the case and grab the hard drive. It’s much easier to make off with a hard disk in your pocket than to carry a full tower off the premises. Many computers come with case locks to prevent opening the case without a key.
#7: Protect the portables Laptops and handheld computers pose special physical security risks. A thief can easily steal the entire computer, including any data stored on its disk as well as network logon passwords that may be saved. If employees use laptops at the ir desks, they should take them with them when they leave or secure them to a permanent fixture with a cable lock. Handhelds can be locked in a drawer or safe or jus t slipped into a pocket and carried on your person when you leave the area. Motion sensing alarms can be installed.
#8: Pack up the backups Backing up important data is an essential element in disaster recovery, but don’t forget that the information on those backup tapes, disks, or discs can be stolen and used by someone outside the company. Many IT administrators keep the backups next to the server in the server room. They should be locked in a drawer or safe at the very least. Ideally, a set of
backups should be kept off site, and you must take care to ensure that they are secured in that offsite location. Don’t overlook the fact that some workers may back up their work on floppy disks, USB keys, or external hard disks. If this practice i s allowed or encouraged, be sure to have policies requiring that the backups be locked up at all times.
#9: Disable the drives If you don’t want employees copying company information t o removable media, you can disable or remove floppy drives, USB ports, and other means of connecting external drives. Simply disconnecting the cables may not deter technically savvy workers. Some organizations go so far as to fill ports with glue or other substances to permanently prevent their use, although there are software mechanisms that disallow it. Disk locks, such as the one at SecurityKit.com, can be inserted into floppy drives on those computers that still have them to lock out other diskettes.
#10: Protect your printers You might not think about printers posing a security risk, but many of today’s printers store document contents in their own on-board memories. If a hacker steals t he printer and accesses that memory, he or she may be able to make copies of recently printed documents. Printers, like servers and workstations that store important information, should be located in secure locations and bolted down so nobody can walk off with them. Also think about the physical security of documents that workers print out, especially extra copies or copies that don’t print perfectly and may be just abandoned at the printer or thrown intact into the trash can where they can be retrieved. It’s best to implement a policy of immediately shredding any unwanted printed documents, even those that don’t contain confidential information. This establishes a habit and frees the end user of the responsibility for determining whether a document should be shredded.
Summary Remember that network security starts at the physical level. All the firewalls in the world won’t stop an intruder who is able to gain physical access t o your network and computers, so lock up as well as lock down.
Section B: System Access:
System access is defined as the process of Logging Into Your computer System. The first way in which a system provides computer securit y is by controlling access to that system: Who's allowed to log in? You tell the system who you are, and the system proves that you are (or you aren't) who you claim to be. In security terms, this two-step process is called identification and authentication.
Identification and Authentication Identification is the way you tell the system who you are. Authentication is the way you prove to the system that you are who you say you are. In just about any multi-user system, you must identify yourself, and the system must authenticate your identity, before you can use the system. There are three classic ways in which you can prove yourself: 1. Something you know . The most familiar example is a password. The theory is that if you know the secret password for an account, you must be the owner of that account. There
is a problem with this theory: You might give your password away or have it stolen from you. If you write it down, someone might read it. If you tell someone, that person might tell someone else. If you have a simple, easy-toguess password, someone might guess it or systematicall y crack it. 2. Something you have . Examples are keys, tokens, badges, and smart cards you must have to "unlock" your terminal or your account. The theory is that if you have the key or equivalent, you must be the owner of it. The problem with this theory is that you might lose the key, it might be stolen from you, or someone might borrow it and duplicate it. Electronic keys, badges, and smart c ards are gaining acceptance as authentication devices and as access devices for buildings and computer rooms. With the proliferation of automatic teller machines (ATMs), people are becoming increasingly familiar with this type of authentication. 3. Something you are . Examples are physiological or behavioral traits, such as your fingerprint, handprint, retina pattern, voice, signature, or keystroke pattern. Biometric systems compare your particular trait against the one stored for you and determine whether you are who you claim to be. Although biometric systems occasionally reject valid users and accept invalid ones, they are generally quite accurate. The problem with these authentication systems is that, on the whole, people aren't comfortable using them.
Hints for Protecting Passwords Both system administrators and users share responsibility for enforcing password security. Remember, password security is everyone's responsibility. In addition to damaging your own files, someone who uses your password to break into a system can also compromise all of the files in your system or network. From the USENET: "A password should be like a toothbrush. Use it every day; change it regularly; and DON'T share it with friends."
Don't allow any logins without passwords. If you're the system administrator, make sure every account has a password. Don't keep passwords that may have come with your system. Change all test or guest passwords – for example, root, system, test, demo, etc., before allowing users to log in. Don't ever let anyone use your password. Don't write your password down – particularly on your terminal, computer, or anywhere around your desk. If you ever do write your password down, don't identify it as a password and don't write the phone number of the computer on the same piece of paper. Don't type a password while anyone is watching. Don't record your password online or send it anywhere via electronic mail. In The Cuckoo's Egg , Cliff Stoll reports how his intruder scanned electronic mail messages for references to the word "password." Don't make a bad situation worse. If you do share your password – deliberately or inadvertently – change it immediately (or ask your administrator to change it). Don't keep the same password indefinitely. Even if your password hasn't been compromised, change it on a regular basis.
Passwords are your main defense against intruders. To protect your system and your data, you must select good passwords, and you must protect them carefully.
Protecting Passwords
Access decisions are the heart of system security, and access decisions are based on passwords, so it's vital that your system protect its passwords and other login information. Most systems protect passwords in two important ways: they make passwords hard to guess and login controls hard to crack, and they protect the file i n which passwords are stored. Protecting Your Login and Password on Entry
Most vendors offer a whole smorgasbord of login controls and password management features that the system administrator can mix and match to provide optimal protection of a particular system. Because these security features are commerciall y attractive and relatively easy to implement, most systems tend to have a lot of them. Examples of such features are shown in Table 3-1. Table 3-1: Sample Login/Password Controls Feature
Meaning
System messages
Most systems display welcome and announcement messages before and/or after you successfully log in. Some systems allow the system administrator to suppress these messages, because the y may provide a clue to an observer as to the type of system being accessed. If an intruder dials in and finds out he's talking to a VMS system, for example, that's a valuable clue.
Limited attempts
After a certain number of unsuccessful tries at logging into the system (the number can be specified by the system administrator), the system locks you out and prevents you from attempting to log in from that terminal. Some systems lock you out without informing you that this has happened. This allows for the possibility of taking evasive action – identifying the account as a suspicious one without letting you know you're under investigation.
Limited time periods
Certain users or terminals may be limited to logging in during business hours or other specified times.
Last login message
When you log in, the system may display the date and time of your last login. Many systems also display the number of unsuccessful login attempts since the time of your last successful login. This may give you a chance to discover that your account was accessed by someone else – for example, by noticing a login in the middle of the night or by noticing a pattern of repeated attempts to log in. If you weren't responsible for these attempts, notify your system administrator right away.
Userchangeable passwords
In many systems, you're allowed to change your own password at any time after its initial assignment by the system administrator.
Systemgenerated passwords
Some systems require you to use passwords generated randomly by the system, rather than relying on your own selection of a difficult-to- guess password. The VAX/VMS Version 4.3 system, and many other systems, ensure that these passwords are pronounceable. Some systems let you view several random choices from which you can pick one you think you'll be able to remember. A danger of system-generated passwords is that they're often so hard to remember that users may tend to write them down. Another danger is that if the algorithm for generating these passwords becomes known, your entire system is in jeopardy.
When a specified time is reached – for example, the end of the month – all passwords in the system may expire. The new passwords usually must not be identical to the old passwords. The system should give reasonable notice Password aging before requiring you to change your password; if you have to pick a and expiration password quickly, you're likely to pick a poor one. In some systems, the system administrator can respond to a security breach by forcing a particular password, or all passwords, to expire immediately.
This controls further access to the system until the damage can be assessed. The system may keep track of your passwords for an exte nded period to make sure you don't reuse one that might have been guessed. Minimum length
Because short passwords are easier to guess than long ones, some systems require that passwords be a certain length, usually six to eight characters.
Locks allow the system administrator to restrict certain users from logging in Password locks or to lock login accounts that haven't been used for an extended period of time. System passwords
System passwords control access to particular terminals that might be targets for unauthorized use. Usually a system password must be entered before you enter your individual password.
Primary and secondary passwords
Some systems require that two users, each with a valid password, be present to log in successfully to certain extremely sensitive accounts.
Dial-in password
Some systems require that special passwords be used to access dial-in lines.
Section C: Data Access: Protecting Your Data The second important way in which a system provides computer security is by controlling access to the data stored in a system: Who can read your files? Who can change your files? Can you decide to share your data with other users? How does the s ystem make decisions about access control? If you work alone on a PC, you don't need to worry about access controls. You own all of your files, and you can read and write them as you wish. If you want to share a file with someone, you can copy it onto a diskette and hand it over. With shared computers, it isn't as easy. As soon as you begin to work on a system that supports multiple users, you'll have to start worrying about data protection and access controls. You may not want every user in the system to be able to re ad your files. You certainly won't want them to change your files. There are two basic types of access controls that provide different levels of protection to the files in your system: discretionary access control and mandatory access control . With discretionary access control (DAC) you decide how you want to protect your files, and whether to share your data. With the more complex mandatory access control (MAC) the system protects your files. In a MAC system, everything has a l abel. Using the security policy relationships established for your organization, the system decides whether a user can access a file by comparing the label of the user with the label of the file. The following sections introduce these types of access controls.
Discretionary Access Control Discretionary access control (DAC) is an access policy that restricts access to files (and other system objects such as directories and devices) based on the identity of users and/or the groups to which they belong. What's discretionary about discretionary access control? In contrast to mandatory access control, in which the system controls access, DAC is applied at your own discretion. With DAC, you can choose to give away your data; with MAC, you can't. Not only does DAC let you tell the system who can access your data, it lets you specify the type of access allowed. For example, you might want everyone in the system to be able to
read a particular file, but you might want only yourself and your manager to be able to change it. Most systems support three basic t ypes of access: Read If you have read access for a file, you can read the file. Write If you have write access for a file, you can write (change or replace) the file. Execute The execute permission is relevant only if the file is a program. If you have execute permission for a file, you can run the program. Ownership
There are many types of discretionary access control. One simple method involves ownership of files, directories, and devices. If you create a file, you're the owner of the file. Your login ID, or some other identifier, is entered in the file header. A system might base all of its access decisions on file ownership. If you're the owner of the file, the system lets you read and change the file. If you're not the owner, you have no rights to the file. This is a simple scheme, but not a very practical one. For one thing, it doesn't let you share the file with anyone. Virtually every system keeps track of file ownership and bases many access decisions upon it (for example, regardless of other mechanisms, the s ystem might let you delete a file only if you're the file owner). Access Control Lists
Access control lists (ACLs) are lists of users and groups, with their specific permissions. They offer a more flexible way of providing discretionary access control. AC Ls are implemented differently on different systems. For example, in a UNIX-bas ed trusted system that uses the UNIX security kernel developed by Atlanta-based SecureWare, you'd protect PAYROLL with ACLs in the form: ‹john.acct, r›
Figure 3-2: Discretionary Access Control With an Access Control List
Mandatory Access Control Mandatory access control (MAC) is an access policy supported for systems that process especially sensitive data (e.g., government classifi ed information or sensitive corporate data). Systems providing mandatory access controls must assign sensitivity label s to all subjects (e.g., users, programs) and all objects (e.g., files, directories, devices, windows, sockets) in the system. A user's sensitivity label specifies the sensitivity level, or level of trust, associated with that user; it's often called a clearance. A file's sensitivity label specifies the level of trust that a user must have to be able to access that file. Mandatory access controls use sensitivity labels to determine who can access what information in your system. Together, labeling and mandatory access control implement a multi-level security policy – a policy for handling multiple information classifications at a number of different security levels within a single computer system.
