Planning Network Security

The Need for Computer / Network Security:a virus.
Computer / network security includes:If the administrator is logged on as the domain
Control of physical accessibility to computers /administrator, the virus will have administrator privileges
networkon all computers in the domain and thus unrestricted
Prevention of accidental dataaccess to nearly all data on the network.
Erasure, modification, compromiseDefense in Depth:
Detection and prevention ofImagine the security of your network as a series of
Intentional internal security breacheslayers.
Unauthorized external intrusions (hacking)Each layer you pull away gets you closer to the
All three legs of the triangle must exist for a networkcenter, where the critical asset exists.
intrusion to occur:On your network, defend each layer as though the
Motiveprevious outer layer is ineffective or nonexistent.
A reason to want to breach your securityThe total security of your network will dramatically
Meansincrease if you defend at all levels and increase the
The abilityfault tolerance of security.
OpportunityExample: to protect users from launching an
The chance to enter the networke-mail-borne virus, in addition to antivirus software on
This last item is the administrator's only chance atthe users' computers, you could use e-mail client
controlling events.software that blocks potentially dangerous file types
Principles of Network Security:from being executed, block potentially dangerous
Network security goals are sometimes identified asattachments according to their file type, and ensures
Confidentiality.that the user is running under a limited user account.
Only the sender and intended recipient should "see" theReducing the Attack Surface:
message Integrity.An attacker needs to know of only one vulnerability to
Sender and receiver want to make sure that theattack your network successfully, whereas you must
message is not altered in transit, or afterwords.pinpoint all you vulnerabilities to defend your network.
AuthenticationThe smaller your attack surface, the better chance
The sender and receiver want to confirm each other'syou have of accounting for all assets and their
identity Availability.protection.
Services and resources must be available andAttackers will have fewer targets, and you will have
accessible.less to monitor and maintain.
Understanding Risk Management:Example: to lower the attack surface of individual
A key principle of security is that no network iscomputers on your network, you can disable services
completely secure.that are not used and remove software that is not
Information security deals principally with risknecessary.
management.Addressing Security Objectives:
The more important an asset, the more it is exposedControlling Physical Access to
to security threats, thus the more resources you mustServers
put into securing it.Networked workstations
Understanding Risk Management - 2:Network devices
In general, without training, administrators respond to aCabling plant
security threat in one of three ways:Being aware of security considerations with wireless
Ignore the threat, or acknowledge it but do nothing tomedia related to portable computers.
prevent it from occurring.Recognizing the security risk.
Address the threat in an ad hoc fashion.Of allowing data to be printed out.
Attempt to completely security all assets to theInvolving floppy disks, CDs, tapes, other removable
utmost degree, without regard for usability ormedia.
manageabilityRecognizing Network Security threats:
None of these strategies take into account what theTo protect your network, you must consider the
actual risk is, and all of them will usually lead tofollowing:
long-term failure.Question: from whom or what are you protecting if?
What are Some Risks?Who: types of network intruders and their motivations.
EavesdroppingWhat: types of network attackers and how they
Interception of messageswork.
HijackingThese questions form the basis for performing a
Taking over the role of a sender or receiver.threat analysis.
InsertionA comprehensive threat analysis should be the
Of messages into an active connectionproduct of brainstorming among people who are
Impersonationknowledgeable about the business processes, industry,
Spoofing a source address in a packet or any field in asecurity, and so on.
packetClassifying specific Types of Attacks:
Denial of service (DOS).Social engineering attacks
Prevent others from gaining access to resources,DOS attacks
usually by overloading system.Scanning and spoofing
Managing Risk:Source routing and other protocol exploits
Once the assets and their corresponding threats haveSOFTWARE and system exploits
been identified risk management can consist of:Trojans, Viruses and worms
AcceptanceIt is important to understand the types of threats in
Mitigationorder to deal with them properly.
TransferenceDesigning a Comprehensive Security Plan:
AvoidanceRFC2196, the Site Security Handbook.
Accepting Risk:Identify what your are trying to protect.
If you take no proactive measures, you accept the fullDetermine what you are trying to protect it from.
exposure and consequences of the security threats toDetermine how likely the anticipated threats are.
an asset.Implement measures that will protect your assets in a
Should accept risk only as a last resort when no othercost-effective manner.
reasonable alternatives exist, or when the costs areReview the process continually and make
extremely high.improvements each time a weakness is discovered.
When accepting risk, it is always a good idea toSteps to Creating a Security Plan:
create a contingency plan.Your security plan will generally consist of three
A contingency plan details a set of actions that will bedifferent aspects of protecting your network.
taken after the risk is realized and will lessen thePrevention: the measures that are implemented to
impact of the compromise of loss of the asset.keep your information from being modified, destroyed,
Mitigating Risk:or compromised.
The most common method of securing computersDetection: the measures that are implemented to
and networks is to mitigate security risks.recognize when a security breach has occurred or
By taking proactive measures either to reduce anhas been attempted, and possibly, the origin of the
asset's exposure to threats or reduce thebreach.
organizations dependency on the asset, you areReaction: the measures that are implemented to
mitigating the security risk.recover from a security breach to recover lost or
A simple example: installing antivirus software.altered data, to restore system or network operations,
Transferring Risk:and to prevent future occurrences.
Transfer security risk to another party has manySecurity Ratings:
advantage including:The U.S. government provides specifications for the
Economies of scale, such as insurance.rating of network security implementations in a
Use of another organization expertise and services.publication often referred to as the Orange Book,
Example: using a web hosting service.formally called the DOD Trusted Computer System.
When undertaking this type of risk transference, theEvaluation criteria, or TCSEC.
details of the arrangement should be clearly stated in aThe Red book, or Trusted Network Interpretation of
contract known as a service level agreement (SLA).the TCSEC (TNI) explains how the TCSEC
Avoiding Risk:evaluation.criteria are applied to computer networks.
The opposite of accepting risk is to avoid the riskCanada has security rating systems that work in a
entirely.similar way.
To avoid risk, you must remove the source of theCTPEC
threat, exposure to the threat, or your organizationSecurity Ratings -2:
reliance on the asset.To obtain a government contract, companies are
Generally, you avoid risk when there are little to nooften required to obtain a C2 rating.
possibilities for mitigating or transferring the risk, orA C2 rating has several requirements.
when the consequences of realizing the risk farThat the operating system in use be capable of
outweigh the benefits gained from undertaking the risk.tracking access to data, including both who accessed
An example can be a military or law enforcementit and when it was accessed.
dBase that, if compromised, could put lives at risk.That users' access to objects be subject to control
Implementing Security:(access permissions).
Think of security in terms of granting the least amountThat users are uniquely identified on the system (user
of privileges required to carry out the task.account name and password).
Example: consider the case of a network administratorThat security-related events can be tracked and
unwittingly opening an e-mail attachment that launchespermanently recorded for auditing (audit log).