Planning Network Security

The Need for Computer / Network Security:

Computer / network security includes:

Control of physical accessibility to computers / network
Prevention of accidental data
Erasure, modification, compromise
Detection and prevention of
Intentional internal security breaches
Unauthorized external intrusions (hacking)

All three legs of the triangle must exist for a network intrusion to occur:
A reason to want to breach your security
The ability
The chance to enter the network
This last item is the administrator’s only chance at controlling events.

Principles of Network Security:
Network security goals are sometimes identified as Confidentiality.
Only the sender and intended recipient should “see” the message Integrity.
Sender and receiver want to make sure that the message is not altered in transit, or afterwords. Authentication
The sender and receiver want to confirm each other’s identity Availability.
Services and resources must be available and accessible.

Understanding Risk Management:
A key principle of security is that no network is completely secure.
Information security deals principally with risk management.
The more important an asset, the more it is exposed to security threats, thus the more resources you must put into securing it.

Understanding Risk Management – 2:
In general, without training, administrators respond to a security threat in one of three ways:
Ignore the threat, or acknowledge it but do nothing to prevent it from occurring.
Address the threat in an ad hoc fashion.
Attempt to completely security all assets to the utmost degree, without regard for usability or manageability
None of these strategies take into account what the actual risk is, and all of them will usually lead to long-term failure.

What are Some Risks?
Interception of messages
Taking over the role of a sender or receiver.
Of messages into an active connection
Spoofing a source address in a packet or any field in a packet
Denial of service (DOS).
Prevent others from gaining access to resources, usually by overloading system.

Managing Risk:
Once the assets and their corresponding threats have been identified risk management can consist of:

Accepting Risk:
If you take no proactive measures, you accept the full exposure and consequences of the security threats to an asset.
Should accept risk only as a last resort when no other reasonable alternatives exist, or when the costs are extremely high.
When accepting risk, it is always a good idea to create a contingency plan.
A contingency plan details a set of actions that will be taken after the risk is realized and will lessen the impact of the compromise of loss of the asset.

Mitigating Risk:
The most common method of securing computers and networks is to mitigate security risks.
By taking proactive measures either to reduce an asset’s exposure to threats or reduce the organizations dependency on the asset, you are mitigating the security risk.
A simple example: installing antivirus software.

Transferring Risk:
Transfer security risk to another party has many advantage including:
Economies of scale, such as insurance.
Use of another organization expertise and services.
Example: using a web hosting service.
When undertaking this type of risk transference, the details of the arrangement should be clearly stated in a contract known as a service level agreement (SLA).

Avoiding Risk:
The opposite of accepting risk is to avoid the risk entirely.
To avoid risk, you must remove the source of the threat, exposure to the threat, or your organization reliance on the asset.
Generally, you avoid risk when there are little to no possibilities for mitigating or transferring the risk, or when the consequences of realizing the risk far outweigh the benefits gained from undertaking the risk.
An example can be a military or law enforcement dBase that, if compromised, could put lives at risk.

Implementing Security:
Think of security in terms of granting the least amount of privileges required to carry out the task.
Example: consider the case of a network administrator unwittingly opening an e-mail attachment that launches a virus.
If the administrator is logged on as the domain administrator, the virus will have administrator privileges on all computers in the domain and thus unrestricted access to nearly all data on the network.

Defense in Depth:
Imagine the security of your network as a series of layers.
Each layer you pull away gets you closer to the center, where the critical asset exists.
On your network, defend each layer as though the previous outer layer is ineffective or nonexistent.
The total security of your network will dramatically increase if you defend at all levels and increase the fault tolerance of security.
Example: to protect users from launching an e-mail-borne virus, in addition to antivirus software on the users’ computers, you could use e-mail client software that blocks potentially dangerous file types from being executed, block potentially dangerous attachments according to their file type, and ensures that the user is running under a limited user account.

Reducing the Attack Surface:
An attacker needs to know of only one vulnerability to attack your network successfully, whereas you must pinpoint all you vulnerabilities to defend your network.
The smaller your attack surface, the better chance you have of accounting for all assets and their protection.
Attackers will have fewer targets, and you will have less to monitor and maintain.
Example: to lower the attack surface of individual computers on your network, you can disable services that are not used and remove software that is not necessary.

Addressing Security Objectives:
Controlling Physical Access to
Networked workstations
Network devices
Cabling plant
Being aware of security considerations with wireless media related to portable computers.
Recognizing the security risk.
Of allowing data to be printed out.
Involving floppy disks, CDs, tapes, other removable media.

Recognizing Network Security threats:
To protect your network, you must consider the following:
Question: from whom or what are you protecting if?
Who: types of network intruders and their motivations.
What: types of network attackers and how they work.
These questions form the basis for performing a threat analysis.
A comprehensive threat analysis should be the product of brainstorming among people who are knowledgeable about the business processes, industry, security, and so on.

Classifying specific Types of Attacks:
Social engineering attacks
DOS attacks
Scanning and spoofing
Source routing and other protocol exploits
SOFTWARE and system exploits
Trojans, Viruses and worms

It is important to understand the types of threats in order to deal with them properly.

Designing a Comprehensive Security Plan:
RFC2196, the Site Security Handbook.
Identify what your are trying to protect.
Determine what you are trying to protect it from.
Determine how likely the anticipated threats are.
Implement measures that will protect your assets in a cost-effective manner.
Review the process continually and make improvements each time a weakness is discovered.

Steps to Creating a Security Plan:
Your security plan will generally consist of three different aspects of protecting your network.
Prevention: the measures that are implemented to keep your information from being modified, destroyed, or compromised.
Detection: the measures that are implemented to recognize when a security breach has occurred or has been attempted, and possibly, the origin of the breach.
Reaction: the measures that are implemented to recover from a security breach to recover lost or altered data, to restore system or network operations, and to prevent future occurrences.

Security Ratings:
The U.S. government provides specifications for the rating of network security implementations in a publication often referred to as the Orange Book, formally called the DOD Trusted Computer System.
Evaluation criteria, or TCSEC.
The Red book, or Trusted Network Interpretation of the TCSEC (TNI) explains how the TCSEC evaluation.
criteria are applied to computer networks.
Canada has security rating systems that work in a similar way.

Security Ratings -2:
To obtain a government contract, companies are often required to obtain a C2 rating.
A C2 rating has several requirements.
That the operating system in use be capable of tracking access to data, including both who accessed it and when it was accessed.
That users’ access to objects be subject to control (access permissions).
That users are uniquely identified on the system (user account name and password).
That security-related events can be tracked and permanently recorded for auditing (audit log).