IP Security
This chapter discusses security issues regarding TCP/IP networks and provides an overview of solutions to resolve security problems before they can occur. The field of network security in general and of TCP/IP security in particular is too wide to be dealt with in an all encompassing way in this book, so the focus of this chapter is on the most common security exposures and measures to counteract them. Because many, if not all, security solutions are based on cryptographic algorithms, we also provide a brief overview of this topic for the better understanding of concepts presented throughout this chapter.
Security Issues
This section gives an overview of some of the most common attacks on computer security, and it presents viable solutions to those exposures and lists actual implementations.
Common Attacks
For thousands of years, people have been guarding the gates to where they store their treasures and assets. Failure to do so usually resulted in being robbed, neglected by society or even killed. Though things are usually not as dramatic anymore, they can still become very bad. Modern day I/T managers have realized that it is equally important to protect their communications networks against intruders and saboteurs from both inside and outside. We do not have to be overly paranoid to find some good reasons why this is the case:
• Tapping the wire: to get access to clear text data and passwords
• Impersonation: to get unauthorized access to data or to create unauthorized e-mails, orders, etc.
• Denial-of-service: to render network resources non-functional
• Replay of messages: to get access to and change information in transit
• Guessing of passwords: to get access to information and services that would normally be denied (dictionary attack)
• Guessing of keys: to get access to encrypted data and passwords (brute-force attack, chosen ciphertext attack, chosen plaintext attack)
• Viruses, trojan horses and logic bombs: to destroy data
Though these attacks are not exclusively specific to TCP/IP networks, they should be considered potential threats to anyone who is going to base his/her network on TCP/IP, which is what the majority of enterprises, organizations and small businesses around the world are doing today. Hackers (more precisely, crackers) do likewise and hence find easy prey.
Observing the Basics
Before even thinking about implementing advanced security techniques such as the ones mentioned in the following sections, you should make sure that basic security rules are in place:
• Passwords: Make sure that passwords are enforced to be of a minimum length (typically six to eight characters), to contain at least one numeric character, to be different from the user ID to which they belong, and to be changed at least once every two months.
• User IDs: Make sure that every user has a password and that users are locked out after several logon attempts with wrong passwords (typically five attempts). Keep the passwords to super user accounts (root, supervisor, administrator, maint, etc.) among a very limited circle of trusted system, network and security administrators.
• System defaults: Make sure that default user IDs are either disabled or have passwords that adhere to the minimum requirements stated above. Likewise, make sure that only those services are enabled that are required for a system to fulfill its designated role.
• Physical access: Make sure that access to the locations where your systems and users physically reside is controlled appropriately. Information security begins at the receptionist, not at the corporate firewall.
• Help desk: Make sure that callers are properly identified by help desk representatives or system administrators before they give out "forgotten" passwords or user IDs. Social engineering is often the first step to attack a computer network.
Solutions to Security Issues
With the same zealousness that intruders search for a way to get into someone's computer network, the owners of such networks should, and most likely will, try to protect themselves. Taking on the exposures mentioned earlier, here are some solutions to effectively defend yourself against an attack. It has to be noted that any of those solutions solve only a single or just a very limited number of security problems. Therefore, a combination of several such solutions should be considered in order to guarantee a certain level of safety and security.
• Encryption: to protect data and passwords
• Authentication and authorization: to prevent improper access
• Integrity checking and message authentication codes (MACs): to protect against the improper alteration of messages
• Non-repudiation: to make sure that an action cannot be denied by the person who performed it
• Digital signatures and certificates: to ascertain a party's identity
• One-time passwords and two-way random number handshakes: to mutually authenticate parties of a conversation
• Frequent key refresh, strong keys and prevention of deriving future keys: to protect against breaking of keys (crypto-analysis)
• Address concealment: to protect against denial-of-service attacks
• Content inspection: to check application-level data for malicious content before delivering it into the secure network