Introduction

Course backgroundSearch on YouTubeBookmarkSaved

Course aimSearch on YouTubeBookmarkSaved

The course is CSS411: Cryptography and Network Security. It studies how to protect information during transmission and storage.

The focus of the course is Internet Security. It consists of measures to deter, prevent, detect, and correct security violations that involve the transmission and storage of information.

Changed requirementsSearch on YouTubeBookmarkSaved

Information security requirements changed in recent times:

• Traditionally, security came from physical and administrative mechanisms.
• Computer use needs automated tools to protect files and other stored information.
• Networks and communication links need measures to protect data during transmission.

DefinitionsSearch on YouTubeBookmarkSaved

Security attacksSearch on YouTubeBookmarkSaved

Three aspects of securitySearch on YouTubeBookmarkSaved

The slides consider three aspects of information security:

1. Security attack: any action that compromises the security of information owned by an organization.
2. Security mechanism: a feature that detects, prevents, or recovers from a security attack.
3. Security service: a service that counters security attacks. It uses one or more security mechanisms.

Information security prevents attacks on information-based systems. If prevention fails, information security detects the attacks. The slides use threat and attack to mean the same thing most of the time. There is a wide range of attacks, so the slides focus on two generic types: passive and active.

Passive attacksSearch on YouTubeBookmarkSaved

Passive attacks are eavesdropping on, or monitoring of, transmissions. The goal of the opponent is to obtain information that is being transmitted. The slide shows Darth, who reads the contents of a message from Bob to Alice. The message does not change, so detection is very difficult.

Active attacksSearch on YouTubeBookmarkSaved

Active attacks involve some modification of the data stream or the creation of a false stream. They are difficult to prevent because of the wide variety of physical, software, and network vulnerabilities. The goal is to detect attacks and to recover from any disruption or delays that they cause.

The slide shows replay in two phases. Darth captures a message from Bob to Alice. Later, Darth replays the message to Alice.

Four attack categoriesSearch on YouTubeBookmarkSaved

The slides show four more attack categories with pictures:

Each category attacks one security property (standard textbook mapping):

$$\begin{aligned} \text{Interruption} &\mapsto \text{availability} \\ \text{Interception} &\mapsto \text{confidentiality} \\ \text{Modification} &\mapsto \text{integrity} \\ \text{Fabrication} &\mapsto \text{authenticity} \end{aligned}$$

Security servicesSearch on YouTubeBookmarkSaved

What a service doesSearch on YouTubeBookmarkSaved

A security service has these properties:

• It enhances the security of data processing systems and information transfers of an organization.
• It is intended to counter security attacks.
• It uses one or more security mechanisms.
• It often replicates functions of physical documents. Such documents have signatures and dates. They need protection from disclosure, tampering, or destruction. They are notarized or witnessed, recorded, or licensed.

The five servicesSearch on YouTubeBookmarkSaved

Security mechanismsSearch on YouTubeBookmarkSaved

What a mechanism doesSearch on YouTubeBookmarkSaved

A security mechanism is a feature designed to detect, prevent, or recover from a security attack.

• No single mechanism supports all the services required.
• One element underlies many of the mechanisms in use: cryptographic techniques. This is why the course focuses on cryptography.

Specific mechanismsSearch on YouTubeBookmarkSaved

The slide lists eight specific mechanisms. The purpose column is a standard textbook summary.

Pervasive mechanismsSearch on YouTubeBookmarkSaved

Security modelsSearch on YouTubeBookmarkSaved

Network security modelSearch on YouTubeBookmarkSaved

The slide draws the model with these elements:

To use this model, do these four tasks:

1. Design a suitable algorithm for the security transformation.
2. Generate the secret information (keys) that the algorithm uses.
3. Develop methods to distribute and share the secret information.
4. Specify a protocol that lets the principals use the transformation and secret information for a security service.

Network access security modelSearch on YouTubeBookmarkSaved

The second model guards access to an information system. The opponent is a human (for example, a cracker) or software (for example, a virus or worm). The opponent comes in through the access channel.

The information system holds computing resources (processor, memory, I/O), data, processes, and software. It has two lines of defense:

• Gatekeeper function: stands at the access channel and identifies users.
• Internal security controls: protect the resources inside the system.

To use this model, do these two tasks:

1. Select appropriate gatekeeper functions to identify users.
2. Implement security controls so that only authorized users access designated information or resources.

Trusted computer systems may help to implement this model.

Quick self-testSearch on YouTubeBookmarkSaved

What does the word cryptography mean, from the Greek origin?

Secret writing. The quiz options were corrupting data, secret writing, open writing, and closed writing. The process that transforms a message to unreadable form is encryption.

Name the three aspects of information security.

Security attack, security mechanism, and security service. An attack compromises the security of information. A mechanism detects, prevents, or recovers from an attack. A service counters attacks with one or more mechanisms.

Give the two types of passive attacks and one line for each.

Release of message contents: the opponent reads the transmitted contents. Traffic analysis: encryption hides the contents, so the opponent observes message patterns. From these patterns, the opponent guesses the nature of the communication.

Why are passive attacks hard to detect?

No data changes, so no trace remains. The attacker only observes. Thus the defense is prevention, for example encryption.

Name and define the four types of active attacks.

Masquerade: one entity pretends to be a different entity. Replay: passive capture of a data unit and later retransmission for an unauthorized effect. Modification of messages: alteration, delay, or reordering of a legitimate message. Denial of service: prevents or inhibits the normal use or management of communications facilities.

Why are active attacks hard to prevent, and what is the goal?

There is a wide variety of physical, software, and network vulnerabilities. So the goal is to detect active attacks and to recover from any disruption or delays.

Match interruption, interception, modification, and fabrication to the security property each attacks.

Interruption: availability. Interception: confidentiality. Modification: integrity. Fabrication: authenticity.

List the five security services with one-line meanings.

Authentication: the communicating entity is the one claimed. Access control: prevention of unauthorized use of a resource. Data confidentiality: protection from unauthorized disclosure. Data integrity: received data is as sent by an authorized entity. Non-repudiation: protection against denial by one of the parties.

List four specific and the five pervasive security mechanisms.

Specific: encipherment, digital signatures, access controls, data integrity, authentication exchange, traffic padding, routing control, notarization (any four). Pervasive: trusted functionality, security labels, event detection, security audit trails, security recovery.

State the four tasks of the network security model.

Design a suitable algorithm for the security transformation. Generate the secret information (keys) that the algorithm uses. Develop methods to distribute and share the secret information. Specify a protocol that lets the principals use the transformation and secret information for a security service.

State the two tasks of the network access security model.

Select appropriate gatekeeper functions to identify users. Implement security controls so that only authorized users access designated information or resources. Trusted computer systems may help to implement this model.