In this video, you will learn to describe various network security models. So let's take a look at a couple of networks security models so we understand mechanically in terms of processes and in terms of logical decomposition, what we're looking to achieve. So let's talk for a moment about a generalized model for network security. Here on slide 17, we see an extract from the starlings text about communication between a sender and the receiver. So this was Alice and Bob in our sample. They had the communication channel between them that is non secure. They wish to send a message that is protected, can be intercepted, has integrity components to this, has confidentiality components to that, and there's an availability part of the network. So what can Bob and Alice do? Well obviously, we have the initial clear text message and that's this element that we see right here from Alice sending to Bob. So sender is Alice, recipient is Bob. So the security-related transformation process is encryption 99 times out of 100. So there's some secret content right here that is maintained and the secret content is actually the encryption keys. So the encryption keys allow the security related transformation or the encryption of the message. Here is this encrypted or secure message right now. Alice puts this onto the information channel or adversary. Here can intercept the message, but because the adversary, Trudy, doesn't have access to the keys that are found here, we'll not be able to read this. So then Bob pulls the message off of the communication channel. So this message here is the same thing as this message here, applies his key here. Now, the keys can be the same or different we'll explain in a little bit later, but he's using the same encryption decryption protocol that Alice is using and then we have the clear text. So the message here is the same as the message there. Now that we have the generalized model plus the foundational concept described in Module 1, understood. Let's start moving into security architectures and what it means to have an attack against a security architecture. So a quick review of what security means is that within X.800, which is that International Telecommunication Union document part of the UN governance element on that, what is meant by security? That's actually used just simply in terms of managing the vulnerabilities and their exposure of risks to both assets and resources. So asset, right here, can mean anything. So in our context, that means the valuable information maintained by an enterprise, it also means the security enforcement point, that technical implementation of a security policy that if it's disabled increases the risk factor for the enterprise. So both of those are in play in terms of security asset. So a vulnerability [inaudible] says any weakness that can be exploited the violate a system or the information that it contains in the actual lexicon of a security professional, a vulnerability is an underemployed exploit. We think about a vulnerability from a software manufacturer, from a security company, is a back door. It's a window, it's way that security policies can be circumvented and information could be stored. Now, a vulnerability that's put into play is called an export. So a threat is the potential violation of security. So we have a definition for security and then the threats right here right are what we are protecting against. So we can have at security, architecture, and motivation. So 801, 800 rather right here right talks about the motivation for security and open systems. So let's define open systems for a moment. The absolute opposite of an open system is a proprietary or a closed system. Open systems need not be defined by standards, most standards organizations move at a pace that only a geologist can appreciate, but those protocols, those interfaces are published to the open. This is IBM's approach to security and software systems. We are open systems not necessarily a standard. So CCITT, which is a group that comes out of that ITU, has a piece of rocket science here that says we need to enhance security of open systems because of societies increasing dependence on computers that are accessed or linked by data communications which acquire protection against various threats. So that's ground truth, the world's becoming more connected needs more protection. So there's several countries that have increasing legislation about data protection. The European Union comes to mind, safe harbor in terms of managing some of the risks that are associated with that. So the deliverer, let's use that rather than the term suppliers, so the deliverer of a secure enterprise needs to take into consideration the risks and the legal ramifications of it systems. So this is some marketing from ITU right here, there's these number of standards but open systems generally very popular and should be. So we have security, architecture, and protective elements of that, one of the questions that we need to take a look at is what actually what needs to be protected. So this is not rocket scientists, we've talked about this before. Obviously, the information and data needs to be protected. This is the crown jewels of the enterprise, the customer, credit card information, health records, bank information, all of the elements around that including security measures such as the passwords. When we think about the Yahoo breach where passwords were stolen, all of that is target fair games for the adversary. We also have the context of communication and data processes services right here. This is a the security enforcement points that we talked about earlier. Remember security enforcement points are technical implementations of security policies that are derived from business policies. We obviously need to protect against modification, destruction of our equipment and facilities.