In this video, you will learn to identify and classify the various forms of active and passive attacks. The second style of an attack from the Stallings end of it on the active attack, is that of the replay. So this is where a copy of a legitimate message is captured by Trudy, our interceptor and re-transmitted later. So this could be a message that was simply like, "let's break for lunch, let's go to drinks," and instead, it's intercepted, delayed, and then sent on Thursday. Bob receiving this message somehow thinking it's from Alice, in fact it is from Alice, just delayed, that lunch is going to be on Thursday as opposed to Wednesday. So you can understand now in the context of financial services how a delay in a message of complete this stock order, transfer this money, really impacts the mission of the financial service, the core mission capabilities about faithfully executing commands, executing orders from its clients. So it's a very big problem within those communities. So this is actually not surprisingly an attack on the integrity of the system. So it's an attack on the integrity because if not sent in a timely manner, the actual message is legitimate. So this is transfer $100 from my savings account to my checking account. It's a legitimate message, but it's re-transmitted at a later time. So this is the integrity failure. So we think about has a message been modified or has it been delayed. So we talked earlier about the attacks, the previous ones have been attacks on the integrity of legitimate messages, right? So those are delays, those are modifications. If we move ahead into some additional components for active attacks against an enterprise, one of the largest ones that is still in play, right of denial of service attacks. So with a denial of service attack, Trudy the opponent is preventing Bob and Alice, the two authorized users from accessing a system. This could be their email system, text messaging, something in the communication channel. So it's preventing the authorized users, Bob and Alice, from accessing the communication channel to communicate. This is an availability attack because there's a timeliness factor. Alice can send Bob a message, may not be delivered for days on then if it ever gets there. So that's the tiny part of it and the accessibility part whether the service is available at all as a function of time.