Network Security: Overview
Hi. So, we will be continuing our discussion on Computer Networks and Internet Protocol. Today we will be discussing on a topic of called Network Security; or per see rather initially we will be discussing as a security of the Computing System per se whatwe mean, and then we will look at the Network Security. So, to say we as per as the course is concerned, it may not be within the very core of the overall course of computer networks and internet protocol, and but what we thought that without talking ordiscussing something on network security, the overall phenomenon may not be complete, alright.So, we thought that we will add one if possible 2 lectures on computer per se this network security, right. And but for your convenience that will be most likely not including these in your exam per se. So, that is more of a thing what we like to say thatto see the security aspects and what are the approaches things, but do not bother about the exams.So, what why this is becoming important? Because see today’s world or today’s enterprises or today’s day to day interaction are all becoming dependent on not only the computers, but more dependent on the network level activities or computer networks,right whether you are booking a ticket, or even paying your different your utility bills like electricity bills and water bills and type of things.Even sending messages or looking for things, looking from information for some aspects and everywhere what we see this is a omnipresent; like, if you even look at the banking sectors. So, a more or less we are going to a scenario where you do not have to visit bank at any point of time, everything you are doing on the system. So, in other sense that becomes a this become a becoming one of part and per sell of our not only the enterprisenetwork or organisation. It is also a becoming part and per sell of our day to day life right whether it is requirement or infotainment, where we see the security become the this network become a important aspects.
And in several as several activities, they are there is some sort of financial transaction is involved, right. And whenever there is a financial transaction involve, that becomes important to make it secured, right, or weather at all loopholes are there. I can say thatthe network is per se is secured network. Then there is no loophole right. So, whether there is a loop hole is there, where is a chance of loop hole is there, or what sort of quote unquote attacks can be there on the overall our network infrastructure; whether it is onlyaffect the network or also the systems things, and different aspects of the things.So, security is becoming a necessity rather than a yet another subject type of things, right. If you look at the overall academic courses, this network security, computer security, information security, these are becoming a not only a subject a line of vertical quotes altogether.So it is not possible to cover everything, but we will try to open up or look at the thing that different aspects of the security aspect. So, in this lecture we will initially will try to look at that what are the different aspects of security, which is related to computer andinformation security, and network security also and then what specifically we need to look at the, how what are the mechanisms and way we can make our infrastructure or the network secured.
So, what we see that, when we look at the security per se, then what we are trying to look at? Primarily 3 aspects we want to look at confidentiality, integrity and availability, alright. So, these are the things if these are bridged we say that the security is bridgedright. So, confidentially deals with keeping the data and the resource hidden alright, so that is confidential. So, if you are if I am sending a message to you, or you’re sending a message to me, so if it is mean for me only so it should be kept confidential. There should not be anybody who is listening to this message or reading this message, right. So, confidentiality keeping the data and resources hidden or confidential integrity, what we say that data level integrity is that the message what I am sending should be reachingto the destination the same fashion. So, that the data is not being tampered right. If I amsending a message, so the data level integrity is there. There is another issue of originintegrity or what we say authentication; like, how do I know that who is sending is acorrect person, alright. So, if I am say getting a message that today there will be asomething say power cut and shut down the system, or something, then I how do I knowthat it is from the correct authenticate that thing, right.So, this is also a question of integrity and then availability, enabling access to the dataand resources right. I say that there is nobody looking at the data, no body tempering thedata, no there is a message is coming on the same thing, but what I do there is a hugeamount there is some way or other I not make the thing available to you, right. Like whatI mean to say that, I if there is a attack like this by which you cannot access the internet.Otherwise everything is working fine. There is no question of integrity or confidentiality,but the internet is not accessible due to some problem, right. There may be physicalproblem of disrupting the things or there can be some other problem of say lot of trafficincreases congestion etcetera.So, there is what we say a attack on availability the resource is not available, enablingaccess to the data and resources this is the availablity. So, if you see this CIA, primarilyrules the all above things whether it is network related, whether it is computer related, forthat matter any type of document related.
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Now, what are the different types of security attacks can be there? So, if you see therecan be typically 4 category of the things. One is interruption like, so if I interruption,interception, modification, fabrication, right.(Refer Slide Time: 07:36)
So, these are the 4 type, basic model is that a message is being sent to source todestination. So, interruption is the attack on availability right; so it is blocked some wayor other, either physically or through congestion or something that so that messagecannot reach to the destination.
So, sometimes we can say that this is a type of denial of service. So, if you cannot this tothe things. There is a attack on another kind what is interception right. So, attack onconfidentiality A C sending to D, but that intercepted and it is also I is listening, or aattacker is listening to the things, so it is a attack on confidentiality.(Refer Slide Time: 08:19)
There can be a attack on modification. S is sending something to D, it is beingintercepted and modified by I and send to D. So, it is a attack on integrity, integrity ofdata is there. And there can be a fabrication, I is sending to D pretending to be S right.So, I is sending to D pretending to be S; that means, there is a attack on authenticity ofthat particular origin. So, I cannot somebody else is pretending to be somebody else. So,these are the type of attacks which can be there.
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And if you look at the type of disclosures, so one is disclosure is a type of threats, one isdisclosure that is snooping. Deception, modification, spoofing, repudiation of origin,denial of receipt and type of things are deception, right.So, this can be deception. There is a threat of disruption of services; that is that can be athreat of disruption. And there can be a threat of usurpation, that modification spoofingdelay denial of service. So, these are the different category of threat. So, what you aretrying to see? What are the different types of attack, what are the different types ofsecurity attack, what are the different types of security concerns, and what are thedifferent types of security threats, right.
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And then what we try to do? We try to make some policies and mechanisms which willenforce my mechanism which will enforce my policy. Like, so I have some securitypolicy, this may happen this may not happen etcetera, etcetera and there should be amechanism to enforce. So, policy says what is not allowed. So, what is allowed and whatis not allowed. This defines the security of the site system etcetera right. Mechanism isenforce on the policy enforcement of the policies is by through mechanism, and there canbe composition of policies, policy conflicts, discrepancies may create securityvulnerabilities right.So, there can be if there are I have a policy and there is a mechanism to implement thethings, if there is a conflicting policies, then there may be a security vulnerabilities mayarise right. So, it becomes system becomes vulnerable right. So, why policy mayconflict? Because sometimes the in a large organisation or large system, the policies maynot be all globally decided, this is piecewise decided. But when you piece wise decide,when you integrate the things, there may be a problem in the conflict of the policy.There can be other way the policy may not be a conflicting, but while implemented in adistributed manner that can be conflicting the things. Like I will give you one example,suppose IIT Kharagpur policy says that during a time period say, class hours or at midnight, there should not be any internet connection from the hall to internet, right.
However, this is a policy however the same in the same policy document that is there;however, that connects in from labs to the internet it is not restricted, because that isallowed. So from the hall of residences or students hostilities may be restricted say this isthe; now policy wise this is documented by when implementing implemented the policyin the hall particular security server or your switch which is say security enabled. Andanother thing we implement at in the departmental switch or departmental say they are 4plus switch.Now, see I can way this does not restrict the hall to access the departmental server, andmake a hop from the departmental server to the internet. So, in a sense I have violatedthe policy. But as such the overall implementing mechanism may not be that tough to dothat, right. Now it is may not be that straight forward to do in that, but there is a way tocreate this what we say it is a vulnerability, right. Vulnerability may also crop up if thereis a something where policies are conflicting. We will see some of the things.(Refer Slide Time: 13:00)
Now, well what goal of security, what we do we want first of all we want to prevent,right prevent attackers from violating security policies. If I have a security policies,prevent.So, it is even if we look at our normal say what we say security of our particularbuilding, particular campus, etcetera forget about the network that is also things arethere. So, it is a prevention to prevent the violating security policy, if there is a another
thing is that, it is a detection, if there is a attack the detect attacker violation of thesecurity policy, I should be able to find out that where that attacker things are there. Andthen another aspect is the recovery, stop attack, access and repair the damage, continue tofunction correctly, even if the attack has success.So, that is a case of continuing with the function even there is a attack on the thing, sothis is a called a recovery. So, prevention, detection, recovery are 3 components of atypical security goal.(Refer Slide Time: 14:05)
Now there is other co things comes up. There is a concept of there is a concept of trustand assumption. Underlie all aspects of security. So, say in our normal thing if I amhaving a security guard at the entrance of the building, I trust that guard, alright. Andalso I assume some of the things right. Like the attacker is likely to enter through this, Ithink that the attacker will be this category, this category of guard or mechanism able tosolve it and type of things.So, there are underlying any security things, whether it is network security or computersecurity or any other security, I have some sort of a trust on some of the things. And alsoI assume that this is the overall environment where the things are need to work, right. So,the based on that we want to formulate policies unambiguously partitioning, the systemstate right. So, I say this is the security state, this is non security state, correctly capturingthe security requirements right. So, if I want to see that the a particular building or say
IIT Kharagpur what are the security requirement network infrastructure of IITKharagpur, first of all I need to know that what are the requirement.And then if I want to implement divide or partition them into particular system state, thatif this system is going to this system, and this state to the state and type of things, then itis; what are the security consequences. And finally, I should be have some mechanismswhich assume to enforce this policy. Support mechanism work correctly. So, I havepolicies and mechanisms and there based on the trust and assumption.(Refer Slide Time: 15:49)
So, types of mechanisms. Suppose these are set of reachable states. So so what you see?That any system or network is a dynamic and active system, right.So, in the sense that, every activities it is going on the things we can think of the systemis going from one state to another right, say for example, for simplicity I have a laptop.So, I install say particular operating system, then I put the security patches. So, while Iinstall the operating system, it is in some state S1, when I do a patch the security patches,it goes to some state S2, then I put another application over on the same system, so itmay bring some vulnerability, may not bring some vulnerability, but goes to some S3.And so that means, and I go on working with the things put pen drive etcetera, etcetera itgo on what we say at different level of or different type of security states, right.
Same is true for the network right, you have different modules add devices, add networklevel devices, change the network level operating system, enhance those things, patchwith new type of things, and it goes on going to the state. So, if I look at the IITKharagpur overall network, so it is a, what we say? Lively thing, right it is goes on thedifferent state. So, I say state S1 S2 and S3. So, our goal is that that if it is it should bewithin the secure state. So, I say that set of reachable state is identified by this diagram,and set of secured state is this. So, these are set of reachable state, so if I say whatever Ido I am always within the secured state.So, if the secured state is a super set of the reachable state, then I am secure. It can bedirectly precise like, whatever is it is on the directly mapping on the things or one to onemaking (Refer Time: 18:09) precise state. It can be brought like some of the some of thereachable state outside the security perimeter then what we say? It is some broad levelsecurity, but there are some security things which are beyond this type of things. So, thisis true for definitely for network security it is true for any type of security aspects right;so our basic thing that it should be hovering around this two; if it is always good if I canput it like this right. But as we understand, security is a costly affair right.
So, putting them together; so what we have we have threats based on the threats weframe policies. To implement policies, we design specification. Specification are with thehelp of specification we design the overall security scheme or mechanisms, andimplement those mechanism and then I operationalise right. And then if there is and itgoes on in different loop. So, from there it goes on implementation or design change or
specification change or policy change, or while operating it may generate new threatsright. So, this is a very dynamic and some sort of a lively thing. I should not say fullyreal time, or some sort of in your real time or a lively thing which is very dynamic andmutable things right type of things.(Refer Slide Time: 02:35)
Setting all set is means giving all those things. So, if we look at the attacks, so there arebroadly 2 category of attack. One is passive attack; another is active attack. So, passiveattack obtain information that is transmitted, so some of a eavesdropping. So, there arethere about we say that it is sniffing and doing and information gathering, but it is notinvolving active attack. They are more information gathering type of information. So,that can be a some software which is residing and carrying information about networkwhich is etcetera, etcetera and go on transmitting to the somebody, so that it can launch aactive attack.So, 2 type of release of message content, it may be desirable to prevent the opponentfrom land landing the content of a transmission system. So, that it is clamped on thethings traffic analysis. Opponent can determine the location and identity of thecommunicating host, observe the frequency and length of the messages etcetera. So, itcan analyse the traffic and try to see that what sort of things are there. So, it can be 2things very difficult to attack detect this type of passive attacks, because they are not perse, so any manifests on the system. So, they has to gather on gather information and pass
it to somebody else and that goes for a active attack. So, they are not immediatelyinvolved in the thing. So, some sort of a spying and type of things on the network at thenetwork level.(Refer Slide Time: 24:10)
So, active attack on the other hand involves some modification of the data stream orcreates any false stream and type of things. So, that is a active attack 4 categories arereplay may be there that is masquerade, one identity pretends to be a different identity,replay passive capture of the data units. And it is subsequent retransmission to producean unauthorised effect. So, it is replay type of attack it can be modification, some portionof the legitimate message is altered. So, it is modified, it can be denial of service,prevents the normal use of the communication facilities.So, there can be a denial of service right. So, dos attack very, what we say quote unquotepopular attack so to say to create a denial of service everything is in place, but youcannot access the information. So, there is a denial of service attack.
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So, to say right so these are my militarized zone. So, but some of the things I want to expose right like my web server I want to expose, people should see that my webpage and other things. There can be different other some of the applications which people can want to work from the outside that is to be exposed. So, these are to be put into somewhere what we say demilitarized zone alright. So, this is important to look at that what are the different scenarios of this demilitarized zone. So, the network design should reflect this policy should this policy placement of rules and firewalls; the deployment of intrusion detection systems.So, where do I put the firewall? What should be the fire wall rules? And there should be a deployment of intrusion detection system. So, if there is a intrusion is there how to detect that system, rather there is a another sort of systems called IPS intrusion protection system.So, implementation of security policy; so implementing a security policy include installing and configuring firewalls. It may there are different way of handling this. So, we are not going to the details of the things. So, IP tables is a common free firewall configuration for Linux, some of you may be worked on it or knowing it. Rules for incoming traffic should be created. Rules for outgoing traffic should be created. Like, I can say that incoming traffic only http is allowed, where as outgoing I can allow we allow telnet ftp type of things.
So, both the rules should be should be there in the firewall. We will try to see those things when we look at that little aspect some aspects of firewall configuration. Installing and configuring IDSes like so or that intrusion system detection systems. So, there are different tools some freewares are available, some are paid things are available, right. So, one is not is a free and upgradable IDSes for several platforms. Most IDSes are send alerts to the log files regularly. So, it is logged serious events anti guard paging email and telephone right.So, by these 2 things what we are trying to look at is the one aspect is that determining the security policy. Say, what will be the different de security policies. Another aspect is how to implement the security policies right. So, these are 2 things are important, other than other miss will come to that other aspects of the things. So, when we frame a network right. So, when we try to trying to design a network. So, along with performance, efficiency, reachability, scalability, we need to also keep in to mind that what should be my security policy, while implementing, or deploying the network whether those security policies are implemented into the system or not that needs to be looked into right.So, what we will do? We will continue our discussion on network security in our subsequent lecture, and with keeping in mind that our basic network infrastructure into thing. Also we will try to see some aspects of the things like whatever we have seen that, in the TCP/IP layer, what we can do with those things with the security things, right. Now we see the TCP/IP layer or OSI layer per se does not talk about the security aspects.And security comes additionally in doing so we should be careful that intermediatedevices which gives this packet with there should not be any problem with the standardright. If there is a problem or if there is a intervention or there is a interference with thestandard that the packet may not be forwarded to the next hop right. So, in there are lotof consideration which need to be looked into. We will try to see some aspects andoverview of the things which keep as a overall feel of the what are the network securityaspects.Thank you.
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