Lec-81: Symmetric Key Cryptography in Network Security with examples
Lec-81: Symmetric Key Cryptography in Network Security with examples
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In this video Symmetric Key Cryptography in Network Security is explained in this video.
Symmetric key cryptography is any cryptographic algorithm that is based on a shared key that is used to encrypt or decrypt text/cyphertext, in contrast to asymmetric key cryptography, where the encryption and decryption keys are different.
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Content
0.769 -> hello friends, welcome to the Gate Smashers
3.166 -> the topic is Symmetric key Cryptography
5.468 -> so what is the meaning of Symmetric key
7.554 -> Same Key....
8.57 -> Means we use only one key.
10.961 -> One key means..
12.539 -> let say sender
13.939 -> want to send a message to receiver
16.476 -> So we discussed earlier that sender
19.004 -> and receiver
19.814 -> always use unsecured channel
21.465 -> like we
23.183 -> if we are using internet
24.778 -> that is what
25.785 -> unsecured channel
27.338 -> now what is the meaning of this unsecured channel
29.904 -> that there
31.103 -> No dedicated line between us and receiver
33.97 -> There is no dedicated link
35.601 -> if we send California messages from here,
38.069 -> then I obviously know that
39.333 -> from here to California
40.837 -> No direct line
41.956 -> not a wire from my house, which goes to California,
44.737 -> we are using unsecured channel
47.225 -> even we don't even know that
49.09 -> When the message is out from our system,
50.854 -> then which node it will go next
52.912 -> then if we are using this unsecured channel
55.697 -> then we do not send the message
57.233 -> in normal plain text
59.729 -> then we encrypt that message
63.301 -> with a key,
64.616 -> let say if I encrypting the message,
66.743 -> with key K1,
68.62 -> let say K1 key which
70.661 -> we have different Symmetric key algorithm
73.6 -> Symmetric key means same key
75.746 -> (DES, triple DES, AES)
79.123 -> Data Encryption Standard
80.984 -> Data Encryption
84.88 -> Standard
87.902 -> like this Triple DES is and AES is
90.237 -> Advanced Encryption Standard
92.256 -> this Different method which is used in real life
95.713 -> 56 bits key is used in DES
99.47 -> in triple-DES 192,
101.838 -> AES has different version,
103.552 -> minimum which is 128
105.207 -> and maximum 256 bits key is used
108.265 -> if I talk about 56 bit
110.163 -> means two raise to power 56
112.626 -> possibilities is there
114.048 -> if someone is applying brute force method
116.886 -> brute force means 0 0 0 to 111 all the
120.794 -> permutations if he is checking
123.448 -> then so many values check him If we have to do it,
125.95 -> then the key means
127.897 -> that the key with which
129.612 -> we are encrypting the message
131.79 -> and we are converting it into cipher-text
134.308 -> and I send this cipher-text
136.477 -> to the receiver,
137.97 -> what will the receiver do to it, the decrypt
140.353 -> receiver will take that
142.022 -> and same key
143.46 -> to K1
145.478 -> used for inscription
147.321 -> use K1 key for decryption
149.641 -> and again sad
151.143 -> And again after converting it to M
153.033 -> and reading it,
154.751 -> then it is actually funded in which Symmetric key
158.103 -> Symmetric key is, by the way, easy method
160.414 -> and method before asymmetric
162.683 -> means we have
163.986 -> come to it which is the method of Symmetric key
166.227 -> The big challenge is what is key exchange
169.856 -> key exchange means
171.634 -> let say if I
173.154 -> went to my house with a lock
175.648 -> and let say after a while someone comes
177.905 -> and if he wants to unlock
179.343 -> then he needs the same key
181.294 -> with which I put the lock
182.616 -> now There may also be a case here is a duplicate key
185.445 -> that he has one that I have
187.168 -> if we remove that case
188.893 -> There is only one key
190.394 -> to lock that lock and unlock
193.214 -> and if I leave the lock,
195.336 -> how will I unlock it?
198.355 -> So I put the lock and leave the key in the lock
201.523 -> Then why did you lock it?
203.416 -> Or else I give the key to that guy and come
205.934 -> so to come with the key
207.428 -> It's obvious that I had to leave at some point.
209.262 -> I will give him the key first
210.931 -> Give him Key
212.012 -> NO....
212.608 -> So here..
213.651 -> the biggest challenge here is what is that in the Symmetric key that the exchange
217.661 -> of which Sending a message to the fellow
219.901 -> he will also have to give the key
222.325 -> and can't give key with message
224.311 -> if I give the key along with the message,
227.079 -> then will anyone use that key and unlock it,
230.349 -> so here it is the best. The big challenge
233.262 -> We use different methods for that like deffy-Hellmen there is a method
236.726 -> by which we exchange keys securely among themselves
240.418 -> and this is real life methods
242.445 -> which are encryption methods
244.701 -> which use symmetric-key
246.675 -> method
247.983 -> So
249.254 -> the most important point here is
250.905 -> that we use the same key
252.597 -> and what is the challenge,
253.974 -> apart from this there is one more question
255.656 -> which is Appeared in GATE exam
257.492 -> and also appeared in these UGC NET
259.566 -> let say if we have
261.551 -> 4 devices connected together,
264.23 -> if we have 4 devices connected together
267.837 -> then how many symmetric keys will we need
270.682 -> like if two devices are connected then how many keys are needed
274.026 -> One...
274.883 -> because from which the sender
276.862 -> is scripting
278.094 -> that The receiver is decrypting with that key
280.54 -> but if the receiver
282.225 -> also wants to send some message
284.068 -> then he will use the same key,
285.69 -> still it will happen in both
288.454 -> but if the number of nodes is 4
290.941 -> then how many keys do I need
293.046 -> then in this case how many keys do I need
296.296 -> is N C 2 this is the formula
298.917 -> this is actually the formula of
301.531 -> complete graph also
302.809 -> number of edges
304.198 -> in complete graph
305.671 -> What is N stands for
307.434 -> Number of Vertex
309.285 -> Number of Vertex
311.286 -> If we talk about this graph.
313.788 -> Let say we have 4 nodes
315.667 -> 4 devices
317.071 -> d1 d2 d3 d4
319.644 -> so how can these four devices be connected
322.356 -> to each other how much maximum
323.318 -> can d1 d2 be connected in this way
325.46 -> they can be connected
327.151 -> then between d1 and d2 there will be 1 key
330.143 -> one key here
331.397 -> one key here
332.644 -> one here
333.643 -> and apart from this 2 keys, here
335.918 -> means how many keys are needed,
337.413 -> Six....
339.413 -> then by this method,
341.103 -> whoever asked you Forget the number and devices,
343.903 -> let's say 20 devices are connected with each other device,
346.968 -> for this I need the maximum symmetric key
350.784 -> 20 C 2
352.071 -> So this is the formula you need to remember
354.408 -> and more I don't need you to do
356.905 -> this is more than enough for The UGC NET Exam
359.507 -> and GATE exam
360.365 -> there in addition we can also read a little bit about DES
