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Lec-80: Cryptography in computer network in Hindi | Cryptography in Information Security - YouTube
Channel: Gate Smashers
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Hello friends, Welcome to Gate Smashers
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The topic is cryptography.
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Cryptography is such a technique
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through which
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we can convert plain text to cipher text.
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And cipher text is converted to plain text again.
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Now you must be thinking the meaning
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of plain text and
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cipher text.
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Plain text is a message,
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a normal ,message
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that anyone can read
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and understand.
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That what is written in this message.
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But cipher text is
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such a message.
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We can say a secret message.
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That anyone can
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read but
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cannot understand.
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Meaning the message can be seen.
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But what is written,
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the meaning of that.
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That can never be understood.
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So why do we convert from plain text to cipher text.
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We use cryptography
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to achieve confidentiality.
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Confidentiality.
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When we talk about network security. There is one important concept in network security.
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Of CIA.
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Confidentiality, Intergrity, and Availability.
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Intergrity, and Availability.
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Now the C in CIA is .
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confidentiality
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Confidentiality means.
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What we
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understand from confidentiality
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that no one could
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take my message.
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No one should
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take my message.
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Meaning if I am sending a message from here.
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To another receiver.
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Let's say receiver is sitting somewhere else.
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Receiver is sitting
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1000km away.
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Now someone is
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taking my message on the way.
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He is trying to hack
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my message in
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an unauthorised way.
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But it does not mean that your confidentiality
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is breached.Confidentiality becomes zero.
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No. Anyone can take the message.
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Because what is internet
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On internet all the devices are
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connected in a vulnerable manner.
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Vulnerable means
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that any person
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with some knowledge.
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If he knows the
skill of .
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hacking
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He can
take
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your packet.
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But taking the packet does not mean.Taking the data does not mean.
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That he can read the data.
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If the person can also read the data.Understand that.
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Then you can say confidentiality zero.
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But if on the way any person
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trace
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your packet.
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Trace does not means that
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he will
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understand
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what is written in the packet.
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So that is the meaning of confidentiality.
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Now we are talking that the
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sender has to send a plain text.
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Plain text means a
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normal message that anyone can read.
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It is a normal message.
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Now if
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send that message
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to receiver.
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There is no dedicated wire here.
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We don't have a dedicated wire on internet.
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Let's say I have to send a message from India to California.Send an email.
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So is there a dedicated
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line from India to california.
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A dedicated link.No.We are using internet.
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Meaning when the message exits our machine.
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On which router,
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on which node does it go.
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Meaning this channel,
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this medium
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is unsecure.
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It is .
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unsecure
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So an unsecure medium,
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unsecure channel.We are sending a message on.
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Any unauthorized person
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can
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take that message.
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So there is no problem of confidentiality here.
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It can take any .
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message
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But if we send that
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message as plain text.
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Anyone can read that message.
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Understand it.
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But we don't want this.
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For that we use cryptography.
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What do we do.
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Sender,
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before sending the plain text use
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encryption method.
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In encryption we use many algorithms.
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I will tell you about that algorithms.
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What do these algorithms do.
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The most important part
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here is key. They use a key.Lock, the lock that
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we put in our house.
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What is that lock
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It get locks, and get opened with a key.
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So that is the key.
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They will lock with this key.
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After applying the lock.
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It becomes cipher text.Cipher text is a secret message
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which nobody can read.
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No one can understand.
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When we will
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send that message on this channel.
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On this unsecured channel.If we send.
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Then anyone can take that on the way.
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But that
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M is not M.
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That M has become M'.Because we are not sending M as it is.
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Not sending plain text as it is.
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We are sending after converting into cipher text.
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So M becomes
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.Let's say M'.
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So the unauthorized person that is reading this on the way.
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He thinks that
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sender is sending M'.
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But we are sending M.
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And as the message reaches receiver.
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Receiver will
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decrypt that message.
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Because when we are saying that no one can understand the message
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So how will the receiver understand it
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So the receiver has
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to decrypt the message.
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Decrypt means convert
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M'
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to M again.
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Meaning
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convert cipher text
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to plain text.
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So sender
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does encryption
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Receiver does
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decryption
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And after decrypting he will read plain text.
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So along the way the
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unauthorized user
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will think it is M'
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But it is M.
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So cryptography
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is not a new term.
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Although it is becoming very popular.
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Because if we talk about
network
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security
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If we talk about
network security or
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cyber security
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in today's time.
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It is very popular.
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But it does not mean
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that cryptography is used in today's time.
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Cryptography started at the time of Caesar.
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King of Rome was Caesar.
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He used a technique called
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caesar's cipher And through it if he talked to another king.
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So they used to encode the message
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in such a way that no one could
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encode that message.
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But after
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attacking
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the message carrier.
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Anyone could take the message.
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But it does not mean that
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they could read the message
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They have to decrypt to read that message.And for decrypting
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we need a key
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And he would not
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have that key.
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That is called
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cryptography
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Or you can say encryption.
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And how do we achieve confidentiality.
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Through
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encryption method
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Here we have an
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important concept
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That we use cryptography in two ways.
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Symmetric
and
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asymmetric.
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Symmetric and
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asymmetric
means of
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same
Symmetric
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key
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Meaning with the key
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used for encryption.
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With the same key it will decrypt
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Like same, the lock that we use at home.
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With the key we closed the lock.
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If I take my neighbours key and
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unlock it.So anyone can unlock it.
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No.With the key used to lock.
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With the same key
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we will
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unlock
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That is the symmetric key.
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Asymmetric means.
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We will use two keys.
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With one key we will lock.
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And with some another key
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we will unlock.
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We will see about this in detail
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This is just the introduction of
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cryptography
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This is very important for
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UGC net and
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GATE exam.
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Because many questions are asked on
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cryptography in that.
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So that is the basic introduction.
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Then we will see
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symmetric and asymmetric key.
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Thank you.
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