What is Cryptography? | Introduction to Cryptography | Cryptography for Beginners | Edureka

Summary

This video script by Aria from Eddie Rocca delves into the world of cryptography, a crucial tool for secure communication. It outlines the basics of cryptography, explains its importance in protecting data, and covers various cryptographic classifications including symmetric and asymmetric key cryptography. The script provides a practical demonstration of the RSA algorithm, showcasing how it secures data on platforms like YouTube. It also explores encryption techniques such as transposition and substitution ciphers, stream and block ciphers, and the significance of digital certificates in cybersecurity.

Takeaways

• 🔒 Cryptography is essential for securing data and protecting against unauthorized access, identity theft, and tampering.
• 📚 The video session will cover the basics of cryptography, classifications, and a demonstration of the RSA algorithm.
• 🗣 The example of Andy and Sam illustrates the need for secure communication over public channels like the internet.
• 🔑 Cryptography involves converting messages into numeric forms, encrypting them with a key, and then decrypting them with a corresponding key.
• 🔄 The process of encryption and decryption is vital to ensure that messages remain private and intact during transmission.
• 🔒🔓 Cryptography is divided into symmetric key cryptography, which uses the same key for encryption and decryption, and asymmetric key cryptography, which uses a pair of keys.
• 🔄🔄 Symmetric key cryptography includes classical methods like transposition and substitution ciphers, and modern methods like stream and block ciphers.
• 🔑🔑 Asymmetric cryptography, or public key cryptography, uses a public key for encryption and a private key for decryption, enhancing security.
• 🔐 The RSA algorithm, used widely on the internet, is an example of asymmetric cryptography that relies on the difficulty of factoring large prime numbers.
• 🌐 The security of modern cryptography systems, like RSA, depends on keeping the private key secret while the public key can be openly distributed.
• 📈 The strength of public key cryptography systems is based on the computational difficulty of deriving the private key from the public key, ensuring robust security.

Q & A

What is the primary purpose of cryptography?

The primary purpose of cryptography is to securely protect data and communication from unauthorized access, ensuring the privacy and integrity of information such as corporate secrets, classified information, and personal data.

What is the scenario presented in the video to explain cryptography?

The scenario involves a person named Andy who wants to send a private message to his friend Sam over the internet. The goal is to secure the message against eavesdroppers and potential tampering by a third party named Eve.

How is the message converted into a numeric form in cryptography?

The message is first converted into a numeric form, which is then combined with an encryption key using an encryption algorithm to produce a ciphertext that can be securely transmitted.

What is a ciphertext?

A ciphertext is the result of encrypting a message using an encryption key and an encryption algorithm, transforming the original message into a form that is unreadable without the decryption key.

How does cryptography help secure the connection between Andy and Sam?

Cryptography helps secure the connection by allowing Andy to convert his readable message into an unreadable form (ciphertext) using a key. This ensures that even if someone intercepts the message, they cannot decipher it without the proper decryption key.

What are the two broad classifications of cryptography mentioned in the script?

The two broad classifications of cryptography are symmetric key cryptography and asymmetric key cryptography, also known as public key cryptography.

What is symmetric key cryptography?

Symmetric key cryptography is a type of cryptography where the same cryptographic key is used for both encryption and decryption of the message. This requires the key to be shared between the communicating parties.

What is the difference between a transposition cipher and a substitution cipher?

A transposition cipher rearranges the positions of the plaintext characters according to a system, while a substitution cipher replaces each plaintext character with another character based on a fixed system or rule.

What is a block cipher and how does it differ from a stream cipher?

A block cipher is an encryption method that applies a symmetric key to encrypt a fixed-size block of text at once, rather than encrypting one bit at a time as in stream ciphers.

What is asymmetric cryptography and how does it differ from symmetric cryptography?

Asymmetric cryptography, also known as public key cryptography, uses a pair of keys consisting of a public key (which can be widely distributed) and a private key (which is known only to the owner). This allows for both encryption and authentication, where only the paired private key can decrypt messages encrypted with the public key.

What is the significance of the RSA algorithm mentioned in the script?

The RSA algorithm is a widely used public key encryption system that is based on the computational difficulty of factoring large prime numbers. It is commonly used for secure data transmission over the internet and is an example of asymmetric cryptography.

Outlines

00:00

🔒 Introduction to Cryptography

The video script begins by emphasizing the importance of cryptography for securing data against unauthorized access. It introduces the speaker, Aria from Eddie Rocca, and outlines the topics to be covered, including the definition of cryptography, its classifications, and a demonstration of the RSA algorithm. The script uses a scenario involving a person named Andy who wants to securely send a message to his friend Sam, highlighting the need for secure communication against potential eavesdroppers or tampering by a character named Eve. Cryptography is defined as the practice of securing communication and data in the presence of adversaries, involving the conversion of messages into numeric forms, encryption with a key, and decryption by the intended recipient using a corresponding key.

05:00

🔑 Exploring Symmetric and Asymmetric Cryptography

This paragraph delves into the two main types of cryptography: symmetric key cryptography and asymmetric key cryptography. Symmetric key cryptography uses the same key for encryption and decryption, representing a shared secret between parties. The paragraph explains classical and modern symmetric cryptography, including transposition and substitution ciphers, as well as stream and block ciphers. It also introduces the Data Encryption Standard (DES) as a popular symmetric key system. Asymmetric cryptography, also known as public key cryptography, uses a pair of keys, one public and one private, for encryption and authentication. The strength of this system lies in the difficulty of deriving the private key from the public key, allowing the public key to be distributed without compromising security.

10:02

🔄 Understanding Cryptography Techniques

The script continues by explaining various cryptographic techniques in detail. It describes transposition ciphers that rearrange the positions of plaintext characters according to a systematic scheme, creating a ciphertext that is a permutation of the original message. Substitution ciphers are also discussed, where each letter of the alphabet is replaced with another letter or symbol according to a fixed system. The paragraph further explains stream ciphers, which encrypt data bit by bit, and block ciphers, which encrypt data in larger chunks. The security and reliability of block ciphers, such as the Advanced Encryption Standard (AES), are highlighted, emphasizing their use in modern cryptography.

15:03

🌐 Practical Demonstration of Public Key Encryption

The final paragraph of the script provides a practical demonstration of public key encryption, specifically using the RSA algorithm. It guides viewers on how to view digital certificates on YouTube as an example of public key cryptography in action. The script then walks through the process of generating a public and private key pair, encrypting a message using the public key, and decrypting it with the private key. The RSA algorithm is introduced, explaining the process of key generation, encryption, and decryption. The video concludes by inviting viewers to learn more about RSA and other cryptographic systems, encouraging them to engage with the content through likes, comments, and subscriptions.

Keywords

💡Cryptography

Cryptography is the practice and study of techniques for securing communication and data in the presence of adversaries. It is central to the video's theme, as it discusses the importance of cryptography in protecting sensitive information from unauthorized access. The script uses the term to introduce various cryptographic methods and algorithms, such as RSA, which are essential for securing online communications.

💡Encryption Key

An encryption key is a crucial element in cryptography used to convert plaintext into ciphertext, making the message unreadable to anyone without the key. In the script, the encryption key is used in conjunction with an encryption algorithm to secure messages sent over the internet, ensuring that only the intended recipient can decrypt and read the original message.

💡Ciphertext

Ciphertext refers to the output of an encryption algorithm, which is an unreadable form of the original message. The script explains that once a message is converted into ciphertext using an encryption key, it can be safely transmitted over a network, as only the person with the corresponding decryption key can convert it back into plaintext.

💡Decryption Key

A decryption key is used to reverse the encryption process, transforming ciphertext back into its original plaintext form. The script emphasizes the importance of the decryption key in ensuring the security of the message by allowing the intended recipient to access the original content after it has been encrypted and transmitted.

💡Symmetric Key Cryptography

Symmetric key cryptography is a type of cryptography where the same key is used for both encryption and decryption. The script mentions this concept while discussing the classifications of cryptography, highlighting that symmetric key algorithms require a shared secret between parties, which can be a drawback compared to asymmetric cryptography.

💡Asymmetric Key Cryptography

Asymmetric key cryptography, also known as public key cryptography, uses a pair of keys: a public key for encryption and a private key for decryption. The script explains that this method allows for secure communication over public channels, as the public key can be widely distributed without compromising security, while the private key remains secret.

💡Transposition Cipher

A transposition cipher is a method of encryption that rearranges the positions of plaintext characters according to a system, creating a permutation of the original text. The script provides an example of a transposition cipher, demonstrating how it can be used to reorder a message 'meet me after the party' into ciphertext using a specific key.

💡Substitution Cipher

A substitution cipher involves replacing each letter or group of letters in the plaintext with another letter or symbol according to a fixed system. The script describes a simple substitution cipher using the keyword 'zebra' to shift the alphabet and create a cipher alphabet, which is then used to encrypt the message 'flee at once we are discovered'.

💡Stream Cipher

A stream cipher is a method of encryption where a cryptographic key and algorithm are applied to each binary digit in a data stream one bit at a time. The script mentions stream ciphers as an alternative to block ciphers, noting that they are less commonly used in modern cryptography due to their potential vulnerabilities.

💡Block Cipher

A block cipher is an encryption method that applies a symmetric key to encrypt a fixed-size block of text at once, rather than one bit at a time as in stream ciphers. The script explains that block ciphers like AES are widely used in modern cryptography, providing a secure way to encrypt data in larger chunks.

💡RSA

RSA is a popular public key cryptosystem used widely on the internet for secure data transmission. The script discusses RSA in detail, explaining its unique algorithm for key pair generation and encryption/decryption processes. It also mentions that RSA is used by YouTube for securing its digital certificates, illustrating its practical application in real-world scenarios.

Highlights

Cryptography is essential for securing data against unauthorized access, protecting corporate secrets, classified information, and personal data from identity theft.

The session will cover the basics of cryptography, classifications, and a demonstration of the RSA algorithm.

Cryptography secures communication by converting messages into numeric form and applying an encryption key.

The concept of a secure communication channel between Andy and Sam is introduced to illustrate the use of cryptography.

Ciphertext is produced by encrypting the numeric form of a message with an encryption key, ensuring secure transmission.

The importance of keeping encryption and decryption keys secret is emphasized for the security of modern cryptography systems.

Symmetric key cryptography uses the same key for encryption and decryption, representing a shared secret between parties.

Transposition ciphers rearrange the positions of plaintext characters according to a systematic scheme.

Substitution ciphers replace letters or groups of letters with others according to a fixed system or key.

Stream ciphers encrypt data bit by bit using a cryptographic key and algorithm, contrasting with block ciphers.

Block ciphers like AES encrypt fixed-size blocks of text with a key of a predetermined length.

Asymmetric or public key cryptography uses a pair of keys, one public for encryption and one private for decryption.

The security of public key cryptography relies on the computational difficulty of deriving the private key from the public key.

RSA is a widely used encryption algorithm demonstrated through YouTube's digital certificates.

The RSA algorithm involves key pair generation and encryption/decryption processes using large prime numbers.

The strength of RSA encryption is due to the difficulty of factorizing large prime numbers.

The video provides a practical demonstration of public key encryption using an online demo.

The session concludes with an in-depth look at RSA, highlighting its significance and widespread use on the Internet.

Transcripts

[Music]

cryptography is essentially important

because it allows you to securely

protect data that you don't want anyone

else to have access to it is used to

protect corporate secrets secure

classified information and to protect

personal information to guard against

things like identity theft hi guys my

name is aria from Eddie Rocca and I

welcome you all to another session on

cyber security and today's video is

basically going to be about cryptography

now before we actually jump into the

session let me give you guys a brief on

the topics that we're gonna cover today

so first of all we're gonna cover what

is cryptography to the help of a very

simplistic scenario then we are going to

go through the classifications of

cryptography and how the different

classification of algorithm works in the

end I'm going to show you guys a nifty

demo on how a popular algorithm called

RSA actually works so let's get started

now I'm going to take the help of an

example or a scenario to actually

explain what is cryptography all right

so let's say we have a person and let's

call him Andy I suppose Andy sends a

message to his friend Sam who is on the

other side of the world now obviously he

wants this message to be private and

nobody else should have access to the

message now he uses a public forum for

example the internet for sending this

message the goal is to actually secure

this communication and of course we have

to be secure against someone now let's

say there is a smart guy called Eve who

is secretly got access to your

communication channel since this guy has

access to your communication he can do

much more than just eavesdrop for

example he can try to change the message

in itself now this is just a small

example what if Eve actually gets access

to your private information well that

could actually result in a big

catastrophe so how can Andy be sure that

nobody in the middle could access the

message sent to Sam the goal here is to

make communication secure and that's

where cryptography comes in so what

exactly is cryptography well

cryptography is the practice and the

study of techniques for securing

communication and data in the presence

of adversaries so let me take a moment

to explain how that actually happens

well first of all we have a message this

message is firstly converted into a

numeric form

and then this numeric form is applied

with a key called an encryption key and

this encryption key is used in an

encryption algorithm

so once the numeric message and the

encryption key has been applied in an

encryption algorithm what we get is

called a ciphertext now this ciphertext

is sent over the network to the other

side of the world where the other person

whose message is intended for will

actually use a decryption key and use

the ciphertext as a parameter of a

decryption algorithm and then he'll get

what we actually sent as a message and

if some error had actually occurred he'd

get an error so let's see how

cryptography can help secure the

connection between Andy and Sam so to

protect his message Andy first converts

his readable message to an unreadable

form here he converts a message to some

random numbers and after that he uses a

key to encrypt his message after

applying this key to the numerical form

of his message he gets a new value in

cryptography we call this ciphertext so

now if Andy sends the cipher text or

encrypted message over communication

channel he won't have to worry about

somebody in the middle of discovering

the private message even if somebody

manages to discover the message he won't

be able to decrypt the message without

having a proper key to unlock this

message so suppose Eve here discovers

the message and he somehow manages to

tamper with the message and message

finally reaches Sam Sam would need a key

to decrypt the message to recover the

original plaintext so using the key he

would convert a ciphertext to numerical

value corresponding to the plaintext now

after using the key for decryption what

will come out is the original plaintext

message or an arrow now this error is

very important it is the way Sam knows

that message sent by Andy is not the

same as a message that he received so

the error in a sense tells us that Eve

has tampered with the message now the

important thing to note here is that in

modern cryptography the security of the

system purely relies on keeping the

encryption and decryption key secret

based on the type of keys and encryption

algorithms cryptography is classified

under the following categories now

cryptography is broadly classified under

two categories namely symmetric key

cryptography and asymmetric key

cryptography popularly also known as

public

now symmetric key cryptography is

further classified as classical

cryptography and modern cryptography

further drilling down classical

cryptography is divided into two which

is transposition cipher and substitution

cipher on the other hand modern

cryptography is divided into stream

cipher and block cipher in the upcoming

slides I'll broadly explain all these

types of cryptography so let's start

with symmetric key cryptography first so

symmetric key algorithms are algorithms

for cryptography that use the same

cryptographic keys for both encryption

of plaintext and decryption of

ciphertext the keys may be identical but

there may be some simple transformation

to go between the two keys the keys in

practice represent a shared secret

between two or more parties that can be

used to maintain a private information

link this requirement that both parties

have access to the secret key there's no

the main drawbacks of symmetric key

encryption in comparison to publicly

encryption also known as a symmetric key

encryption now symmetric key

cryptography is sometimes also called

secret key cryptography and the most

popular symmetric key system is the data

encryption standards which also stands

for DES next up we're going to discuss

transposition cipher so in cryptography

a transposition cipher is a method of

encryption by which the positions held

by units of plaintext which are commonly

characters or groups of characters are

shifted according to a regular system so

that the ciphertext constitutes a

permutation of the plaintext that is the

order of units is changed the plaintext

is reordered now mathematically speaking

a bijective function is used on the

characters position to encrypt and an

inverse a function to decrypt so as you

can see that there is an example on the

slide so on the plaintext side we have a

message which says meet me after the

party now this has been carefully

arranged in the encryption matrix which

has been divided into six rows and the

columns so next we have a key which is

basically four two one six three five

and then we rearrange by looking at the

plaintext matrix and then we get the

cipher text which basically is some

unreadable gibberish at this moment so

that's how this whole algorithm work

on the other hand when the ciphertext is

being converted into the plaintext the

plaintext matrix is going to be referred

and it can be done very easily going on

we are going to discuss substitution

cipher

so substitution of single letters

separately simple substitution can be

demonstrated by writing out the

alphabets in some order to represent the

substitution this is termed a

substitution alphabet the cipher

alphabet may be shifted or reversed

creating the Caesar and app stash cipher

respectively or scrambled in a more

complex fashion in which case it is

called a mixed alphabet or deranged

alphabet traditionally mixed alphabets

may be created by first writing out

keyboard removing repeated letters in it

then writing all the remaining letters

in the alphabet in the usual order now

consider this example is shown on the

slide using the system we just discussed

the keyword zebra's gives us the

following alphabets from the plaintext

alphabet which is a to C so the

ciphertext alphabet is basically zebras

then followed by all the alphabets we

have missed out in the zebrawood so as

you guys can see it's zebras followed by

SC D F G H and so on now suppose we were

to actually encrypt a message using this

code so as you guys can see on the

screen I've shown you an example which

is a message flee at once we are

discovered is being actually encrypted

using this code so if you guys can see

out here though F letter actually

corresponds to s and then the L letter

actually corresponds to I out here then

we actually get the cipher text which is

s I is that you using the code and the

process that I just discussed now

traditionally the cipher text is written

out in blocks of fixed length omitting

punctuation x' and spaces this is done

to help avoid transmission errors to

disguise the word boundaries from the

plaintext

now these blocks are called groups and

sometimes a group count that is the

number of groups is given as an

additional check now five letter groups

are traditional as you guys can see that

we have also divided our ciphertext into

groups of five and this dates back to

when messages were actually used to be

transmitted by telegraph now if the

length of the message happens not to be

divisible by five it may be padded at

the end with nulls and these can be any

character

that can be decrypted too obvious

nonsense so the receiver can easily spot

them and discard them next on our list

is stream cipher so a stream cipher is a

method of encrypting text to produce

cipher text in which a cryptographic key

and algorithm are applied to each binary

digit in a data stream one bit at a time

this method is not much used in modern

cryptography the main alternative method

is block cipher in which a key and

algorithm are applied to block of data

rather than individual bits in a stream

okay so now that we've spoken about

block cipher let's go and actually

explain what block cipher does a block

cipher is an encryption method that

applies a deterministic algorithm for

the symmetric key to encrypt a block of

text rather than encrypting one bit at a

time as in stream ciphers for example a

common block cipher AES encrypts 128-bit

blocks with a key of predetermined

length that is either 128 192 or 256

bits in length now block ciphers are

pseudo ranbir mutation families that

operate on the fixed size of block of

bits these PRPs are function that cannot

be differentiated from completely random

permutation and thus are considered

reliable I've been proven to be

unreliable by some source ok so now it's

time that we discuss some asymmetric

cryptography so asymmetric cryptography

also known as public key cryptography is

any cryptographic system that uses pair

of keys which is a public key which may

be this emanated widely and private keys

which are known only to the owner this

accomplishes two functions

authentication where the public key

verify is that a holder of the paired

private key sent the message and

encryption where only the paired private

key holder can decrypt the message

encrypted with the public key in a

public key encryption system any person

can encrypt a message using the

receivers public key that encrypted

message can only be decrypted with the

receivers private key so to be practical

the generation of public and private key

pair must be computationally economical

the strength of a public key

cryptography system relies on

computational efforts required to find

the private key from its paired public

key so effective security only requires

keeping the private key private and the

public key can be openly distributed

without compromising security okay so

now that I've actually shown you

hobb cryptography actually works and how

the different classifications are

actually applied let's go and do

something interesting so you guys are

actually watching this video on YouTube

right now so if you guys actually go and

click on the secure part besides the URL

you can actually go and view the digital

certificates that are actually used out

here so click on certificates and you'll

see the details in the details tab now

as you guys can see the signature

algorithm that is used for actually

securing YouTube is being sha-256 with

RSA and RSA is a very very common

encryption algorithm that is used

throughout the internet then the

signature hash algorithm that is being

used is sha-256

and the issuer is Google in Internet

Authority and you can get a lot of

information about sites and all their

authority key identifier their

certificate policy is the key usage and

a lot of thing about security just from

this small little button audio also let

me show you a little how public key

encryption actually works so on the side

which is basically called web start CS

door UTA dot edu you can actually demo

out public key encryption so suppose we

had to send a message first we would

need to generate keys so as you can see

I just click generate keys and it got me

two keys which is one is the public key

which I will distribute or the network

and one the private key which I will

actually keep secret to myself now I

want to send message saying hi there

when is the exam tomorrow so now we are

going to encrypt it using the public key

because that's exactly what's

distributed so now as you can see we

have got our ciphertext so this huge

thing right out here is ciphertext and

it absolutely makes no sense whatsoever

now suppose we were to actually then

decrypt the message we would use the

private key that goes along with our

account and we would decode the message

and as you guys can see voila we have hi

there when is the exam tomorrow so we

have actually sent a message on the

Internet in a very secure fashion above

that there's also RSA that needs some

explaining because our promise at two

now RSA is a very very commonly used

algorithm that is used throughout the

internet and you just saw it being used

by YouTube so it has to be common

so RSA has a very unique way of applying

this algorithm there are many actual

parameters that you actually need to

study okay so now we're actually going

to discuss RSA which is a very popular

algorithm that is used throughout the

internet and you also saw that it's

being used by YouTube right now so this

crypto system is one of the initial

system it remains the most employed

crypto system even today and the system

was invented by three scholars which is

Ron Rivest Adi Shamir and Len Adleman

hence the name RSA and we will see the

two aspects of the RSA cryptosystem

firstly generation of key pair and

secondly encryption decryption

algorithms so each person or a party who

desires to participate in communication

using encryption needs to generate a

pair of keys namely public key and

private key so the process followed in

the generation of keys is as follows

first we have to actually calculate n

now n is actually given by multiplying p

and q as you guys can see out here so p

and q are supposed to be very large

prime numbers so out here P will be 35

but for some very strong encryption we

are going to choose very large prime

numbers then we actually have to

calculate Phi now Phi is you can see the

formula goes is P minus 1 into Q minus 1

and this helps us determine for the

encryption algorithm now then we have to

actually calculate e now he must be

greater than 1 and less than Phi which

is P minus 1 into Q minus 1 and there

must be no common factors for e and Phi

except for one so in other words they

must be co-prime to each other now to

form the public key the pair of numbers

m and e form the RSA public key system

this is actually made public and is

distributed throughout the network

interestingly though

n is a part of the public key and the

difficulty in factorizing a large prime

number ensures that the attacker cannot

find in finite time the two Prime's that

is P and Q that is used to obtain M this

actually ensures the strength of RSA now

in the generation of the private key the

private key D is calculated from P Q and

for a given n and E there is a unique

number D now the number D is the inverse

of e modulo 5

this means that D is the number less

than Phi such that when multiplied by e

it gives 1 so let's go and actually fill

up these numbers so n should be 35 out

here and if we generate them we get the

value of 5 which is 24 which is

basically 4 into 6 and then we should

also get e it's now it should be

co-prime so we are going to give it 11

as 11 is co-prime to both so now for the

actual encryption part we have to put in

E and n out here so e out here for us is

11 and n is 35 and then we're gonna pick

a letter to actually cipher which is a

and then we are going to encode it as a

number so as you guys can see we've

encoded as 1 and out here now after

we've given the message its numerical

form you click on encryption and we get

it now to actually decrypt the message

we are gonna need D and n now D for us

was 5 and n was 35 so 5 and 35 and then

we're gonna take encrypted message from

above and we're going to decrypt this

message so after you decrypt it we have

the numerical form of the plaintext and

then decode the message is like your

decode message and as you guys can see

we have decoded a message using RSA so

guys that's how RSA works I explain all

the factors that we actually use an RSA

from n 2 v 2e e 2 D and I hope you

understood a part of it if y'all are

still more interested you all can

actually research a lot on RSA it's a

very in-depth cryptography system and

also that brings us to the end of this

session I hope you guys had fun learning

about cryptography and the different

methods that are actually used on the

Internet that's it for me goodbye

I hope you have enjoyed listening to

this video please be kind enough to like

it and you can comment any of your

doubts and queries and we will reply

them at the earliest do look out for

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