1 - Cryptography Basics

Summary

This script delves into the world of cryptography, a practice as old as communication itself. It explains the fundamental need for secure messaging and introduces the concept of transforming readable messages into unreadable 'ciphertext' to prevent unauthorized access. The script covers encryption and decryption algorithms, distinguishing between symmetric and asymmetric methods, and highlights the importance of key sizes in security. It also explores hashing algorithms, emphasizing their role in ensuring message integrity rather than confidentiality, and explains the use of HMAC for user authentication in secure communications.

Takeaways

• 🔒 Cryptography is an ancient concept, designed to secure messages from unauthorized access.
• 📜 The core of cryptography is transforming readable plain text into unreadable cipher text to ensure security during transmission.
• 🔄 The process involves both encryption, converting plain text to cipher text, and decryption, converting cipher text back to plain text.
• 🔑 Keys are essential in cryptography, used in conjunction with algorithms to encrypt and decrypt messages, ensuring that only authorized parties can read the content.
• 🔒🔑 Symmetric algorithms use the same key for both encryption and decryption, while asymmetric algorithms use a pair of keys, one for each process.
• 🔑🔑 Asymmetric algorithms, like RSA, have larger key sizes and require more computational resources, making them slower but also more secure.
• 🔐 Advanced Encryption Standard (AES) is considered a highly secure symmetric algorithm, with variable key sizes up to 256 bits.
• 🔎 Hashing algorithms are one-way functions that create a digital fingerprint of data, ensuring the integrity but not the confidentiality of the message.
• 📈 Different hashing algorithms, such as MD5, SHA-1, and SHA-2, have varying levels of security and generate hash files of different lengths.
• 🔒🔍 Hashed Message Authentication Code (HMAC) combines hashing with a secret key to verify both the integrity and authenticity of a message.
• 🌐 HMAC is used in protocols like SSL to ensure secure communication, demonstrating the practical applications of cryptographic techniques.

Q & A

What is the fundamental purpose of cryptography?

The fundamental purpose of cryptography is to transform a message into a secure form so that unauthorized individuals cannot read the content of the message.

What is the difference between plaintext and ciphertext?

Plaintext is a readable message, while ciphertext is the result of an encryption process that makes the message unreadable to anyone without the decryption key.

What is an encryption algorithm?

An encryption algorithm is a process used to convert plaintext into ciphertext, ensuring the message is secure from unauthorized access.

Why is a key necessary in the encryption process?

A key is necessary to ensure that only those with the correct key can decrypt the ciphertext back into plaintext, thus maintaining the confidentiality of the message.

What are the two main types of encryption algorithms?

The two main types of encryption algorithms are symmetric algorithms, which use a single key for both encryption and decryption, and asymmetric algorithms, which use a pair of keys, one for encryption and one for decryption.

What is the difference between symmetric and asymmetric encryption algorithms?

In symmetric encryption, the same key is used for both encryption and decryption, while in asymmetric encryption, a public key is used for encryption and a private key, known only to the recipient, is used for decryption.

What is the Advanced Encryption Standard (AES)?

The Advanced Encryption Standard (AES) is a widely used symmetric encryption algorithm that can work with multiple key sizes, such as 128, 192, or 256 bits, making it highly secure.

Why are larger key sizes in encryption algorithms considered more secure?

Larger key sizes make it computationally more difficult for unauthorized individuals to crack the encryption through brute force methods, thus enhancing the security of the encryption.

What is a hashing algorithm and how does it differ from encryption algorithms?

A hashing algorithm is a one-way function that converts an input message into a fixed-size output called a hash or digest. Unlike encryption, it is not meant to be decrypted; it is used to verify the integrity of the message.

What is the purpose of a hashing algorithm in the context of message integrity?

The purpose of a hashing algorithm is to ensure that the message has not been altered in any way during transmission. The recipient can verify the integrity by generating a hash of the received message and comparing it with the hash provided by the sender.

What is Hashed Message Authentication Code (HMAC) and how is it used for message authentication?

HMAC is a technique that combines a hashing algorithm with a secret key to provide an additional layer of security and authentication. It ensures that the message came from the claimed sender and has not been tampered with during transmission.

Why might asymmetric encryption be slower than symmetric encryption?

Asymmetric encryption might be slower than symmetric encryption because it requires more computational power to handle the larger key sizes and the more complex mathematical operations involved in the encryption and decryption processes.

Outlines

00:00

🔒 Cryptography: The Art of Secure Communication

This paragraph introduces the fundamental concept of cryptography, which has been in existence for thousands of years to address the concern of unauthorized access to messages. It explains that cryptography is the practice of transforming readable messages (plain text) into a non-readable form (cipher text) to prevent unauthorized reading. The process involves using an encryption algorithm along with a key to encode the message, and the same key is required to decode it back to plain text. The paragraph also distinguishes between symmetric and asymmetric encryption algorithms, highlighting the use of a single key in symmetric algorithms like DES and triple DES, and two different keys in asymmetric algorithms like RSA. It concludes by emphasizing the importance of the key in maintaining the security of the message.

05:00

🗝️ Key Sizes and Encryption Strength

The second paragraph delves into the importance of key size in encryption algorithms, illustrating how larger keys contribute to stronger encryption. It mentions the Data Encryption Standard (DES) with a 56-bit key and the Advanced Encryption Standard (AES), which supports variable key sizes of 128 or 256 bits. The paragraph also discusses the trade-offs between symmetric and asymmetric algorithms, noting that while asymmetric algorithms offer larger key sizes and are more secure, they require more computational resources and can slow down communication. Additionally, it introduces hashing algorithms as a third type of cryptographic function, which are one-way and used to ensure the integrity of a message rather than its confidentiality.

10:01

📜 Hashing Algorithms and Their Applications

This paragraph focuses on hashing algorithms, which are used to create a digital fingerprint or a fixed-size digest of a message. It explains that hashing is a one-way process and contrasts it with the two-way encryption process. The paragraph lists various hashing algorithms, including MD5, SHA-1, SHA-2, and RIPEMD, and discusses their evolution and the increasing security they offer with larger hash sizes. It also describes how hashing is used in applications like HMAC (Hash-based Message Authentication Code) to authenticate the sender of a message by using a shared secret key in conjunction with a hashing algorithm.

15:02

🔗 HMAC and Its Role in Secure Communications

The final paragraph discusses the application of HMAC in secure communications, particularly in protocols like SSL. It provides a practical example of how HMAC can be used between two users, Alice and Bob, to ensure that a message indeed comes from the claimed sender. The process involves Alice encrypting a message with a shared secret key and generating a hash file using a hashing algorithm. She then sends the hash file and the encrypted message to Bob. Upon receipt, Bob uses the same hashing algorithm and secret key to verify the hash file's integrity, confirming the message's authenticity before decrypting it. This use case highlights the importance of HMAC in maintaining both the integrity and authenticity of messages in digital communications.

Keywords

💡Cryptography

Cryptography is the practice of secure communication techniques that allow only the intended recipient to understand the message. It is central to the video's theme as it discusses its historical importance and modern applications. The script explains that cryptography transforms readable messages into a secure form to prevent unauthorized access, illustrating this with the example of a general sending a message to another general securely.

💡Plain Text

Plain Text refers to the original, human-readable form of a message before it is encrypted. In the context of the video, plain text is the starting point for the encryption process, which is essential for understanding how messages are secured. The script mentions that plain text is converted into cipher text through cryptographic processes to ensure confidentiality.

💡Cipher Text

Cipher Text is the result of encrypting plain text using a cryptographic algorithm. It is a key concept in the video as it represents the unreadable form of a message that protects the content from unauthorized readers. The script explains that cipher text is created by transforming plain text through encryption algorithms, ensuring that even if someone intercepts the message, they cannot understand its content without the key.

💡Encryption Algorithm

An Encryption Algorithm is a set of mathematical processes used to convert plain text into cipher text. The video emphasizes the importance of these algorithms in securing messages. The script provides examples such as the Data Encryption Standard (DES) and Advanced Encryption Standard (AES), explaining how they use keys to transform messages into a secure form.

💡Key

In cryptography, a Key is a piece of information that determines the output of the encryption algorithm. It is crucial to the video's narrative as it ties the security of messages to the use of keys. The script explains that keys are used in conjunction with encryption algorithms to create cipher text and are essential for both encryption and decryption processes.

💡Symmetric Algorithm

A Symmetric Algorithm is a type of encryption algorithm that uses the same key for both encryption and decryption. The video discusses this concept to illustrate a common method of securing messages. The script mentions that symmetric algorithms like DES and Triple DES use a single key, making them efficient but requiring secure key distribution.

💡Asymmetric Algorithm

Asymmetric Algorithm, also known as public-key cryptography, uses two different keys: one for encryption and one for decryption. The video explains that this type of algorithm allows for more secure key management. The script provides RSA as an example, highlighting that it uses a larger key size compared to symmetric algorithms, which affects performance and security.

💡Hashing Algorithm

A Hashing Algorithm is a one-way function that converts an input into a fixed-size string of characters, which is typically used for verifying data integrity. The video introduces this concept to show a different application of cryptography. The script explains that hashing algorithms like MD5 and SHA-1 produce a digest that ensures the integrity of a message without the ability to decrypt it.

💡Digest

In the context of hashing, a Digest is the output generated by a hashing algorithm, often referred to as a digital fingerprint or hash file. The video discusses digests to illustrate the one-way nature of hashing. The script mentions that regardless of the size of the input, the output (digest) is always of the same size, ensuring consistency.

💡HMAC

HMAC, or Hashed Message Authentication Code, is a specific type of message authentication mechanism that uses cryptographic hash functions in combination with a secret cryptographic key. The video explains its application for user authentication. The script describes how HMAC works with a secret key and a hashing algorithm to ensure that a message has not been tampered with during transmission.

💡SSL Protocol

SSL (Secure Sockets Layer) Protocol is a security technology for establishing an encrypted link between a web server and a web client. The video briefly mentions its application of HMAC for secure communication. The script indicates that SSL uses cryptographic techniques, including HMAC, to ensure data integrity and confidentiality during web transactions.

Highlights

Cryptography has been a concept for thousands of years, addressing the concern of unauthorized access to messages.

Cryptography is the art of transforming a message into a secure form to prevent unauthorized reading.

The process involves converting plain text to ciphertext, making it unreadable without the proper key.

Encryption algorithms are used to convert plain text to ciphertext and vice versa.

A key is essential in cryptography to ensure that only authorized parties can decrypt the message.

There are two types of encryption algorithms: symmetric and asymmetric.

Symmetric algorithms use a single key for both encryption and decryption.

Asymmetric algorithms use a pair of keys, one for encryption and another for decryption.

Data Encryption Standard (DES) and Triple DES are examples of symmetric algorithms.

Advanced Encryption Standard (AES) is widely used and considered highly secure.

Key size in encryption algorithms affects the strength of the encryption.

Asymmetric algorithms require more computational resources and are slower than symmetric ones.

Hashing algorithms are one-way functions used to ensure the integrity of a message.

Hashing algorithms produce a fixed-size digest or digital fingerprint of the input message.

MD5, SHA-1, and SHA-2 are examples of popular hashing algorithms with varying levels of security.

HMAC is used for message authentication by combining a secret key with a hashing algorithm.

SSL protocol utilizes HMAC for secure communication.

The choice between symmetric and asymmetric algorithms depends on the application's need for speed and security.

Transcripts

cryptography is a concept that has been

around for

thousands of years so it's not something

new

and the reason for that is that people

have always had this concern that when

they send a message

to a recipient someone unauthorized get

access to that message and read the

content of the message

now that message could be something that

a general is sending to

another general or it could be something

that you know a person is sending to

another family member

so cryptography is an answer to that

concern

now what is cryptography it's basically

the art of

transforming a message into a secure

form so that

someone unauthorized cannot read the

content of the message

so we're transforming a clear text

message

to some gibberish that is not readable

and understandable by people

so you have a plain text a readable

message

and you send that readable message

through some processes

and in that processes the message gets

converted to

something which is not readable to some

gibberish that

if somebody gets access to that message

they cannot read it

so that uh message which is not readable

is called ciphertext so i have plain

text

i send it through some processes and

then i get

cipher text now during this process

you're basically encoding your message

or you're in ciphering the message now

when the recipient receive

this message they cannot read the

message either

so what they do is they have to send

that message

through the same processes and get the

message converted back to something

which is readable which we call it plain

text

now this process of converting message

from plain text to ciphertext

is called encryption algorithm so the

whole process

is called algorithm and when you use it

for encryption

we call it encryption algorithm now the

problem with

this process of converting plaintext to

ciphertext

using an encryption algorithm is that if

an

unauthorized person gets access to the

ciphertext

and if they come to know what algorithm

you've used

then nothing stops them from sending

your ciphertext through the same

algorithm to get the plain text and read

the content of the message

now to address this issue

they have come up with a key so

when you're sending your message the

plaintext through the

encryption algorithm you send that key

to that algorithm too

so you use the key and plain text

together

in that algorithm to convert the plain

text message

to some gibberish or to cipher text so

i'm not going to say gibberish anymore

i'm going to say cipher text from now on

so now i have the ciphertext and

i use the plain text with the algorithm

and the key

to get that ciphertext so as i mentioned

before if you want to

convert the ciphertext to uh plain text

then you have to send that ciphertext

and the key to the same algorithm

and get your text converted back to

plain text

now the algorithm when it's used for

encryption

we call it encryption algorithm and when

we use the same algorithm for decryption

we call it decryption algorithm all

right

now that you know that we have an

algorithm that can be used for

transforming

a plain text to ciphertext or ciphertext

to plain text

you need to know that we have different

types of encryption algorithms

we basically have two types of

encryption algorithm

one is symmetric algorithm in symmetric

algorithm you use

one key to transform the plain text to

ciphertext

and you use exactly the same key to

transform the ciphertext to plaintext

the second type of algorithm is

asymmetric algorithm

now in asymmetric algorithm you have two

keys

you use one key for encryption and you

use the other key for decryption

if you use the first key for encryption

you have to use the second key for

decryption

you cannot use the first key for

decryption

and if you use the second key for

encryption then you have to use the

first key for

decryption that is the difference

between these two algorithms

now we have so many different algorithms

that are

categorized under symmetric and

asymmetric

so if you look at this slide we have a

data encryption standard that's

an encryption algorithm which is a

symmetric algorithm

we have a triple des which is basically

data encryption standard but you use it

three times

and the reason that you do that is to

make the algorithm

more stronger more secure

another type of algorithm that we have

which has been widely used nowadays and

it's the most secure one

is called advanced encryption standard

or aes

if you look at all these algorithms you

can see that they have different

sizes of keys that can be used with for

example data encryption is

a standard has a key of 50

56 bit so that means when you want to

use this algorithm

the key that you're going to use is

going to be 56 bits of

key you send that key and your text

to this algorithm to get the ciphertext

when it comes to advanced encryption

standard it can

work with multiple sizes of keys

you can have a key of size 128 bit

or 256 bit so the larger the size of

your key

the stronger your encryption can be and

the difference between this symmetric

algorithm is

basically the mathematic procedures that

they use

to convert the plaintext to ciphertext

now if the mathematic procedure is very

sophisticated

then that makes the algorithm more

powerful

stronger algorithm and if the key size

is longer

that makes even the algorithm stronger

now on the right side of screen you can

see we have asymmetric

algorithm and rsa is an example of that

we have more

asymmetric algorithms of course but i

have

just put the most popular one uh which

is rsa and it's been around for

quite a long time so as you can see the

size of the key with the

asymmetric algorithm is significantly

bigger than

what we have in symmetric algorithm now

you may be asking

that since asymmetry has larger key size

compared to a symmetric algorithm

why do we need to use symmetric

algorithm why don't we use asymmetric

algorithm for everything

well one reason for that is the

resources that you need to handle

asymmetry keys

for example if you're using asymmetric

key

the communication the speed of the

communication might be

much slower than symmetric algorithm and

you need a lot of

cpu power to handle asymmetric algorithm

imagine you're accessing a website using

a secure http protocol

and if that website uses asymmetric

algorithm all the way then the

communication with that website is going

to be really slow and you will see that

your cpu usage is going to be really

high to handle all these encrypted

traffics using asymmetric algorithm

the third type of cryptographic

algorithm that we have is called

hashing algorithm now the difference

between hashing algorithm and the

previous two

is that hashing algorithm is a one-way

algorithm

so when you encrypt your message you

cannot decrypt it back

and technically with hashing algorithm

you're not really

encrypting your message the result of

hashing algorithm is called

a digest or a digital fingerprint

or a hash file so when you send your

message through a hashing algorithm

it goes through some calculations some

mathematical procedures

and the end result is going to be a

digest of the file

or a hash of that file now you may be

asking

why do we need such an algorithm if i

cannot decrypt the message that i

encrypted

then what's the point of using this

algorithm

well that's a very good question that i

asked for you

in the symmetric and asymmetric

algorithm

you are encrypting a message so these

algorithms protect the confidentiality

and

integrity of the message hashing

algorithm

is just for the integrity of the message

because in hashing algorithm you don't

need to have a key you

just need to know the algorithm so when

i send a message to someone i just tell

them

what hashing algorithm i used and then

they can use the same algorithm to check

the integrity of the message that i sent

to them

now the way that this works is that when

i want to send the message to someone

else

i calculate a hash of that message

and then i send the message with the

hash file to the recipient

then when the recipient receives that

message they're going to use the

same hashing algorithm to generate a

hash of that file

if the produced hash is exactly the same

as the one that i sent to them

then they know that the message is

intact and

nothing with the content of that message

has been changed

so when you use this algorithm you don't

really care that

someone sees the content of your message

what you care is

the recipient receives the exact message

that you sent to them

now one thing about the hashing

algorithm

is that whether you send a letter a page

or 10 volume book as an input to the

hashing algorithm

the end result is going to be the same

size

now the same way that we had multiple

algorithms

with symmetric and asymmetric algorithms

in hashing also we have different types

of

algorithms and the main difference

between these

different algorithms is in the

mathematical calculation of the digital

fingerprint or the hash file

one of the earliest and most popular

hashing algorithm

is md5 or message digest five

now the five is the version of this

algorithm so it started from message

digest one and

two and then it reached the message

digest 5.

as you can see the length of the hash

file that is generated by message digest

5

or md5 is 128 bit so as i said whether

you send a letter

or a page to this uh hashing algorithm

the end result is going to be 128 bit

now later some vulnerabilities were

found with

md5 and then sha1 was

introduced as a more secure hashing

algorithm

as you can see sha generates a 106

bit hash file so whatever you send to

sha

1 the end result is going to be 160 bit

and then sha 1 also was found to be

a little bit vulnerable and then shot 2

was introduced as a more secure version

of

sha-1 and sha2 generates a different

hash sizes

as you can see the hash length can be

224 bit

all the way to 512 bit recently

shot 3 has been introduced as the most

secure version of

sha2 another type of hashing algorithm

that we have

is called race integrity primitives

evaluation message digest or

ripemd now this algorithm

was created by race which is a european

union affiliated

organization as you can see this

algorithm also generates

hash files in different sizes

now there are other hashing algorithms

out there but

what you see in these slides are the

most common and popular ones

one of the usage or applications of

the hashing algorithm is in hashed

message

authentication code as the name says

here this hashed message authentication

code is used for

authenticating a user let me explain how

it works

let's say we have two users alice and

bob

and these two uh when they send a

message to each other they want to make

sure that the message came from the

right person

so they want to use hmac for

authenticating each other

now both of these users have same secret

key so they both agreed on the same

encryption algorithm and they generated

as the same secret key to use with that

symmetric algorithm when they exchange

messages now let's say alice wants to

send a message to bob so

she uses the same secret key that they

have to encrypt that message

and then she uses a hashing algorithm

to generate a hash file for that

encrypted message

and the key the secret key that she has

the end result is gonna be a hash file

now

next thing that she's gonna do is send

this hash file and the encrypted message

to bob

when bob receives the message before

decrypting the message

he is going to make sure that the

message actually came from alice

so the way that he is going to do that

is by using the same hashing algorithm

he's gonna send the same encrypted file

and the secret key that he has to that

hashing algorithm

to generate a hash file then

when he generates that hash file he's

gonna compare that hash file with the

one that

alice sent to him if these two hash

files are exactly the same

then he knows that the message came from

alice because

alice is the one who has that key and

without that key there was no way that

bob could get the same

hash file so now that he knows that the

message came from alice

he can use the same secret key that he

has to decrypt the message

and see the content of that message so

that's how

the hashed message authentication code

works

one of the application of hmac is

in for example ssl protocol i'll talk

about ssl protocol in another lesson

but that's one of the application of

this hmac protocol

alright so that's it for this lesson and

i'll see you in another video