WEBVTT

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In this lesson,

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we will learn about symmetric algorithms.

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First, there are two basic types of encryption algorithms:

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Symmetric and Asymmetric.

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In this lesson, we'll focus on symmetric encryption.

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Symmetric encryption algorithms are encryption methods

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that result in the creation of a single key.

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The resultant symmetric key is used for both encryption

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and decryption.

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Common symmetric encryption algorithms

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include the Advanced Encryption Standard (AES),

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the Data Encryption Standard (DES),

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Triple DES, Blowfish, Twofish, Rivest Cipher 4 (RC4),

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and ChaCha20.

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Let's learn more about each

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of these symmetric encryption algorithms.

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But before we dive into the details

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of symmetric encryption algorithms,

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let's take a minute to define encryption.

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Encryption is the process

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of converting readable information, known as a plaintext,

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into an unreadable form called ciphertext

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using an encryption algorithm and a secret key.

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This process is two-way,

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meaning that encrypted data

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can be decrypted back to plaintext with the correct key.

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Now, for most folks,

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this is a fairly simple thing to understand

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because symmetric key encryption

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works just like the things you use on a daily basis,

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like a door lock on your house or your car.

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After all, when you go home

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and unlock your front door tonight,

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you're going to be using a physical form

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of symmetric key encryption.

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If you share your house with somebody else,

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like a spouse or a roommate,

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you're both going to have your own copy of the same key,

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and that same key is going to be used to both lock

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and unlock the front door.

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This makes it a symmetric key

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because the exact same key is used to lock

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and unlock the door.

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Now, when you hear the word symmetric key,

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I want you to remember that this refers

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to both people having the same key.

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Symmetric equals same.

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So symmetric cryptography is an encryption method

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where the same key is used for both encryption

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and decryption of data,

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making it efficient and fast,

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ideal for securing large amounts of data very quickly.

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Symmetric encryption is further divided

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into two types of encryption methods:

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Stream ciphers and Block ciphers.

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Stream ciphers are a type of symmetric encryption

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that encrypt data bit by bit

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or byte by byte using a pseudo-random stream generated

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by a secret key.

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This approach allows stream ciphers

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to encrypt data continuously,

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making them perfect for real-time applications like audio

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or video streaming,

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where the total length of the data stream is unknown.

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With stream ciphers,

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the key stream generator produces

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a pseudo-random bit stream,

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which is then combined

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with the plaintext being encrypted using an XOR,

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or Exclusive OR operation, to create encrypted ciphertext.

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Think of stream ciphers like a zipper on a jacket.

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The key stream generator

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is like one side of the zipper,

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creating a series of teeth

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that match up perfectly with the other side,

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which is the plaintext that's being encrypted.

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As the zipper, representing the XOR operation,

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pulls the two sides together,

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it locks them into a new tightly interwoven pattern,

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creating a secure barrier, which represents the ciphertext.

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Just like the zipper combines the teeth

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to keep the jacket closed,

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the XOR operation combines the key stream

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and plaintext into a secure message.

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The beauty of XOR is its reversibility.

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Just like unzipping a zipper,

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applying an XOR with the same key stream

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to the ciphertext restores the original plaintext.

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Overall, the security of a stream cipher

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depends on the uniqueness of the key stream,

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which, remember, is one side of the zipper

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that is generated using an initialization vector.

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An initialization vector, which changes constantly,

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ensures that each key stream is unique

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even when encrypting the same plaintext multiple times.

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However, if the initialization vector is weak

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or predictable, the encryption can be compromised.

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For example, wired equivalent privacy, or WEP,

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used a short 24-bit initialization vector,

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making it vulnerable to brute force attacks

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and rendering its encryption insecure.

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Block ciphers are a type of symmetric encryption

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that encrypt data in fixed-size blocks,

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usually 64 or 128 bits, using a secret key.

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This method means

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that block ciphers process data in chunks,

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making them ideal for applications like file encryption

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and secure communications

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where the data size is known and large.

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The block cipher encryption process

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involves breaking the plaintext into blocks,

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applying the encryption algorithm to each block,

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and combining the blocks to form the ciphertext.

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Because block ciphers handle data in chunks,

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they offer strong security through structured encryption.

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Block ciphers use a combination of confusion

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and diffusion techniques to secure the data.

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Confusion makes the relationship between the key

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and the ciphertext complex.

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While diffusion spreads the plaintext information

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throughout ciphertext,

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ensuring that even a small change in the plaintext

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or key significantly alters the output.

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You can think of confusion

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and diffusion techniques like writing a secret message

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into a puzzle with letters on the puzzle pieces.

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Confusion is like scrambling the letters of the message,

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so the words are hard to recognize

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even if you can see them all.

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Diffusion is like scattering those scramble pieces

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all across the puzzle,

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making it difficult

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to spot any coherent groups of the letters.

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This dual approach of confusion

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and diffusion makes block ciphers resilient to attacks

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that aim to reveal the key

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or plaintext by analyzing patterns.

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Unlike stream ciphers, which encrypt continuously,

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block ciphers apply multiple rounds of these transformations

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to each block,

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enhancing the security of the encrypted data.

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A critical aspect of block ciphers

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is their use of different modes of operation,

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which define how each block interacts with other blocks

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during the encryption.

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Common modes include electronic code book, or ECB,

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cipher block chaining, or CBC,

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and the Galois/Counter Mode, or GCM.

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The security of a block cipher depends on its algorithm,

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key length, and mode of operation.

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Now, let's categorize some specific encryption algorithms.

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First, we have the Advanced Encryption Standard, or AES.

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AES is one of the most widely used

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symmetric encryption algorithms today.

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AES can operate as both a block cipher,

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encrypting fixed-size 128-bit blocks of data,

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and as a stream cipher,

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using configurations like Galois/Counter Mode, or GCM,

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to handle continuous data streams.

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The ability to operate as both a block

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or stream cipher is unique and distinguishable to AES.

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This versatility makes AES suitable

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for a range of applications, including securing files,

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data communications,

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and even encrypting storage on mobile devices.

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AES supports key sizes of 128, 192, and 256 bits,

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providing scalable security levels

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depending upon the sensitivity of the data.

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AES is commonly used in WPA2 and WPA3 Wi-Fi security,

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securing file transfers, and encrypting messaging apps.

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Additionally, modern processors,

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like those found in smartphones,

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often have built-in hardware acceleration for AES,

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allowing it to perform encryption tasks quickly

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without significant impact on performance.

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Second, we have the Data Encryption Standard, or DES,

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and Triple DES (3DES).

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The Data Encryption Standard was one

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of the earliest encryption standards,

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using a 56-bit key to encrypt 64-bit data blocks.

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Despite its initial popularity,

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DES's short key length made it vulnerable

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to brute force attacks, rendering it unsecure.

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To improve security, Triple DES was developed.

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Triple DES applies the DES algorithm three times

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using three different keys.

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This increases the effective key length to 112 bits,

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significantly enhancing security,

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but also slowing down the encryption process.

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Triple DES was widely adopted in banking and legacy systems

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but has largely been replaced by AES

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due to AES's superior performance and security.

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Despite being more secure than DES,

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Triple DES's repeated encryption steps make it slower

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and less efficient for modern applications.

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Third, we have Blowfish and Twofish.

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Blowfish is known for its speed and flexibility,

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with key lengths ranging from 32 to 448 bits.

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This adaptability made Blowfish popular

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in earlier software applications and encryption tools.

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However, it used a 64-bit block size,

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which can pose security risks

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when encrypting large volumes of data.

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Block sizes of 64 bits

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and below are no longer considered secure

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as they are vulnerable to collision attacks

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where identical blocks

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of data may produce the same ciphertext,

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especially when used within large data sets.

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This weakness makes Blowfish less suitable

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for securing extensive

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or high-security data compared to newer algorithms

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with larger block sizes.

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Twofish, a successor to Blowfish,

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was designed to address these limitations.

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Twofish encrypts data in 128-bit blocks

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using key sizes of up to 256 bits,

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providing enhanced security and faster performance.

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Fourth and finally, we have Rivest Cipher 4, or RC4,

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and ChaCha20.

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RC4 is a pure stream cipher that processes data one bit

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or byte at a time,

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making it extremely fast

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and efficient for real-time applications

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such as secure communications and streaming data.

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RC4 was once widely used

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in protocols like secure sockets layer, or SSL,

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and wired equivalent privacy, or WEP, for Wi-Fi.

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However, vulnerabilities were discovered

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that allowed attackers to exploit weaknesses

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in the initial key stream state of the algorithm.

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This is why we should no longer be using WEP

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in our Wi-Fi networks.

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So ChaCha20 was developed as a secure replacement for RC4.

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It uses a more robust design that avoids the pitfalls of RC4

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while maintaining high speed and efficiency.

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ChaCha20 is particularly popular

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in scenarios where low latency

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and strong security are required,

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such as internet protocols

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like transport layer security, or TLS,

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for secure web browsing.

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ChaCha20's resilience against cryptographic attacks

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and efficient performance on both high-end servers

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and low-power devices make it a preferred choice.

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So remember, symmetric encryption is a type of encryption

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that uses the same key for both encrypting

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and decrypting data.

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It is known for its speed and efficiency,

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making it ideal for securing large amounts

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of data very quickly.

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Symmetric encryption is divided into two main types,

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stream ciphers, which encrypt data bit by bit

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or byte by byte,

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and block ciphers, which encrypt data in fixed block sizes.

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Common symmetric encryption algorithms

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include the Advanced Encryption Standard, or AES,

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the Data Encryption Standard, or DES, Triple DES,

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Blowfish, Twofish, Rivest Cipher 4, or RC4,

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and a ChaCha20.

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Each algorithm has unique strengths and weaknesses,

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making them suitable for different applications

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and levels of security.