In this lesson,
we will learn about symmetric algorithms.
First, there are two basic types of encryption algorithms:
Symmetric and Asymmetric.
In this lesson, we'll focus on symmetric encryption.
Symmetric encryption algorithms are encryption methods
that result in the creation of a single key.
The resultant symmetric key is used for both encryption
and decryption.
Common symmetric encryption algorithms
include the Advanced Encryption Standard (AES),
the Data Encryption Standard (DES),
Triple DES, Blowfish, Twofish, Rivest Cipher 4 (RC4),
and ChaCha20.
Let's learn more about each
of these symmetric encryption algorithms.
But before we dive into the details
of symmetric encryption algorithms,
let's take a minute to define encryption.
Encryption is the process
of converting readable information, known as a plaintext,
into an unreadable form called ciphertext
using an encryption algorithm and a secret key.
This process is two-way,
meaning that encrypted data
can be decrypted back to plaintext with the correct key.
Now, for most folks,
this is a fairly simple thing to understand
because symmetric key encryption
works just like the things you use on a daily basis,
like a door lock on your house or your car.
After all, when you go home
and unlock your front door tonight,
you're going to be using a physical form
of symmetric key encryption.
If you share your house with somebody else,
like a spouse or a roommate,
you're both going to have your own copy of the same key,
and that same key is going to be used to both lock
and unlock the front door.
This makes it a symmetric key
because the exact same key is used to lock
and unlock the door.
Now, when you hear the word symmetric key,
I want you to remember that this refers
to both people having the same key.
Symmetric equals same.
So symmetric cryptography is an encryption method
where the same key is used for both encryption
and decryption of data,
making it efficient and fast,
ideal for securing large amounts of data very quickly.
Symmetric encryption is further divided
into two types of encryption methods:
Stream ciphers and Block ciphers.
Stream ciphers are a type of symmetric encryption
that encrypt data bit by bit
or byte by byte using a pseudo-random stream generated
by a secret key.
This approach allows stream ciphers
to encrypt data continuously,
making them perfect for real-time applications like audio
or video streaming,
where the total length of the data stream is unknown.
With stream ciphers,
the key stream generator produces
a pseudo-random bit stream,
which is then combined
with the plaintext being encrypted using an XOR,
or Exclusive OR operation, to create encrypted ciphertext.
Think of stream ciphers like a zipper on a jacket.
The key stream generator
is like one side of the zipper,
creating a series of teeth
that match up perfectly with the other side,
which is the plaintext that's being encrypted.
As the zipper, representing the XOR operation,
pulls the two sides together,
it locks them into a new tightly interwoven pattern,
creating a secure barrier, which represents the ciphertext.
Just like the zipper combines the teeth
to keep the jacket closed,
the XOR operation combines the key stream
and plaintext into a secure message.
The beauty of XOR is its reversibility.
Just like unzipping a zipper,
applying an XOR with the same key stream
to the ciphertext restores the original plaintext.
Overall, the security of a stream cipher
depends on the uniqueness of the key stream,
which, remember, is one side of the zipper
that is generated using an initialization vector.
An initialization vector, which changes constantly,
ensures that each key stream is unique
even when encrypting the same plaintext multiple times.
However, if the initialization vector is weak
or predictable, the encryption can be compromised.
For example, wired equivalent privacy, or WEP,
used a short 24-bit initialization vector,
making it vulnerable to brute force attacks
and rendering its encryption insecure.
Block ciphers are a type of symmetric encryption
that encrypt data in fixed-size blocks,
usually 64 or 128 bits, using a secret key.
This method means
that block ciphers process data in chunks,
making them ideal for applications like file encryption
and secure communications
where the data size is known and large.
The block cipher encryption process
involves breaking the plaintext into blocks,
applying the encryption algorithm to each block,
and combining the blocks to form the ciphertext.
Because block ciphers handle data in chunks,
they offer strong security through structured encryption.
Block ciphers use a combination of confusion
and diffusion techniques to secure the data.
Confusion makes the relationship between the key
and the ciphertext complex.
While diffusion spreads the plaintext information
throughout ciphertext,
ensuring that even a small change in the plaintext
or key significantly alters the output.
You can think of confusion
and diffusion techniques like writing a secret message
into a puzzle with letters on the puzzle pieces.
Confusion is like scrambling the letters of the message,
so the words are hard to recognize
even if you can see them all.
Diffusion is like scattering those scramble pieces
all across the puzzle,
making it difficult
to spot any coherent groups of the letters.
This dual approach of confusion
and diffusion makes block ciphers resilient to attacks
that aim to reveal the key
or plaintext by analyzing patterns.
Unlike stream ciphers, which encrypt continuously,
block ciphers apply multiple rounds of these transformations
to each block,
enhancing the security of the encrypted data.
A critical aspect of block ciphers
is their use of different modes of operation,
which define how each block interacts with other blocks
during the encryption.
Common modes include electronic code book, or ECB,
cipher block chaining, or CBC,
and the Galois/Counter Mode, or GCM.
The security of a block cipher depends on its algorithm,
key length, and mode of operation.
Now, let's categorize some specific encryption algorithms.
First, we have the Advanced Encryption Standard, or AES.
AES is one of the most widely used
symmetric encryption algorithms today.
AES can operate as both a block cipher,
encrypting fixed-size 128-bit blocks of data,
and as a stream cipher,
using configurations like Galois/Counter Mode, or GCM,
to handle continuous data streams.
The ability to operate as both a block
or stream cipher is unique and distinguishable to AES.
This versatility makes AES suitable
for a range of applications, including securing files,
data communications,
and even encrypting storage on mobile devices.
AES supports key sizes of 128, 192, and 256 bits,
providing scalable security levels
depending upon the sensitivity of the data.
AES is commonly used in WPA2 and WPA3 Wi-Fi security,
securing file transfers, and encrypting messaging apps.
Additionally, modern processors,
like those found in smartphones,
often have built-in hardware acceleration for AES,
allowing it to perform encryption tasks quickly
without significant impact on performance.
Second, we have the Data Encryption Standard, or DES,
and Triple DES (3DES).
The Data Encryption Standard was one
of the earliest encryption standards,
using a 56-bit key to encrypt 64-bit data blocks.
Despite its initial popularity,
DES's short key length made it vulnerable
to brute force attacks, rendering it unsecure.
To improve security, Triple DES was developed.
Triple DES applies the DES algorithm three times
using three different keys.
This increases the effective key length to 112 bits,
significantly enhancing security,
but also slowing down the encryption process.
Triple DES was widely adopted in banking and legacy systems
but has largely been replaced by AES
due to AES's superior performance and security.
Despite being more secure than DES,
Triple DES's repeated encryption steps make it slower
and less efficient for modern applications.
Third, we have Blowfish and Twofish.
Blowfish is known for its speed and flexibility,
with key lengths ranging from 32 to 448 bits.
This adaptability made Blowfish popular
in earlier software applications and encryption tools.
However, it used a 64-bit block size,
which can pose security risks
when encrypting large volumes of data.
Block sizes of 64 bits
and below are no longer considered secure
as they are vulnerable to collision attacks
where identical blocks
of data may produce the same ciphertext,
especially when used within large data sets.
This weakness makes Blowfish less suitable
for securing extensive
or high-security data compared to newer algorithms
with larger block sizes.
Twofish, a successor to Blowfish,
was designed to address these limitations.
Twofish encrypts data in 128-bit blocks
using key sizes of up to 256 bits,
providing enhanced security and faster performance.
Fourth and finally, we have Rivest Cipher 4, or RC4,
and ChaCha20.
RC4 is a pure stream cipher that processes data one bit
or byte at a time,
making it extremely fast
and efficient for real-time applications
such as secure communications and streaming data.
RC4 was once widely used
in protocols like secure sockets layer, or SSL,
and wired equivalent privacy, or WEP, for Wi-Fi.
However, vulnerabilities were discovered
that allowed attackers to exploit weaknesses
in the initial key stream state of the algorithm.
This is why we should no longer be using WEP
in our Wi-Fi networks.
So ChaCha20 was developed as a secure replacement for RC4.
It uses a more robust design that avoids the pitfalls of RC4
while maintaining high speed and efficiency.
ChaCha20 is particularly popular
in scenarios where low latency
and strong security are required,
such as internet protocols
like transport layer security, or TLS,
for secure web browsing.
ChaCha20's resilience against cryptographic attacks
and efficient performance on both high-end servers
and low-power devices make it a preferred choice.
So remember, symmetric encryption is a type of encryption
that uses the same key for both encrypting
and decrypting data.
It is known for its speed and efficiency,
making it ideal for securing large amounts
of data very quickly.
Symmetric encryption is divided into two main types,
stream ciphers, which encrypt data bit by bit
or byte by byte,
and block ciphers, which encrypt data in fixed block sizes.
Common symmetric encryption algorithms
include the Advanced Encryption Standard, or AES,
the Data Encryption Standard, or DES, Triple DES,
Blowfish, Twofish, Rivest Cipher 4, or RC4,
and a ChaCha20.
Each algorithm has unique strengths and weaknesses,
making them suitable for different applications
and levels of security.