# Symmetric Key Cryptography Explained

## Basics

Symmetric key cryptography, also known as symmetric encryption, involves using a single key for both encryption and decryption of messages. It has been used for several decades to enable secure communication between governments and militaries. Nowadays, symmetric key algorithms are widely used in different computer systems to improve data security.

## How Does Symmetric Encryption Work?

Symmetric encryption involves the use of a single key that is shared between two or more parties for encrypting and decrypting messages or data. The process of encryption involves running the input, also known as plaintext, through an algorithm called a cipher, which produces the output, known as ciphertext. The key is then used to decrypt the ciphertext back into plaintext.

The strength of symmetric encryption systems depends on the difficulty of randomly guessing the key to brute force the encryption. Longer keys make brute force attacks harder to execute, and 256-bit keys are considered highly secure and resistant to quantum computer attacks. For instance, a 128-bit key would take billions of years to guess using common computer hardware.

Block and stream ciphers are two common types of symmetric encryption schemes. Block ciphers encrypt predetermined blocks of data using the corresponding key and encryption algorithm, while stream ciphers encrypt data in increments of 1 bit at a time. Both schemes can be used to enhance data security in various computer systems.

## Symmetric vs. Asymmetric

Modern computer systems employ two major methods of data encryption: symmetric and asymmetric encryption. Symmetric encryption uses a single key to encrypt and decrypt data, while asymmetric encryption, also known as public key cryptography, employs two keys: a public key and a private key.

One key difference between the two methods is that asymmetric encryption is more complex and slower compared to symmetric encryption. Asymmetric encryption requires longer keys to provide similar security to shorter symmetric keys, as the keys used in the asymmetric scheme are mathematically related to some degree.

In asymmetric encryption, the public key can be shared publicly, while the private key must be kept private. On the other hand, in symmetric encryption, the same key is used for both encryption and decryption, making it faster and simpler. Understanding the differences between these two encryption methods is essential in enhancing data security in computer systems.

## How Is It Currently Used?

Modern computer systems widely use symmetric encryption algorithms to ensure data security and user privacy. The Advanced Encryption Standard (AES) is a popular example of a symmetric cipher that is used in secure messaging applications and cloud storage. Hardware-based symmetric encryption schemes often rely on AES 256, which is a specific variant of the Advanced Encryption Standard with a 256-bit key size.

It is important to note that Bitcoin's blockchain does not use encryption, despite common misconceptions. Instead, it uses Elliptic Curve Digital Signature Algorithm (ECDSA), a digital signatures algorithm that generates digital signatures without encryption. Although ECDSA is based on elliptic-curve cryptography (ECC), which can be used for encryption, the ECDSA algorithm itself cannot be used for encryption.

## Pros and Cons

Encrypting and decrypting messages using symmetric encryption algorithms provide high levels of security and speed. They are also logistically advantageous, requiring less computing power than asymmetric systems, and their security can be scaled up by increasing key lengths.

However, a major disadvantage of symmetric encryption is the problem of transmitting keys, which can be intercepted and compromise the security of encrypted data. To solve this, many web protocols use a combination of symmetric and asymmetric encryption, such as the TLS cryptographic protocol used to secure large portions of the modern internet. Nevertheless, all types of computer encryption are susceptible to vulnerabilities due to improper implementation, which can create weaknesses that cyber attackers can exploit.

## Conclusion

Symmetric encryption plays a crucial role in modern computer security due to its high level of security and speed, making it ideal for a variety of applications, including securing internet traffic and protecting data stored on cloud servers. While there are some concerns with transmitting keys securely, symmetric encryption remains an essential part of computer security and is often paired with asymmetric encryption to create secure connections. Overall, the simplicity and effectiveness of symmetric encryption ensure that it will continue to be a critical tool in securing digital information.