What Is Symmetric Key Cryptography?

Symmetric key cryptography (also known as symmetric encryption) is a form of encryption system that uses the same key to encrypt and decrypt communications. In recent decades, this type of encoding information has been widely employed to permit secret communication between governments and militaries. Symmetric key algorithms are now commonly used in numerous sorts of computer systems to improve data security.

How does symmetric encryption work?

Symmetric encryption techniques use a single key shared by two or more users. The same key is used to encrypt and decrypt the plaintext (which represents the message or data being encoded). Encryption is accomplished by passing plaintext (input) through an encryption technique known as a cypher, which produces ciphertext (output). If the encryption technique is strong enough, the only way to read or access the information contained in the ciphertext is to decrypt it with the associated key. Decryption is the process of transforming ciphertext back to plaintext. The security of symmetric encryption systems is determined by how difficult it is to brute force the appropriate key at random. Using standard computer hardware, guessing a 128-bit key would take billions of years. The longer the encryption key, the more difficult it is to crack. Keys of 256 bits are often considered to be highly secure and theoretically immune to quantum computer brute force assaults. 

Block and stream cyphers are the foundations of two of the most widely used symmetric encryption techniques today. Block cyphers divide data into predefined blocks, and each block is encrypted with the associated key and encryption method (for example, 128-bit plaintext is encrypted into 128-bit ciphertext). Stream cyphers, on the other hand, encrypt plaintext data in 1-bit increments rather than blocks (1-bit plaintext is encrypted into 1-bit ciphertext at a time).

Symmetric vs. asymmetric encryption

In modern computer systems, symmetric encryption is one of the two primary methods of encrypting data. The other significant application of public key cryptography is asymmetric encryption. The fundamental distinction between these methods is that asymmetric systems require two keys rather than the one key used by symmetric schemes. One key can be disclosed publicly (public key), while the other must be kept private (private key). The use of two keys rather than one results in several functional changes between symmetric and asymmetric encryption. Asymmetric algorithms are more complex and take longer to execute than symmetric algorithms. Because the public and private keys used in asymmetric encryption are mathematically related, the keys themselves must be significantly longer to give the same level of security as shorter symmetric keys.

Uses in modern computer systems

Many current computer systems use symmetric encryption methods to improve data security and user privacy. A symmetric cypher is the Advanced Encryption Standard (AES), which is commonly used in secure communications apps and cloud storage. AES can be implemented directly in computer hardware, in addition to software implementations. Hardware-based symmetric encryption techniques often use AES 256, a variation of the Advanced Encryption Standard with a key size of 256 bits.

It is important to note that, contrary to popular belief, Bitcoin’s blockchain does not use encryption. Instead, it employs the Elliptic Curve Digital Signature method (ECDSA), a type of digital signature method (DSA) that generates digital signatures without the use of encryption. The ECDSA is based on elliptic-curve cryptography (ECC), which can be used for a variety of applications such as encryption, digital signatures, and pseudo-random number generators. The ECDSA, on the other hand, cannot be used for encryption at all.

Advantages and disadvantages

Symmetric algorithms give a reasonable level of security while allowing messages to be encrypted and decrypted fast. Symmetric systems have a logistical advantage in that they demand less computational resources than asymmetric systems. Furthermore, the level of security given by symmetric encryption can be increased simply by increasing key lengths. The difficulty of cracking a symmetric key via a brute force assault increases exponentially for every single bit added to its length. While symmetric encryption has many advantages, it has one big disadvantage: the inherent challenge of transferring the keys used to encrypt and decrypt data. These keys are vulnerable to being intercepted by malevolent third parties when shared over an unprotected connection. When an unauthorized user obtains access to a specific symmetric key, the security of any data encrypted with that key is jeopardized. Many web protocols utilize a combination of symmetric and asymmetric encryption to establish secure connections to address this issue. The Transport Layer Security (TLS) cryptographic protocol, which is used to secure vast swaths of the modern internet, is one of the most known examples of such a hybrid system.

Closing thought

It should also be mentioned that all methods of computer encryption are vulnerable to flaws caused by incorrect implementation. While a sufficiently lengthy key can render a brute force attack mathematically impossible, programming flaws frequently generate weaknesses that open the door to cyber-attacks. 

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