Cryptography systems are currently divided into two main fields of study: symmetric and asymmetric cryptography. While symmetric encryption is often used interchangeably with symmetric encryption, asymmetric encryption encompasses two primary use cases: asymmetric encryption and digital signatures.

Therefore, we can represent the groups as follows:

  • Symmetric key encryption

    • Symmetric encryption

  • Asymmetric cryptography (or public key cryptography)

    • Asymmetric encryption (or public key encryption)

    • Digital signatures (may or may not include encryption)

This article will focus on symmetric and asymmetric encryption algorithms.


Symmetric vs. Symmetric Encryption Asymmetric Encryption

Encryption algorithms are often divided into two categories, known as symmetric and asymmetric encryption. The fundamental difference between these two encryption methods is based on the fact that symmetric encryption algorithms make use of a single key, while asymmetric encryption makes use of two different but related keys. Such a distinction, although seemingly simple, points out the functional differences between the two forms of encryption techniques and the ways in which they are used.


Understanding encryption keys

In cryptography, encryption algorithms generate keys as a series of bits that are used to encrypt or decrypt information. The way in which these keys are used is responsible for the difference between symmetric and asymmetric encryption.

While symmetric encryption algorithms use the same key to perform encryption and decryption functions, the asymmetric encryption algorithm uses one key to encrypt data and another key to decrypt it. In asymmetric systems, the key used for encryption is known as the public key and can be freely shared with others. On the other hand, the key used to decrypt is the private key and must be kept secret.

For example, if Alice sends Bob a message protected by symmetric encryption, she will need to share with Bob the same key she used to encrypt it, so that he can decrypt the message. This means that if a malicious actor intercepts the key, they will have access to the encrypted message.

However, if Alice uses an asymmetric system, she will encrypt the message with Bob's public key, so that Bob can decrypt it with his private key. Thus, asymmetric encryption offers a higher level of security, because even if messages are intercepted and the public key is found, they will not be able to decrypt the message.


Key length

Another functional difference between symmetric and asymmetric encryption is related to the length of the keys, which is measured in bits and is directly related to the level of security provided by each encryption algorithm.

In symmetric systems, keys are selected randomly and their lengths are typically set to 128 or 256 bits, depending on the level of security required. In asymmetric encryption, however, there must be a mathematical relationship between the public and private keys, that is, there is a mathematical pattern between the two. Because this pattern can potentially be exploited by attackers to break encryption, asymmetric keys need to be much longer in length to provide an equivalent level of security. The difference related to key length is so great that a 128-bit symmetric key and a 2048-bit asymmetric key provide approximately equal levels of security.

 

Advantages and disadvantages

Both types of encryption have relative advantages and disadvantages. Symmetric encryption algorithms are much faster and require less computational processing power but their main weakness is key distribution. As the same key is used to encrypt and decrypt information, this key must be distributed to anyone who needs to access the data, which naturally generates an increase in security-related risks (as illustrated previously).

On the other hand, asymmetric encryption solves the key distribution problem by using public keys for encryption and private keys for decryption. The disadvantage, however, is that asymmetric encryption systems are very slow compared to symmetric systems and require much more processing power due to their longer key lengths.


Use cases

Symmetric encryption

Due to its greater speed, symmetric encryption is widely used to protect information on many modern computer systems. For example, the Advanced Encryption Standard (AES) is used by the United States government to encrypt classified and confidential information. AES replaced the Data Encryption Standard (DES), which was developed in the 1970s as a standard for symmetric encryption.


Asymmetric encryption

Asymmetric encryption can be applied to systems in which a larger number of users may need to encrypt and decrypt a message or a set of data, especially when speed and computational processing capacity are not the main concerns. An example of this system is encrypted email, in which a public key can be used to encrypt the message and a private key can be used to decrypt it.


Hybrid systems

In many applications, symmetric and asymmetric encryption are used together. Typical examples of such hybrid systems are the Security Sockets Layer (SSL) and Transport Layer Security (TLS) encryption protocols, which were designed to provide secure communication on the Internet. SSL protocols are currently considered insecure and their use should be discontinued. On the other hand, TLS protocols are considered secure and have been widely used by all major web browsers.


Do cryptocurrencies use encryption?

Encryption techniques are used in many cryptocurrency wallets as a way to provide higher levels of security to end users. Encryption algorithms are applied, for example, when users set a password for their cryptocurrency wallet, which means that the file used to access the software has been encrypted.

However, because Bitcoin and other cryptocurrencies use public-private key pairs, many mistakenly believe that blockchain systems make use of asymmetric encryption algorithms. As mentioned earlier, asymmetric encryption and digital signatures are the two main use cases for asymmetric encryption (public key encryption).

Therefore, not all digital signature systems use encryption techniques, even if they present a public key and a private key. In fact, a message can be digitally signed without being encrypted. RSA is an example of an algorithm that can be used to sign encrypted messages but the digital signature algorithm used by Bitcoin (called ECDSA) does not use encryption.


Final considerations

In today's digitally dependent world, both symmetric and asymmetric encryption play important roles in keeping information confidential and communications secure. Although both can be useful, each has its own advantages and disadvantages and is therefore used in different applications. As the science of cryptography continues to evolve to defend against newer and more sophisticated threats, symmetric and asymmetric cryptographic systems will likely continue to be relevant to computer security.