Symmetric and asymmetric encryption: a comparative analysis

In the field of modern cryptography, two main branches of study are distinguished: symmetric cryptography and asymmetric cryptography. Symmetric encryption is often equated with symmetric cryptography, while asymmetric cryptography encompasses two fundamental applications: asymmetric encryption and digital signatures.

This classification can be represented as follows:

Symmetric key cryptography includes symmetric encryption, while asymmetric cryptography ( also known as public key cryptography ) encompasses both asymmetric encryption and digital signatures, which may or may not involve the use of encryption.

In this article, we will focus on examining symmetric and asymmetric encryption algorithms.

Symmetric vs. Asymmetric Encryption

Encryption algorithms are generally categorized into two groups: symmetric and asymmetric encryption. The fundamental distinction between the two methods lies in that symmetric algorithms use a single key, while asymmetric ones use two different but related keys. This seemingly simple difference has significant functional implications and determines how these encryption methods are applied.

Relationship between keys

In the field of cryptography, encryption algorithms generate keys in the form of bit sequences that are used to encode and decode information. The way these keys are used distinguishes symmetric methods from asymmetric ones.

While symmetric algorithms use the same key for both operations, asymmetric ones employ one key for encryption and another for decryption. In asymmetric systems, the encryption key, also known as the public key, can be shared openly. In contrast, the decryption key is private and must be kept secret.

For example, if Ana sends Carlos a message protected with symmetric encryption, she will need to provide him with the same key she used to encrypt it so that he can read it. This means that if an attacker intercepts the communication, they could access the encrypted information.

On the other hand, if Ana uses the asymmetric method, she will encrypt the message with Carlos's public key, who will be able to decrypt it with his private key. In this way, asymmetric encryption offers a higher level of security, since even if someone intercepts the messages and obtains the public key, they will not be able to do anything with it.

Key Length

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

In symmetric systems, the keys are randomly chosen and their commonly accepted length ranges from 128 to 256 bits, depending on the required level of security. In asymmetric encryption, there must be a mathematical relationship between the public and private keys, meaning they are linked by a specific mathematical formula. For this reason, attackers can exploit this pattern to attempt to break the encryption, which implies that asymmetric keys must be significantly longer to provide an equivalent level of security. The difference in key length is so notable that a 128-bit symmetric key and a 2048-bit asymmetric key provide approximately the same level of security.

Advantages and disadvantages

These two types of encryption have advantages and disadvantages over each other. Symmetric encryption algorithms are considerably faster and require less computing power, but their main drawback is key distribution. Since the same key is used to encrypt and decrypt information, it must be shared with everyone who needs access, which naturally poses certain risks (as mentioned earlier).

Asymmetric encryption, for its part, solves the key distribution problem by using public keys for encryption and private keys for decryption. The downside is that asymmetric systems are significantly slower compared to symmetric ones and require much more processing power due to the length of the keys.

Practical Applications

Symmetric encryption

Due to its speed, symmetric encryption is widely used to protect information in numerous contemporary computer systems. For example, the U.S. government employs the Advanced Encryption Standard (AES) to encrypt classified information. AES replaced the older Data Encryption Standard (DES), developed in the 1970s as a symmetric encryption standard.

Asymmetric encryption

Asymmetric encryption can be applied in systems where multiple users need to encrypt and decrypt messages or data packets, especially when speed and processing power are not a priority. A simple example of this type of system is encrypted email, where a public key can be used to encrypt messages and a private key to decrypt them.

Hybrid systems

In numerous applications, symmetric and asymmetric encryption are combined. A good example of these hybrid systems is the cryptographic protocols Security Sockets Layer (SSL) and Transport Layer Security (TLS), developed to provide secure communications over the Internet. Currently, SSL protocols are considered insecure and their use is not recommended. In contrast, TLS protocols are considered secure and are widely used by all modern web browsers.

Use of encryption in cryptocurrencies

Numerous cryptocurrency wallets implement encryption methods as a way to provide a higher level of security to end users. Encryption algorithms are applied when the user sets a password for their wallet file, which is used to access the software.

However, because Gate and other cryptocurrency platforms use a pair of public and private keys, there is a misconception that blockchain systems employ asymmetric encryption algorithms. Nevertheless, as mentioned earlier, asymmetric encryption and digital signatures are the two main use cases of asymmetric cryptography (public key cryptography).

As a result, not all digital signature systems use encryption, even if they provide public and private keys. In fact, a message can be digitally signed without employing encryption. RSA is an example of an algorithm that can be used to sign encrypted messages, but the digital signature algorithm used in Bitcoin ( called ECDSA) does not involve encryption.

Final reflections

Both symmetric and asymmetric encryption play a crucial role in ensuring the security of information and confidential communications in today's digital environment. Both types of encryption can be useful, as each has its own strengths and weaknesses, which is why they are applied in different scenarios. As cryptography as a science continues to evolve to protect against more recent and serious threats, symmetric and asymmetric cryptographic systems will remain relevant for computer security.