The difference between symmetric and asymmetric encryption

If you’re familiar with web encryption or SSL certificates, you’ve probably heard the terms symmetric encryption and asymmetric encryption at some point in your travels. If you’ve ever wondered about what these terms mean, what differentiates them, and which form of encryption is better than the other, then you’ve come to the right place. In this article, we’ll go through the ins and outs of both forms of encryption and which is the most secure option.

But first, a primer on encryption. 

How encryption works

As you may already know, encryption is what happens when someone visits a website with an SSL certificate installed via their web browser. An SSL helps create a secure connection between a website’s server and a browser. Any information sent over this connection is encrypted, which means that regular plaintext is turned into ciphertext, rendering it unreadable. 

Encryption works through the use of algorithms and keys. An algorithm is a set of mathematical steps that must be followed to carry out a specific process. Central to encryption algorithms is the use of keys. Keys are random strings of text and numbers that are used to encrypt (render unreadable) data and decrypt (make it readable again) data.

Let’s use a very basic example. Say someone wants to send a message to customer support using a chat function on an SSL-secured website. The person hits send on the message, and a key will encrypt or “lock” the message while it’s in transit so that it can’t be read by anyone who doesn’t have the correct key. When the recipient receives the message, a key is used to decrypt or “unlock” the message. 

But how do the server and browser on each end of the connection have the correct key for encrypting and decrypting data? The answer to that question is actually the main difference between symmetric and asymmetric encryption. First, let’s take a look at how symmetric encryption works. 

Defining symmetric encryption

In symmetric encryption, data is encrypted and decrypted by the same secret key that is shared by the recipient and the sender. This means that the key needs to be shared with the recipient in a secure way so that they and nobody else has access to it. It’s a high-speed method of encryption.

Defining asymmetric encryption

A more complicated process, asymmetric encryption works by using two different but mathematically related keys, the public key and the private key, to encrypt and decrypt data. The public key, which anyone can access, is used to encrypt the data. Only the complementary private key can be used to decrypt the message. 

Symmetric vs. Asymmetric encryption — the key differences

While symmetric encryption uses a single shared key to encrypt and decrypt data, asymmetric uses two separate keys. Symmetric encryption uses shorter keys (usually 128 or 256 bits). In comparison, asymmetric keys are a lot longer (sometimes 2048 bits or longer). This is why asymmetric encryption takes a little bit longer than symmetric. 

However, although symmetric encryption is a faster, more straightforward process, it’s more vulnerable to security risks due to the nature of keeping the shared key a secret. Meanwhile, asymmetric encryption may be a more complex and resultantly slower process, but it’s ultimately a far more secure encryption method. Unlike symmetric encryption, it can authenticate identities, which makes it ideal for messages sent between two parties previously unknown to each other (for example, a user visiting a website for the first time). 

On the other hand, symmetric encryption tends to mostly be used in internal IT security environments, where the secret key can be shared safely and securely between recipient and sender. 

TLS 1.3 and working in tandem

By now, you probably have a better idea of the differences between symmetric and asymmetric encryption and what kind of environments each is best suited to. But when it comes to SSL certificates, you don’t need to choose between the two. This is because TLS 1.3 — the current cryptographic protocol that underpins how SSLs work — uses a combination of both symmetric and asymmetric encryption. How exactly does that work?

For a user visiting a HTTPS website for the first time, the initial connection is made using asymmetric encryption. During the SSL handshake, the website server sends the client (the user’s browser) its public key. The client authenticates the public key, then uses it to create what’s known as a pre-master secret key. It encrypts this key with the public key and sends it back to the server. The server will then decrypt the pre-master secret key using the related private key. This pre-master secret key will be used to encrypt communications between the client and the server from this point forward, switching from asymmetric encryption to symmetric encryption.

By using this hybrid encryption system, TLS 1.3 has both the security benefits of asymmetric encryption with all the speed of symmetric encryption. 

Wrap up

Hopefully, you leave this article with a better understanding of the differences between symmetric and asymmetric encryption, as well as their strengths and weaknesses. While both types of encryption have pros and cons, they are equally important in their own right, particularly when used in combination with each other. 
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