Symmetric vs Asymmetric Encryption: What’s the difference?

In this blog post, we explain the major differences between symmetric vs asymmetric encryption. This article will also explain which encryption method you should use.

Key Takeaways

• Symmetric encryption uses a single shared key (a password or passphrase) to both encrypt and decrypt data. It is fast and lightweight, making it ideal for large files and quick exchanges.
• Asymmetric encryption uses a key pair: a public key to encrypt and a private key to decrypt. It removes the need to share a secret in advance, but is slower and more resource-intensive.
• When to choose which: use symmetric (password-based) encryption when your recipient does not have an OpenPGP public key, or when speed matters. Use asymmetric (public-key) encryption when you can verify your recipient’s public key and need features such as digital signatures.
• Best practice: combine both methods. Most modern protocols, including OpenPGP, use a hybrid approach where a symmetric session key encrypts the message and asymmetric encryption protects that session key.
• For step-by-step guidance, see How to send encrypted emails and Email encryption for small businesses.

Some words about different encryption methods

In today’s world, scammers and other cybercriminals are becoming increasingly present, affecting millions of users. To prevent these individuals from stealing our data, we have to encrypt everything. Luckily, there are three different encryption methods that you can use: symmetric encryption, asymmetric encryption, and hash functions (Keyless).

Right now, we’ll focus on symmetric encryption vs asymmetric encryption and leave the third (hash functions) for a later time.

Mailfence uses symmetric and asymmetric encryption, as each method has pros and cons. You will learn more about that later. Both encryption methods use keys to encrypt and decrypt data. The main difference is that symmetric encryption uses the same key to encrypt and decrypt data. In contrast, asymmetric encryption uses a pair of keys – a public key to encrypt data and a private key to decrypt information.

What is symmetric encryption?

Symmetric encryption, aka symmetric key cryptography, uses one single key to encrypt and decrypt data. You have to share this key with the recipient. Let’s say you want to sent “I love you Mom”. You would write your email, then set a secret key, or password, to encrypt it. Then, you would simply send it. When mom receives the message, she would enter the same secret key to decrypt the email.

Pros and cons of symmetric encryption

Let’s take a look at some of the pros and cons of symmetric encryption:

Pros:

• Easier to implement and use
• Faster than asymmetric encryption
• Less resource-intensive
• Good for handling and transferring larger amounts of data

Cons:

• Loss of a key will mean that data encrypted with it is compromised
• Key has to be shared securely with the other party

How does Mailfence incorporate symmetric key cryptography?

Mailfence offers password-encrypted messages (PEM) based on symmetric encryption. Our solution allows you to set a password hint that helps the recipient decrypt the message. You can share your passphrase via SMS, a phone call, or during a physical meeting.

Also, with Mailfence’s PEM, you can set an expiration date for the email. After the expiration date, the email cannot be decrypted any more. Furthermore, we store password-encrypted messages in a zero-knowledge environment and encrypt them with your password. That way, only you and the intended recipient can access the message.

In case you would like to know more, visit our dedicated knowledge base.

Best practices for password-encrypted messages:

1. Never use your OpenPGP passphrase
2. Never use your Mailfence account password
3. If you are sending a sensitive message, make sure unwanted readers cannot guess your password

There are many symmetric encryption algorithms, such as AES, DES, 3DES, IDEA. For your information, Mailfence uses AES in combination with other ciphers.

What is asymmetric encryption?

As stated earlier, public-key encryption requires two keys to work. Firstly, a public key must be made public to encrypt the data. Also, a private key is used to decrypt the data. It sounds complicated enough, but we made it easy to use. Let me break it down. Basically, it would be like sharing lockers with anyone wanting to contact you, whereas you’re the only one with access to the key.

The public key and the private key are not the same thing, but they are related. You write your message, then encrypt it with the recipient’s public key. After that, if the recipient wants to decrypt your message, they would have to do it with their private key. Keep the private key private at all times. The best practice would be to store it locally. One requires greater knowledge than the average person to make this happen.

The emailing software of the recipient will see if the private key corresponds with the public key, and then it will prompt the user to type the passphrase to decrypt the message.

Some best practices for asymmetric encryption:

1. Use 2048-bit or longer keys
2. Store your private key locally, so you don’t forget it
3. Don’t share your private key with anyone

Creating strong keys is the foundation of asymmetric encryption. A good encryption practice would be to use multiple encryption methods instead of just one. Not everyone knows how to use public-key encryption, so there may be occasions you have to use different encryption methods.

Mailfence uses asymmetric encryption based on the RSA-algorithm for OpenPGP-based keys. ECC (Curve 25519) algorithm for OpenPGP-based keys is also supported.

Pros and cons of asymmetric encryption

Asymmetric encryption also has its advantages and disadvantages. Let’s take a look at what they are:

Pros:

• Data can only be decrypted using the private key held by the owner
• If the public key is lost or stolen, data won’t be compromised
• Provides authentication and non-repudiation in addition to confidentiality

Cons:

• It’s slower than symmetric encryption
• Uses more resources
• If the private key is lost, there is no way to retrieve it

How Mailfence Uses Asymmetric Encryption

Mailfence supports asymmetric encryption based on the OpenPGP standard (RFC 4880). You can generate and manage your OpenPGP key pair directly within Mailfence. Both RSA and ECC (Curve 25519) algorithms are supported.

Creating strong keys is the foundation of asymmetric encryption. Not everyone is familiar with public-key encryption, so there will be occasions when you need to fall back on password-based (symmetric) encryption instead.

Which encryption should you use?

The right method depends on your situation. Here is a practical guide:

Use symmetric (password-based) encryption when:

• Your recipient does not have an OpenPGP public key
• You need to send a quick, one-off encrypted message
• You are transferring large files and speed matters

Use asymmetric (public-key) encryption when:

• You have your recipient’s verified OpenPGP public key
• You need non-repudiation, such as proof the sender cannot deny sending
• You want to combine encryption with digital signatures for maximum security

Consider a hybrid approach for the best of both worlds. In hybrid encryption, a random symmetric key encrypts the message (for speed), and asymmetric encryption protects that symmetric key (for secure key exchange). This is how most modern protocols, including OpenPGP and TLS, work in practice.

For more detail, see our guides on how to send encrypted emails and email encryption for small businesses.

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