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Symmetric EncryptionvsPublic-Key Cryptography
What is the difference between symmetric and asymmetric encryption?
Updated 2 min read6 differences
In short
Symmetric encryption uses one shared secret key and is fast, while asymmetric uses a public and a private key, which solves key sharing but is much slower.
Symmetric Encryption
Symmetric encryption uses the same secret key to encrypt and decrypt data; it is fast, so it protects most stored and transmitted data, usually with AES.
Read the page on Symmetric EncryptionPublic-Key Cryptography
Public-key cryptography is a method that uses a pair of linked keys, a public key anyone can see and a private key kept secret, to encrypt and sign data.
Read the page on Public-Key CryptographySymmetric Encryption and Public-Key Cryptography compared
| Aspect | Symmetric Encryption | Public-Key Cryptography |
|---|---|---|
| Keys | One shared secret key | A public and private key pair |
| Speed | Very fast | Much slower |
| Key sharing | Hard: the secret must be exchanged safely | Easy: the public key can be published |
| Also provides | Encryption, plus authentication with modes like GCM | Digital signatures and key exchange |
| Typical key size | 128 or 256 bits | 2048+ bits for RSA, 256 bits for elliptic curves |
| Examples | AES, ChaCha20 | RSA, ECDSA, Ed25519, X25519 |
The difference, explained
With symmetric encryption, such as AES or ChaCha20, the same key locks and unlocks the data. It is extremely fast and protects almost all stored and transmitted data: disks, databases, backups and the bulk of every HTTPS connection. Its weakness is distribution: both sides must already share the secret key, and anyone who intercepts it can read everything.
Asymmetric, or public-key, cryptography uses a key pair. The public key can be shared with anyone; data encrypted with it can only be decrypted with the matching private key, which never leaves its owner. The same key pairs create digital signatures, where the private key signs and anyone can verify with the public key. RSA, published in 1977, and elliptic-curve algorithms are the main families.
Real systems combine them. In a TLS handshake, the browser and server use asymmetric cryptography to verify the server's certificate and agree on a fresh symmetric key, then switch to fast symmetric encryption for the actual traffic. Messaging apps, email encryption and VPNs follow the same hybrid pattern.
A common misconception is that asymmetric encryption is stronger because it is more complex. A 128-bit AES key is considered secure, while RSA needs keys of thousands of bits for comparable strength. Each solves a different problem: symmetric keys protect data efficiently, asymmetric keys solve how to share keys and prove identity.
Which one should you use?
Choose Symmetric Encryption when…
- You encrypt large amounts of data, such as files, disks or traffic.
- Both sides already share a key, or a key manager holds it.
- Performance matters.
Choose Public-Key Cryptography when…
- You need to agree on a key with someone over an insecure channel.
- You need digital signatures to prove who sent something.
- Many people must be able to encrypt data for one recipient.
Readers ask
Does HTTPS use symmetric or asymmetric encryption?
Both. The TLS handshake uses asymmetric cryptography to authenticate the server and agree on keys, then the connection's data is encrypted with fast symmetric encryption.
Why not use asymmetric encryption for everything?
Because it is far slower and limited in how much data it can encrypt directly. Using it only to exchange a symmetric key gives the best of both.
Is AES symmetric?
Yes. AES is the standard symmetric cipher, using the same key to encrypt and decrypt, with key sizes of 128, 192 or 256 bits.