What's the difference between AES and RSA?

AES is symmetric — one shared key locks and unlocks, and it's fast enough to encrypt large data. RSA is asymmetric — a public key locks and a separate private key unlocks, which solves how two strangers agree on a key, but it's too slow for bulk data. They're used together: RSA exchanges the key, AES encrypts the data.

Which is more secure, AES or RSA?

Neither is 'more secure' — they do different jobs. AES-256 and a properly sized RSA (or elliptic-curve) key are both considered unbreakable by foreseeable computing. Security comes from using each for what it's for: asymmetric to exchange a key safely, symmetric to encrypt the actual data quickly.

Why not just use RSA for everything?

RSA is orders of magnitude slower than AES and impractical for encrypting large amounts of data. It's used to encrypt one small thing — the AES key — after which the fast AES cipher does the heavy lifting. Using RSA for bulk data would make everything crawl.

Does HTTPS use AES or RSA?

Both. When your browser connects, an asymmetric handshake (RSA or an elliptic-curve equivalent) securely exchanges a random AES key, and then all the actual page data is encrypted with that fast AES key. Asymmetric handles the introduction; symmetric does the work.

AES vs RSA: symmetric and asymmetric encryption explained

They're not competitors — they solve different problems

The framing 'AES vs RSA' is misleading, because they aren't racing. They're two tools built for two different jobs, and almost every secure system you touch uses both at once. AES is fast and encrypts your actual data. RSA is slow and solves the problem AES can't: how two people who have never met agree on a key without anyone listening in able to steal it.

Understanding why you need both is the whole point, so start with what each one is.

Symmetric encryption (AES): one shared key

Symmetric means both sides use the same key — to lock and to unlock. AES is the symmetric standard: it's extremely fast, it can encrypt gigabytes without breaking a sweat, and at 256-bit key length it's considered unbreakable by any foreseeable computer. This is what actually protects your data: your encrypted file, the contents of an HTTPS page, your backups.

It has exactly one weakness, and it's not the maths. Both sides need the same key, and getting that shared key to the other person is the hard part. If you email the key, anyone reading the email has it. If you could already send the key securely, you wouldn't need the encryption. This is the key-distribution problem, and it's what the second scheme exists to solve.

Asymmetric encryption (RSA): a public lock, a private key

Asymmetric means two different keys that are mathematically linked: a public key that locks, and a private key that unlocks. You can hand your public key to the entire world — publish it, put it on your website — and anyone can use it to encrypt a message that only your private key can open. The public key locks; it cannot unlock. That asymmetry is the whole trick.

This solves the key-distribution problem exactly. Two strangers can now communicate secretly: I encrypt with your public key, only you can decrypt. Nobody had to share a secret in advance. The catch is that RSA is slow — orders of magnitude slower than AES — and impractical for encrypting large amounts of data. So it isn't used to encrypt your file. It's used to encrypt one small thing: the AES key.

How they work together — the part that matters

Here's the move that runs the secure internet. When your browser connects to an HTTPS site, or when you send an encrypted message, this happens: a random AES key is generated for this one session. That AES key — small, just a handful of bytes — is encrypted with the recipient's RSA public key and sent over. Only the recipient's private key can unwrap it. Now both sides have the same AES key, and nobody watching could have stolen it. From that point on, all the actual data is encrypted with fast AES.

So the honest answer to 'AES vs RSA' is: RSA to exchange the key, AES to encrypt the data. Asymmetric solves the introduction; symmetric does the work. When you encrypt a file with a passphrase using [AES-256](/security/aes/), you're skipping the RSA step because you'll deliver the key yourself — which is why the guide on [sharing that password safely](/guides/how-to-encrypt-a-file-with-a-password/) matters. When you load an HTTPS page, both are running, invisibly, in the handshake before the first byte of content arrives.

So which should you use?

Encrypting a file to store or send with a password you'll deliver yourself: AES. It's fast, strong, and you're handling the key distribution manually.
Letting strangers send you secret messages without a pre-shared key: asymmetric (RSA, or modern elliptic-curve equivalents). This is what PGP email and messaging apps use.
In practice, for almost anything you do by hand, it's AES — because you're the one carrying the key to the other side. RSA is doing its job for you automatically, inside HTTPS and your messaging apps, without you choosing it.

If you want to see symmetric encryption directly, the [AES tool](/security/aes/) encrypts text or a file in your browser and shows you the result. For the specifics of what GCM mode adds — authentication on top of secrecy — the [AES-GCM guide](/guides/aes-gcm-encryption-explained/) has it.

Tools used in this guide

FAQ

What's the difference between AES and RSA?: AES is symmetric — one shared key locks and unlocks, and it's fast enough to encrypt large data. RSA is asymmetric — a public key locks and a separate private key unlocks, which solves how two strangers agree on a key, but it's too slow for bulk data. They're used together: RSA exchanges the key, AES encrypts the data.
Which is more secure, AES or RSA?: Neither is 'more secure' — they do different jobs. AES-256 and a properly sized RSA (or elliptic-curve) key are both considered unbreakable by foreseeable computing. Security comes from using each for what it's for: asymmetric to exchange a key safely, symmetric to encrypt the actual data quickly.
Why not just use RSA for everything?: RSA is orders of magnitude slower than AES and impractical for encrypting large amounts of data. It's used to encrypt one small thing — the AES key — after which the fast AES cipher does the heavy lifting. Using RSA for bulk data would make everything crawl.
Does HTTPS use AES or RSA?: Both. When your browser connects, an asymmetric handshake (RSA or an elliptic-curve equivalent) securely exchanges a random AES key, and then all the actual page data is encrypted with that fast AES key. Asymmetric handles the introduction; symmetric does the work.