RSA-OAEP (SHA-256)

What it is made of

Kind

Hybrid public-key envelope

Protects the data with

AES-256-GCM, under a random one-time key

Protects that key with

RSA-OAEP, SHA-256

Needs a passphrase

No — a public key encrypts, the private key opens

Runs in

Your browser and the server

What it is

Wraps the content key directly with the recipient's RSA public key. Needs a 2048-bit key or larger.

Where it runs

Both lanes. By default the lab runs it in your own browser over the Web Crypto API, so nothing leaves your device — there is no upload, no size limit and no queue. The server lane is there when you want it, and it is the only way an agent or a script can reach the same engine.

Why it is hybrid, and why that is not a shortcut

Public-key cryptography does not encrypt your file. RSA can only encrypt a couple of hundred bytes, and ECDH cannot encrypt anything at all — it agrees on a shared secret. So every real system, this one included, generates a random one-time key, protects the data with that, and protects the key with the public key of whoever is meant to read it. "RSA encrypts your file" is the most common wrong belief about all of this, and the lab shows you the wrapped key sitting in the header.

Try it

Open the Keys bench in the lab, generate a keypair, and seal a file to the public half. Then open it with the private half — and try opening it with a different one, which fails exactly as it should. The lab is a Leumas membership away; everything on this page is free.