ECDH Key Exchange
See how two people who have never met agree on a secret key — while everyone can see what they exchange.
👩 Alice
Alice's private key never leaves her device.
👨 Bob
Bob's private key never leaves his device.
● 🔒 Your data is processed locally in your browser with the Web Crypto API and is never uploaded to our servers.
How it works
Each person generates a key pair and sends only the public key. Combining your private key with their public key gives a point on the curve that both sides compute identically — an eavesdropper who sees both public keys can't compute it. That shared secret is then passed through HKDF to produce an AES key. This is how TLS (HTTPS), Signal and WhatsApp agree on encryption keys.
On its own, ECDH doesn't prove who you're talking to; real protocols sign the public keys to stop man-in-the-middle attacks.